Questions Flashcards
Which of the following medications may affect successful contact lens wear?
A. Antacids
B. Antihistamines
C. Aspirin
D. Laxatives
The answer is: B, Antihistamines
Antihistamines are beneficial when treating allergies and cold symptoms because they dry out the mucous membranes of the nasal passage. However, this may also lead to dehydration of the tear film. Antihistamines have also been known to slow down the blink rate and increase corneal sensitivity.
Which term refers to a sensitivity to light?
A. Presbyopia
B. Photophobia
C. Pannus
D. Ptosis
The answer is: B, Photophobia
Photophobia refers to a sensitivity (“phobia”) to light (“photo”). Presbyopia is the condition that results when patients are no longer able to focus on objects at a near point. Pannus is the invasion of blood vessels onto the cornea. Ptosis is the drooping of the upper eyelid.
The following is an example of what type of astigmatism?
K’s 42.50 @ 180 / 40.50 @ 90
A. With-the-rule astigmatism
B. Lenticular astigmatism
C. Against-the-rule astigmatism
D. Irregular astigmatism
The answer is: C, Against-the-rule astigmatism
Against-the-rule astigmatism is present when the keratometer readings are steeper in the horizontal meridian (42.50 @180) than in the vertical meridian (40.50 @90).
The cornea receives nutrients from:
- ) Aqueous humor
- ) Tears
- ) Limbal blood vessels
- ) Orbicularis Occuli
A. 1, 3 and 4
B. 2 and 3
C. 1, 2 and 3
D. 3 and 4
The answer is: C, 1, 2, and 3 (aqueous humor, tears, gimbal blood vessels)
The normal cornea is devoid of blood vessels. To provide metabolites, the cornea is nourished by diffusion of nutrients and oxygen by the aqueous humor, tears and vascular blood vessels in the limbus. The orbiculares occuli is a muscle in the eyelid whose primary function is lid closure.
The increased loss of ability of the crystalline lens to accommodate is called:
A. Presbyopia
B. Myopia
C. Hyperopia
D. Aphakia
The answer is: A, Presbyopia
Presbyopia is the gradual loss of accommodation due to the hardening of the crystalline lens that takes place as a person ages.
Which instrument can provide simultaneous information about the cornea, lids, conjunctiva, lashes, contact lens surface and fit?
A. Radiuscope
B. Corneascope
C. Slit lamp
D. Keratometer
The answer is: C, slit lamp
The radarscope will measure the base curve of a rigid contact lens. The corneascope and keratometer will give important information about the surface of the cornea. Only the slit lamp (or biomicroscope) can provide simultaneous information about the cornea, lids, conjunctiva, lashes, contact lens surface and fit.
The classic model of the pre-corneal tear film is composed of three layers. They are:
A. Lysozyme, oil, lacrimal
B. Sebaceous, mucoid, BAK
C. Lipid, aqueous, mucin
D. Water, mucoid, Lysozyme
The answer is: C, lipid, aqueous, mucin
The classic model of the pre-corneal tear film is composed of the lipid, aqueous, and mucin layers. The lipid layer is traditionally thought of as most anterior (front) while the mucin layer is most posterior (back).
Transpose the following Rx into minus cylinder form:
Rx -4.50 + 1.25 x 94
A. -3.25 -1.25 x 4
B. -3.25 -1.25 x 94
C. -4.50 -1.25 x 4
D. -5.75 -1.25 x 4
The answer is: A, -3.25 -1.25 x 4
To transpose a prescription from plus to minus cylinder, first add the amount of cylinder to the sphere power: -4.50 + (+1.25) = -3.25.
Then change the sign of the cylinder power from plus to minus: +1.25 becomes -1.25.
Finally, add or subtract 90 degrees from the cylinder axis: 94 - 90 = 4.
The average pH value of the human tear is:
A. 6.6
B. 7.4
C. 7.8
D. 10.0
The answer is: B, 7.4
Values higher than 7.4 are considered relatively alkaline, whereas values lower than 7.4 are considered relatively acidic.
If the manufacturer’s guidelines suggest a minimum of 4 hours for disinfection, what would you suggest to the patient?
A. Never leave lenses in disinfectant overnight
B. 2 to 3 hours is probably enough
C. Use surfactant cleaner and preserved saline
D. A minimum of 4 hours is required
The answer is: D, a minimum of 4 hours is required
Patients should always be directed to follow the manufacturer’s guidelines and not try to cut corners by leaving lenses in any solution for less than the recommended time. While overnight is longer than recommended and would not pose a problem for most patients, they should always be given very specific guidelines for time.
The main supply of oxygen to the corneal epithelium is derived from the:
A. Stroma
B. Collagen fibrils
C. Basal membrane
D. Tear film
The answer is: D, Tear film
The cornea is exposed to the atmosphere which contains 21% oxygen. Through a process known as diffusion, oxygen from the atmosphere dissolves into tears where it can be utilized by the corneal epithelium.
What is the term for the condition in which there is a loss of vision without any apparent disease to the eye?
A. Amblyopia
B. Aniridia
C. Astigmatism
D. Aphakia
The answer is: A, Amblyopia
Patients are amblyopic when they are not able to attain 20/20 vision with an eye that has not experienced any disease or trauma. Aniridia is the absence of an iris. Astigmatism refers to a refractive error in which light rays do not focus in a single point. Aphakia is the absence of the crystalline lens.
Which auxiliary trial lens will extend the keratometer range to approximately 30.00 D?
A. +1.00 D
B. +1.25 D
C. -1.00 D
D. -1.50 D
The answer is: C, -1.00 D
By placing a -1.00 D lens over the aperture of the keratometer, you can extend the low end range from 36.00 D to 30.00 D.
Which step should be performed first when taking keratometer measurements?
A. Rotate the drum to reflect the cylinder axis
B. Adjust the patient so that they are comfortable
C. Focus the eyepiece
D. Cover the patient’s eye that is not being measured
The answer is: C, Focus the eyepiece
Before then patient is seated int he keratometer, the examiner should focus the eyepiece. This is particularly important if you are not the only person using the keratometer during the day.
The following is an example of what type of astigmatism?
K’s 44.00 @ 180 / 44.50 @ 90
Rx -3.00 -2.50 x 180
A. Lenticular astigmatism
B. Against-the-rule astigmatism
C. Irregular astigmatism
D. Oblique astigmatism
The answer is: A, Lenticular astigmatism
Lenticular astigmatism is present when there is significantly more astigmatism in the patient’s refraction (2.50 D) than on their corneal surface (0.50 D). In this case, the astigmatism is not represented on the cornea and is most likely found in the crystalline lens.
Ocular signs of aging include:
- ) Tear film abnormalities
- ) Reduced lid elasticity
- ) Lens opacities
- ) Loss of accommodation
A. 1 only
B. 1 and 3
C. 2 and 4
D. All of the above
The answer is: D, all of the above (Tear film abnormalities, reduced lid elasticity, lens opacities, loss of accommodation).
All of these listed signs are normal physiological changes as we become older.
Transpose the following Rx into minus cylinder form:
Rx +1.50 +1.00 x 75
A. +1.50 -1.00 x 75
B. +2.50 -1.00 x 75
C. +2.50 - 1.00 x 165
D. +2.50 - 1.00 x 175
The answer is: C, +2.50 -1.00 x 165
To transpose a prescription from plus to minus cylinder, first add the amount of cylinder to the sphere power: +1.50 +(+1.00) = +2.50
Then change the sign of the cylinder power from plus to minus: +1.00 becomes -1.00
Finally, add or subtract 90 degrees from the cylinder axis: 75 + 90 = 165
The pre-corneal tear film provides:
- ) A smooth optical surface
- ) Metabolic nutrients to the epithelium
- ) Oxygen to the endothelium
- ) Limbal hyperemia
A. 1 and 3
B. 1 and 2
C. 2 and 3
D. 3 and 4
The answer is: B, 1 and 2 (A smooth optical surface and; Metabolic nutrients to the epithelium)
The pre-corneal tear film provides a smooth optical surface for the cornea. This is maintained by the blink mechanism, further providing metabolites (e.g., oxygen) to and from the cornea as well as removing waste products such as CO2 and dead epithelial cells. The endothelium receives its oxygen from aqueous humor within the anterior chamber. Limbal hyperemia is redness from engorged blood vessels in the gimbal area.
The cornea has five distinct layers. In order from anterior (front) to posterior (back) they are:
A. Epithelium, Descemet’s membrane, Stroma, Bowman’s layer, Endothelium
B. Endothelium, Stroma, Bowman’s layer, Descemet’s membrane, Epithelium
C. Epithelium, Bowman’s layer, Stroma, Descemet’s membrane, Endothelium
D. Endothelium, Bowman’s layer, Stroma, Descemet’s membrane, Epithelium
The answer is: C,
(anterior)
Epithelium Bowman's layer Stroma Descemet's membrane Endothelium
(posterior)
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
The answer is: A, Endothelium
The corneal endothelium provides the pumping mechanism of the cornea to expel fluid from the tissue and maintain corneal transparency. Bowman’s layer is an acellular layer which provides strength to the cornea. The epithelium is the outermost layer of the cornea and only plays a minor role in corneal metabolism. The basal membrane is a basement membrane which provides an attachment surface for the epithelium to adhere to Bowman’s layer.
A normal tear break-up time is:
A. 6-7 seconds
B. 10-12 seconds
C. Less than 5 seconds
D. More than 20 seconds
The answer is: B, 10-12 seconds
Typically fluorescein will remain on the cornea for 10-12 seconds before it begins to break up and dry spots appear. Less than seven seconds is considered a short break-up time and may limit the success of contact lens fitting.
A whitish haze in the peripheral corneal storm which does not stain and is often seen in the elderly is known as:
A. Neovascularization
B. Dellen
C. Arcus Senilus
D. Fuch’s Dystrophy
The answer is: C, Arcus Senilus
Arcus seniles consists of cholesterol deposits in the corneal periphery and does not affect contact lens wearing. A seller is a depressed area of compromised epithelial tissue on the cornea which stains due to lack of wetting from the pre-corneal tear film. It is generally found adjacent to an elevated area. Neovascularization is the abnormal growth of new blood vessels into the cornea. Fuch’s dystrophy is a corneal endothelial dystrophy affecting the central cornea.
Patients with keratitis sicca are more prone to:
A. Secondary infections
B. Loss of eyelashes
C. Losing their contact lenses
D. Steepening corneas
The answer is: A, 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. Loss of eyelashes or contact lenses and steep corneas are not related to keratitis sicca.
Upon removal of the crystalline lens, the patient is:
A. Aphakic
B. Myopic
C. Hyperopic
D. Astigmatic
The answer is: A, Aphakic
Aphakia is the absence of the crystalline lens.
The following Rx: represents:
OD +2.00 = 20 / 20
OS -3.00 -2.00 x 180 = 20/20
A. Presbyopia
B. Anisometropia
C. Amblyopia
D. Emmetropia
The answer is: B, 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 patient in the previous question (with Anisometropia) will best achieve stereopsis with which of the following modalities?
A. Contact Lenses
B. Spectacles
C. IOL
D. Bifocals
The answer is: A, Contact Lenses.
A patient’s depth perception (stereopsis) will be compromised if fitted with spectacles. An IOL (intraocular lens) is used for aphakia.
Tom’s spectacles with a power of -12.00 +0.50 x90, sit 10 mm in front of his cornea. The likely soft contact lens prescription for Tom would be:
A. -10.50 D
B. -11.75 D
C. -12.00 D
D. -12.50 D
The answer is: A, -10.50 D
The vertex distance correction is usually derived from a standard table. In the conversion of a prescription from the spectacle plane to the corneal plane, additional plus power is needed.
Comp = (D^2)/1000 * mm moved
The keratometer is an instrument used to measure:
A. Corneal curvature
B. Lens power
C. Lens diameter
D. Lens thickness
The answer is A: a keratometer measures corneal curvature.
A lensometer measures power. A diameter gauge measures diameter. A thickness gauge measures thickness.
The average life span of a corneal epithelial cell from mitosis through maturation and desquamation most nearly approximates:
A. One day
B. One week
C. One month
D. One year
The answer is: B, One week
A typical cycle may range from four to ten days
Which auxiliary trial lens will extend the keratometer range to approximately 61.00 D?
A. -1.25 D
B. +1.25 D
C. -1.50 D
D. +1.50 D
The answer is: B, +1.25 D
The range of the keratometer is 36.00 D to 52.00 D. To extend the range above 52.00 D, a +1.25 D lens is used.
Wearing lenses in high altitudes and dry environments may result in complaints of all but the following:
A. Photophobia
B. Chalazion
C. Grittiness
D. Burning sensation
The answer is: B, Chalazion
Photophobia, burning sensations and feelings of grittiness can all be attributed to dry, low oxygen environments. A chalazion is an inflammation of a meibomian gland and is not related to dryness.
The first line of defense in the protective system of the eye is formed by the:
A. Sebaceous glands
B. Lacrimal glands
C. Eyelids
D. Caruncle and semilunar folds
The answer is: C, Eyelids
The eyelids remove debris as we blink, control the amount of light that enters the eye and distribute tears across the cornea and conjunctiva to keep those tissues from drying out.
Transient keratometric mire distortion is usually due to:
A. Pre-ocular tear film
B. Prolonged rigid lens wear
C. Prolonged soft lens wear
D. Irregular corneal astigmatism
The answer is: A, 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.
In against-the-rule astigmatism, the steepest corneal meridian:
A. Is at or near 180 degrees
B. Is at or near 135 degrees
C. Is at or near 90 degrees
D. Is at or near 45 degrees
The answer is: A, Is at or near 180 degrees
In against-the-rule astigmatism, the cornea has a vertical ellipsoidal shape. This puts the long flat meridian at 90 degrees and the short, steep meridian at 180 degrees.
An inability to bring all of the keratometer mires into focus at the same time may indicate:
A. With-the-rule astigmatism
B. Against-the-rule astigmatism
C. Irregular astigmatism
D. Oblique astigmatism
The answer is: C, Irregular astigmatism
In cases of irregular astigmatism the major meridians are not 90 degrees apart causing the mires to not focus all at the same time. The meridians are 90 degrees apart when measuring with-the-rule, against-the-rule and oblique astigmatism.
In an alignment lid attachment GP fit, the fluorescein pattern should show:
A. Apical clearance and 360 degrees of bearing in the mid-periphery
B. A thin, even layer of fluorescein and less than 180 degrees of bearing in mid-periphery
C. Apical bearing and tear pooling inferiorly
D. Apical bearing and maximum edge lift
The answer is: B, A thin, even layer of fluorescein and less than 180 degrees of bearing in mid-periphery
Lid attachment GP fits should show a thin, even edge-to-edge layer of fluorescein stained tear film that exhibit alignment or slight apical feathering as well as less than 180 degrees of bearing in the mid-periphery to allow for a good tear exchange with each blink. Choice A, apical clearance with 360 degrees of bearing in the mid-periphery indicates a steep, tight fit with complete seal-off and no tear exchange. Choices C and D are indicative of an excessively flat fit.
In a GP wearer, an arcuate stain on the cornea may be due to:
A. Failure to close the lids completely when blinking
B. A lens fit that is excessively flat
C. Poorly blended secondary curves
D. Solution sensitivity
The answer is: C, Poorly blended secondary curves
Choice A, failure to close the lids completely when blinking, would result in 3 and 9 o’clock staining. Choice B would cause apical staining. Choice D would usually cause a very fine, diffuse superficial punctate keratitis (SPK) from limbus to limbus.
In a Schirmer I test:
A. The patient should produce sufficient tears to saturate the paper strip in 3 minutes
B. An anesthetic drop is instilled in the eye to eliminate reflex tearing
C. Fluorescein must be instilled in the eye to measure tear film break-up time
D. A patient with an un-anesthetized eye and normal tear output should wet at least 15mm of the filter paper in 5 minutes
The answer is: D, A patient with an un-anesthetized eye and normal tear output should wet at least 15mm of the filter paper in 5 minutes
The Schirmer I test is done without anesthesia and a patient with normal tear output should we at least 15mm of the strip in 5 minutes. Choice C refers to a test of tear quality, not quantity, that is timed and observed with the patient seated at a slip lamp.
The most powerful refracting surface of the eye is the:
A. Retina
B. Cornea
C. Crystalline lens
D. Ciliary Muscle
The answer is: B, Cornea
The cornea averages 43 diopters of refractive power. The retina is the innermost layer of the eye and contains nerve cells that receive the image that we see and transmit it to the brain. The crystalline lens plays a small role in the retraction of light with about 20 diopters of refractive power, accommodates to assist in bringing near objects into focus and helps to focus the image on the retina. The ciliary muscle assists with accommodation by contracting and allowing the lens to become thicker and more convex so it can bring near objects into focus.
Which keratometer reading indicates with-the-rule astigmatism?
A. 45.00 @ 175 / 44.50 @85
B. 48.00 @ 45 / 46.50 @135
C. 44.50 @ 15 / 44.75 @ 105
D. 46.00 @ 180 / 46.00 @ 90
The answer is: C, 44.50 @ 15 / 44.75 @ 105
With-the-rule astigmatism is characterized with the flattest corneal meridian being at, or close to, the 180 degree axis.
When evaluating tear film break-up time:
A. Rose Bengal will give a more accurate reading than fluorescein
B. Fluorescein should be instilled in the eye and the patient not allowed to blink until a reading is taken
C. A break-up time of less than 10 seconds may preclude success with contact lenses
D. The patient is seated at the keratometer, fluorescein is instilled in the eye and the patient told to blink to spread the fluorescein evenly across the cornea before timing is begun
The answer is: C, A break-up time of less than 10 seconds may preclude success with contact lenses
Rose Bengal is attracted to devitalized cells; it is not used to stain the tear film. Break-up time (BUT) testing 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. Generally, a BUT of greater than 10 seconds is needed for successful contact lens wear, Choice D is incorrect because testing is done at the slit lamp, not the keratometer.
The preservative in contact lens solutions:
A. Must demonstrate efficacy in killing bacterial, viral and fungal microorganisms
B. I usually a mercury compound such as thimerosal
C. Must kill all microorganisms on a contact lens in a 4 hour soak period
D. Is formulated to keep microorganisms from multiplying in a bottle of contact lens solution after it has been opened.
The answer is: D, Is formulated to keep microorganisms from multiplying in a bottle of contact lens solution after it has been opened.
Choices A and C are incorrect because preservatives are bacteriostatic, not bactericidal. They do not kill microorganisms, but only prevent them from multiplying in solution bottles after they are opened. Mercury compounds are rarely used anymore, due to their high rate of sensitivity.
Results of a refraction show a patient to see best at distance with a power of +1.25 +1.00 x 95, and at near with a power of +2.50 +1.00 x 95. What is the “add” power?
A. +1.25 D
B. -1.25 D
C. +1.75 D
D. +1.25 + 1.00 x 95
The answer is: A, +1.25 D
Add power is the algebraic difference between the distance Rx and the near Rx. Adds are always plus, and always contain sphere power only.
A pre-presbyopic myopic patient who is still able to read with single vision glasses may find that:
A. They are unable to see fine print when fit with contact lenses
B. If the vertex distance is reduced, near vision will be clearer
C. Monovision is impossible to adapt to
D. It is even more difficult to see the computer than to read with contact lenses that contain their distance prescription
The answer is: A, 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. Choice B is irrelevant to patients who wear contact lenses as the lenses fit directly on the cornea and cannot be moved closer to or further from the eye. Moving spectacles further from the eye will increase vertex distance and help near vision. Choice C is a means of allowing the presbyopic patient to read by fitting one eye for distance the other for near vision. Choice D is incorrect, since accommodation is needed to see the computer, which is further from the eye, than to read.
Amy’s +8.50 D spectacles sit 12 mm from the cornea. The power of a soft contact lens for Amy, properly vertexed, would be:
A. +8.00 D
B. +8.50 D
C. +9.50 D
D. +11.00 D
The answer is: C, +9.50 D
Vertex distance must be taken into account when spectacle power is +/- 4.00 D. In the conversion of a prescription from 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 @ 90
Rx: -3.00 +0.25 x 90
A. GP lens: 45.25 - 3.00
B. GP lens with toric posterior curves
C. Soft toric lens
D. Spherical soft lens
The answer is: D, Spherical soft lens
The patient’s refractive astigmatism is 0.25 D, which is essentially a spherical correction. A soft spherical lens will correct this although corneal astigmatism is present.
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 @ 90
Rx: -2.00 -1.00 x 180
A. 42.50 - 2.50 8.5
B. 41.50 - 1.50 8.5
C. 42.00 - 2.00 9.5
D. 41.50 - 1.50 9.5
The answer is: A, 42.50 - 2.50 8.5
An intrapalpebral fit is a small diameter, steep fitting lens designed to center between the upper and lower eyelids, The other choices are either large diameter or flat fitting lenses.
Which contact lens would best correct this patient’s visual needs, given the following information:
K’s 46.00 @ 180 / 45.50 @ 90
Rx: -3.00 -1.50 x 90
A. A soft spherical lens
B. A soft toric lens
C. A back surface toric GP lens
D. A front surface toric GP lens
The answer is: B, A soft toric lens
A soft spherical lens would not correct the lenticular astigmatism. GP lenses tend to decenter on against-the-rule corneas. There is not enough toricity for a GP lens with toric curves on the back surface to stabilize.
The average HVID for a patient is:
A. 15 seconds
B. 44.00 D
C. 11.5 mm
D. 0.9%
The answer is: C, 11.5 mm
HVID stands for Horizontal Visible Iris Diameter and is a measurement represented by millimeters (mm) of diameter.
If a patient has 1.50 D of refractive cylinder and keratometer readings of 44.00 @ 180 / 44.50 @ 90, you would expect a spherical gas permeable lens to:
A. Give them their best correctable vision
B. Result in residual astigmatism
C. Ride nasally
D. Ride temporally
The answer is: B, 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 that 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. There is no reason, given the information listed, to believe that the lens will either ride temporally or nasally.
Application of fluorescein should be used in which of the following situations?
A. Evaluation of gas permeable lens fit
B. Evaluation of soft contact lens parameters
C. Evaluation of vascularization of the cornea
D. Evaluation of gas permeable lens over-refraction
The answer is: A, Evaluation of gas permeable lens fit
Fluorescein is a valuable tool in evaluating the lens to cornea relationship of a gas permeable lens. A special type of fluorescein (fluorosoft) should be used to evaluate the staining beneath a soft contact lens but will not be useful in evaluating the parameters of that lens. Fluorescein will not add any information when observing corneal vascularization or performing over-refractions.
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?
A. Decreasing overall lens diameter
B. Increasing overall lens diameter
C. Increasing optic zone diameter
D. Increasing sagittal depth
The answer is: A, 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:
A. The lacrimal lens is a minus cylinder lens
B. Spectacle lenses are made in minus cylinder form
C. Most phoropters contain only minus cylinders
D. Minus cylinders make it easier to perform retinoscopy
The answer is: A, The lacrimal lens is a minus cylinder lens.
The contact lens power is determined by L.C. + 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 contact lens power.
Rx OU -3.00 -0.50 x 180, Add +1.25 D.
If spherical soft lenses are being fit using the monovision technique, what is the desired power for the eye fitted for near?
A. -2.00
B. -3.25
C. +1.25
D. -1.75 -0.50 x 180
The answer is: A, -2.00
The spherical equivalent power for the distance is -3.25 D. Combining the add power of +1.25 D results in the need for a total reading power of -2.00 D.
Which of the following lens designs would provide the best visual result for this patient?
K’s 43.00 @ 180 / 46.00 @ 90
Rx -3.00 sphere
A. Soft toric lens
B. Spherical gas permeable lens with increased center thickness
C. Truncated gas permeable lens
D. Soft spherical lens
The answer is: D, Soft spherical lens
A soft toric lens is not indicated in this instance. A spherical gas permeable lens would result in residual astigmatism. With an increased center thickness, corneal astigmatism will be corrected, which may actually blur the patient.
Which edge design is recommended for a +15.00 D aphakic GP lens?
A. Hyperflange
B. Lenticular myoflange
C. Concentric design
D. Intrapalpebral design
The answer is: B, 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 @ 90
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
The answer is: C, 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 soft lens will not be able to correct this amount of astigmatism. but, a soft toric lens will be able to correct all of the astigmatism.
What Rx would be ordered for a gas permeable lens fit on K?
K’s 43.00 @ 180 / 44.00 @ 90
Rx -3.00 +1.00 x 90
A. -1.00 D
B. -2.00 D
C. -3.00 D
D. -4.00 D
The answer is: B, -2.00
To determine the Rx of a gas permeable lens, first put the Rx in minus cylinder form: -3.00 +1.00 x 90 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 minus cylinder: -2.00 D.
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?
A. Hyperflange
B. More Prism
C. Truncation
D. Thinner edge design
The answer is: C, 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 placed on a patient’s eye:
43.50 -2.00 9.2
An over-refraction is performed with the following results: plano + 1.50 x 95
Which of the following lens parameters would you order for the patient?
A. 43.50 -0.50 -1.50 x 5 9.2
B. 43.50 -2.00 -1.50 x 5 9.2
C. 43.50 plano -1.50 x 95 9.2
D. 43.50 plano +1.50 x 5 9.2
The answer is: A, 43.50 -0.50 -1.50 x 5 9.2
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 95 becomes +1.50 -1.50 x 5
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: -1.50 x 5
The following soft lens is placed on a patient’s eye: 8.8 -4.00 14.0
An over-refraction is performed resulting in -0.75 D sphere. Which of the following lens parameters would you order for the patient?
A. 8.8 -3.25 14.0
B. 8.8 -4.00 14.0
C. 8.8 -4.75 14.0
D. 8.8 -5.25 14.0
The answer is: C, 8.8 -4.75 14.0
When applying the results of a 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:
A. Radiuscope
B. Lensometer
C. Profile analyzer
D. Contacto gauge
The answer is: C, 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: -2.50 -1.00 x 170
Diagnostic Lens: 8.7 -2.50 -1.00 x 170
A. 8.7 -2.50 -1.00 x 160
B. 8.7 -2.50 -1.00 x 170
C. 8.7 -2.50 -1.00 x 180
D. 8.7 -2.50 -1.00 x 10
The answer is: A, 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.
Which of the following lens designs would not provide a good visual result for this patient?
K’s 42.50 @ 180 / 44.00 @ 90
Rx -2.50 +1.50 x 90
A. Soft toric lens
B. Soft spherical lens
C. Spherical gas permeable lens
D. Aspheric gas permeable lens
The answer is: B, Soft spherical lens
A soft spherical lens will not correct the astigmatism present in this patient’s refraction so it will not provide adequate vision. A soft toric lens, spherical and aspheric gas permeable lens will correct the astigmatism.
In prescriptions of 4.00 D or greater, fitting contact lenses requires compensating the power for the change in vertex distance. When moving from the spectacle plane to the corneal plane, the compensated power will be:
A. More plus
B. More minus
C. More plus for plus lenses only
D. More minus for plus lenses only
The answer is: A, More plus
Regardless of whether the original spectacle power is plus or minus, when the position of the lens is moved toward the eye, more plus power is required to give the same effect as the original. For example, a +4.00 D spectacle Rx requires a +4.25 D contact lens power, and a -4.00 D spectacle wearer needs a -3.75 D contact lens. In both cases, the contact lens power is more plus than the spectacle Rx.
A prism ballast GP lens requires how much prism for proper orientation?
A. 0.75 to 1.50 D
B. +3.00 D at 6 o’clock
C. 1.50 to 3.00 D
D. Always 0.75 D
The answer is: A, 0.75 to 1.50 D
most cases that call for prism ballasting of a GP lens will require between 0.75 and 1.50 D of prism.
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
The answer is: 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. The base curve of a lens is not the measurement of a curve at all. It is a measurement of its radius of curvature.
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?
A. 8.4 -2.00 14.2
B. 8.4 -2.75 14.2
C. 8.4 -3.25 14.2
D. 8.4 -3.75 14.2
The answer is: C, 8.4 -3.25 14.2
When applying the results of an over-refraction to a soft lens, transpose the over-refraction to minus cylinder. Then determine the spherical equivalent (-1.25 D in this case) and add this to the existing power.
