Socrative Flashcards
A prism ballast GP lens requires how much prism for proper orientation?
0.75 to 1.50D (She says in most cases)
In against-the-rule astigmatism, the short/ steepest corneal meridian:
At or near 180
In with-the-rule astigmatism, the longest/flatest corneal meridian:
At or near 90
What is the term for the condition in which there is loss of vision without any apparent disease to the eye?
Amblyopia
is the absence of an iris
Aniridia
What should be suspected when there are large fluctuations in a patient’s refractive error?
In diabetics, the sudden shift in blood sugar levels can cause changes in the refractive error
Corneal edema, a sensation of soreness. injection, foggy vision and ghost images usually indicate:
A lens that prevents tear exchange and elimination of corneal debris and metabolic waste products may cause corneal edema which could be due to a tight-fitting lens
What does it mean when we say the soft lens must equilibrate on the eye?
The polymer of the lens must reach the same temperature as the tear film 98.6 degrees
Punctal occlusion may be most beneficial for?
Tear deficient dry eye, occlusion of the lacrimal drainage apparatus simply increases tear volume by slowing the rate of outflow.
In a GP lens, a poorly finished transitional zone between the optic zone and the lens edge can be evaluated by:
Profile analyzer which helps in evaluating the quality of the peripheral blends of a GP lens.
A patient will have a much greater awareness of a loose lens and may experience a constant foreign body sensation when wearing a lens that…
Is too loose
Soft lenses fit steeper than K
A soft lens that is fit steeper than K will vault the cornea centrally and seal off around the periphery. Vision will fluctuate with each blink
It is important that the practitioner inform the patient not to use lotions, creams, make-up, sprays and all cosmetics (before/after) lens insertion.
before
Things to be documented with a patient:
the care system the patient is using and any systems they had problems with, as well as lens parameters and materials are all vital pieces of information to have documented in the patient’s permanent record.
With a rigid contact lens in place, a fluorescein pattern shows a concentration of fluorescein inferiorly and superiorly beneath the lens. Which one of the following types of astigmatism is represented by this pattern?
With the rule astigmatism: the flattest corneal curvature is horizontal and steepest curvature is vertical.
Fluorescein will be absent or minimal where the cornea is (flatter/steeper), and pool or collect where the cornea is (flatter/steeper).
Flatter
Steeper
Astigmatism that is inside the eye and not on the cornea.
lenticular/residual astigmatism
The base curve of a rigid lens was ordered 7.84mm and was received measuring 7.94mm. this lens is ________than ordered.
0.50 flatter
Every 0.05mm of radius equals approximately 0.25 diopters. The lens ordered was 43.00D, but was received as a 42.50D
Which of the following modifications to a gas permeable lens can be made in the office?
Blending of peripheral curves
Polishing lens surface
Addition of minus power
Which of the following modifications to a gas permeable lens can not be made in the office?
Changing the base curve
Application of fluorescein should be used in…
Evaluations of gas permeable lens fit
The main purpose of a rigid lens wetting solution is to:
Convert the hydrophobic surface of a rigid lens to one that is temporarily hydrophilic
If a soft contact lens is not properly neutralized, how does residual hydrogen peroxide affect the cornea?
It is likely to cause epithelial damage
contact lenses that have a non-spherical back surface are called:
Aspheric lenses
Lenses that have central base curves that are spherical.
Tricurve and spherical lenses
A lens that refers to the removal of plastic on the lower portion of the lens to aid in positioning of a bifocal or toric GP lens.
Truncated lens
A technician can perform a preliminary evaluation of soft contact lens movement by:
Observing the movement of the lens edge in relation to the position of a conjunctival vessel
Observing movement and lens lag in upward and lateral gaze with a penlight
Having the patient look up and blink
In a GP wearer, an arcuate stain on the cornea may be due to:
Poorly blended secondary curves
Failure to close the lids completely when blinking results in:
3 & 9 o’clock staining.
To aid in the positioning of a GP prism ballast lens riding too low and slipping underneath the lower lid:
Truncation would help provide a flatter, thicker surface to interact with the lower lid, enabling the lens to rest in the proper position.
The slit lamp illumination that gives an overall view of the cornea but limits detail is:
Diffuse
Two narrow illuminations
Sclerotic scatter and specular reflection
Up until the recent introduction of silicone hydrogel lenses the Dk/t of previous hydrogel lenses was limited by:
Water content and center thickness
Which edge design is recommended for a +15.00D aphakic GP lens?
Lenticular myoflange, this minus carrier design increases edge thickness and enables a low-riding high plus lens to center better.
The LARS principle provides us with a means of:
Compensating for axis rotation of a soft lens, “LARS” stands for Left Add Right Subtract. If a soft toric lens orients with its markings rotated to the fitter’s left, the number of degrees of rotation must be added to the patient’s refractive axis (not the axis of the diagnostic lens) in order to counterbalance the lens so it will align with the patient’s correct corneal cylinder axis in the eye. If the diagnostic lens orients with iits markings rotated to the fitter’s right, the number of degrees of rotation must be subtracted from the patient’s refractive axis when ordering the patient’s lens.
two methods of stabilizing the rotation of rigid bifocal contact lenses?
Truncation and Prism Ballast
These lenses must be stabilized in order for the proper segment to align correctly with the pupil.
Translating or alternating gas permeable bifocal lenses
The bottom portion of the lens is removed, producing a ledge that interacts with the lid, aligning the lens in its proper position.
Truncation
the bottom portion of the lens is made thicker than the top portion.
Prism ballast
Inferior punctate staining may be a sign of:
Lagophthalmos, the inability of the upper lid to close completely prevents the inferior cornea from being bathed with tears that rest along the lower lid. As much as one-third of the population has a slight lagophthalmos during sleep.
Corneal Edema characteristics
Reports of smoky vision and spectacle blur are common in patients with severe corneal edema. The contact lens professional may also notice a steepening of the keratometer readings for those patients
What Rx would be ordered for a gas-permeable lens fit on K?
K’s 43.00 @ 180/44.00 @ 090
Rx -3.00 +1.00 x 090
-2.00D
To determine the Rx of a gas permeable lens, first put the Rx in minus cylinder form: -3.00 +1.00 x 090 becomes -2.00 -1.00 x 180
Next, drop the cylinder. When fitting a lens on K order the sphere power corrected for vertex distance when the Rx is in the minus cylinder: -2.00D
If a patient with exophthalmic eyes due to thyroid disease requires a toric lens:
It may dehydrate excessively due to the lid retraction and dry eye condition that often accompanies thyroid disease
Stability will be difficult to maintain since there are no lid forces to keep the lens in position
bifocal designs that represent a translating design (not mentioned in any review?)
Crescent design
If an adapted contact lens wearer complains of a sudden onset of discomfort, the technician should suspect:
A damaged contact lens
A change in corneal curvature creates…
a gradual decrease in lens comfort
tight lens syndrome
a gradual decrease in lens comfort
Ph value of human tear
7.4
Tear Ph higher than 7.4 is
alkaline
Tear Ph lower than 7.4 is
acidic
To correct a flat fitting gas permeable lens, you could:
Enlarge the optical zone: only if there is no change in lens diameter.
Decrease in sagittal vaulting
creates a flatter lens to cornea relationship
decreasing overall lens diameter
decreases sagittal depth
tear break up time is done by:
instilling fluorescein, having the patient blink once to spread the fluorescein across the cornea and timing the interval between the blink and the development of the first dry spot (tear break-up) on the cornea.
Given the following information, which set of lens specifications would best simulate a lid attachment rigid lens fitting?
K’s 42.00 @ 180/43.00 @ 090
Rx -2.00 -0.87 x 180
Upper lid positioned 2mm below the superior limbus
A
41.50 -1.50 9.5
B
42.50 -2.50 8.5
C
43.00 -2.50 9.5
D
43.00 -3.00 8.2
A 41.50 -1.50 9.5
“Lid attachment” lenses are designed to fit with the upper edge of the lens positioned under the upper eye lid. To achieve this positioning, a flatter than K, larger diameter (over 9.0mm) is generally used.
Which type of slit lamp illumination will allow you to determine corneal thickening, thinning and distortion and depth of foreign bodies or opacities in the cornea?
Optic section
The tolerance for the overall lens diameter according to the ANSI standards is
+/- 0.05 mm
Carole’s GP contact lenses are fit on flat K. her refraction is -5.00+2.00x090. What is the power of her contact lenses?
-3.00D
Reason: Convert to minus, when a rigid lens is fit on K, no compensation is needed for the resulting tear film so the lens power remains -3.00D.
Given the following information, which of the following GP lens designs would you order to best correct this patient’s vision?
K’s 45.00 @ 180/42.00 @ 090
Rx -2.00-4.25x090
A
45.00 -2.00
B
42.00 -2.00-4.25x090 prism ballasted
C
42.00 -2.00
D
42.00/45.00 -2.00/-5.75 (drum readings)
D 42.00/45.00 -2.00/-5.75 (drum readings)
A bitoric lens design will provide the best lens orientation on against-the-rule corneal topography. The other answers are incorrect because the spherical base curves will not contribute to proper positioning of the lens on the against-the-rule cornea.
Which of the following preservatives produces the least toxic response of the eye?
A
Polyquad
B
Chlorhexidine
C
Sorbate or sorbic acid
D
Thimerosal
A polyquad
Clinical studies indicate that solutions preserved with polyquad can be used without as much risk of toxic or allergic reaction as the other preservatives listed.
When corneal epithelial cells suffer trauma, the first step toward resolution is:
Sliding and migrating of the adjacent remaining epithelial cells
Epithelial Cells are highly reproducible and quickly work toward covering any area that has suffered trauma. In the first twenty-four hours, the adjacent remaining epithelial cells slide and migrate over to cover the open area. During the next 48 to 72 hours, the epithelium will generate new cells to completely fill in the traumatized area.
best measure the convex curve of the rigid lens
Radiuscope
Given the following information, which of the listed rigid lens designs would you order to best correct this wearer’s vision?
K’s 42.00 @ 180/45.00 @ 090
Rx -3.00 -2.25 x 180
42.00/45.00 -3.00-2.25 (Rx form)
The base curves will parallel the K readings and the power in the lens will properly correct the astigmatism. A spherical lens design will rock on the 180 degree meridian causing discomfort and the chance of lens displacement or expulsion.
When the patient has Graves’ disease they can be fitted for soft lenses
True
contraindication for soft lenses
A
When the patient has Graves’ disease
B
When the patient has cylindrical keratometric readings
C
When the patient has irregular corneal astigmatism
D
When the patient has more than 1.50D of refractive cylinder
C When the patient has irregular corneal astigmatism
During the diagnostic evaluation of the following patient you note the lens rotates 10 degrees to your left. Which of the following lens parameters would you order for the patient?
Patient’s refraction -3.00-1.25x160
Diagnostic lens 8.4 -3.00-1.25x280 14.5
8.4 -3.00-1.25x170 14.5
To compensate for rotation of a diagnostic soft toric lens, add the amount of rotation if it rotates to your left and subtract the amount of rotation if it rotates to your right. The degrees of rotation are subtracted from the patient’s refractive axis, not the axis of the diagnostic lens.
A rigid lens shows two curves on the convex surface when measured with the radiuscope. On the lensometer, it shows one power. What type of lens is this?
warped
a warped lens will show two curvatures on the radiuscope that are close (usually within 0.15mm) but the power will read spherically, or close to spherical. A lens that has toric surfaces on the front, back or both, will all read two distinct powers on the lensometer
If a soft contact lens becomes adherent to the cornea, the patient should:
Irrigate the eye with saline or rewetting drops until the lens begins to move freely again
A lens adheres to the cornea when it is not:
wet enough or salty enough
The following ametropia frequently results in high riding rigid lenses:
High myopia
Due to the increased edge thickness of a high minus lens it will frequently “catch” under the upper lid causing it to ride high.
Gross corneal edema, which manifests itself clinically as central corneal haze, is verified by the slit lamp using sclerotic scatter illumination. What specific technique does the examiner use to see this condition?
the naked eye and an angle between the slit lamp beam and the eye of 90 degrees
First develops intracellularly (in the cells). In the beginning stages, the swelling (collection fo fluid) is easier to see without the microscope. When the condition worsens, it can be seen with the microscope, but it will be deeper into the cornea.
Epithelial edema
An instrument that allows simultaneous verification of lens diameter, optic zone width and peripheral curve width is
measuring magnifier
An instrument that allows simultaneous verification of lens diameter, optic zone width and peripheral curve width is
measuring magnifier
The average HVID for a patient is
11.5mm
To steepen the lens to cornea relationship of a gas permeable lens you could:
A
Increase overall diameter and decrease optic zone diameter
B
Increase overall diameter and increase optic zone diameter
C
Increase optic zone diameter and decrease overall diameter
D
Increase optic zone diameter and flatten base curve
B Increase overall diameter and increase optic zone diameter
decreasing the optic zone diameter, decreasing the overall lens diameter and flattening the base curve will … the relationship.
A flatten
B loosen
C tighten
D Steepens
B loosen
If a patient with exophthalmic eyes due to thyroid disease requires a toric lens:
It may dehydrate excessively due to the lid retraction and dry eye condition that often accompanies thyroid disease
Stability will be difficult to maintain since there are no lid forces to keep the lens in position
Tom’s spectacles with a power of -12.00 +0.50 x 090, sit 10mm in front of his cornea. The likely soft contact lens prescription for Tom would be:
-10.50D
In the conversion of a prescription from the spectacle plane to the corneal plane, additional plus power is needed. Usually a standard table
The following soft lens is placed on a patient’s eye:
14.0/8.8 -4.00
An over-refraction is performed resulting in -0.75D sphere. Which of the following lens parameters would you order for the patient?
14.0/8.8 -4.75
When applying the results of an over-refraction to a soft lens, first put the over-refraction in minus cylinder. Then determine the spherical equivalent and add this to the existing power.
The best technique to evaluate the movement of a thin hydrogel lens is:
Push up test
While observing in the slit lamp, the examiner takes his/her thumb and presses on the patient’s lower lid and pushes upward to move the lens. If the lens moves up freely and descends back into place freely, it is a good fitting lens. If the lens is difficult to move or drops slowly into place after it is moved, the fit may be too tight. The other forms of checking lens movement are not as accurate with some thin hydrogel lenses.
Transient keratometric mire distortion is usually due to:
Pre-ocular tear film
While prolonged rigid lens wear, prolonged soft lens wear and irregular corneal astigmatism may all cause mire distortion, the mire distortion will remain constant. Of the choices listed, only the tear film results in transitory mire distortion which can be cleared up if you ask the patient to blink.
Which type of lens would best satisfy this patient’s visual needs given the following information?
K’s 43.00 @ 160/44.00 @ 075 3+ distortion
Rx -2.00 +1.00 x 075
Spherical GP
The 3+ distortion is most probably due to irregular astigmatism and is best corrected with a rigid lens option
If a patient has 1.50D of refractive cylinder and keratometer readings of 44.00 @ 180/44.50 @ 090, you would expect a spherical gas permeable lens to:
Result in residual astigmatism
The rigid back surface of a lens will only correct the astigmatism that is found on the surface of the cornea. Therefore, when there is significantly more astigmatism in the refraction than on the surface of the cornea, residual astigmatism will result. Since there would appear to be a great deal of residual astigmatism, even though the lens is rigid, the patient would not realize their best correctable vision.
FDA group I soft lenses
Have a water content less than 50% and a non-ionic surface
Non-ionic surfaces do not carry an electrostatic charge and stay cleaner than ionic surfaces. Ionic surfaces, since they are negatively charged, attract positively charged tear lipids and proteins and coat more readily.
Cleaners that contain isopropyl alcohol should not be used on rigid lenses because they:
May cause parameter changes, brittleness, cracking
Aliphatic alcohols, such as ethyl, methyl and isopropyl alcohol will damage GP materials and are approved for use with PMMA and soft lens materials only. Benyzl alcohol is the only alcohol that is FDA approved and safe to use in GP solutions.
Dry eyes are a common side effect of:
Oral contraceptives, Accutane and antihistamines
In an alignment lid attachment GP fit, the fluorescein pattern should show:
A thin, even layer of fluorescein and less than 180 degrees of bearing in the mid-periphery
What is an essential characteristic of an ideal wetting solution?
they should be formulated so that they can be instilled directly into the eye without causing irritation or sensitization
hey should be made isotonic which means they try to mimic the normal tear pH and are neither acidic nor alkaline. Solutions must also be adequately preserved to be dispensed in a sterile manner.
When verifying a rigid lens on a radiuscope, you notice that the mires are not in focus in all principal meridians. This might indicate a:
Warped lens, back toric lens or front toric lens
A front toric lens will show a spherical posterior curve on the radiuscope and a sphero-cylindrical Rx on the lensometer.
Fluorescein is not used for
Corneal striae
If a soft contact lens is not properly neutralized, how does residual hydrogen peroxide affect the cornea?
It is likely to cause epithelial damage
A good example of a bifocal contact lens that may rotate without vision impairment is:
Aspheric
do not have independent near and distance zones.
What are the requirements of a good contact lens case?
The contact lens case should have enough depth to allow the lens to be stored totally immersed in the storage solution. It should be made of plastic and not contain any sponge rubber which may concentrate chemicals or be degraded by them.
Which of the following cold disinfection chemicals is least likely to cause a reaction when the product is used according to directions?
Hydrogen peroxide
When used according to directions, hydrogen peroxide is neutralized into preservative-free saline solution and oxygen with a catalytic disc or catalase tablet or saline and other harmless substances with a chemical reducing agent.
The increased loss of ability of the crystalline lens to accommodate is called:
Presbyopia
In calculating the prescription for a rigid lens, one must:
The spherical power of a rigid lens must always be calculated with the prescription in minus cylinder form. They cylindrical power does not come into consideration, since the rigid lens places a new, spherical surface in front of the eye, and masks any corneal astigmatism. If the patient has some residual (lenticular or internal in nature) astigmatism, vision may be improved by using the spherical equivalent of the residual, not the total refractive astigmatism. Adding minus power to a rigid lens is done to compensate for a positive (plus) tear layer. Plus power will compensate for a negative tear layer.
Poor GP insertion on recentering techniques may result in:
Arcuate staining
since the edge of a GP lens is curved, it will damage epithelial cells in an arcuate pattern if it is inserted or recentered incorrectly. 3 & 9 o’clock staining is related to peripheral desiccation and can be caused by lid gap, incomplete blinking and failure to resurface the areas just outside the lens edge with tear film mucin with each blink. Lack of a fulcrum (or earing point) for a GP lens is unrelated to lens insertion or recentering techniques. Choice D, coalesced SPK (superficial punctate keratitis) centrally, could be due to excessive apical bearing from a flat lens, central corneal clouding from a tight, steep lens or a lens that supplies insufficient oxygen to the cornea. It could also be caused by a foreign body that has been trapped centrally under the lens.
A soft lens has edge lift when observed on a cornea. How can this be corrected?
Steepen the base curve
Edge lift is indicative of a flat fitting soft lens and therfore a steeper base curve is indicated.
Prism ballast, double slab-off and peri-ballast are all what type of lens design?
Soft toric
Which auxiliary lens will extend the keratometer range to approximately 30.00D?
A
+1.00D
B
+1.25D
C
-1.00D
D
-1.50D
-1.00
By placing a -1.00D lens over the aperture of the keratometer, you can extend the low-end range from 36.00D to 30.00D.
The following is an example of what type of astigmatism?
K’s 44.00@180/44.50@090
Rx -3.00 -2.50 x 180
Lenticular astigmatism
present when there is significantly more astigmatism in the patient’s refraction (2.50D) than on their corneal surface (0.50D). In this case, the astigmatism is not represented on the cornea and is most likely found in the crystalline lens.
The pre-corneal tear film provides:
1) A smooth optical surface
2) Metabolic nutrients to the epithelium
3) Oxygen to the endothelium
4) Limbal hyperemia
1 and 2
The pre-corneal tear film provides a smooth optical surface for the cornea. This is maintained by the blink mechanism, further providing metabolites (eg, oxygen) to and from the cornea as well as removing waste products such as C02 and dead epithelial cells.
The endothelium receives its oxygen from __________ within the anterior chamber.
Aqueous humor
Limbal hyperemia
redness from engorged blood vessels in the limbal area.
The normal cornea is transparent due to the pump action creating proper fluid balance. Which layer of the cornea is most responsible for maintaining this function?
A
Endothelium
B
Basal membrane
C
Epithelium
D
Bowman’s layer
Endothelium
The corneal endothelium provides the pumping mechansim of the cornea to expel fluid from the tissue and maintain corneal transparency.
Bowman’s layer
an acellular layer which provides strength to the cornea.
Basal membrane
a basement membrane which provides an attachment surface for the epithelium to adhere to Bowman’s layer.
Normal tear break-up time
10-12 seconds
less than 7 may limit success with contacts
Patients with keratitis sicca are more prone to:
Secondary infections
Keratitis sicca is a severe dryness of the cornea. This leaves the cornea at risk, exposing it to complications related to secondary infections.
The following Rx represents:
OD +2.00 = 20/20
OS -3.00 -2.00 x 180 = 20/20
Anisometropia
Anisometropia is present when the refractive errors of a patient’s two eyes are so different from one another that retinal images of disparate sizes result. Because of the different sizes, fusion of the two images may not occur.
The average life span of a corneal epithelial cell from mitosis through maturation and desquamation most nearly approximates:
1 week
Which auxiliary trial lens will extend the keratometer range to approximately 61.00D?
+1.25D
The range of the keratometer is 36.00D to 52.00D. To extend the range above 52.00D, a +1.25D lens is used.
Transient keratometric mire distortion is usually due to:
Pre-ocular tear film
While prolonged rigid lens wear, prolonged soft lens wear and irregular corneal astigmatism may all cause mire distortion, the mire distortion will remain constant. Of the choices listed, only the tear film results in transitory mire distortion which can be cleared up if you ask the patient to blink.
An inability to bring all of the keratometer mires into focus at the same time may indicate:
In cases of irregular astigmatism the major meridians are not 90 degrees apart causing the mires to not focus all at the same time.
Generally, a TBUT of greater than ______seconds is needed for successful contact lens wear.
10
The preservative in contact lens solutions is formulated to keep ______ from multiplying in a bottle of contact lens solutions after it has been opened.
Microorganisms
They do not kill microorganisms, but only prevent them from multiplying in solution bottles after they are opened.
A pre-presbyopic myopic patient who is still able to read with single vision glasses may find that
They are unable to see fine print when fit with contact lenses
Contact lenses require myopic patients to use more accommodation and convergence than spectacles. Patients who are approaching presbyopia may find that their near vision is still adequate with glasses but cannot see small print when fit with contact lenses.
Amy’s +8.50D spectacles sit 12mm from the cornea. The power of a soft contact lens for Amy, properly vertexed, would be:
+9.50D
Vertex distance must be taken into account when spectacle power is +/-4.00D. In the conversion of a prescription form the spectacle plane to the corneal plane, additional plus power is needed. Thus, less minus power is required for a high myope’s contact lenses compared to their spectacle prescription. Additional plus power is needed for a high hyperope’s contact lenses compared to their spectacles.
Which of the following choices would work best for the patient’s visual need given the following information:
K’s 44.00 @ 180/45.25 @ 090
Rx -3.00 +0.25 x 090
Spherical soft lens
Which of the following set of lens specifications would best simulate an intrapalpebral GP fitting given the following information:
K’s 42.00 @ 180/43.00 @ 090
Rx -2.00 -1.00 x 180
Upper lid positions 2mm above the superior limbus
42.50/8.5 -2.50
An intrapalpebral fit is a small diameter, steep fitting lens designed to center between the upper and lower eyelids.
(47)
Whiich contact lens would best correct this patient’s visual needs, given the following information:
K’s 46.00 @ 180/45.50 @090
Rx -3.00 -1.50 x 90
A soft toric lens
GP lenses tend to decenter on against-the-rule corneas. There is not enough toriciy for a GP lens with toric curves on the back surface to stabilize.
If a patient has 1.50D of refractive cylinder and keratometer readings of 44.00 @ 180/44.50 @ 090, you would expect a spherical gas permeable lens to:
Result in residual astigmatism
The rigid back surface of a lens will only correct the astigmatism that is found on the surface of the cornea. Therefore, when there is significantly more astigmatism in the refraction than on the surface of the cornea, residual astigmatism will result. Since there would appear to be a great deal of residual astigmatism, even though the lens is rigid, the patient would not realize their best correctable vision.
If the diagnostic gas permeable lens placed on the eye results in minimal movement, which of the following will increase the movement on the lens ordered for the patient?
Decreasing overall lens diameter
Increasing the overall diameter, increasing the optic zone diameter as well as increasing the sagittal depth will all decrease the movement of the gas permeable lens. Decreasing the overall lens diameter will loosen the fit and increase the movement of the lens.
Contact lens technicians work with prescriptions in minus cylinder form because:
The lacrimal lens is a minus cylinder lens
The contact lens power is determined by C.L. + L.L = Spectacle Rx. Because the lacrimal lens is a minus cylinder, the spectacle Rx must also be in minus cylinder form to arrive at the correct lens power.
Rx OU -3.00 -0.50 x 180, Add +1.25D
If spherical soft lenses are being fit using the monovision technique, what is the desired power for the eye fitted for near?
-2.00
The spherical equivalent power for the distance is -3.25D. Combining the add power of +1.25D results in the need for a total reading power of -2.00D.
Which edge design is recommended for a +15.00D aphakic GP lens?
Lenticular Myoflange
This minus carrier design increases edge thickness and enables a low-riding high plus lens to center better.
Which of the following lens designs would provide the best visual result for this patient?
K’s 42.00 @ 180/42.50 @ 090
Rx -3.50 -1.75 x 180
A Spherical gas permeable lens
B Spherical soft lens
C Soft toric lens
D Back surface toric gas permeable lens
Soft toric lens
Since the astigmatism is lenticular and is not found on the cornea, a spherical gas permeable lens will not mask the astigmatism. There is not enough corneal astigmatism to stabilize a back surface toric lens.
a spherical gas permeable lens will not mask the _____ astigmatism.
Lenticular
To aid in the positioning of a GP prism ballast lens riding too low and slipping underneath the lower lid, which of the following might be helpful?
Truncation
Truncating the lower edge of the lens would help to provide a flatter, thicker surface to interact with the lower lid, enabling the lens to rest in the proper position.
The following gas permeable diagnostic lens is placced on a patient’s eye:
43.50/9.2 -2.00
An over-refraction is performed with the following results: plano +1.50 x 095
Which of the following lens parameters would you order for the patient?
43.50/9.2 -0.50-1.50 x 005
When applying the sphero-cylindrical over-refraction to a spherical gas permeable lens, first put the over-refraction into minus cylinder form:
plano +1.50 x 095 becomes +1.50-1.50x005
Add the spherical component to the existing spherical component:
-2.00 plus +1.50 becomes -0.50
Then simply tag on the cylindrical portion of the over-refraction:
-1.50x005
The following soft lens is placed on a patient’s eye:
14.0/8.8 -4.00
An over-refraction is performed resulting in -0.75D sphere. Which of the following lens parameters would you order for the patient?
14.0/8.8 -4.75
When applying the results of an over-refraction to a soft lens, first put the over-refraction in minus cylinder. Then determine the spherical equivalent and add this to the existing power.
In a GP lens, a poorly finished transitional zone between the optic zone and the lens edge can be evaluated by
profile analyzer
A profile analyzer’s function is to aid the contact lens professional in evaluating the quality of the peripheral blends of a GP lens.
During the diagnostic evaluation of the following patient you observe that the lens rotates 10 degrees to the right. Which of the following lens parameters would you order for the patient?
Patient’s Refraction -2.00 -1.00 x 170
Diagnostic lens 8.7 -2.50 -1.00 x 170
8.7 -2.50 -1.00 x 160
To compensate for the rotation of a diagnostic soft toric lens, the “LARS” principle tells you to add the number of degrees of rotation if it rotates to the practitioner’s left and subtract the amount of rotation if it rotates to the practitioner’s right. In this case, the lens rotates to the right and the degree of rotation must be subtracted from the original axis.
In prescriptions of 4.00D or greater, fitting contact lenses requires compensating the power for the change in vertex distance. When moving from the spectacle plane, the compensated power will be:
More plus
For example, a +4.00D spectacle Rx requires a +4.25D contact lens power, and a -4.00D spectacle wearer needs a -3.75D contact lens. In both cases, the contact lens power is more plus than the spectacle Rx.
The longer the radius of curvature of a contact lens:
A
The steeper the lens
B
The flatter the lens
C
The larger the diameter
D
The smaller the diameter
B The flatter the lens
the radius of curvature of a contact lens is a measure of the distance from the imaginary center of the lens to its periphery. For a given diameter, as the distance is increased from the center to the periphery (the radius of curvature is lengthened), the flatter the curvature will be.
For a given diameter, as the distance is increased from the center to the periphery (the radius of curvature is lengthened), the _______ the curvature will be.
flatter
The following soft lens is placed on a patient’s eye: 8.4 -2.00 14.2
An over-refraction is performed with the following results: -1.00 -0.50 x 174
Which of the following lens parameters would you order for the patient?
8.4 -3.25 14.2
When applying the results of an over-refraction to a soft lens, transpose the over-refracetion to minus cylinder. Then determine the spherical equivalent (-1.25D in this case) and add this to the existing power.
Given the following information:
K’s 45.00 @ 180/44.00 @ 090
Rx -3.00 +1.00 x 180
Upper lid positioned at superior limbus. Which of the following set of lens specifications would best simulate an intrapalpebral GP lens fit?
A
43.50 -1.50 8.5
B
43.50 -1.50 9.5
C
44.50 -2.00 8.5
D
44.50 -2.50 8.5
D 44.50 -2.50 8.5
An intrapalpebral fit is a small diameter, steep fitting lens designed to center between the upper and lower eyelids.
Given the following information, which of the following GP lens designs will best correct this wearer’s vision?
K’s 42.50 @ 180/42.50 @ 090
Rx -3.00 -1.00 x 090
(74)
Anterior Toric design
With an anterior toric design, the base curve will parallel the spherical cornea and the prism ballast will position the cylinder in the lens on the axis of the Rx. A bitoric lens’ base curves will create an additional cylindrical effect and will rotate creating fluctuating vision because there is no corneal toricity to keep the lens in position. A Soper cone lens design is used for keratoconus.
Given the following refraction and K readings, select the correct base curve and power recordings (drum readings):
K’s 44.00 @ 180/41.00 @ 090
Rx -1.00 -3.00 x 090
A
41.00/44.00 -1.00/-3.00
B
41.00/44.00 -1.00/-4.00
C
41.00/44.00 -4.00/-1.00
D
44.00/41.00 -1.00/-3.00
B 41.00/44.00 -1.00/-4.00
A toric rigid lens should always be recorded with the flat meridian first and the steep meridian second. The total power in each meridian is written to correspond respectively.
A bifocal lens in which the power gradually changes from the central area of the lens to a periphery is known as:
an aspheric lens
How many diopters of power will bring parallel rays of incident light to a focus at a distance of one meter?
1D
The patient has a horizontal visible iris diameter (HVID) of 12.5mm. the best choice for initial soft lens diameter would be:
14.5mm
Rule of thumb for determining soft lens diameter is to choose a lens 2.0mm larger than the cornea. With 1mm on either side of the cornea it will aid lens centration.
In which of the following types of corneal astigmatism is a GP lens most indicated?
Irregular
With irregular corneal astig the GP lens creates a tear lens that neutralizes the irregularity of the corneal surface providing the best optical correction
Spherical equivalent powers position which of the following on the retina?
Circle of least confusion
In astigmatic imagery, no point focus is possible. The closest thing to it is the circle of least confusion, formed by the meridian that is halfway between the principal meridians of the cylindrical refractive surface.
Keratoconus and penetrating keratoplasty fittings are best accomplished by which of the following methods?
diagnostic fitting
Due to irregular astigmatism secondary to keratoconus and penetrating keratoplasty (PKP), reliable K readings are not obtainable. Therefore, diagnostic fitting is the most practical means of lens fitting.
A toric soft lens will correct:
A
Residual astigmatism
B
Moderate astigmatism (greater than 2.00D)
C
Low astigmatism (0.75 the 2.00D)
D
All of the above
D all of the above
Therapeutic soft lenses should be fit with minimal movement in which case?
A
Keratitis sicca
B
Trichiasis
C
Recurrent erosion
D
Keratoconus
C Recurrent erosion
a rigid lens corrects astigmatism by
forming a new spherical refracting surface in front of the cornea
This makes the rigid lens eliminate the cornea s the major refractive component of the eye
Concentric, aspheric and diffractive lens designs are all
Simultaneous image lenses
A translating bifocal lens design
this type of lens must move upward to see near vision and intends to project altering images (D + N) on the retina
A segmented lens is a
Translating bifocal lens
Prism ballast, double slab-off and peri-ballast are all what type of lens design?
Soft toric
Prism ballast
the bottom portion of the lens is made thicker than the top portion, the thicker portion of the lens will be forced from the upper lid first, positioning it along the bottom lid. This Stabilizes the rotation of the contacts.
When a diagnostic soft toric lens rotates clockwise, the amount of rotation is added to the … cylinder axis.
refractive
The FDA classification for “disposable lenses” means:
the lens is disposed of after removal
Given the following information:
K’s 42.00 @ 180/42.00 @ 090
Rx -3.00-2.00x180
A front surface toric GP lens will probably be necessary to correct the patient’s residual astigmatism
A patient’s K reading are 43.50 @ 180/41.50 @ 090. A spherical GP lens can be expected to:
Displace down and in, or down and out with each blink
This patient has against-the-rule astigmatism and the cornea has a vertical ellipsoidal shape. When a GP lens is placed on this type of cornea, a fulcrum or bearing point is established at 6 & 12 o’clock in the vertical meridian. There are no bearing points in the horizontal meridian to help guide the lens in its downward excursion and the lens will tend to decenter nasally or temporally with the blink.
Which special GP lens design would be beneficial for this patient given the following information?
K’s 44.00 @ 180/46.50 @ 090
Rx -11.00 +2.50 x 090
A
Hyperflange
B
Back toric design
C
Thick edge design
D
Myoflange
A hyperflange
This design reduces the edge thickness of a high minus lens increasing patient comfort and allowing the lens to center better.
During the diagnostic evaluation of the following patient you note the lens rotates 10 degrees to your left. Which of the following lens parameters would you order for the patient?
Patient’s refraction -3.00-1.25x160
Diagnostic lens 8.4 -3.00-1.25x280 14.5
8.4 -3.00-1.25x170 14.5
A patient is diagnostically fit with a gas permeable lens with the following parameters:
42.50 -3.00 9.5
If you wish to flatten the lens to cornea relationship, which of the following lenses would you order?
42.50 -3.00 9.0
If you flatten the base curve (42.00) but increase the diameter (10.0) you will not effectively change the lens to cornea relationship. If you increase the base curve (43.00 and 43.50) and do not significantly reduce the lens diameter, you will steepen the lens to cornea relationship. Only “B” will flatten the lens to cornea relationship because it reduces the lens diameter without alternating (steepening) the base curve.
When are soft lenses contraindicated?
A
When the patient has cylindrical keratometric readings
B
When the patient has more than 1.50D of refractive cylinder
C
When the patient has Graves’ disease
D
When the patient has irregular corneal astigmatism
D When the patient has irregular corrneal astigmatism
For this patient, the best option is a spherical rigid lens.
The tolerance for the overall lens diameter according to the ANSI standards is
+/- 0.05mm
All of the following will enable the practitioner to verify the overall gas permeable lens diameter except:
A
Slot gauge
B
Shadowgraph
C
Measuring magnifier
D
Radiuscope
Radiuscope
placing the concave side of a gas permeable lens against the lens stop of the lensometer will provide you with which of the following:
Back vertex power
An instrument that allows simultaneous verification of lens diamter, optic zone width and peripheral curve width is
measuring magnifier
When using the thickness gauge on a rigid contact lens, that gauge measures 0.73mm. This lens is most likely which type of lens?
High plus power
The instrument used for magnification of the edge of a rigid contact lens is a
Shadowgraph
The tolerance for a rigid lens power under +/-5.00D is:
0.12D
The tolerance for a rigid lenses between 5.12 and 10.00D
0.18
Lensometer spherical rx
radiuscope one base curve
spherical lens
lensometer spherical rx
radiuscope two base curves
Warped lens
Lensometer Sphero-cylindrical Rx
Radiuscope one base curves
Front Toric lens
Lensometer Sphero-cylindrical Rx
Radiuscope two base curves
back toric lens
Lensometer Sphero-cylindrical Rx
Radiuscope two base curves
Bi-toric
Which of the following statements is most accurate?
A
Routine cosmetic daily wear patients should be seen at 3 month intervals for a contact lens evaluation
B
Patients with a history of GPC should be refit with disposable soft lenses and followed on a bi-weekly basis for 6 months
C
New soft lens fits should be seen one week, one month, three months and 6 months from the time of their initial fit, then every 6 to 12 months
D
Patients who are wearing GP lenses after penetrating keratoplasty need fewer follow-up visits than keratoconus patients because their corneas are now spherical
C New soft lens fits should be seen one week, one month, three months and 6 months from the time of their initial fit, then every 6 to 12 months
Choice A would be correct only for patients who have already gone through the sequence of follow-up care recommended for new contact lens werers as outlined in choice C. choice B involves an excessive number of follow-up visits which can be inconvenient for the patient and impractical for the practitioner. If the GPC is so severe that the patient must return every 2 weeks, they are not yet ready to be refit with contact lenses. Choice D is incorrect because it is rare that a penetrating keratoplasty results in a spherical cornea and post-graft patients tend to be more difficulat to fit with contact lenses. Once must also wastch the graft/host junction closely for problems.
When using the LARS principle for lens rotation correction and comparing the degrees to clock minutes, a toric lens that rotates exactly half-way between 5 o’clock and 6 o’clock must be compensated for by an adjustment of:
15 deg
Which type of lens would best satisfy this patient’s visual needs given the following information?
K’s 43.00 @ 160/44.00 @ 075 3+ distortion
Rx -2.00 +1.00 x 075
A
Spherical soft lens
B
Soft toric lens
C
Soft bifocal lens
D
spherical GP
D Spherical Gp
The 3+ distortion is most probably due to irregular astigmatism and is best corrected with a rigid lens option
A rigid contact lens measures +15.00D BVP. The FVP will measure:
a lesser dioptric reading
The power of a high plus lens will always measure a larger numerical value to back vertex power (BVP) when compared to the reading in front vertex power (FVP).
Patients who are fit with lenses that will be worn overnight on a flexible or extended wear basis:
Should be seen as early as possible in the morning for follow-up of overnight wear
It is important to see patients who sleep in their lenses as soon as possible after awakening in order to detect corneal edema. The edema resolves as oxygen is transmitted through the lens in an open-eye environment and will probably be gone if the follow-up visits are scheduled later in the day. It is important to see all extended wear patients the morning after they sleep with their lenses for the first time to detect any advers reactions, even if the patients have been long-term successful wearers of daily wear lenses.
Patients who are fit with lenses that will be worn overnight on a flexible or extended wear basis:
Should be seen as early as possible in the morning for follow-up of overnight wear
It is important to see patients who sleep in their lenses as soon as possible after awakening in order to detect corneal edema. The edema resolves as oxygen is transmitted through the lens in an open-eye environment and will probably be gone if the follow-up visits are scheduled later in the day. It is important to see all extended wear patients the morning after they sleep with their lenses for the first time to detect any advers reactions, even if the patients have been long-term successful wearers of daily wear lenses.
The base curve of a rigid lens was ordered 7.84mm and was received measuring 7.94mm. this lens is ________than ordered.
A
0.50D Steeper
B
1.00D Steeper
C
0.50D Flatter
D
1.00D Flatter
0.50D Flatter
Every 0.05mm of radius equals approximately 0.25 diopters. The lens ordered was 43.00D, but was received as a 42.50D
Given the following information:
K’s 42.50 @ 180/44.50 @ 090
Rx -3.50 -2.50 x 090
Select the lens power if the lens is ordered one half diopter steeper than K:
-4.00
Jill is wearing a rigid lens with the base curve of 44.00D and a power of +3.00D sphere. she requires an over-refraction of -0.50D and the lens needs to be steepened by 0.50D. What parameters should be ordered for the new lens?
44.50 +2.00
Begin with the new base curve. by steepening the lens by 0.50D, the new base curve will be 44.50D (44.00D plus the additional 0.50D). Add the over-refraction of -0.50D to the original lens power of +3.00D to arrive at the new lens power of +2.50D. However, by steepening the base curve by 0.50D, and additional 0.50D of plus tear lens has been created (Steep ADD Minus, Flat ADD Plus) requireing an additional 0.50D of minus power to compensate. This brings the new power to +2.00D
Carole’s GP contact lenses are fit on flat K. her refration is -5.00+2.00x090. What is the powere of her contact lenses?
-3.00D
The first step is to convert the prescription to minus cylinder which results in -3.00-2.00x180. the cylinder and axis are dropped which leaves -3.00 sphere. When a rigid lens is fit on K, NO COMPENSATION is needed for the resulting tear film so the lens power remains -3.00D.
During a follow-up exam, a patient wearing soft lenses, reports that their vision is clearer immediately after the blink and then blurs. The most likely cause is:
A steep fitting lens
Because of the flexible nature of soft lenses they may flex during the blink cycle causing the vision to fluctuate
What is the definition of “disinfection” as it relates to the care of contact lenses?
A procedure that reduces the level of microbial contamination on lens surfaces
The measuring magnifier may be used to measure which of the following GP parameters?
Posterior optic zone diameter and overall diameter
Which soft lens care system is most effective in the removal of deposits?
Hydrogen peroxide systems
Hydrogen peroxide is hypotonic (meaning solutions that are below normal saline concentrations or less acidic) and causes swelling of the lens secondary to osmosis. This results in surface expansion and breaking off some protein and lipid bonds. This therefore, aids in the removal of trapped debris. Later, lens shrinkage continues to rupture bonds, further sloughing off deposits.
Which of the following statements abou eye make-up is correct?
Eyeliner and mascara should be replaced ever 3-6 months to avoid contamination
If 3% generic hydrogen peroxide is substituted for the solution in one of the FDA-approved hydrogen peroxide care systems:
the solution may discolor the lens
Although generic peroxides are less expensive than the peroxides that are specially formulated for contact lens disinfection, many of them contain impurities, such as heavy metal residues or stabilizing agents, such as acetyl salicylic acid, that will cause green, brown or black discoloration of the contact lenses.
Use of a Wratten #12 or Tiffen yellow filter is important in evaluating the fluorescein pattern of patients with GP lenses because:
Many patients are wearing lenses containing UV inhibitors that block fluorescein
Newly fitted extended wear patients should have their first recheck in:
24 hours
If a GP lens fails to provide acceptable visual acuity, the fitter should first:
Have a sphero-cylindrical over-refraction performed to see if the reduced acuity is due to residual astigmatism
3 & 9 o’clock staining in GP lens wearers can best be eliminated by:
Reducing center and edge thickness and teaching the patient to blink completely
Which of the following statements concerning lens movement is not correct:
A
A tight lens may cause blanching of the limbal vessels
B
A tight lens may cause scleral indentation
C
A loose lens may cause blurred vision immediately following the blink
D
A loose lens will be consideraby more comfortable than a tight lens
D A loose lens will be consideraby more comfortable than a tight lens
A patient will have a much greater awareness of a loose lens and may experience a constant foreign body sensation when wearing a lens that moves excessively. A “tight” lens, on the other hand, may not cause immediate symptoms, but may cause burning, stinging and foggy vision due to corneal edema serveral hours after insertion.
In-office polishing of the anterior surface of a gas permeable lens surface will provide many benefits to the patient. Which of the following is not a benefit of polishing the lens in the office?
A
Cleaner lens surface
B
Increased lens comfort
C
Thinner lens edge
D
Removal of scratches on the lens surface
C Thinner lens edge
Polishing of the anterior lens surface will result in a reduction of deposits and scratches on thelens which will result in a cleaner lens surface and increased comfort for the patient. However, a thinner lens edge should not be a product of polishing the lens surface.
Which of the following is not characteristic of corneal edema?
A
Smoky vision
B
Spectacle blue
C
Increase in K readings
D
Peripheral flare
D Peripheral Flare
Which of the following is not used when blending peripheral curves in the office?
A
Slot gauge
B
Radius tools
C
Polishing compound
D
Suction cups or a spinner tool
A Slot gauge
When keratometric mires reflected off a soft contact lens are only clear when the wearer blinks, the lens fit is too:
A
Small
B
Large
C
Steep
D
Flat
Steep
The vaulting effect of a steep fitting soft lens will be flattened by the upper lid when the patient blinks, causing the mire reflection to clear immediately following the blink. When a soft lens is fitted too flat, the mires blur immediately following the blink and then clear as the lens settles into place. A soft lens that is too small or too large is not normally evaluated by keratometeric mire reflection.
When inspecting the blend on the bevel of a GP lens with a fluorescent tube:
An ideal blends should show a J-shaped or ski pattern in a smooth curve
The fluorescent tube should be in front of and higher than the examiner. The examiner should be positioned so the bare fluorescent tube is directly infront of and parallel to his or her shoulder. The lens must be held so the reflection of light on their posterior surface of the lens falls on its inferior portion, appproximately 65-75% of the distance from the top to the bottom of the lens. The lens must be tilted and positioned slightly to the side so the reflection is continuous to the edge of the lens.”
Diffuse central punctate staining is an indication of:
tight lens
A foreign body trapped under the lens and an excessively wide transitional zone would not result in diffuse central punctate staining.
Sandy returns to your office after being fit with soft contact lenses. She has complaints of the lenses becoming uncomfortable and burning as the day progresses. What might be the reason?
The lens is too tight
Complaints of a burning sensation may precede limbal compression and can be a forewarning of a tght lens. These symptoms are more common later in the day as the lens has been woorn for a number of hours and begins to tighten.
Mary is wearing a gas permeable lens with a base curve of 43.50D and a power of +2.75D. She requires a -0.75D sphere over this lens. If you wish ot order her a new lens with a curve of 43.00D, what will the new power be?
+2.50
The total effective power of a rigid contact lens is determined by the Rx in the lens and the induced power created by the lacrimal lens (tear film). A rigid lens fitted on K will not induce any power in the tear film. However, 0.25D of minus power is created in the tear film for every 0.25D fitted FLATTER than K with a rigid contact lens. When fitting steeper than K, 0.25D of PLUS power is created in the tear film for every 0.25D fitted STEEPER. Therefore, you must calculate the over-refraction and calculate the amount of induced tear film power to determine the required Rx of the lens to be ordered. You must calculate the over-refraction:
+2.75D Diagnostic lens Rx
-0.75D Over-refraction equals
+2.00D Rx of lens with base curve of 43.50D
You must also calculate the induced power change in the tear film if a 43.00D base curve is ordered
43.50D Diagnostic base curve
43.00D Ordered base curve results in
0.50D Minus tear film
All power changes can be remembered by this simple formula: when you fit “Steeper Add Minus” (SAM), “Flatter Add Plus” (FAP). Since the ordered lens will be flatter than the diagnostic lens, the base curve change must be added to calculate the induced tear film power.
Corneal edema is observed inferiorly under a prism ballast toric soft lens. What is the probable cause?
prism thickness is too great
If the lens was too tight or if the cornea required more oxygen, the edema would not be localized inferiorly. the thickness of the prism at the inferior portion of the lens inhibits the oxygen permeability of the lens.
Corneal microscysts are most apparent via biomicroscopy with which method of illumination?
retro
Indirect retro-illumination reflecting off the iris creates a suitable backdrop to highlight these very small, optically empty cysts.
Which type of slit lamp illumination is used for observing tear break up time?
Diffuse
When observing the break up of fluorescein on the cornea, it is best to use the widest, most diffuse illumination to encompass as much of the cornea s possible.
A non-wetting gas permeable lens may cause:
A
Hazy, filmy vision
B
Lens awareness
C
Dryness or grittiness
D
All of the above
All of the above
Causes of lens flexure may include:
1) Pressure exerted by the upper lid
2) High Dk lens material
3) Apical clearance lens design
4) Against-the-rule corneal toricity
all of the above
In patients with tight lids, the force of the upper lid may produce lens flexture. These patients often complain of difficulty focusing while doing near point activites such as reading and working on computers due to the increased lid action in a down gaze. Lens materials also play a role in lens flexure. Apical clearance lens designs may tend to flex more than alignment designs due to sagittal vaulting. Against-the-rule corneal toricity and oblique astigmatism cause more problems with flexure than with-the-rule astigmatism.
When evaluating fluorescein patterns, a special filter must be used with
Polymers with a UV blocker
Silicone acrylates and polymethylmethacrylates (PMMA) can both be evaluated with fluorescein. Hydroxyethyl methacrylate (HEMA) is a soft lens material and will turn yellow when exposed to fluorescein. Any lens materials with UV protectors will impede the ability to read fluorescein patterns and a special filter (Wratten #12) is necessary.
The wratten filter is used with the biomicroscope to:
Enhances fluorescein evaluation
Which of the following could cause a patient’s rigid contact lens to displace frequently and pop out without cause?
1) Excessive posterior peripheral curve
4) Flat base curve relationship
A patient with a high degree of with-the-rule astigmatism fitted with a spherical gas permeable lens will show touch:
on the horizontal meridian
Characteristically, there would be a band-shaped area of touch on the flattest meridian which is located horizontally on corneas exhibiting with-the-rule astigmatism.
a rigid lens showing apical touch is an indication of
a flat fit
Typically with a flat lens fit, there is apical touch with no fluorescein in the area of contact.
A rigid lens showing excessive apical pooling is an indication of:
A
A steep fit
B
An alignment fit
C
A flat fit
D
An astigmatic fit
A steep fit
A rigid lens showing central vaulting is indicative of:
Apical clearance fit
In an apical clearance fit, there will be vaulting over the apical zone of the cornea with come central pooling and absence of fluorescein in the intermediate area.
A rigid lens showing a band-shaped area of touch on the flattest meridian is an indication of a lens fit on a(n):
Astigmatic cornea
Fluorescein patterns on an astigmatic cornea are typically respresnted by a band-shaped area of touch that aligns with the flattest meridian. The steeper meridian will show areas of pooling.
When there is a slight pooling of fluorescein the peripheral curve portion of a rigid lens, it indicates:
Slight edge lift
This type of pattern indicates a lens to cornea relationship that enables tears to be flushed from under the lens with each blink.
On a compromised cornea, such as one that has undergone a corneal graft, what lens characteristic would be most beneficial?
High Dk/t
lenses that allow more oxygen to the cornea are beneficial for compromised cornea
What two design changes might be helpful in centering a high riding myopic lens?
Hyperflange lenticular
prism ballast
A hyperflange reduces the edge thickness of a high minus lens, therefore reducing the upward displacement of thelens from eyelid pressure. Prism ballast creates heavy edge on the inferior portion of the lens and helps it to orient lower by force of gravity and the “watermelon seed effect” (the upper lid squeezes the thinner apex of the lens forcing it downward). Flatter than K fitting and a myoflange would be counter-productive.
Gas permeable lens flexure may be eliminated by:
reducing sagittal vaulting
Increasing center thickness
Choosing a lower Dk material
Sagittal vaulting (lenses fitted steeper than flat K) may lead to lens flexure in higher Dk materials. You can reduce flexure by reducing the vault, increasing the center thickness or choosing a lower Dk material.
Corneal striae
not found in the corneal epithelium, therefore, the use of fluorescein is not necessary
Mike, a welder whose Rx is -6.00 +2.00 x180, has been advised to trade his PMMA lenses of 20 years for a modality that allows more oxygen to the cornea. The first lens of choice would be:
Low to mid Dk GP
A low to mid Dk lens would provide oxygen to the cornea and be more durable than a high Dk lens. It is unlikely that vision would be satisfactory for this patient in a soft contact lens until the cornea stabilized.
To increase tear exchange with a gas-permeable lens, all of the following should be attempted EXCEPT:
A
reduce the overall lens diameter
B
Flatten the peripheral curves
C
Increase the sagittal depth
D
Decrease the optic zone
Increase sagittal depth
This will tighten the lens fit and further reduce the tear exchange.
In order to create a smooth blend between the intermediate and peripheral curve of the following contact, which radius tool should be used?
CPC 7.50mm (45.00D), IPC 8.5mm, PPC 10.50mm
9.5 mm
The 10.2mm and 11.5mm tools are too flat. The 8.5mm is too steep and would create an uneven finish.
To correct a flat-fitting gas permeable lens, you could:
Enlarge the optical zone
A larger optic zone steepens a lens fit even if there is no change in the overall lens diameter. A decrease in the optic zone flattens the fit by enlarging the peripheral curve. A decrease in sagittal vaulting creates a flatter lens to cornea relationship. Decreasing the overall lens diameter also decreases the sagittal depth.
Which of the following will not increase the movement of a tight fitting gas permeable lens?
A
Enlarge the posterior optic zone
B
Decrease the posterior optic zone
C
Decrease the sagittal vaulting
D
None of the above
Enlarge the posterior optic zone
This will increase sagittal vaulting further tightening the fit and restricting lens movement.
