Contact Lenses CH3

Question 1

In order to determine the base curve for a patient’s contact lens, one must perform:
a) keratometry
b) lensometry
c) refractometry
d) slit-lamp exam

Answer 1

a) The keratometer measures the curvature of the cornea. The base curve of the lens is then
selected to complement this measurement.

Question 2

Soft contact lens diameter can be selected by measuring the patient’s:
a) pupillary distance
b) vertex distance
c) visible iris diameter
d) corneal curvature

Answer 2

c) A soft lens should extend beyond the limbus, so one needs to measure the visible iris diameter (limbus-to-limbus).

Question 2

For most contact lens fitting purposes, it is acceptable to measure corneal diameter:

a) using an ophthalmoscope set on +10.0 and a millimeter rule
b) by measuring the visible iris with a millimeter rule
c) by using a pachymeter
d) by anesthetizing the eye and using calipers

Answer 2

b) A millimeter rule is adequate for measuring the limbus-to-limbus value.

Question 3

Which of the following is not a factor in determining the appropriate power of a contact lens?

a) pupil diameter
b) refractive error
c) vertex distance
d) astigmatism

Answer 3

a) Pupil diameter could possibly figure in on the design of a rigid contact lens, but is not a
factor in the power of a soft or rigid lens.

Question 4

Your patient, a 63-year-old woman, wants to try contact lenses. Which of the following
should be done?

a) tear evaluation
b) pachymetry
c) glare test
d) conjunctival biopsy

Answer 4

a) Tear production and quality is an important consideration when fitting a woman of menopausal age or anyone in whom dry eye might be a concern. A Schirmer’s tear test, tear break-up time, and slit-lamp exam are the most common tear evaluations.

Question 5

Your patient is going to be fit with rigid gas permeable (RGP) lenses. In addition to
the usual parameters, you should also measure:
a) corneal thickness
b) palpebral fissures
c) axial length
d) contrast sensitivity

Answer 5

b) RGPs are more dependent on eyelid structure than soft lenses because it is critical that they move with each blink. The distance between the upper and lower lids (the palpebral fissure) should be measured with a simple millimeter rule.

Question 6

A good rule of thumb when instructing patients regarding contact lenses is to:

a) provide a training session offering oral and written instruction
b) provide written instruction and tell the patient to call with questions
c) provide a training session and oral instruction
d) develop a support group where successful lens wearers teach others

Answer 6

a) Patients should be given a training session that includes verbal instruction plus written
instructions to refer to at home. Providing only written instruction or no written material at all is an invitation to failure. Trusting patient instruction to other patients is ill advised.

Question 7

The first rule to teach patients about handling contact lenses is:
a) always use a mirror
b) work over a clean surface
c) always wash hands first
d) never touch the lens itself

Answer 7

c) Patients should be taught to wash his or her hands before handling lenses. (This is one
of the rare times where “always” does not signal a wrong answer!)

Question 8

Before inserting a soft lens, the patient should make sure it is not inverted. This can
be done by:
a) visual inspection or the taco test
b) visual inspection or the jelly roll test
c) inserting the lens in an inversion tester
d) viewing the lens’ reverse image in the mirror

Answer 8

a) Patients can be taught to recognize an inverted lens by both visual inspection and the taco test. The taco test involves holding the lens on thumb and forefinger and gently squeezing. If the lens edges flip inward, like a taco shell, then it is not inverted. (There’s no such thing as the jelly roll test or an inversion tester.)

Question 9

To insert a soft lens:
a) the lens should be dry and the finger wet
b) the lens and finger should be dry
c) the lens should be wet and the finger dry
d) the lens and finger should be wet

Answer 9

c) Inserting a soft lens is easiest if the lens is wet (not dripping) and the finger is dry (to
prevent sticking).

Question 10

The patient should be instructed to place a contact lens:
a) directly on the cornea
b) on the inferior sclera, then slide it up
c) on the margin of the lower lid
d) on the nasal sclera, then slide it over

Answer 10

a) The lens should be placed directly on the cornea, bull’s-eye style. Sliding is not a good
idea with a rigid lens, as this can cause a corneal abrasion. A lens on the lid margin is almost sure to be blinked out.

Question 11

Use of lotion or moisturizer before handling lenses or use of makeup, hair spray, or
face cream after inserting contact lenses can cause:
a) lens film
b) corneal edema
c) degradation of the lens
d) giant papillary conjunctivitis

Answer 11

a) To prevent a filmy build-up on the lens, only hand soap that is free of moisturizers and other additives should be used. Makeup, face cream, and hair spray should be used before inserting lenses. Hand lotion should be used after.

Question 12

The patient asks what he or she should do if the contact lens drops into the sink while
trying to insert the lens. You tell the patient:

a) rinse the lens with saline and insert
b) rinse the lens with rewetting drops and insert
c) clean and disinfect the lens as per solution instructions
d) replace the lens

Answer 12

c) A dropped lens should be cleaned and disinfected before wearing. No exceptions.

Question 13

Soft contact lenses are most easily removed by:
a) using a plunger cup
b) blinking them out
c) squeezing them out
d) pinching them out

Answer 13

d) Soft lenses are pinched out with thumb and forefinger at the 9 and 3 o’clock positions. A plunger could tear a soft lens. Blinking and squeezing do not work.

Question 14

Damage to soft contact lenses is frequently caused by:
a) enzymatic cleaners
b) rolling them between the fingers
c) long fingernails
d) defective materials

Answer 14

c) Long fingernails are the nemesis of soft contact lenses. A person who is unwilling to cut the nails can learn to adapt, however, by turning the fingers slightly to keep the nails away from the lens and eye.

Question 15

Rigid contact lenses are often removed by blinking them out. For this technique to
work:
a) the lens should be moved onto the sclera first
b) the lens must be centered on the eye
c) the patient must flip the edge of the lens with the finger
d) the patient must squint and look up

Answer 15

b) Blinking out a rigid lens requires the patient to look down, open both eyes wide, and pull the temporal canthus with thumb or finger. The lens must be centered on the eye for this to work.

Question 16

All of the following are helpful/proper techniques for using a plunger to remove a
rigid lens except:
a) locate the lens on the eye before applying the plunger
b) wet the plunger with wetting solution first
c) run the plunger over the cornea and sclera to locate a “lost” lens
d) carry an extra plunger in your pocket or purse for emergency removal

Answer 16

c) Teach your patients never to apply the plunger to the eye unless they know exactly where the contact lens is. “Fishing” for a lost lens with the plunger is disastrous and painful if the plunger adheres to cornea or sclera. A drop of wetting solution helps the lens stick to the plunger, and carrying an extra plunger is always a good idea.

Question 17

Soft lenses should be cleaned immediately after removal because:

a) grunge is easier to remove at body temperature
b) the patient might forget to do it later
c) grunge is harder to remove once the lens has dried out
d) otherwise enzymes are needed

Answer 17

a) Body temperature grunge is easier to remove. A soft lens should not be allowed to dry out.

Question 18

The difference between cleaning and disinfecting is:
a) cleaning is mandatory; disinfecting is optional
b) cleaning removes film and debris; disinfecting kills germs
c) cleaning kills germs; disinfecting removes film and debris
d) cleaning is optional; disinfecting is mandatory

Answer 18

b) Neither cleaning nor disinfecting is optional. Disinfectant cannot reach all the surfaces of a dirty lens. Cleaning removes dirt, film, and deposits; disinfectant kills germs.

Question 19

When using a one-step contact lens solution, what should one do upon removing a lens
from the eye?

a) put the lens directly into the case with fresh solution
b) place the lens in the palm, add solution, and gently rub with fingertip
c) rinse lens with solution and rub vigorously between the thumb and index finger
d) rinse the lens under the water faucet and gently rub with fingertip

Answer 19

b) It is recommended that the contact be cleaned with solution and gentle friction even
when using a “no-rub” or all-in-one formula.

Question 20

Enzymatic cleaners may be used weekly for daily-wear soft lenses and gas-permeable
lenses in order to:

a) sterilize the lenses
b) prolong the life of the lens material
c) remove protein deposits
d) reduce splitting and chipping

Answer 20

c) Enzyme cleaners are used to remove protein build-up on soft and gas-permeable lenses. They do not provide the advantages listed in answers a, b, or d.

Question 21

When not being worn, even rigid lenses should be stored in soaking solution because:

a) this prevents warping
b) this reduces the chances of chipping the lens
c) this maintains the power of the lens
d) this maintains the integrity of the plastic

Answer 21

a) A rigid lens that is stored dry for a period of time can warp.

Question 22

If a gas-permeable lens dries out:
a) it must be replaced
b) it can still be worn immediately
c) it should be soaked for at least 4 hours
d) it should be soaked for a week before wearing

Answer 22

c) If a gas-permeable lens dries out, the base curve may change. It should return to normal
after soaking for 4 hours or overnight.

Question 23

If soft contact lenses are not going to be worn for a few days:

a) add more soaking solution periodically to keep the lenses covered
b) screw the case lid on tight to prevent evaporation
c) use only nonpreserved saline as a soak
d) change the soaking solution every day to maintain disinfection

Answer 23

d) For disinfection to be maintained, the disinfecting solution should be changed daily.
Adding a little active disinfectant to a chamber of old disinfectant dilutes the active solution, rendering it too weak for the purpose. Saline (preserved or otherwise) does not disinfect.

Question 24

Which of the following regarding “topping off” cleaning/disinfecting solutions is
false? (“Topping off” refers to the practice of adding a little fresh solution to what was
left in the case from the last cleaning.)

a) it weakens the lens material
b) it contaminates the solution
c) it dilutes the solution
d) disinfection is compromised

Answer 24

a) Topping off simply adds a little fresh solution to used solution that is “used up.” But once you stick your finger in the solution to put the lenses in, it is contaminated. Top off a couple times in a row, and there is no disinfecting going on.

Question 25

Wetting solutions are used to:

a) keep lenses sterile while stored in the case
b) enable tears to spread evenly on the lens surface
c) make the lens resistant to deposit build-up
d) prevent scratches on the lens surface

Answer 25

b) Wetting solutions, used with rigid lenses, cause the tear film to spread evenly over the
lens. This increases comfort. Wetting solution does not sterilize, reduce deposits, or prevent
scratches.

Question 26

Rewetting solutions are used to:
a) disinfect the lenses while on the eye
b) remove deposits
c) rehydrate the lenses while on the eye
d) treat ocular redness

Answer 26

c) Rewetting drops are used to ease dryness and mild discomfort caused by dryness during lens wear. This increases lens movement and comfort.

Question 27

Which of the following is the least sterile of these unapproved, ill-advised, and danger-
ous rewetting fluids?

a) saliva
b) tap water
c) urine
d) water from a swimming pool

Answer 27

a) Gross as it may be, urine is more sterile than saliva. (Telling your patients this may dis-
courage the terrible habit of wetting a rigid lens in the mouth!) Saliva harbors all kinds of
nasty, infection-causing bacteria. Tap water and pool water (although “cleaner” than saliva) are not the right solutions either and can cause the lens to adhere to the cornea, as well as cause corneal edema.

Question 28

Every patient who wears extended-wear contact lenses should be told to:

a) remove the lenses and clean them daily
b) allow the lenses to remain in the eye for up to 1 month
c) use lubricating drops every morning and during the day
d) endure occasional pain and redness as a matter of course

Answer 28

c) See answer 38. It is not necessary for every patient to remove and clean the lenses every
day, although some do and should, nor is it advisable to blithely allow every patient to wear them for a month at a time. Most physicians recommend weekly removal. If the eye is red or painful, the lens must always be removed.

Question 29

All of the following are true regarding a contact lens case except:

a) it can be boiled in water
b) it should be washed weekly with hot water and soap
c) it should be rinsed daily with fresh lens solution
d) the interior is disinfected along with the contacts

Answer 29

b) The contact lens case should not be washed with soap because residue could interfere with the disinfectant or cause a film on the lenses. The entire case should be replaced every couple of months.

Question 30

Patients who work around smoke, dust, and chemical fumes should be told:
a) they are not good candidates for contact lenses
b) they should wear rigid lenses, which will not absorb fumes
c) they should not wear contacts at work
d) they should change jobs if they want to wear contacts

Answer 30

c) A patient who works around smoke, dust, and fumes still can wear contacts, just not at
work!

Question 31

The contact lens patient should be told that if the eye ever becomes red or painful:
a) try another lens
b) irrigate the eye
c) bear with it
d) remove the lens

Answer 31

d) Before the new contact lens wearer walks out the door, the final, cardinal rule to be
emphasized is to remove a lens if the eye becomes red and/or painful. No exceptions.

Question 32

Corneal vascularization can result from chronic:
a) hypoxia
b) solution sensitivity
c) conjunctival injection
d) giant papillary conjunctivitis

Answer 32

a) Vascularization, or the development of new, abnormal blood vessels in the cornea, results from a lack of oxygen (hypoxia).

Question 33

The area of the cornea that most commonly becomes vascularized is the:
a) inferior limbal area
b) superior limbal area
c) 9 o’clock limbal area
d) 3 o’clock limbal area

Answer 33

b) The superior limbal area of the cornea (under the upper lid) is most often the spot where vascularization occurs.

Question 34

Corneal edema is caused by:
a) excess oxygen permeability
b) insufficient oxygen
c) excess carbon monoxide
d) excess tear production

Answer 34

b) Corneal edema is caused by a lack of oxygen to the cornea.

Question 35

Symptoms of corneal edema include:
a) blurred vision
b) rainbows around lights
c) injection and burning
d) all of the above

Answer 35

d) Symptoms of corneal edema include blurred vision, halos around lights, redness, and burning.

Question 36

Which of the following has been associated with Acanthamoeba infections in contact
lens wearers?
a) nonpreserved saline
b) thimerosal-preserved solutions
c) homemade saline
d) sample bottles of solutions

Answer 36

c) Acanthamoeba has been linked with homemade saline using salt tablets and distilled water.

Question 37

Patients who remove his or her extended-wear lenses only once a month experience a
higher percentage of all of the following except:
a) decreased need for artificial lubrication
b) redness
c) corneal anesthesia
d) exposure keratitis when lenses are removed

Answer 37

a) Every patient who wears contact lenses on an extended basis needs to lubricate the
lenses regularly, especially every morning. Corneal anesthesia is a loss of sensation.

Question 38

Giant papillary conjunctivitis is suspected to be:
a) an allergic response
b) an infection
c) a response to mechanical irritation
d) a sign of overwear

Answer 38

a) Giant papillary conjunctivitis is considered to be an allergic response of the body to the
protein deposits on a contact lens (usually soft). As the deposits break down, an allergic
response is triggered.

Question 39

In addition to mucus formation, itching, and lens intolerance, the hallmark of giant
papillary conjunctivitis is:

a) corneal ulcers
b) inflamed pinguecula
c) papillae on the palpebral conjunctiva of the upper lid
d) papillae on the bulbar conjunctiva under the upper lid

Answer 39

c) The signs and symptoms of giant papillary conjunctivitis include itching, mucus, lens
intolerance, and the formation of large papillae on the inner surface of the upper eyelid.
(The palpebral conjunctiva lines the lids, and the bulbar conjunctiva covers the sclera.)

Question 40

The patient with excess tear secretion may experience:
a) “sucked on” lens syndrome
b) increased risk of neovascularization
c) excessive lens movement
d) circumcorneal indentation

Answer 40

c) Excessive tears equal excessive movement as the lens floats around on the surplus fluid.
Answers a, b, and d are seen in a tight/dry lens situation.

Question 41

Patients using the monovision technique might experience problems:

a) taking the driver’s license vision test
b) in very bright light
c) looking from the desk to the board in classroom situations
d) when peripheral vision is checked by confrontation

Answer 41

a) The test for the driver’s exam is a distance vision test. Often, the eye fit for near will fail
to see the required distance figures. In this case, a letter or form may be required from the physician, explaining the situation.

Question 42

The advantages of soft lenses include all of the following except:

a) they are more comfortable than rigid lenses
b) they provide crisper vision than rigid lenses
c) there is less lens displacement
d) there is less lens loss

Answer 42

b) As a rule, soft lenses (being very flexible) do not provide the crisp, sharp vision of rigid
lenses.

Question 43

One of the main disadvantages of soft lenses is:
a) frequent lens loss
b) poor durability
c) low oxygen permeability
d) corneal injury on insertion

Answer 43

b) The soft lens’ flexible nature also makes it vulnerable to problems of durability. The lens
can be torn easily. (Nondisposable types may also crack or split with age. The life expectancy of a nondisposable soft lens is generally considered to be only about 1 year.) However, there is less lens loss, better oxygen permeability, and a lower risk of injury on insertion because the edges are soft.

Question 44

The characteristic of soft lens material that is responsible for most of the lens’
advantages (and disadvantages) is its:

a) tear exchange under the lens
b) ability to absorb water
c) resistance to deposits
d) larger diameter

Answer 44

b) The soft lens is hydrophilic, which means “loves water.” The fact that it absorbs water is
responsible for its entire nature. This includes comfort, flexibility, and oxygen transmission. There is very little tear exchange under a soft lens (as opposed to a rigid lens). These
lenses are not resistant to deposits. A larger diameter is possible because of oxygen transmissibility, but the diameter in and of itself is not responsible for the lens’ advantages and
disadvantages.

Question 45

One of the main risks of wearing soft contact lenses is:
a) modifications are impossible
b) residual astigmatism
c) infection
d) lens discoloration

Answer 45

c) The biggest risk listed is that of infection. The pores of soft lens material generally are
too small for bacteria to penetrate. However, once the lens forms deposits, there is a rough
surface on which bacteria may grow. In addition, the removal of a deposit may create a pit in the lens large enough to harbor bacteria. While it is true that modifications are impossible, residual astigmatism goes uncorrected, and the lenses can discolor, these hardly qualify as risks.

Question 46

Which patient is a poor candidate for soft lenses?
a) a patient with dry eye
b) a patient with a spherical refractive error
c) an infant or child
d) a recreational basketball player

Answer 46

a) If a hydrophilic lens does not get the water it “wants” from the tear film, its thickness
(and, thus, optics) can change, making the patient with dry eye a less-than-ideal contact
lens patient. Soft lenses usually correct spherical errors quite well. An infant and a child are good candidates because the soft lens provides more comfort and a low rate of lens loss on impact. Rigid lenses may pop out on impact, which makes the soft lens a good choice for the recreational basketball player as well.

Question 47

Fitting a dry eye with a soft lens can be difficult because:

a) tear supplements cannot be used with soft lenses
b) the lens will move excessively
c) the diameter of the lens will change as it dries
d) the optical properties of the lens will change as it dries

Answer 47

d) As a soft lens dries out, its base curve (not diameter) changes, altering its optical qualities and producing blurred vision. Selected tear supplement drops can be used with soft contact lenses in place. The dry lens moves little if at all.

Question 48

All of the following are poor candidates for extended-wear lenses except:

a) those who work in a dusty environment
b) those with chronic blepharitis
c) those taking blood thinners
d) those with pre-existing giant papillary conjunctivitis

Answer 48

c) There is no connection between taking blood thinners and wearing contact lenses.

Question 49

Which of the following probably would be a poor candidate for the monovision tech-
nique?

a) a public speaker
b) a teacher
c) a bookkeeper
d) an actor

Answer 49

c) Anyone who continuously works up close and requires “perfect” near vision all the time
(such as a bookkeeper or accountant) probably is not a good candidate for monovision. Monovision involves a trade-off. Both distance and near vision are somewhat compromised, and binocular vision is sacrificed, but the patient does not have to cope with bifocals (glasses or contacts). Those people listed in the other answers do some up-close work, but also need to look frequently at a distance to see his or her audience.

Question 50

Monovision contact lens fitting for presbyopia involves:
a) fitting both eyes for distance and using reading glasses for near
b) fitting one eye (usually the dominant eye) for distance and the other eye for near
c) fitting one eye (usually the dominant eye) for near and the other eye for distance
d) wearing a contact lens for near in one eye and leaving the other eye uncorrected

Answer 50

b) In the monovision technique, one eye (usually the dominant eye) is fitted for distance and the other eye is fitted for near. In some cases, the dominant eye might be fitted for near, but this is not the routine procedure.

Question 51

The lower the water content of a soft lens:
a) the more durable the lens
b) the greater oxygen permeability
c) the less frequently it needs to be cleaned
d) the smaller the diameter

Answer 51

a) The lower the soft lens’ water content, the more rigid it is and, hence, the more durable.
Still, the soft lens does not approach rigidity in the sense that a hard or gas-permeable lens does. A low water content lens is less oxygen transmissible.

Question 52

A soft contact lens with a high water content will:
a) be more stable if lens dehydration occurs
b) allow for greater oxygen transmission
c) need to be disinfected by thermal methods only
d) be more durable if it is made of hydroxyethyl methacrylate (HEMA)

Answer 52

b) The higher the water content of a soft lens, the more oxygen can be transmitted to the
cornea. Unfortunately, these lenses are sensitive to dehydration if the environment changes. They also are heat sensitive, and some types may not be disinfected using thermal methods. Given the same water content, the non-HEMA lenses are more durable.

Question 53

The “Dk value” of a contact lens refers to its:

a) carbon dioxide permeability
b) oxygen permeability
c) carbon monoxide permeability
d) deciliter per kilogram value

Answer 53

b) The Dk value of a contact lens is a laboratory measurement of the oxygen permeability of a material. That is not to say, however, that the Dk is a measurement of how much oxygen actually reaches the cornea.

Question 54

The oxygen supply to the cornea can be increased by selecting a lens:
a) with a high Dk value or reduced thickness
b) with a low Dk value or reduced thickness
c) with a high Dk value or increased thickness
d) with a low Dk value or increased thickness

Answer 54

a) A high Dk value indicates greater oxygen permeability. A thinner lens also increases
oxygen transmission to the cornea.

Question 55

Selecting the power of a spherical soft contact lens is based on:

a) the spherical element found on refractometry
b) the cylindrical element found on refractometry
c) the spherical equivalent of the refractometric measurement
d) the refractometric and keratometric measurements

Answer 55

c) The power of a spherical soft contact is chosen by the spherical equivalent of the refractometric measurement. The K readings are not used for calculating the power.

Question 56

To obtain the spherical equivalent:

a) add half of the sphere to the cylinder algebraically, keeping the cylinder
b) add half of the cylinder to the sphere algebraically, keeping the cylinder
c) add half of the sphere to the cylinder algebraically, deleting the cylinder
d) add half of the cylinder to the sphere algebraically, deleting the cylinder

Answer 56

d) To find the spherical equivalent, add half of the cylinder to the sphere, then drop the
cylinder (and axis).

Question 57

You want to fit a spherical soft contact. The refractometric measurement is
–3.00 + 1.00 × 180. Your lens choice is:
a) –3.00 sphere
b) –3.50 sphere
c) –2.00 sphere
d) –2.50 sphere

Answer 57

d) The spherical equivalent is necessary because you are fitting a soft spherical contact. Half of the cylinder is +0.50. Add this to the sphere power: –3.00 + 0.50 = –2.50.

Question 58

With spherical soft lenses, a small amount of corneal astigmatism is:
a) increased
b) eliminated
c) tolerated
d) a reason to fit toric lenses

Answer 58

c) A small amount of astigmatism in a spherical soft lens wearer is merely tolerated, not eliminated. As long as the patient tolerates it, there is no reason to rush into fitting a toric lens.

Question 59

The amount of astigmatism that is present after the patient is fitted with lenses is
referred to as:
a) residual astigmatism
b) corneal astigmatism
c) lenticular astigmatism
d) irregular astigmatism

Answer 59

a) Astigmatism that is “left over” after the eye is fit with a contact lens is called residual
astigmatism.

Question 60

The most common source of residual astigmatism in contact lens wearers is:
a) the tear lens
b) the cornea
c) the crystalline lens
d) the retina

Answer 60

c) Residual astigmatism is most often caused by lenticular astigmatism, or irregular curvature of the crystalline lens (which does not show up on K readings).

Question 61

The patient with astigmatism may tolerate spherical soft contact lenses up to the point
that the astigmatism is:

a) less than one-third of the total refractive error
b) less than half of the total refractive error
c) lenticular
d) with the rule

Answer 61

a) As long as the astigmatism is less than one-third of the total refractive error, there is a
good chance that the patient can tolerate the vision provided by a spherical soft contact
lens.

Question 62

You plan to fit a soft toric contact lens. Which of the following is true regarding the
refractometric measurement?

a) it must be converted to plus cylinder
b) you will use the spherical equivalent
c) you want the patient to accept the most cylinder power possible
d) you want the patient to accept the least cylinder power possible

Answer 62

d) When fitting a soft toric, you want the least amount of cylinder correction that the patient
will accept, because the lens will rotate a bit on the eye. The higher the amount of cylinder, the more pronounced the visual problems caused by this rotation.

Question 63

The major difficulty with fitting toric lenses is:

a) patient discomfort
b) lens stability on the eye
c) arriving at the correct prescription
d) obtaining accurate over-refractions

Answer 63

b) Keeping the cylinder properly aligned means keeping the lens aligned. A spherical lens is normally pushed around and rotates during blinking. This spells disaster for a toric lens fit.

Question 64

An aid in evaluating the stability of a soft toric lens is:
a) the movement gauge
b) etch or laser marks on the lens
c) a protractor in the slit-lamp ocular
d) the contact lens gauge

Answer 64

b) Soft toric lenses have etch marks or dots either at the base or at the horizontal meridian. These can be observed with the slit lamp. The examiner looks for lens rotation as the patient blinks.

Question 65

Most practitioners would prefer to fit a gas-permeable contact lens instead of a tradi-
tional hard polymethylmethacrylate (PMMA) lens because:
a) vision with a gas-permeable lens is better
b) gas-permeable lenses are easier to handle
c) gas-permeable lenses are available for astigmatism
d) corneal warpage is less with gas-permeable lenses

Answer 65

d) Because a PMMA lens is not oxygen permeable, nearly all PMMA lenses cause some degree of corneal anoxia (an- means without and -oxia means oxygen). This, in turn, is responsible for corneal warpage. Because gas-permeable lenses do allow oxygen to reach the cornea, the incidence (and risk) of corneal warpage is much less. In the absence of corneal complications, both rigid lens types should provide crisp vision, are equally easy to handle, and can be ground to correct astigmatism.

Question 66

Which of the following makes a patient a poor candidate for gas-permeable contact
lenses?
a) history of giant papillary conjunctivitis
b) exophthalmos
c) corneal irregularity
d) neovascularization from soft lenses

Answer 66

b) An exophthalmic (bulging) eye usually is fit better with a soft lens, which is more stable
on the eye and does not interfere with the lids. Cases represented by the other answers are good candidates.

Question 67

The fact that gas-permeable contact lens material allows more oxygen to the eye
means that:
a) the lens can be larger than a PMMA lens
b) the lens is more comfortable than a PMMA lens
c) lens movement is not an important factor
d) the lens can be allowed to rest on the lower lid margin

Answer 67

a) Because a gas-permeable contact lens allows more oxygen to get to the cornea, the eye can tolerate a larger lens. True, it is more comfortable than a PMMA lens, but this is due to the fit (sliding under the upper lid versus bumping into it), not permeability. Lens movement still is important. The properly fit gas-permeable lens does not sit on the lower lid.

Question 68

The average life of a rigid gas-permeable lens is:
a) 6 to 9 months
b) 12 months
c) 18 to 24 months
d) 36 months

Answer 68

c) The average life of a rigid gas-permeable contact lens is 18 to 24 months. (The gas-
permeable material is not as tough as PMMA.)

Question 69

Over-refractometry of a contact lens is useful in fine tuning:
a) lens power
b) lens diameter
c) lens centration
d) lens base curve

Answer 69

a) Over-refractometry is used to refine the power of the contact lens and has little application in answers b through d.

Question 70

When taking a refractometric measurement over a contact lens of a patient over
40 years old:
a) first find out how the patient is corrected for presbyopia
b) measure each eye for distance only
c) measure each eye for near only
d) measure the right eye for distance and the left eye for near

Answer 70

a) If the patient is presbyopic, find out how the lenses are fit before pulling the refractor
forward. Are they monofit? Bifocals? Maybe distance in both eyes with reading glasses?
Knowing what to expect before you start will make your job easier.

Question 71

Bandage contact lenses are routinely used for all of the following except:

a) correction of a refractive error
b) promoting healing and protection
c) patient comfort
d) drug reservoir

Answer 71

a) While a bandage lens of a specific power may be chosen, correcting the refractive error
is not the priority in a bandage lens. In fact, a plano lens usually is preferred because it is
thinner (in the center for a plus lens and at the edges for a minus lens) and thus more oxygen permeable.

Question 72

The key in selecting a bandage contact lens is:

a) the patient’s refractive error
b) the patient’s ability to handle the lens
c) oxygen permeability
d) the patient’s corneal curvature

Answer 72

c) Getting oxygen to the cornea is the key in selecting a bandage lens. A bandage lens is
generally not handled by the patient. K readings may be taken and used, but not in every case.

Question 73

Even if a patient has a hyperopic refractive error, it is best to try a plano bandage lens
first because:
a) refractive correction may trigger ciliary spasms
b) a plano lens is thinner
c) a plano lens has a higher water content
d) the patient should avoid using the eye anyway

Answer 73

b) See answer 72.

72 answer: a) While a bandage lens of a specific power may be chosen, correcting the refractive error is not the priority in a bandage lens. In fact, a plano lens usually is preferred because it is thinner (in the center for a plus lens and at the edges for a minus lens) and thus more oxygen permeable.

Question 74

All of the following are suitable bandage contact lenses except:
a) a collagen disintegrating lens
b) a disposable soft lens
c) a low water content lens
d) a thin soft lens

Answer 74

c) A high water content lens versus a low water content lens is preferred because it is more oxygen permeable.