Refractometry CH14 Flashcards
Label the following (Figure 14-1):
compound hyperopic astigmatism, compound myopic astigmatism,
emmetropia,
hyperopia,
mixed astigmatism,
myopia,
simple hyperopic astigmatism,
simple myopic astigmatism,
F) compound hyperopic astigmatism
A) emmetropia
H) mixed astigmatism
D) simple hyperopic astigmatism
G) compound myopic astigmatism
B) hyperopia
C) myopia
E) simple myopic astigmatism
Which of the following prescriptions denotes emmetropia?
a) +2.00 sphere
b) –2.00 sphere
c) Plano + 2.00 × 180
d) Plano sphere
d) Emmetropia is the absence of refractive error, hence no correction (plano sphere) is
required.
In hyperopia:
a) the object image focuses on the retina
b) the object image focuses on the cornea
c) the object image focuses in the vitreous
d) the object image focuses beyond the macula
d) The hyperopic eye does not have enough plus power to focus the image on the retina.
Instead, the image falls beyond the retina/macula. (Technically, of course, this is not possible, except in a “virtual” sense.)
Myopia can be caused by:
a) irregular curvature of the cornea
b) removal of the crystalline lens
c) an eyeball that is “too long”
d) a stretched-out retina
c) The myopic eye is usually longer than average, causing the image to fall in front of the retina.
A refractive error of +2.00 + 2.00 × 180 would be classified as:
a) mixed astigmatism
b) compound hyperopic astigmatism
c) compound myopic astigmatism
d) simple hyperopic astigmatism
b) Hyperopia combined with plus cylinder astigmatism is termed compound hyperopic astigmatism.
The condition of having no lens is referred to as:
a) astigmatism
b) ametropia
c) aphakia
d) pseudophakia
c) The prefix a- means without. The term -phakia refers to the lens. So, aphakia means
without a lens.
Farsightedness may be caused by all of the following except:
a) heredity
b) removal of the crystalline lens
c) orbital tumor
d) migraine headaches
d) Migraine headaches do not cause any type of refractive error. An orbital tumor can cause
farsightedness if it has pushed the retina forward.
If your patient complains of blurred vision at near, the most likely cause is:
a) hyperopia
b) presbyopia
c) astigmatism
d) need more information
d) The answer depends on the age of the patient and her previous refractive status. There is not enough information here to make a good choice.
The classic symptom of myopia is:
a) blurred vision at near
b) blurred vision at distance
c) blurred vision at near and distance
d) headaches
b) Myopia is “nearsightedness”; the patient’s vision is at near (ie, blurred at a distance).
All of the following are characteristic of nearsightedness except:
a) it tends to be hereditary
b) it tends to accelerate during adolescence
c) the patient is more prone to retinal detachment
d) presbyopia is delayed
d) Myopia does not delay presbyopia; the myopic eye ages at the normal rate. (It is true,
however, that a mildly myopic patient might not notice the effects of presbyopia until later
than average.) The myopic eye tends to be longer than normal. This may result in the retina’s being stretched, predisposing one to retinal detachment (as in answer c).
Astigmatism occurs when:
a) the cornea is irregularly curved
b) the cornea is curved equally in all directions
c) an individual reaches his or her 40s
d) the retina is irregularly curved
a) Irregular curvature of the cornea is the textbook definition of astigmatism.
A 12-year-old patient complains of problems seeing the board at school. Most likely
the patient is:
a) myopic
b) presbyopic
c) malingering
d) hyperopic
a) A young patient who is having trouble seeing at a distance is most likely myopic. Presbyopia begins around age 40. Hyperopia blurs the near vision. Malingering means to lie, and we have to assume most patients (regardless of age) are telling the truth!
A 45-year-old male who has never worn glasses complains of decreased near vision.
Most likely he is:
a) myopic
b) presbyopic
c) astigmatic
d) aphakic
b) Presbyopia begins around age 40 and onward, whether the patient has worn glasses before or not. Myopia blurs vision at a distance. Astigmatism would likely have been
detected by age 45. Aphakia is the condition of having no crystalline lens in the eye, and
the patient is legally blind without correction (eg, intraocular lens, contact lens).
Presbyopia is caused by:
a) removal of the crystalline lens
b) loss of muscle tone in the ciliary muscle
c) degeneration of the zonules
d) loss of elasticity of the crystalline lens
d) As we age, the lens forms layers that compact, forming a hard nucleus. Thus, the lens loses its elasticity. It is true that the ciliary muscle tone decreases, but this is not the major factor in presbyopia.
A classic complaint of the presbyopic patient is:
a) “I cannot see where I’m going in a dark movie theater.”
b) “My arms are too short.”
c) “My eyes itch and burn.”
d) “My eyes draw and pull.”
b) The loss of near vision is often compensated for by holding reading material at arm’s length. Thus, the patient complains that his or her arms are too short.
Using a plus lens or an add corrects presbyopia because:
a) it restores plus power lost by the crystalline lens
b) it restores minus power lost by the crystalline lens
c) it neutralizes the patient’s hyperopia
d) it neutralizes the patient’s astigmatism
a) It takes more plus to see up close. When the presbyopic eye has lost the ability to add
enough plus, the plus is restored by using glasses with plus lenses.
A presbyopic myope with distance correction may find that his or her near vision
improves if the patient:
a) closes one eye
b) wears contact lenses
c) holds the reading material closer
d) takes off his or her glasses
d) A myope is corrected with minus power. Thus, taking off his glasses adds plus power to the eye, bringing near objects into better focus.
A presbyopic patient who is prescribed his or her first pair of single-vision reading
glasses should be told:
a) that distant objects will appear blurred through the glasses
b) that near objects will appear blurred through the glasses
c) that the glasses can be worn for all activities
d) to wear the glasses at all times to get used to them
a) The focal distance of a pair of reading glasses is usually 14 to 16 inches. Anything further away than that will be blurry. The patient should be warned about this.
Your patient is delighted because suddenly, at age 65, she can now read without her
bifocals. The most likely cause of this symptom is:
a) cataract
b) hyperopia
c) presbyopia
d) ocular hypertension
a) The onset of cataracts causes a myopic shift in the refractive error, often restoring reading vision lost by presbyopia.
A 75-year-old patient states that he wears contact lenses because he had cataract surgery without implants. You need to remove the contacts for part of the exam, but the patient objects. Why?
a) He is virtually blind without them.
b) He can read without the contacts, but cannot drive.
c) He can drive without the contacts, but cannot read.
d) His eyes are more comfortable with the lenses in.
a) A patient with no crystalline lens is legally blind without contacts or glasses. Driving
home without them would be impossible. Even walking around the office would be difficult and possibly embarrassing.
A 2-year-old male wearing -15.00 lenses screams if you take his glasses off. Why?
a) He has gotten used to feeling them on his face.
b) He is totally blind without them.
c) He cannot see more than several inches beyond his face without them.
d) He is probably punished at home if he takes the glasses off.
c) A –15.00 myope is not totally blind without glasses, but is certainly legally blind. A
2-year-old cannot articulate his frustration at not being able to see—he can only cry.
A new patient calls, complaining of poor vision with some glasses made elsewhere. She
wants to start over with your doctor. You should:
a) refuse to see her because she should really go back to her original physician
b) make the appointment, and ask her to bring the problem glasses plus her previous
glasses
c) tell her to return to her optician
d) make the appointment, and ask her to bring only her previous glasses
b) You might suggest that she see the original doctor or optician, but do not refuse to see
her. If she brings both pairs of glasses, you can analyze them and hopefully find the problem.
The automated refractor is an example of:
a) subjective testing
b) objective testing
c) self-testing
d) vision testing
b) The autorefractor takes the reading with no response from the patient, treating the patient as an “object.” This is an easy way to remember the difference between objective and subjective.
An automated refractor reading is especially helpful when the patient:
a) is new and has no glasses
b) has a previous refraction on record
c) has cataracts
d) has a written glasses prescription with him or her
a) In cases b and d, there is information from which a refractometric measurement could
be started. A patient with cataracts may not get an accurate AR measurement because of the opacities, plus the information given in the question does not state whether or not the patient has been seen before. An AR on the new patient (ie, with no refractive record in your practice) who has no glasses (ie, from which to read a prescription) would be the most useful of the bunch.
An autorefraction reading would be helpful in all of the following cases except:
a) prescribing glasses (without subjective testing)
b) following cataract surgery
c) evaluating an aphasic patient
d) evaluating the refractive error of a child
a) It is not usually accepted practice to prescribe an AR as glasses; subjective refinement via refractometry is required. An AR would be useful in all of the other cases. Aphasia means “without speech.”
The key instruction to the patient during automated refractometry (AR) is:
a) “Don’t blink.”
b) “Tell me if the image blurs.”
c) “Look straight ahead.”
d) “Hold your breath.”
c) Alignment is key for a good AR reading. Most autorefractors are so fast that blinking
will not interfere with the reading. Besides, a good tear film means a clearer path of light
during the analysis. If the patient talks during the reading, alignment will be disturbed.
Holding the breath makes no difference.
Some autorefractors allow the assistant to manipulate the reading in order to provide
the clearest image possible. This pushes the AR into the realm of:
a) subjective testing
b) retinoscopy
c) prescribing
d) duochrome testing
a) Subjective testing of any kind involves asking for a response from the patient. Still, the reading would not be prescribed directly under most circumstances; refinement using
lenses would still be done. Most autorefractors use the principles of retinoscopy: evaluating how light reflects from the eye in order to suggest a possible refraction.
Patient prep for an AR could include all of the following except:
a) explaining the procedure
b) sanitizing areas of patient contact
c) adjusting the table height for comfort
d) instilling topical anesthetic
d) Topical anesthetic is not required for an AR.
Performing an AR after the patient is dilated:
a) provides no useful information
b) will be inaccurate
c) is needed when prescribing bifocals
d) may reveal additional hyperopia
d) If a patient accommodates (ie, focuses at near) during an AR, then the reading may be
less hyperopic than the patient actually is. When accommodating, the eye adds “more plus” to itself, which the AR responds to by adding more minus.
An AR measurement may be used:
a) to plug into an intraocular lens formula
b) to confirm change between current glasses and refraction
c) as a glasses prescription
d) to guide laser-assisted in situ keratomileusis (LASIK) surgery
b) In cases where there is either little or no difference between the refraction and the
patient’s current glasses, or there is a good bit of difference but little vision improvement,
an AR gives another piece of information that may help confirm that the manual refraction
(MR) is accurate. An example might be where the MR shows an axis change of 30 degrees
compared to the patient’s glasses but improves vision only a little.
All of the following could result in erroneous AR measurements except:
a) posterior subcapsular cataract
b) central corneal scar
c) glaucoma
d) miosis
c) Glaucoma itself would make little difference in an AR measurement. Any media opacity (eg, posterior capsular cataract, central corneal scar) can diffract incoming light and render the measurement unusable. Miosis (small pupil) can also make it difficult to get an accurate reading.
The target in most autorefractors simulates distance viewing in order to avoid:
a) accommodation
b) unequal pupil size
c) induced prism
d) visual fatigue
a) See answer 29. However, the fact that the patient knows that the target is not actually far away can, itself, induce accommodation.
ANSWER 29: If a patient accommodates (ie, focuses at near) during an AR, then the reading may be less hyperopic than the patient actually is. When accommodating, the eye adds “more plus” to itself, which the AR responds to by adding more minus.
An appropriate use of an AR measurement would be:
a) to select final contact lens power
b) use in intraocular lens (IOL) calculation
c) starting point for retinoscopy
d) starting point for subjective refractometry
d) The AR is generally entered into the phoroptor and then refined. Selecting a final contact lens power and gathering data for IOL calculation are matters of evaluating the patient’s vision using subjective methods. Generally, the AR takes the place of retinoscopy.
Error in AR measurement can result from:
a) inaccurate pupillary distance
b) having the instrument in a lighted hallway
c) using the incorrect cylinder format
d) induced prism
b) Dim lighting is recommended, as peripheral lighting may inhibit the instrument from aligning properly. PD does not factor into the measurement; in fact, many autorefractors
measure and provide this information.
An AR might include all of the following additional features except:
a) visual acuity
b) glare testing
c) keratometer
d) cover testing
d) Cover testing is an evaluation of the extraocular muscles, not of the eye’s refractive system. An AR with a built-in eye chart is great because it helps verify the accuracy of the reading. Many models also have glare and keratometry capabilities, increasing the instrument’s usefulness.
Which of the following is true regarding the difference between “refraction” and
“refractometry”?
a) Objective measurement is used in refractometry.
b) Only refractions are written in the patient’s chart.
c) Clinical judgment is used in a refraction.
d) Only a licensed practitioner can perform refractometry.
c) Refractometry is the measurement of a patient’s refractive error (by objective and/or
subjective means) and usually is recorded in the patient’s chart. Refraction includes the
clinical judgment necessary to arrive at the prescription based on the refractometric measurement. Ophthalmic medical personnel are allowed to perform refractometry. Refractions are only performed by those licensed to do so (ie, an optometrist or an ophthalmologist).
Which of the following will give the technician the most useful information regarding
the patient’s refractive status?
a) the history
b) the muscle balance check
c) the slit-lamp exam
d) the fundus exam
a) The history will tell you much that can affect the measurement: the presence of any
systemic or ocular disease that may affect vision, any medications that can affect vision,
past vision history, past problems with glasses, or visual symptoms. The option of doing a slit-lamp exam prior to refractometry is preferable, but not as necessary as knowing the patient’s history.
All of the following patients could reasonably be expected to have alterations to his or
her refractive status except:
a) a diabetic
b) a pregnant woman
c) a patient with cataracts
d) a patient taking allergy shots
d) As a general rule, taking allergy shots does not affect the measurement. Answers a, b,
and c can change the measurement.
In order to avoid compromising the distance measurement, refractometry should be
performed prior to:
a) tonometry
b) retinoscopy
c) pupil exam
d) muscle balance testing
a) Refractometry should be done prior to tonometry or any other procedure that applanates the cornea (A-scan, B-scan, pachymetry, cell count, etc). With any of these tests, there is the possibility of some corneal abrasion and/or edema, which can affect the patient’s vision and thus the measurement. Retinoscopy is done prior to refractometry in order to provide a starting point. The pupil test might dazzle the patient for a minute, but you can proceed once he or she recovers.
A slit-lamp exam is useful before refractometry in order to:
a) determine if astigmatism is present
b) measure the intraocular pressure (IOP)
c) check the clarity of the media
d) determine if refractometry is needed
c) The slit-lamp exam will indicate the clarity of the tear film, cornea, aqueous, lens, and
vitreous (collectively called the optical media), giving you an idea of the prognosis of the
measurement. Unless the patient has marked keratoconus, astigmatism will not be seen
with the slit lamp. Applanation tonometry can compromise corneal clarity. The necessity
for refractometry is determined by factors other than the slit-lamp exam.
Label the parts of the refractor (Figure 14-2):
pupillary distance (PD) adjusting knob,
cylinder power, cylinder power dial,
prism, PD scale, sphere dial,
aperture convergence lever, cross-cylinder
sphere power, 3-diopter sphere dial, level,
aperture, cylinder axis dial, aperture knob,
leveling screw
J) PD adjusting knob
A) cylinder power
O) cylinder power dial
M) prism
G) PD scale
D) sphere dial
F) aperture convergence level
I) cross-cylinder
C) sphere power
K) 3-diopter sphere dial
I) level
B) aperture
N) cylinder axis dial
E) aperture knob
H) leveling screw
Before beginning the refractometric measurement on an adult, it is important to:
a) explain the procedure
b) have an autorefractor reading
c) make sure he or she can read 20/20
d) instill artificial tears to clear the tear film
a) Patient education is one of the keys to successful measurements. An autorefractor reading might be nice, but is not necessary. Obviously, not everyone can read 20/20 (or they would not need us). If the tear film is inadequate, eye drops may be needed, but they are not required on every patient.
All of the following are appropriate adjustments to the refractor (phoroptor) before starting the distance measurement except:
a) set to the patient’s PD
b) set to an appropriate vertex distance
c) converge the apertures
d) make sure the instrument is level
c) Always set the PD, vertex distance, and level before measuring. The apertures are converged to test the reading (near) vision, not the distance.
All of the following are true regarding fogging except:
a) it may be used to avoid giving too much plus at near
b) it may be used to help prevent giving too much minus
c) it can be used as an alternative to occlusion
d) it can be used to relax accommodation
a) Fogging is used to reduce accommodation during refractometry, which helps prevent
giving too much minus. It also can be used instead of occlusion, but is not used to avoid
giving too much plus at near.
Fogging is accomplished by:
a) placing a polarized lens in front of the eye to blur the vision
b) placing the Bagolini lens in front of the eye to blur the vision
c) placing enough plus power in front of the eye to blur the vision
d) placing a Maddox rod in front of the eye to blur the vision
c) To fog, add enough plus sphere to blur the vision. (There is no set amount, but I prefer
+3.00.)
In general, the first step in refractometry is to:
a) correct as much of the refractive error as possible with cylinder
b) correct as much of the refractive error as possible with sphere
c) find the cylinder power using the cross-cylinder
d) find the cylinder axis using the astigmatic dial
b) The measurement starts by working with spheres. You want to correct as much of the
refractive error as possible with sphere.
When offering the patient changes in spheres, a good general rule is to:
a) refine the axis before the power
b) offer more plus first
c) offer more minus first
d) always use minus cylinder
b) Always offer more plus first, whether you are going from +2.00 to +2.50, or from –6.25
to –5.75. More minus frequently looks better to an eye that is accommodating. Sphere has
no axis.
You have no prior record on your young patient, and he has never worn glasses. His
vision is 20/80 uncorrected. A correction of –1.50 sphere brings his vision up to 20/30;
–2.00 and –2.50 sphere gives no improvement in vision. Your next step should be:
a) record the final measurement as –1.50 sphere
b) see if –1.75 or –2.25 sphere will help
c) use the duochrome test
d) check for astigmatism
d) If sphere alone does not correct a patient to 20/20, it is not time to stop! Start looking
for astigmatism. If –2.00 and –2.50 sphere did not improve, it is a waste of time to try
–1.75 and –2.25. The duochrome test is performed after best visual acuity has been
obtained using spheres and, if necessary, cylinder.
If your patient has more than 6.00 D of astigmatism:
a) you cannot use the refractor
b) the cross-cylinder will not work
c) the fogging technique must be used
d) an auxiliary cylinder lens must be used
d) Cylinder power in most refractors goes up to 6.00 D, but there is an auxiliary cylinder
lens that you can snap into the aperture to add more. The cross-cylinder is not dependent on a certain amount of astigmatism.
The astigmatic dial is useful for:
a) finding the exact cylinder power
b) refining astigmatic correction
c) finding the exact cylinder direction
d) estimating the cylinder axis
d) The astigmatic dial is useful in estimating the cylinder axis. You still must refine with
the cross-cylinder.
The astigmatic dial looks like:
a) a telephone dial
b) a clock face
c) a circular grid
d) a circle with horizontal lines
b) The astigmatic dial looks like a clock face.
When using plus cylinder, if the patient says that all the lines on the astigmatic dial
seem to be equally clear:
a) the test is over; proceed directly to cross-cylinder refinement
b) turn the cylinder axis knob 45 degrees, and ask again if any lines are darker
c) add +0.50 sphere, and ask again if any lines are darker
d) open the aperture, and try the test with both eyes together
c) If you are using plus cylinder and the lines on the dial appear equally black, add a little
sphere (ie, move in a more plus direction) and ask again. In minus cylinder, give –0.50.
Either way, you are moving the image off the retina enough to see if there is another meridian of focus.
In plus cylinder, if the patient says that the lines on the astigmatic dial running from
12 to 6 are clearer, you will set your axis cylinder at:
a) 90 degrees
b) 180 degrees
c) 0 degrees
d) 45 degrees
a) For plus cylinder, set the cylinder axis parallel to, or in line with, the darkest lines as the patient sees them.
In minus cylinder, if the patient says that the lines on the astigmatic dial running from
12 to 6 are clearer, you will set your axis cylinder at:
a) 45 degrees
b) 90 degrees
c) 135 degrees
d) 180 degrees
d) In minus cylinder, set the cylinder axis perpendicular to, or 90 degrees away from, the darkest lines as the patient sees them.
When using the astigmatic dial, once you have set your axis, you should:
a) add cylinder until all lines are equally clear
b) add sphere until all lines are equally clear
c) use the cross-cylinder until all lines are equally clear
d) remove the dial and refine with the cross-cylinder
a) After setting your axis, slowly give the patient cylinder power until the lines appear to be equally clear.
You are measuring a patient from scratch (no retinoscopy, lensometry, or prior
records). Your best spherical correction is +2.00 sphere for 20/60 vision. You use the
astigmatic dial and find that the lines are equally black with cylinder –1.50 × 180.
What is your next step?
a) Change the sphere setting to +2.75.
b) Change the sphere setting to +1.25.
c) Refine the cylinder axis.
d) Record the measurement.
a) For every 0.50 D of minus cylinder, you should now add 0.25 D of sphere in the plus
direction. This is to maintain equivalence. In plus cylinder, for every 0.50 D of cylinder,
you should subtract 0.25 D of sphere.
The cross-cylinder is used:
a) to refine cylinder axis and power
b) to refine sphere axis and power
c) to refine sphere and cylinder power
d) to refine sphere and cylinder axis
a) Use the cross-cylinder to refine cylinder axis and power. (Spheres do not have an axis.)
Before cross-cylinder testing, it is important to:
a) be close to the sphere power endpoint
b) refine sphere power to the endpoint
c) measure for bifocal add
d) balance the two eyes
a) If the spherical component of your measurement is too far off, your cylinder will not be correct. You will be trying to neutralize with cylinder what would be better corrected with sphere.
On cross-cylinder testing:
a) the power of the sphere should always be measured first, then its axis
b) the axis of the sphere should be measured first, then its power
c) the power of the cylinder should be measured first, then its axis
d) the axis of the cylinder should always be measured first, then its power
d) Always measure the cylinder axis first. (This is one of the few exceptions to my warning
about the word always.) If the axis is not refined first, you cannot get the accurate power.
When refining the axis using minus cylinder, you should follow which dot on the cross-
cylinder?
a) red
b) white
c) blue
d) there are no dots on the cross-cylinder
a) If you are using minus cylinder and are refining axis, follow the red dot. There are no
blue dots. Conversely, if you are using plus cylinder, then follow the white dot.
You are using plus cylinder and are refining cylinder power. The present cylinder
power is +0.50. The patient says that the letters are more clear when the white dot is
showing on the cross-cylinder. What should you do now?
a) rotate the axis toward the white dot
b) change the cylinder power to zero
c) change the cylinder power to +1.00
d) stop because you are at the endpoint
c) When refining power, the red dot means subtract, which is the same as “giving minus,”
and the white dot means add, which is the same as “giving plus,” regardless of whether you are working in plus or minus cylinder. If you are at cylinder power +0.50 and the patient likes the white dot choice better, you are going to move to +1.00 cylinder power. (In reality, you could alternately choose to go to +0.75, adding just +0.25, but that was not offered as an answer in this question.)
You are using minus cylinder and are refining cylinder power. The present cylinder power is –1.00. The patient says that the letters are clearer when the white dot is show-
ing on the cross-cylinder. What should you do now?
a) switch to plus cylinder
b) change the cylinder power to –1.50
c) change the cylinder power to –0.50
d) change the sphere power by +0.50
c) See answer 61. The white dot means give plus, so you should move from –1.00 to –0.50.
The generally accepted endpoint for the cross-cylinder test (for either axis or power
refinement) is:
a) when the first choice is better than the second choice
b) when the second choice is better than the first choice
c) when the two choices appear equal
d) when the patient states his or her vision is most comfortable
c) The cross-cylinder actually straddles a setting, so on one choice, the patient sees the setting with a little “plus” and on the other choice with a little “minus.” When straddling the correct reading, each choice is equidistant from that setting, and the choices will look about the same.
Your patient reads 20/20 with the following setting: –2.00 + 1.25 × 065. To refine the
sphere, you first change the sphere setting to –1.75. The patient says the 20/20 line is
now a bit blurred. You show her –2.00 again, and she says it is clearer. Now, you
change the sphere to –2.25. The patient says the letters are smaller but clearer. She
cannot read 20/15 at any setting. What is your next step?
a) see if –2.50 helps
b) record the final measurement as –2.25 + 1.25 × 065
c) record the final measurement as –2.00 + 1.25 × 065
d) record the final measurement as –1.75 + 1.25 × 065
c) Remember that a minus lens minifies. (You also could say that, compared to a +6.00, a
+2.00 minifies.) The patient’s impression that the letters have gotten smaller is generally an
indication of too much minus. But, it is best to check vision with yet smaller letters to see
if there is an improvement. Therefore, you return to the previous setting of –2.00 + 1.25 × 065 as your end-point.
The duochrome technique of refining sphere depends on:
a) the fact that green rays are refracted more than red rays
b) red rays will appear orange, and green rays will appear blue
c) the patient having normal color vision
d) contrast sensitivity to red light as opposed to green light
a) Green rays are refracted more than red rays, so red hits the retina first. Adding minus
moves the red rays behind the retina (virtually speaking) and pushes the green onto the retina. There is a difference of 0.50 to 0.75 D between the red and green wavelengths. Normal color vision is not required (see answer 70). Note: The duochrome test may also be called the bichrome test.
ANSWER 70: Even a red-green color blind patient who cannot distinguish between vivid hues can be tested using the duochrome if you refer to the left and right halves of the screen instead of the colors. No special lenses or tricks need to be used.
The duochrome test is useful to:
a) determine a patient’s color vision
b) help prevent giving too much plus
c) help prevent giving too much minus
d) refine cylinder correction
c) The duochrome test is used to prevent giving the patient too much minus sphere. It is not a color vision test, nor is it used to refine cylinder. The only time you have to worry about giving a patient too much plus is when measuring the reading add.
Before beginning the duochrome test, do all of the following except:
a) occlude one eye
b) get a final distance correction
c) place a red filter in front of the eye
d) fog with +0.50 sphere
c) The red filter is not used in the duochrome test. Fogging the eye with +0.50 makes the
letters in the red darker, so you can move toward the green by –0.25 steps.
If the patient says that the letters in the red panel are sharper, you should:
a) record this as your endpoint
b) add more cylinder
c) add more plus power to the sphere
d) add more minus power to the sphere
d) If the letters in the red are sharper and more distinct, remove 0.25 D of sphere (ie, reduce plus or increase minus). Go in small steps so you do not miss the endpoint and overminus.
The endpoint for the duochrome test generally is accepted to be when the letters:
a) in the red panel are clearer
b) in the green panel are faded out
c) are equally clear in both panels
d) are no longer visible in both panels
c) The endpoint is when the letters on both sides are equally clear. Some practitioners recommend that you leave the patient “one click into the green,” but that was not given here as a choice.
How is the duochrome test done if a patient is red-green color blind?
a) The duochrome test cannot be used.
b) Place a Maddox rod in front of the right eye.
c) Place a Bagolini lens in front of the right eye.
d) Refer to left and right sides instead of red and green.
d) Even a red-green color blind patient who cannot distinguish between vivid hues can be
tested using the duochrome if you refer to the left and right halves of the screen instead of the colors. No special lenses or tricks need to be used.
If the patient is accommodating during refractometry, this may result in:
a) a prescription that has excess plus
b) a prescription that has excess minus
c) a prescription without necessary cylinder correction
d) a prescription that will cause the eyes to relax too much
b) If the patient accommodates, he or she has added plus power to the eye. This is neutralized with minus sphere, or the removal of plus sphere, during the measurement. If pre-
scribed by the practitioner, this spectacle lens will not have enough plus, and the eye will
have to strain when wearing it, causing even more accommodation to be required for clear
vision.
All of the following may be used to reduce or eliminate accommodation except:
a) duochrome test
b) bringing the distant eye chart closer
c) fogging
d) topical cycloplegics
b) Methods to control or reduce accommodation include the duochrome test, fogging, and topical cycloplegics. Bringing the distant chart closer will stimulate accommodation.
A patient whose prescription is inaccurate due to accommodation will have to:
a) relax accommodation in order to see clearly when wearing the correction
b) have prism in the lenses to reduce diplopia
c) accommodate in order to see clearly when wearing the correction
d) have a bifocal for near vision
c) See answer 71.
ANSWER 71: b) If the patient accommodates, he or she has added plus power to the eye. This is neutralized with minus sphere, or the removal of plus sphere, during the measurement. If prescribed by the practitioner, this spectacle lens will not have enough plus, and the eye will have to strain when wearing it, causing even more accommodation to be required for clear
vision.
If a patient is known to be myopic:
a) one need not worry about accommodation
b) one must still reduce or eliminate accommodation
c) the eye has no ability to accommodate
d) avoiding too much minus is not critical
b) It is a common misconception that if the patient is known to be myopic, you need not
worry about accommodation. This is not true. You might easily refract a young myope who
only needs –2.00 sphere as a –4.00 or more.
The ideal distant refractometric measurement:
a) leaves vision slightly blurred on the plus side to avoid overminusing
b) is slightly overminused in order to stimulate accommodation
c) causes as much accommodation as possible
d) gives the clearest vision possible and relaxes accommodation
d) As a general rule, the ideal situation for distance is for accommodation to be relaxed and vision to be as clear as possible.
Balancing is performed:
a) with the right eye occluded
b) with the left eye occluded
c) with both eyes open
d) while standing on one foot
c) Both apertures are open during balancing. (Standing on one foot?! I thought it was time
for a little levity; optics can get pretty heavy!)
The purpose of balancing is:
a) to ensure that the vision is the same in each eye
b) to make sure that the eyes are accommodating equally
c) to ensure that the measurement in each eye is as nearly the same as possible
d) to make sure that the eyes are not crossing
b) The goal in balancing is to make sure that the eyes are accommodating equally. Ideally,
of course, this means that neither eye is accommodating at all for distance vision.
Your healthy patient has clear media, although you have not looked at the retina. Your best refractometric measurement yields only 20/40 vision. What should you do next?
a) Record the measurement as final.
b) Label that eye as amblyopic.
c) Get a pinhole vision.
d) Perform a stereo test.
c) Anytime a healthy-looking eye does not refract to 20/20, do a pinhole vision. If the pin-hole improves the vision, you should be able to improve acuity with the correct lenses. If the pinhole does not improve the vision, your refractometric measurement is probably the best you can do, and the doctor will look for pathology.
To test for the reading add, the standard near card is placed:
a) at the distance preferred by the patient
b) at 10 inches
c) at 14 inches
d) at 20 inches
a) The technician should measure the distance preferred by the patient, place the near test card at that distance, and move in the direction of plus, giving the least amount of add that will enable the patient to read clearly and comfortably at that distance. It is then important to document the distance at which the add was measured.
The general rule for determining the reading add is to:
a) give the least amount of plus possible
b) give the maximum amount of plus
c) go by the standard age chart
d) never give more than +3.00
a) In general, be cautious with giving plus. The goal is to leave half of the patient’s accommodation (if there is any) in reserve. If you give the maximum plus that the patient will tolerate, you totally eliminate natural accommodation at near. The age chart may be a guide, but each patient should be measured. Some patients will need more than +3.00. The word “never” should have indicated that answer d was not correct.
Using a trial frame might be preferable over using the refractor (phoroptor) when:
a) the patient has facial deformities
b) the patient already wears glasses
c) performing retinoscopy first
d) the patient has a head tremor
d) A patient with head tremors will be easier to work with using the trial frame. It would
be difficult to keep such a patient aligned with the refractor. A patient with facial deformities may not be able to wear or tolerate a trial frame. Retinoscopy is more conveniently
done using the refractor.
When measuring the refractive error of a patient with low vision, it is helpful to:
a) speak a little more loudly and slowly
b) urge him or her to choose quickly between lens options
c) use larger steps (ie, 0.50 or larger) for refinement
d) use smaller steps of 0.25 to increase accuracy
c) Use larger steps for low-vision patients to provide more contrast between the compared lenses. No need to speak louder; they can hear. Go more slowly, rather than quickly. Small steps are harder for them to see and judge.
The best instrument to use when measuring the refractive error of a low vision patient
is:
a) trial lenses and trial frame
b) phoroptor
c) automated refractometer
d) prisms to create separate images for each eye
a) Because low-vision patients often need lenses of high power, thus making vertex distance a very important issue, the trial frame is the instrument of choice. In addition, objective methods do not work well in low-vision patients with media problems. The trial frame also makes it easier to offer the patient larger increments when changing lenses. Low-vision patients may not appreciate a 0.50 D change and may require higher increments to appreciate the difference. By the same token, a 0.50 D cross-cylinder may not provide enough contrast, either. Use one that provides at least 1.00 D. Also, if the patient has a central scotoma, the small apertures in the phoroptor do not provide enough field of vision. For the same reason, full aperture trial lenses are best as well. Finally, the trial frame allows the patient to adopt any head posture that seems to clear the vision a bit.
The patient with nystagmus should be refracted using:
a) no special adaptations
b) the astigmatic dial
c) +3.00 lens instead of an occluder
d) –3.00 lens instead of an occluder
c) Occluding one eye may make the nystagmus worse. Fog the untested eye with +3.00 of plus; using minus would probably stimulate accommodation. Just do not forget to switch when you go to measure the other eye and to remove the +3.00 when doing that final vision check and documenting your results.
