The initial workup may be recorded on a preprinted sheet similar to the one illustrated in Figure 1. The following questions should be answered and the indicated tests performed and recorded during the process of patient evaluation before strabismus surgery.
Why was the patient brought in (why did he or she come in) for an examination?
What have the parents (what has the patient) noted about the eyes? ET, XT, hyper, constant, intermittent, closes one eye, tilts head, elevates or depresses the chin, eyes ‘jiggle,’ etc.?
Age of onset - when did the problem begin?
Birth weight (premature?)
Growth and development
o Present weight
o Sat up when?*
o Walked when?*
* of interest primarily in infants and young children
Any allergies, what medications are currently being used
Significant illness and surgical history
Diplopia (binocular - monocular)
Getting worse or better
Type of exercises
Strabismus - parents, siblings, others
Other eye problems
Trouble with anesthesia (malignant hyperthermia)
Head tilt (nodding)
Variability of deviation
Dancing eyes (nystagmus)
o When prescribed
What was done
A preprinted examination data collection sheet is a useful adjunct to the examination, particularly for the patient’s first visit. This form has been effective in our clinic, but in most instances a practitioner will design a form to meet his or her unique needs. The importance of showing this form is that it includes most of the tests required for a complete examination. Results of other tests such as passive duction evaluation, tensilon test, exophthalmometry, etc. may be noted on this form in the appropriate area with explanatory labels.
Visual acuity testing
Visual acuity is recorded as the smallest object a patient can see at a given distance. 20/20 vision (or 6/6 vision) means that at 20 feet (approximately 6 meters) a patient can see an object that subtends 5 minutes of arc with components of 1 minute. In the decimal system this is recorded as 1.0. The letter E with its 5 combined spaces and bars is an ideal target. If the smallest object an individual can see at 20 feet subtends 5 minutes of arc at 200 feet the object is 10 times larger. This is calculated as 20/200, 6/60, or 0.1. Visual acuity recorded as the viewing distance over the distance the smallest object seen subtends 5 minutes and is recorded: 20/60, 6/18, 0.3, etc.
With an infant or a child too young to cooperate for visual acuity testing, reaction to the examiner's face, a light, a non-illuminated (silent) interesting or compelling object, social situations, and, if poor vision is suspected, to an optokinetic tape or drum should be observed. Notation is made describing the best acuity observed; for example, ‘appears to be (not to be) visually alert to: (a note is made describing the size of the smallest object seen). Strong preference for one eye associated with objection to occlusion of this eye usually indicates amblyopia or an organic visual defect in the other eye. However, even normal infants tend to object vigorously to occlusion of either eye. Cross fixation, or using the eyes alternately, rules out amblyopia. Dim illumination is best for evaluation of vision in the neonate or very young infant. Simply turning off the overhead lights may turn a recalcitrant newborn with closed lids into an interested patient able to fixate on the examiner's face.
The preferential looking technique using Teller acuity cards has been used to quantify resolution acuity in the newborn and infant. This method can be employed to determine an objective value for visual acuity in a very young child. However, to determine relative acuity in order to establish the presence of preference of one eye for fixation and therefore amblyopia, simple clinical observation of fixation preference is sufficient to detect a difference in visual acuity of one octave in most young patients.
An E chart or a STYCAR (HOTV) chart visual acuity test can usually be accomplished at the earliest with girls at age 3 and with boys at age 3 1/2, although exceptions do occur. Linear testing with E's or letters is valid. Testing with isolated E's gives erroneously good vision results in the presence of functional amblyopia because of the absence of the crowding phenomenon. Crowding can be achieved resulting in accurate vision testing even with isolated optotypes by using crowding bars. These are lines equal to the width of the optotype segments placed at each side and above and below the single optotype used for visual acuity testing. We use isolated E's mainly for instruction. Vision in older children is determined with the letter chart. In children where testing with the E chart cannot be accomplished, Lea symbols or other recognizable pictures can be used. The Lea symbols are particularly useful to demonstrate a difference in visual acuity between the two eyes in a child too young to cooperate for other visual acuity testing. In an office or clinic setting, computer generated visual acuity testing provides all of the visual acuity testing options while at the same time providing standardized illumination, random display, and more. This instrumentation is useful but expensive. Relative visual acuity is more useful clinically than absolute acuity in an infant suspected of having amblyopia. Recognition acuity with Snellen optotypes (E's, the alphabet, or symbols) is a more stringent and, therefore, more accurate test than resolution acuity done with stripes. For this reason, we test vision with Snellen optotypes determining recognition acuity whenever we can obtain cooperation from a child.
If decreased vision is found in each eye when checked monocularly, vision should be checked binocularly. The examiner in this case should be looking for latent gross or micronystagmus. Fogging with a plus lens may be used to block vision in one eye but avoid nystagmus when determining monocular visual acuity in a patient with latent nystagmus. Near vision should be checked with E's, isolated letters or numbers, or sentence reading, depending on age.
Visual acuity testing with neutral density filters can differentiate functional from organic amblyopia. Vision in an eye with functional amblyopia remains at or near the same level when neutral filters of increasing density are introduced. Vision in a normal eye or in an eye with an organic cause for poor vision decreases proportionally with the increased density of the filter.
Near point of accommodation is determined in cooperative patients by moving a card with small print closer to the patient until the blur point is reached. The near point of accommodation is recorded in diopters or centimeters.
Pupillary response to light is evaluated by moving a light from in front of one eye to in front of the other in reduced ambient light. A Marcus Gunn afferent pupillary defect indicating decreased optic nerve function can be demonstrated with this test by noting a dilated pupil with the light shining in the involved eye (direct response) and constriction of the pupil when the light shines in the fellow eye (consensual response). With the ‘swinging’ flashlight afferent pupillary defect test, as the light moves rapidly back and forth, both eyes dilate when the light is shining in the abnormal eye and both eyes constrict when the light is shining in normal eye.
Preliminary evaluation of binocular function
If neither eye is preferred for fixation and if the eyes appear grossly straight, fusion may be present or at least apparent. This can be confirmed with a stereo acuity test or with the Worth four-lights. In this case, the word fusion is recorded. In the presence of strabismus, if one eye is preferred for fixation and the other eye deviates, the notation is fixation OD or fixation OS. If either eye is used for fixation with free alternation between the eyes or cross fixation is noted (the left eye fixes in right gaze and the right eye fixes in left gaze) free alternation may be present and is recorded as such. A patient may prefer one eye but hold fixation briefly with the non-preferred eye after the cover has been removed from the preferred eye.
Such a patient usually does not hold fixation in the non-preferred eye through a blink. This type of acuity response is recorded as prefers OD, will hold but not take up fixation OS, will not hold fixation through a blink, etc.
Gross, wandering fixation may be present in the non-preferred eye and should be recorded as such. Nystagmus, if present, is noted and characterized as latent or manifest according to when the nystagmus is present, and horizontal, rotary, vertical, pendular, jerk, and the like according to the pattern of nystagmus. Frequency, amplitude, positions of greater intensity, and null point are also described. Nystagmoid movements differ from nystagmus in that the former are non-rhythmic and usually result from a sensory rather than a motor defect.
A peculiar type of ocular motility and head posture anomaly occurs with ocular motor apraxia. With this condition the eyes do not move in response to voluntary attempts at binocular vision through versions. Instead, the head moves past the point of fixation on the object of regard bringing the eyes along, so to speak. Then when the eyes have established fixation on the intended object, the head rotates back while the eyes maintain fixation on the object. This enigmatic supranuclear congenital condition tends to improve with age and requires no specific treatment.
Asymmetric, often unilateral, horizontal nystagmus with head nodding and torticollis in an otherwise normal child approximately 1 or 2 years old may be spasmus nutans. This is a benign condition that also requires no treatment. Spasmus nutans always improves. Unless this condition can be clearly differentiated from potentially serious causes of acquired nystagmus such as chiasmal glioma or posterior fossa tumor, computed tomography (CT) or magnetic resonance imaging (MRI) of the head should be performed. There are widely differing points of view regarding imaging in cases of apparent spasmus nutans. Some pediatric ophthalmologists and neuroophthalmologists advocate imaging in every case while others, including myself, will do imaging only in cases where an additional physical sign is present such as fussiness, weight loss, or some other added sign.
Vertical nystagmus with retraction is a sign of a lesion around the chiasm. Patients with retraction nystagmus should be studied with appropriate imaging. Any vertical nystagmus, particularly when acquired, should be evaluated with a neurologic workup including CT or MRI. Downbeating nystagmus may be associated with Arnold-Chiari malformation and upbeating nystagmus with rostral brain stem lesions. Rapid, flutter movements are associated with neuroblastoma. Acquired nystagmus in childhood is always a matter of concern. It is the responsibility of the examining physician to make a decision about further workup and/or referral and at the very least to maintain careful follow up, such as three month intervals.
Ductions or monocular movements are evaluated in extreme abduction, adduction, sursumduction, and deorsumduction. In cases where abduction is ‘avoided’ such as occurs in congenital esotropia with cross fixation where the right eye looks left and the left eye looks right, ductions are tested with the Doll’s head test (Figure 2). This is also called the oculocephalic reflex test. This test is done by rotating the head rapidly to one side while particularly observing the eye opposite the direction of head rotation. Ductions are graded 1+ to 4+ overaction (this is a relative value) and -1 to -4 underaction. Forced ductions, muscleforce generation, and saccadic speeds are determined in patients with significant limitation of ductions.
Any face turn, chin elevation or depression, or head tilt is noted and recorded. This observation is an especially helpful clue in patients with vertical muscle palsies and strabismus with limitation of ductions where fusion is present. An anomalous head posture is also a prominent feature of nystagmus with null point. A bizarre head posture may be assumed to aid in fusion or even in some cases to increase the amount of diplopia to aid suppression. A simple diagram showing the head posture and direction of gaze can be useful. At this point any facial asymmetry, a common finding in congenital superior oblique palsy, clefting, skin tags, hypertelorism, unusual palpebral fissure characteristics, etc. should be noted.
Versions, or binocular eye movements, are evaluated in the extreme diagnostic positions comparing movements in the extremes of gaze carried out by yoked muscles. Arrows and hash marks on the record indicate overaction or underaction of the muscles. Arrows outside the figure indicate overaction and hash marks on the lines denote underaction. The lines drawn as paired H figures represent the field of action rather than the location of the yoked extraocular muscles.
In selected cases, certain sensory tests should be performed after the history has been taken but before the eyes have been dissociated with covering and before visual acuity has been determined. Some patients are able to fuse in casual seeing situations that are not stressful, but lose their weak hold on fusion after the slightest dissociation. Patients with any type of intermittent deviation and bifoveal or peripheral fusion should have their stereo acuity determined initially and then should be tested with the Worth four-dot test before resuming the more usual flow of the examination. In addition, stereo acuity testing is a good screening device for patients in whom the surgeon suspects the examination will be normal. Any patient who accurately sees nine out of nine Titmus vectographic targets and, therefore, can appreciate 40 seconds of arc disparity, is unlikely to have a significant problem with their binocular mechanism or visual acuity.
This testing requires an instrument which stimulates the eyes separately but provides images with varying degrees of similarity and is designed to test the ability of the eyes to work together in response to a variety of stimuli. This testing is ordinarily done by an orthoptist.
Doll’s head, oculocephalic response to elicit lateroversions (abduction), in an infant.
The objective angle is determined after dissociation with the haploscope. It represents the patient's manifest or latent strabismus (total fusion free deviation). Since the two targets are presented alternately, this is essentially the same angle found with alternate prism and cover testing. The subjective angle is the angle at which the patient superimposes images of objects by manipulating the arms of the amblyoscope. These angles are determined clinically using dissimilar, incomplete, grade I, simultaneous macular perception slides in the arms of the major amblyoscope or other haploscopic devices; for example, a lion in a cage, etc. Comparison of these two angles indicates the status of retinal correspondence, at least at the level of dissociation created by the amblyoscope. When the objective and subjective angles are the same, retinal correspondence is normal. When the subjective angle is zero and the objective angle is either plus (base out esodeviation) or minus (base in exodeviation), harmonious anomalous retinal correspondence is present. When the subjective angle is less than the objective angle but other than zero, nonharmonious anomalous retinal correspondence is present. If no subjective angle can be determined with grade I slides, first-degree fusion is absent. First-degree fusion and normal retinal correspondence are favorable but by no means certain indications that a functional result with fusion may be obtained from surgery.
Range of fusion. If a subjective angle is found with appropriate slides, grade II fusion targets are inserted into the arms of the major amblyoscope and the patient's fusional amplitudes are determined. Grade II fusion slides are similar in their overall outline and differ only in detail. These differences serve as checkpoints ensuring that both eyes are seeing a target. With grade II targets in the amblyoscope, the arms are first shifted from the subjective angle outward (exo) and then inward (eso). Fusional amplitudes are an expression of the patient's ability to keep the images as one and, therefore, fused by either diverging or converging the eyes as the arms of the amblyoscope are shifted outward and inward. Fusional divergence is usually tested before fusional convergence. A ‘make’ and ‘break’ point for each is recorded; for example, -6 to -4 and +40 to +28. This means that the patient experienced diplopia when the arms got to 6D exodeviation but was able to refuse the images as the arms were returned to 4D exodeviation; fusion was held to 40D of convergence before diplopia appeared and the doubled images were refused at convergence of 28D. The presence of second-degree fusion indicates that a functional result with fusion and fusional amplitudes should be obtainable with proper surgery. Such patients even when slightly overcorrected by surgery are those best able to obtain excellent long-term results. Fusional amplitudes can be measured in free space using the principles of the haploscope but shifting images seen by the two eyes with a prism bar containing horizontal prisms of gradually increasing strength from 1 to 40D.
Stereo acuity. This has been called third-degree fusion, but it should be recognized that these degrees of fusion are not a continuum but actually test different things: first degree - retinal correspondence; second degree - motor fusion; third degree - sensory fusion. The Titmus vectograph is used to test stereo acuity. Findings with this test are recorded as fly (3000 seconds arc disparity); A, B, C animals; and the fraction of the nine dots that the patient can appreciate. The ninth dot on the Titmus vectograph describes 40 seconds of arc disparity.*
Stereopsis is not recordable in manifest strabismus of sufficient size to warrant surgery. However, it may be quite good in intermittent deviations such as intermittent exotropia even with large angles or in small angle manifest strabismus with peripheral fusion.
Stereo acuity is tested using the polarized vectograph method that measures the ability to fuse laterally displaced objects within Panum’s fusional space producing the illusion of depth. But a drawback of this test is that careful study of these images can offer monocular clues. Random dot vectographs have embedded disparity not seen monocularly. This so-called global stereopsis is said to provide more accurate findings of stereo acuity. Both of these tests require viewing with polarized glasses. Stereo acuity can also be measured without the use of spectacles using the Lang test or the Frisbie test. Stereo acuity can also be measured in free space using the Howard-Dolman apparatus which requires the examinee to align distant objects. This test is used primarily in clinical research settings.
* Titmus vectograph findings in seconds of arc disparity are: fly = 3000, cat = 400, rabbit = 200, monkey = 100, 1/9 = 800, 2/9 = 400, 3/9 = 200, 4/9 = 140, 5/9 = 100, 6/9 = 80, 7/9 = 60, 8/9 = 50, 9/9 = 40.
Worth four-dot testing. Worth four-dot testing is performed at variable near distances and at 20 feet. Results of this testing are recorded as fusion, diplopia, alternation, or suppression of one eye. In many instances, patients with small-angle esotropia, central suppression, and peripheral fusion will fuse a fourlight pattern that produces a large retinal image but will suppress one set of lights when the retinal image is made smaller either by reducing the size of the target or increasing the viewing distance. A gross estimation of the size of the central functional scotoma present during binocular vision in patients with strabismus can be made by determining how far the four lights must be removed from the patient and, therefore, how small the retinal image becomes before suppression occurs. The size of the retinal image created by the four lights as the lights recede from the patient can be calculated, but the precise value is not clinically important. The Worth four-dot test may also be considered a gross color vision test and a test of retinal correspondence. If four lights in proper alignment are seen in the presence of a manifest strabismus, harmonious anomalous retinal correspondence may be inferred. This is a gross test and not one that is likely to alter decisions regarding treatment, although four light fusion is considered a favorable finding with the prism adaptation test.
Bagolini striated glasses. Bagolini glasses are essentially ‘see-through, micro Maddox rods’ that turn a point of light into a line while not disturbing vision. These glasses are ordinarily placed in a trial frame with their axes at 135° OD and 45° OS (or equivalent). They are used to determine retinal correspondence in casual seeing. Nearly all strabismic patients when viewing a point of light will see diagonal lines intersecting at the light or where the light is stimulating the retina in cases with a small central scotoma. This finding is compatible with harmonious anomalous retinal correspondence in the strabismic patient. Some patients will see one diagonal line corresponding to the preferred eye while suppressing the non-preferred eye. Other patients will see a complete line corresponding to the preferred eye and an incomplete line, with a missing segment adjacent to the light, with the non-preferred eye. These test results ordinarily do not influence surgical planning. These have been used by investigators for a variety of diagnostic and therapeutic manipulations and for the study of retinal correspondence and abnormal binocular movement.
After-image test. The afterimage test is used to determine retinal correspondence in extreme dissociation. Anomalous retinal correspondence occurring on the afterimage test indicates a deep sensory anomaly. Retinal correspondence tends to be normal or harmonious anomalous when tested with the Bagolini glasses, normal or anomalous with the haploscope, and normal with the after-image test, indicating that retinal correspondence response varies with the testing conditions and the test. All that can be inferred from this testing is how completely the eyes have adapted to the strabismus angle. To do an afterimage test, a bar of bright light with a non-illuminated central fixation point is presented horizontally to the eye used for fixation and then vertically to the other eye. If the afterimage intersects at the fixation point, normal retinal correspondence is present with this test. If the lines do not intersect at the fixation point, deep anomalous correspondence is present.
Sensory fixation. Fixation behavior is determined with an ophthalmoscope that contains a fixation target that the patient is asked to look at with each eye while the fellow eye is occluded. The examiner can compare the retinal point used to fixate this target with the anatomic location of the fovea. This point of fixation is recorded directly on the chart with a small x. Fixation with any retinal point other than the fovea means that acuity in that eye will be reduced. The farther the point of fixation is from the fovea, the greater the reduction in acuity. Amblyopia with peripheral eccentric fixation suggests the possibility of a significant overcorrection of an esodeviation even when moderate surgery is done.
Implications of sensory testing. Sensory testing is useful both preoperatively and postoperatively. The closer to normal the preoperative sensory findings, the more the surgeon should try to create surgical alignment or a slight surgical overcorrection that would lead to fusion. Postoperative sensory testing is a check on surgical results and a guide to further nonsurgical treatment that should be pursued appropriately in the case of an undercorrection or an overcorrection in a potentially fusing patient.
Measurement of alignment - prism cover testing and other methods
Alternate prism and cover testing is a method to measure the maximum deviation. This testing is performed at distance (20 feet) and near (13 inches), with and without glasses (if they are worn) while the patient views an accommodative target in the primary position. The use of an accommodative target and the wearing of glasses are essential because together they control the patient's accommodative convergence. Prism and cover testing is also done in approximately 30° of upgaze and downgaze while the patient wears full correction and views an accommodative target in the distance. If this test is performed at near while measuring for A and V pattern, the patient should wear +3.00 D lenses over the distance correction to eliminate the effects of accommodative convergence, especially in downgaze.
Upgaze and downgaze can be achieved by tilting the patient's head forward and backward. This maneuver uncovers an A or V pattern which is best tested while the patient fixes on a distant target. A 10∆ difference between upgaze and downgaze is significant for diagnosing an A pattern and a 15∆ difference is significant for a V pattern.
Other useful variations of prism and cover testing that can be performed before or after the alternate prism and cover test include the following:
The cover-uncover test differentiates a same time but not differentiated with the alternate prism and cover test. Movement of the covered eye immediately after the cover is removed and while the uncovered eye maintains fixation indicates a phoria. A tropia is noted by first establishing the fixing eye and then covering it while observing the fellow eye for movement. If the fellow eye does not move, the patient is orthotropic. If the eye moves to take up fixation, a tropia is present and the direction should be noted. If the eyes move inward toward the nose, an exoshift is recorded; if the eyes move outward toward the ear, an esoshift is recorded. When the eyes appear straight and/or good stereo acuity has been measured, even while assuming a face turn, head tilt, etc., the surgeon should proceed to the motor evaluation. The patient could have an incomitant mechanical strabismus dealt with by the patient with a face turn, head tilt, or both. This would have been uncovered for example in a case of Brown or Duane while testing ductions. A phoria is the most important feature found with the cover-uncover test. With aligned eyes in casual seeing, a phoria can be measured with alternate prism and cover testing. This testing also measures the total deviation, phoria, and tropia when these coexist.
Lateral gaze prism and cover testing can reveal the presence of lateral incomitance which is especially important in exodeviations and in previously operated patients.
Prism and cover testing with either eye fixing helps to determine the primary and secondary deviation. This test is a variation of the simultaneous prism and cover test.
Simultaneous prism and cover testing (SPC) determines the actual tropia in casual seeing in patients where a tropia and phoria coexist (monofixational esophoria, monofixation syndrome, microstrabismus, or smallangle tropia with peripheral fusion). The fixing eye is first identified. Then it is covered while a prism of appropriate size and orientation is simultaneously placed in front of the deviating eye. The amount of prism is increased or decreased until no movement occurs in the deviating eye. The prism needed to preempt re-fixation with the deviating eye is a measure of the alignment during casual seeing.
The Hirschberg test compares the location of the light reflex which is normally in the center of the pupil of each eye to the anatomic central pupillary axes. It is performed when patient cooperation is poor. For each millimeter of displacement of the corneal light reflex in the non-fixing eye, approximately 7 degrees or 15∆ of deviation is present.
The Krimsky test
determines the amount of prism that must be placed before the fixing eye to center the corneal light reflex in the pupil of the non-fixing eye as this eye passively moves according to Hering’s law
. This test is particularly useful when the patient has such poor vision in one eye that fixation is not taken up well with that eye during prism and cover testing.
Prism and cover testing with either eye fixing in the nine diagnostic positions of gaze is performed in cases of muscle palsy, particularly vertical muscle palsy. This is the premier measurement of alignment.
Alternate prism and cover testing with the head tilted approximately 45° to the right and to the left is called the Bielschowsky test. This test which is said to be positive when a vertical deviation increases with head tilt is useful for identifying isolated cyclovertical muscle palsy.
Dissociated vertical deviation (DVD) is noted when either eye drifts upward the same or differing amounts when occluded and down when the cover is removed with coveruncover testing. It is recorded as +1 (±5∆) to +4 (±25∆). Some surgeons prefer to measure rather than estimate DVD. This measurement may be performed in a manner similar to that with the simultaneous prism and cover test. However, DVD may be present with a coexisting true vertical deviation that is in the same or opposite direction as the DVD. DVD is also often of different amplitude in various fields of gaze and may demonstrate movement in only one eye! DVD may even present as pseudo-overaction of the inferior obliques. This is confirmed by noting a hyperdeviation of the occluded, abducted eye during lateral gaze. With true inferior oblique overaction, and no DVD the occluded abducted eye is more likely to be hypodeviated. Also, a V pattern should be present with true inferior oblique overaction. An eye with DVD that moves upward when covered can drift well below the midline when the cover is removed. This phenomenon has been called a ‘falling eye.’ Some eyes with very poor vision will drift below the midline with an accompanying vertical bobbing of the eye. This is called the Heiman-Bielschowsky phenomenon. An exodeviation of one eye only is called dissociated horizontal deviation (DHD). This is in a way an extension of DVD. The two have been characterized as the dissociated strabismus complex (DSC) by M. E. Wilson.
A translucent occluder* held before one eye forces fixation with the other eye but allows observation of the occluded eye. This is an excellent way to observe the deviation in DVD. This testing is used effectively in telemedicine (see chapter 15).
Red lens and Maddox rod tests are useful subjective tests and for charting in cases of small-angle vertical and/or horizontal strabismus with symptomatic diplopia.
The double Maddox rod test is useful in the diagnosis and measurement of cyclodeviations.
The 4∆ base-out prism test may be used to uncover a scotoma in the macula of one eye in patients with microtropia.
A Hess, Lancaster, or Lees screen may be used to plot directly the deviation in a cooperative strabismic patient.
Diplopia fields are mapped with a Goldmann perimeter or arc perimeter while the patient views the moving fixation target with both eyes open and with the head centrally positioned and stabilized. The documentation provided is valuable for following recovery from an acute paresis and especially for medicolegal and compensation purposes.
* This technique was made popular by Annette Spielmann of Nancy, France.
Refraction has a vital role in the diagnosis and treatment of strabismus. It is imperative that those involved in the care of the strabismus patient understand the principles of refraction, have the skills to perform accurate measurement of the refractive error, and use spectacle correction or the equivalent as required in the treatment of strabismus. If you intend to treat patients with strabismus but are not competent with refraction technique, you should stop here. Learn how to refract and then resume your study. A person ignorant of refraction methods is not fully qualified to treat strabismus!
Work up of the patient with strabismus always starts with the refraction. In heavily pigmented patients a cycloplegic refraction is performed using atropine solution 1.0% (1 drop) or atropine ointment 1% (⁄-inch strip) in each eye for 3 days before the day of examination. When drops are used, the atropine may also be applied on the day of the examination. Careful instructions are given to the parents to avoid overdosage. These instructions include using no more medicine than prescribed and holding a finger over the punctum for 30 seconds after drops are instilled in one eye in the morning and the other in the afternoon. Use of atropine is usually restricted to preschoolaged children, for initial refraction, and when esotropia is present.
When refracting a lightly pigmented patient in the usual office setting, a cycloplegic refraction can be performed satisfactorily approximately 20 to 40 minutes after one or two drops of cyclopentolate (Cyclogyl) 1% have been instilled in the cul-de-sac in children over 1 year. One drop of phenylephrine (Neo-Synephrine) 2.5% may be used in addition to the cyclopentolate in patients with dark irides. In children under 1 year of age, cyclopentolate 0.5% drops are used.
In esodeviating patients the full hyperopia must be elicited. Hyperopia as low as +3.00 D should receive a trial treatment with glasses in patients with esotropia usually beginning after 1 year of age. However, I have seen several patients less than 1 year of age with esotropia relieved by wearing a +3.00 D correction. Echothiophate iodide (Phospholine) drops (0.06% to 0.125%, one drop in each eye each morning for 3 weeks) in lieu of glasses may help to determine what effect the hyperopia (accommodative effort) has on the esodeviation, but because anticholinesterase drops only reduce the effective accommodative convergence/accommodation ratio (AC/A) and do not eliminate the need for accommodation, they are not a true substitute for glasses.
A difference in the refractive error between the eyes is called anisometropia. Difference of as little as +1.00 or +2.00 diopters can be amblyopiogenic and usually indicates the need for the full refractive difference to be prescribed. If glasses are prescribed with the hyperopia reduced, it should be reduced equally. For example, OD +2.00 +1.00 x 90, OS +6.00 +2.00 x 90, could be ‘cut’ to OD +1.00 +1.00 x 90, OS +5.00 +2.00 x90. These glasses would be effective and better tolerated.
Adult patients do not ordinarily require cycloplegia, but in selected cases of convergence excess this may be needed. It is best to avoid use of cycloplegics in pre-presbyopic adults. Use of cycloplegics in such patients can precipitate presbyopia resulting in a very unhappy patient.
Examination of the retina is carried out using a standard or small portable indirect ophthalmoscope. It is a relatively simple matter to see the retina posterior to the equator in a squirming infant using the indirect ophthalmoscope. This examination to rule out pathologic conditions in the posterior pole is an essential part of the evaluation of every strabismus patient. Remember, esotropia is the second most common presenting sign, after white pupil of retinoblastoma! The direct ophthalmoscope is used to study detail of the optic nerves and maculae and to determine fixation behavior in the older child with amblyopia. A total retina examination such as that needed to rule out retinoblastoma in an infant requires an examination under general anesthesia. For purposes of strabismus, examination of the posterior retina as it effects central vision is sufficient.
Examination of the anterior segment should be performed on all patients, particularly when echothiophate iodide is used, because of the possibility of iris cysts and to confirm continued clarity of the lens. A portable slit lamp is a valuable instrument for examining children under 3 years of age. At the very least, the anterior segment should be studied using the direct ophthalmoscope. When nystagmus and decreased vision are noted, iris transillumination defects indicative of albinism, either oculocutaneous or ocular, should be looked for.
The appearance of the lids should be noted. Is there ptosis or epicanthus (superioris or inferioris)? Are the palpebral fissures mongoloid, anti-mongoloid, or normal? Is there proptosis, hypertelorism, microphthalmos? Is lid lag present? Are there conjunctival scars? All of this information should be recorded.
Diagnosis of the strabismus condition
When sufficient historical data and motility and refractive measurements have been recorded, a diagnosis is made. This diagnosis can be made in most cases after the initial examination. Repeated measurements at one or more subsequent visits should be taken in some cases before a final quantitative diagnosis is established and a specific surgical treatment plan determined. For example; congenital esotropia, longstanding superior oblique palsy, sensory esotropia or exotropia and similar types of strabismus can usually be scheduled for surgery at the initial visit and then re-evaluated on the day of surgery. In contrast, intermittent exotropia in the toddler, acute cranial nerve palsies, and residual refractive esotropia may require a longer period of observation along with repeated measurements.
Other special examinations may be employed for complex diagnosis including the following:
Differential intraocular pressure test
Saccadic velocity observed and with electrooculogram recording
Imaging of the orbit with CT or MRI
Generated muscle force
The diagnosis should include as much information as possible about the strabismus problem including notation of some or all of the following:
Direction of deviation (eso, exo, hyper, cyclo)
Refraction, accommodative factors
Manifest or latent
Constant or intermittent
A or V pattern
Mechanical factors (forced ductions)
Cranial nerve status (saccadic velocity - secondary deviation)
Lid fissure configuration
DVD - DHD
Oblique muscle function
Ptosis (upper or lower lid)