Amblyopia/Strabismus Flashcards
Question
A patient presents with a right hypertropia that worsens when he looks to the right and when he tilts his head to the right. Which of the following muscles is MOST likely affected?
Left inferior rectus
Right superior oblique
Left inferior oblique
Right superior rectus
Left inferior oblique
Explanation
Using the Parks three-step method, one can easily isolate the affected muscle. Draw out the muscles and circle appropriately. Remember that for Parks three-step, a right hypertropia entails a circling of the right IR and right SO and the left IO and left SR. Because the hypertropia is worse in right gaze, circle the right SR and the right IR and the left IO and the left SO. Lastly, because his hypertropia is worse when he tilts his head to the right, circle the right SR and the right SO, as well as the left IO and the left IR. The only muscle that has been circled three times is the left inferior oblique.
Question
Which of the following types of refractive error would have the greatest tendency to lead to amblyopia?
A five-year old girl with an uncorrected refractive error of OD: -3.25 DS and OS: -0.75 DS
A four-year old boy with an uncorrected refractive error of OD: +6.00 DS and OS: +1.50 DS
A three-year old boy with an uncorrected refractive error of OD: +1.50 DS and OS: -2.00 DS
A four-year old girl with an uncorrected refractive error of OD: +1.00-1.50 x 180 and OS: +1.50-1.25 x 180
A four-year old boy with an uncorrected refractive error of OD: +6.00 DS and OS: +1.50 DS
Explanation
A prescription in which there is a big refractive difference between the eyes, especially if both eyes are hyperopic, is most likely to cause amblyopia. Consider the prescription of OD: +6.00 DS and OS: +1.50 DS. The left eye will be able to accommodate 1.50 diopters to obtain a clear distance image and, because accommodation is bilateral and equal, the right eye will still be 4.50 diopters out of focus. This defocus will cause the left eye to dominate the cortical neurons, causing a decreased amount of binocular neurons and leading to poor stereopsis and amblyopia of the right eye.
A prescription of OD: -3.25 DS and OS:-0.75 DS will not lead to amblyopia because even though the right eye is blurry in the distance, at 30 cm its image will be clear and in focus. This also applies to the prescription of OD: +1.50 DS and OS:-2.00 DS. Although both patients will have good monocular corrected acuities, they will most likely possess poor stereopsis due to a decreased amount of binocular neurons because the eyes are never in focus at the same distance.
It is important to note that in order for amblyopia to occur, ametropia must be present during the critical period.
Question
A 2 year-old female is referred to your office for the evaluation of a possible eye turn. Upon examination you determine that she has a 15-prism diopter right esotropia. Dry retinoscopy reveals +2.00DS OD, and +1.50DS OS, while wet retinoscopy reveals +5.00DS OD, and +4.50DS OS. Which of the following refractive corrections is MOST appropriate to prescribe?
OD: +3.00DS OS: +2.50DS OD: +2.00DS OS: +1.50DS OD: +1.00DS OS: +0.50 DS OD: +5.00DS OS: +4.50DS Refractive correction is not necessary
OD: +5.00DS OS: +4.50DS
Explanation
There are some general rules that optometrists typically utilize in order to determine the amount of refractive correction to prescribe for children. In cases of hypermetropia, young children presenting with up to 4D of hyperopia, good acuities, and no complaints, spectacle correction is not necessary. With degrees of hyperopia greater than 4D, or complaints of near vision, a general rule of thumb is to prescribe about 2/3 of the full cycloplegic refraction. In patients where an esotropia exists (as in the patient in this question), the full cycloplegic refraction should always be prescribed (if hyperopic), as this may help reduce the angle of the deviation by decreasing the amount of accommodation that must be employed.
While performing the Worth-4-dot test (red lens placed over right eye) your patient reports seeing 3 green circles. Based upon these findings what is the correct extrapolation?
The glasses were placed backwards on the patient
Left eye suppression
Right eye suppression
Alternating suppression
Right eye suppression
Explanation
In the Worth-4-dot test, the red lens is generally placed in front of the right eye. Four dots are then projected onto the screen. The two horizontal circles are green, the top circle is white and the bottom circle is red (in most cases). The right eye alone views the bottom and the top circle as red and pink/red, respectively. The left eye views three green circles. Combined both eyes view four circles, two green, one lower that appears red and the upper one appears red/green. Viewing three green circles to the right of two red circles indicates crossed diplopia. Three green circles viewed to the left of two red circles denote uncrossed diplopia. The perception of three green circles alone is indicative of right eye suppression. If the patient reports two red circles suppression of the left eye is indicated.
Question
The unilateral cover test reveals the following results: cover right eye, left eye turns in: cover left eye, no movement of right eye: cover right eye, no movement of left eye. How would you classify these results?
Constant left exophoria
Constant left exotropia
Intermittent left exophoria
Intermittent left exotropia
Intermittent left exotropia
Explanation
Movement of the uncovered eye on the unilateral cover test indicates that eye was not directed at the target of regard. In this instance, movement of the left eye was noted on the first attempt at covering the right eye but the left eye remained stationary when the test was repeated. Any movement seen on the unilateral cover test is diagnosed as a tropia of the eye that moved. Since the left eye did not move each time the right eye is covered, it is described as an intermittent movement. Since the left eye rotated inward, this is described as a left exotropia.
The presence of a phoria is tested for by administration of the alternating cover test. Phorias cannot be subdivided as intermittent or constant.
Question
A 12-year old white female presents with an intermittent, alternating exotropia of 15 prism diopters at distance and near. Uncorrected visual acuity is 20/20 OD, OS. Wet retinoscopy reveals +0.50 DS OD, OS. What is the most appropriate treatment for this patient?
Prescribe -1.00 spectacles for full-time use with gross convergence exercises; no surgery required at this time
No spectacle prescription or surgery required at this time. Suggest vision therapy, i.e., gross convergence exercises 5 min/day
Prescribe +0.50 OD, OS spectacles for full-time use with gross convergence exercises; consult an ophthalmologist (OMD) for strabismus surgery
No prescription at this time; gross convergence exercises daily; consult OMD for strabismus surgery
No prescription at this time; consult OMD for strabismus surgery
Plano lenses OU with 20 prism diopter of horizontal prism for full-time use; consult OMD for surgery
No spectacle prescription or surgery required at this time. Suggest vision therapy, i.e., gross convergence exercises 5 min/day
Explanation
A strabismus is present with this patient but does not require surgery or correction at this time because the patient does not have a monocular strabismus and the magnitude of the angle of deviation is <20 prism diopters. Additionally, the patient’s visual acuity is 20/20 without correction, so no spectacle correction is required at this time. If the patient had a prescription of -0.50 with decreased acuities, one would consider prescribing spectacles. Gross convergence exercises are recommended for improvement in gross convergence activities and control.
Which of the following methods can be used to test for the presence of eccentric fixation?
Visuoscopy
The Hirschberg test
The Bruckner test
Binocular versions
Visuoscopy
Explanation Angle Kappa (Lambda), visuoscopy, Haidinger's Brush, and the Brock-Givner afterimage transfer tests are all methods of investigating for the presence of monocular fixation. The Hirschberg test allows for the determination of the direction, magnitude, and frequency of the ocular deviation. The Bruckner test may be used to detect small angle deviations, media opacities, anisometropia, and tumors. Binocular versions allows for the determination of the comitancy of the deviation.
You wish to assess the comitancy of your patient’s deviation via the alternate cover test in all nine diagnostic fields of gaze. The results are as noted below from your point of view:
What is the correct diagnosis given these findings? Right Eye Fixating: 5 BO 10 BO 15 BO 5 BO 10 BO 15 BO 5 BO 10 BO 15 BO
Left Eye Fixating:
5 BO 10 BO 30 BO
5 BO 10 BO 30 BO
5 BO 10 BO 30 BO
Answer Choices:
A comitant deviation due to an overacting right medial rectus
A comitant deviation due to an overacting left lateral rectus
A non-comitant deviation due to an underacting right medial rectus
A non-comitant deviation due to an underacting left lateral rectus
A non-comitant deviation due to an underacting left lateral rectus
Explanation
When assessing comitancy, the deviation should be roughly equivalent in all fields of gaze. The primary deviation is assessed when the non-paretic eye is fixating in primary gaze and the deviation is neutralized with prism. The secondary deviation is measured when the paretic eye is fixating and the deviation is neutralized in straight-ahead gaze. The deviation will be greater when the deviated eye is fixating. The deviation will also be greater towards the side of the affected muscle.
What is the name of the sensory perception that results in the simultaneous appreciation of two dissimilar superimposed images caused by stimulation of corresponding retinal points by different objects?
Suppression Pathological diplopia Stereopsis Confusion Physiological diplopia
Confusion
Explanation
At the onset of strabismus, there are two sensory perceptions that arise based on the normal projection of stimulated retinal points. These are known as confusion and pathological diplopia. In order to appreciate these, the patient must possess the ability to perceive images from both eyes simultaneously.
Confusion refers to the simultaneous perception of two dissimilar images that are superimposed upon one another. This occurs in cases of strabismus in which the fovea of the fixating eye is stimulated by the image of the target of regard, while the corresponding retinal point in the non-fixating eye (usually the fovea also) is stimulated by the image of a different object. This results in simultaneous superimposition of two different objects.
Pathological diplopia is the simultaneous appreciation of two images of the same object in two different positions. This occurs in cases of strabismus in which the fovea of the fixating eye is stimulated by the image of a certain object, while that same object falls on a different (non-corresponding) retinal point other than the fovea in the non-fixating eye. This causes the same object to appear in two different locations. In patients with esotropia, the diplopia is considered homonymous (non-crossed), while exotropes experience heteronymous diplopia (crossed).
A concerned father reports that one of his 12-month-old infant’s eyes does not appear straight. You decide to perform the Hirschberg test to evaluate for strabismus. The corneal reflex of the right eye is centered, while the left reflex is displaced 0.5 mm superiorly relative to the center of the pupil. Angle Kappa (Lambda) is zero for each eye. What is the correct deviation and magnitude of the observed strabismus?
Left hypertropia of 11 prism diopters
Left hypertropia of 22 prism diopters
Left hypotropia of 22 prism diopters
Left hypotropia of 11 prism diopters
Left hypotropia of 11 prism diopters
Explanation
The Hirshberg test is performed at a distance of 50 cm. A penlight or transilluminator is held just below the doctor’s preferred eye and the doctor then sits in front of the patient and directs the beam towards the patient’s nose while the patient is instructed to fixate on the light. The position of the corneal reflexes relative to the center of the pupil is assessed in each eye. Superior displacement of the corneal reflex suggests hypotropia, while inferior displacement infers hypertropia. Each millimeter of displacement of the reflex from the center of the pupil equates to roughly 22 prism diopters of deviation.
Which of the following actions will result in UNDER-estimation of the angle of deviation while performing the alternate cover test?
Placing the fixation target slightly below the patient’s eye level
Stacking prisms in the same orientation while attempting to neutralize the ocular deviation
Using an accommodative target of 20/25 in a patient who is correctable to 20/20 vision
Having the patient wear their distance glasses while performing the cover test at a simulated distance of 6 m
Stacking prisms in the same orientation while attempting to neutralize the ocular deviation
Explanation
When attempting to neutralize the patient’s deviation using prism, the stacking of prisms oriented in the same manner will result in the underestimation of the deviation. Stacking of prisms that are oriented in different directions is acceptable (i.e. base-out and base-up). When performing the alternate cover test, it is important to use an appropriate accommodative target as well as having the patient wear their habitual spectacles. Failure to control for accommodation may result in improper measurement of the magnitude of the ocular deviation. When performing the cover test at near, it is often recommended to hold the target slightly below the patient’s eye level.
You have appropriately diagnosed a 42-year old black male complaining of acute, binocular horizontal diplopia with an ischemic Cranial Nerve VI palsy OD. He presented with the following clinical findings:
Visual Acuity (cc): OD: 20/20 OS: 20/20
Habitual Prescription: OD: -2.50 DS OS: -2.50 DS +1.00 add
Systemic Blood Pressure: 210/120 RAS @ 10:30am
Fasting Blood Sugar: 280 mg/dL @8:00a
Unilateral Cover Test: 40 prism diopter constant right esotropia
Versions: -4 restriction in right gaze of the right eye
Diplopia resolves with 30 prism diopter Base Out over the right eye.
What is the most appropriate treatment for this patient?
Answer Choices:
Place a patch over the right eye of his current habitual prescription; refer to ER for immediate systemic work up
Spectacle lenses: OD:-2.50 DS OS: -2.50 DS Add: +1.00 with 15 BO ground in prism OD, OS; refer to emergency room for systemic work up
No treatment at this time; monitor for changes in 4-6 weeks; refer to primary care physician for systemic work up
Occlusion patch over the spectacles of the left eye for full time wear; monitor for changes in 4-6 weeks; refer to primary care physician for systemic work up
5 prism diopter Fresnel prism over the right eye only; refer to the ER for systemic work up
Refer to ophthalmology for strabismus surgery of the right eye
Place a patch over the right eye of his current habitual prescription; refer to ER for immediate systemic work up
Explanation
Placing a patch over the right eye of his current spectacle prescription along with an immediate ER referral is the most appropriate treatment because the Cranial Nerve VI palsy is acute and ischemic. Grinding prism into the glasses would prove useless, as an ischemic cranial nerve palsy is expected to resolve with time with appropriate systemic treatment. Additionally, 30 diopters of prism is too large to grind into a pair of habitual spectacle lenses. Though the deviation of the esotropia is high, surgery is not warranted at this time because it is caused by ischemia and may completely resolve with time.
The ER is warranted in this case, as a primary care physician consult would be more appropriate if the patient’s systemic blood pressure and fasting blood sugar were not extremely high. The patient’s blood pressure is considered a hypertensive emergency.
Which of the following tests for stereopsis does not require the use of polarizing glasses?
The Randot stereo test
The Random dot E test
The Lang stereo test
The Titmus stereo test
The Lang stereo test
Explanation
The Random dot E, the Titmus stereo test, and the Randot stereo test all require the use of polarizing glasses to achieve stereopsis. The Lang stereo test is administered without the use of polarizing glasses, which is helpful with anxious or non-cooperative children. The test plate uses a random dot stereogram pattern to test for bifixation. The card is held at 40 cm and the child is asked to find a star, a car, and a cat (for Lang I) which all represent different levels of stereopsis (600”, 550”, and 1200”, respectively).
Which 2 of the following are TRUE in regards to central and peripheral suppression? (Select 2)
In peripheral suppression, the image from the peripheral retina of the deviating eye is suppressed to avoid diplopia
In peripheral suppression, the image from the peripheral retina of the deviating eye is suppressed to avoid confusion
In central suppression, the image from the fovea of the deviating eye is suppressed to avoid diplopia
In central suppression, the image from the fovea of the deviating eye is suppressed to avoid confusion
In peripheral suppression, the image from the peripheral retina of the deviating eye is suppressed to avoid diplopia
In central suppression, the image from the fovea of the deviating eye is suppressed to avoid confusion
Explanation
Confusion refers to the simultaneous perception of two dissimilar images that are superimposed upon one another. In order to avoid confusion, the image from the fovea of the deviating eye is suppressed.
Pathological diplopia is the simultaneous appreciation of two images of the same object in two different positions. In order to avoid diplopia, the image from the peripheral retina of the deviating eye is suppressed.
Which of the following tests would be the most appropriate to conduct if a patient presented with the following symptoms: unexplained asthenopia, presence of head tilt, and tilt of targets on other tests when dissociated?
Hirschberg Test Double Maddox Rod Accommodative Facility Test Visuoscopy Bruckner Test
Double Maddox Rod
Explanation
Head tilt and tilt of targets would indicate a cyclotorsion. The double Maddox rod would be the most appropriate test to conduct in order to indicate direction and angle size of the torsion. A head tilt can also be attributed to non-concomitancy; hence other tests that could aid in diagnosis include version testing, forced-duction, alternate cover test, Park’s 3-step, and Hess-Lancaster.
Visuoscopy is used to diagnose monocular fixation.
Accommodative Facility Test is used to test accommodative dysfunction.
Although the Bruckner Test is used to detect an ocular deviation, it will not help explain a head tilt.
The Hirschberg Test is also used to detect an ocular deviation, but will not explain a head tilt. This test will provide an estimated amount of ocular deviation, but does not detect any cyclotorsion.
