Pretutorial
    Assessment

Tutorial
Introduction
History
Visual Acuity
Infant and Pre-verbal Visual Acuity Assessment
Preferential Looking Techniques
Pattern-Evoked Potentials
Ocular Motility Evaluation
Cover Testing
Alternate Methods of Measuring the Deviation
Versions (Binocular Eye Movements)
Ductions (Monocular Eye Movements)
Color Vision
Near Points of Accommodation and Convergence
Stereoacuity
The Titmus Test
Tests for Central Suppression
Fusional Vergences
Double Maddox Rod Testing
External Exam
Slit Lamp Examination
Tonometry
Refraction and Retinoscopy
Photoscreening Devices
Ophthalmoscopy
Summary
References

Slides

The Pediatric Eye Exam

Rudolph S. Wagner, MD

Introduction

Performance of a successful eye examination in an infant or young child requires flexibility in approach and a willingness to modify the sequence of the examination when required. Often faced with minimal historic information, it is a quality ophthalmologic examination that provides the means of diagnosing and treating children's ocular disease.

In this tutorial, many helpful examination techniques are described. In addition, some of the newer technological advances that have been found to be helpful although not always critical for the practice of pediatric ophthalmology are incorporated in the appropriate sections.

History

A chief complaint and a detailed history of the present illness are obtained from the parents or guardian. This information should also be obtained from the verbal child as this may also provide useful information. This time is also useful for attempting to establish good rapport with the child. Introducing yourself and directly addressing the child while allaying their fears can get the examination started off in the proper direction. Knowledge of contemporary interests of children in different age groups is useful for stimulating conversation and ultimately eliciting verbal responses to optotype acuity testing.

As in any examination, information as to past medical history, including birth weight, allergies, and medications taken is essential. Familial history is particularly important in suspected inherited disorders.

Visual Acuity

The most important aspect of the pediatric eye examination is the assessment of visual acuity in each eye. The earliest age that objective visual acuity testing with input from the child can be accomplished is approximately 2½ years. It is always useful to measure visual acuity binocularly because this reflects how the child is seeing in normal viewing conditions. It is well recognized that children with latent nystagmus may dramatically see better binocularly than with either eye individually. Furthermore, in the binocular state, compensatory face positions for nystagmus with a null zone or torticollis from paralytic strabismus will be appreciated. In fact, occlusion of one eye may eliminate a compensatory face position in some cases of paralytic strabismus. This finding may help to distinguish an ocular from a non-ocular cause of torticollis.

Distance visual acuity is most useful and ideally should be measured at 20 ft or 6 m. Instruments and charts can be calibrated for distances down to 10 ft to accommodate smaller examining lanes. There are a number of symbols or optotypes available. Line tests with 0.1 log unit differences between the lines should be used.1 Picture charts or symbols such as HOTV are useful for children who have not learned to recognize the standard Snellen letters or numbers. With the HOTV test, a child is

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Visual acuity measured at 1/3 m or 14 inches is not an essential part of the pediatric eye examination, although assessment of the near point of accommodation is useful. Other than an unusual child with accommodative insufficiency, there are no conditions in which a child will have normal distance acuity with subnormal near acuity. Use of single optotype visual acuity cards at near fixation or standard "near cards" should be reserved for situations in which distance acuity testing is not possible. Pathologic vision loss will diminish acuity both for near and distance, and, therefore, near visual acuity testing is appropriate in emergency situations.

Practically, most pediatric ophthalmologists prefer a standard projected chart using the symbols of a horse, duck, car, telephone, and birthday cake. The projector allows the examiner to isolate the individual line, which is useful in keeping the child's attention. The B-VAT II devices and its recent upgrade (Mentor, Santa Barbara, Calif.) are very useful. This device consists of a monitor and remote control that utilizes the above mentioned symbols. Visual acuity using pictures can be presented down to the 20/20 level and the optotypes can be varied to avoid memorization by the child by a random sequencing program. The full-line format eliminates the crowding phenomenon present in many amblyopic eyes. In this instrument, interaction bars surrounding single optotypes can also be presented. This has been reported to improve the ability to detect amblyopia.³ Snellen letters and numbers, Landolt rings, HOTV, and illiterate E's can also be displayed. A moving fixation target is also incorporated in the B-VAT program.

Whatever "eye chart" is used, care must be taken to totally occlude the non-tested eye. Because children may peek around the handheld occluder, it may be useful to occlude the eye with a strip of 2-inch Micropore tape. Clinicians experienced in assessing visual acuity in the preschool verbal age group understand the individual variability and necessity of being flexible in examination technique. A significant effort is often expended in convincing the child to allow the occlusion and subsequently coaxing from them an appropriate response. The time and effort is necessary, however, and the ability to accurately assess the visual acuity in this age group is what helps to define a "pediatric ophthalmologist."

Recently, emphasis has been placed on having vision screening performed by pediatricians and other primary health care providers. They have been instructed to screen for both visual acuity and ocular alignment using either a unilateral cover test at 10 ft or a Random-dot-E stereo test at 40 cm.

Infant and Pre-verbal Visual Acuity Assessment

Infants will begin to smile to a human face at approximately 6 weeks of age and will follow objects in the environment starting at 8 weeks old.⁴ Clinically, one can stimulate the child's interest with a colorful toy or object and observe the child's fixation behavior. Under binocular conditions, the child is observed for the presence of nystagmus or torticollis. It is well recognized that children with good vision in only one eye may function and behave as well as a child with excellent binocular visual acuity. Therefore, it is imperative to assess the vision independently in each eye. Fixation of each eye can be evaluated as (1) central, if not eccentric, (2) steady, and (3) maintained, or CSM, if the fixation does not revert to the fellow eye as in a strabismic child.

The examiner covers one eye (usually with his or her hand, thumb, or occluder) and notes whether the infant looks steadily at a light or fixation target with the unoccluded eye. The eye is then uncovered. A strabismic patient who strongly prefers the eye just uncovered will switch fixation to that eye. A child with poor vision in the absence of strabismus will react strongly to occlusion of the eye with better vision. The anxiety and avoidance maneuvers precipitated by the occlusion provide evidence of poor visual acuity in the uncovered eye.

Cross fixation may be observed in infants with large angle esotropia and essentially equal visual acuity. These children find it more convenient to regard objects to their right with the esotropic left eye, and vice versa. This presents as an apparent diminished ability to abduct either eye and a pseudoparesis of the lateral rectus muscles. Temporary occlusion of either eye or rotating the baby in a chair on an adult's lap will usually demonstrate that abduction is present.

The optokinetic nystagmus, or "OKN response," is evidence of gross vision and can be elicited by an optokinetic drum or tape. Slow, following-type eye movements in one direction and fast restorative movements in the opposite direction constitute the jerk-type optokinetic nystagmus. OKN requires visual detection, not resolution of the target and is thus different from Snellen acuity testing. If nystagmus is elicited, it is thought that the vision is 20/400 or better. Normal infants younger than 3 months of age have asymmetrical OKN responses and some do not demonstrate a response at all, presumably because of inattention. Absence of an OKN response, therefore, does not necessarily imply a visual deficit.⁵

Preferential Looking Techniques

The preferential looking technique is based on the preferred response of infants to fixate on a patterned stimulus. Grating patterns and homogeneous test objects of equal space averaged luminance are assigned randomly to right or left viewing ports and are shown to infants at a constant distance.⁶ The width of the stripes that compose the grating may be reduced until a preference to fixate on the patterned stimulus no longer exists. At this point, both objects appear the same to the infant. Infants are tested with both eyes and with alternate eyes occluded. Visual acuity in newborns has been found to be about 20/400 using preferential looking techniques. A variation of the preferential viewing test is the use of acuity cards with gratings (Teller Acuity Cards) in which the examiner is not masked to the side of the grating.⁷

A problem with all types of preferential viewing tests is that for each stimulus presentation there is a 50% chance of correctly guessing which side the patterned stimulus is on. As a result, there is a large margin of error in recorded acuity. For example, an acuity value found to be 20/140 may actually fall in a range between 20/50 and 20/400. Nevertheless, these techniques are useful in research settings and are clinically useful in the hands of experienced examiners.⁵

Pattern-Evoked Potentials

Pattern-evoked potentials (PEVP) testing has demonstrated that infant visual acuity reaches normal levels at 6 months of age.⁸ This electrophysiologic test can be used clinically to record and monitor visual acuity in young children. PEVP testing, however, requires sophisticated equipment and specially trained technicians to obtain accurate results. Fixation must be monitored continuously during recording. Each laboratory must establish its own age-appropriate norms for accurate interpretation of its data. PEVP should not be confused with flash visual-evoked potentials, which are not useful in recording actual visual acuities.

Ocular Motility Evaluation

The ocular motility evaluation is best performed during the initial part of the evaluation of the child, because it requires good cooperation from the child and can be fatiguing to both the patient and doctor. In many cases, the infant or child is brought to the pediatric ophthalmologist specifically for this evaluation.

Cover Testing

A prerequisite to cover testing is the ability of each eye, in turn, to be capable of central (foveal) fixation when the fellow eye is covered. If organic disease (e.g., cataracts, cloudy media) or functional conditions (e.g., eccentric fixation) prevent central fixation with either eye, cover testing may be invalidated.

Placement of the occluder should be minimally traumatic to the child. The traditional black paddle is handy, but if the child rejects this occluder, the examiner's hand or thumb dropped from above may provide a more familiar, less-threatening cover. For resistant infants, Costenbader advocates the remote cover test. A prescription pad or other handy cover is held approximately 18 inches from the infant's face, while a penlight is flashed at about 3 ft. The pad is placed so as to cast a shadow, first on one eye and then the other.⁹

Prism technique includes the use of single prisms, a prism bar, split prisms (one over each eye, both base in or both base out). Stacked prisms (horizontal and vertical over the same eye) should be avoided.

Fixation targets should be used for all types of strabismus to provide an accommodative stimulus. Vision charts at 20 ft (6 m) and at 13 inches (1/3 m) work well in older preschool and school-age

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Measurements in these portions give information about: (1) A or V patterns, (2) lateral comitance, and (3) the accommodation-convergence relationship.¹⁰ Measurements, as such, may also be performed in the oblique positions of gaze and with the head tilted to either side when indicated.

Ocular deviations may be diagnosed as to presence and type (heterophoria or heterotropia) by three maneuvers: the cover test, the uncover test, and the alternate cover test. Once diagnosed, the deviation may be measured by the addition of a prism of correctly chosen strength to neutralize movement of the eyes during various cover maneuvers.

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If no shift occurs, heterotropia may still exist. If the occluder was placed in front of the deviating eye, the fellow eye would already be fixed on the target, and no shift would be expected. Obviously in most cases the examiner already knows which eye is deviating because one eye is directed at the object of regard and the other is not. However, in small angle deviations, this is often not obvious, and it is sometimes difficult to be sure that very young children are regarding the object intended.

To complete the test, the patient must be returned to binocular viewing for a least several seconds so that fusion can be accomplished if this potential exists. The second eye is covered in the same manner as the first eye. The sequence is (1) cover one eye, observing the fellow; (2) uncover that eye for a few seconds; and (3) cover the second eye while observing the first eye.

The sequence should be repeated to make sure that a subtle, rapid switch in fixation did not occur unnoticed during the binocular interval. Many patients with strabismus can readily alternate fixation, and if a switch occurs during the test, the examiner may be placing the occluder before the deviating eye each time.

The Alternate Cover Test
The alternate cover test is performed by moving the occluder directly from one eye to the other without allowing an interval for binocular viewing. Fusion is suspended throughout the test. If no ocular shift occurs as the occluder is moved directly from one eye to the other, the eyes are truly aligned, or orthophoric. Even with fusion suspended, the foveas are in the position to regard the target without shifting. However, if a shift does occur, a deviation exists. If the deviation is corrected by fusion, that is, if the deviating eye moves into alignment under binocular conditions, the deviation is said to be latent and is called heterophoria (or phoria). It should be apparent that the alternate cover test does not diagnose phoria by itself but depends on the findings of the cover test.

A misconception has been fostered by the unfortunate wording "the occluder is moved swiftly from one eye to the other," leading to the widely held notion that a rapid fanning back and forth of the occluder helps break up fusion. Actually, the occluder need not be moved fast, since the following edge uncovers one eye at about the same time as the leading edge covers the fellow eye. A moment should be allowed for fixation to be accomplished by the uncovered eye before reversing the direction of the occluder.

The Prism and Alternate Cover Test To this point, diagnosis of deviation has been discussed. Addition of a prism allows for measurement of deviations. The prism and alternate cover test is the determination that is used clinically.

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The use of a prism bar is strongly recommended, since rapid selection of the correct prism is important in dealing with the short attention span of children.

The neophyte may be amazed to note that when the occluder is moved from left to right, the effect of the neutralizing prism may be different than it is when moved from right to left. In this case, both measurements are recorded and noted as "OD fixing" and "OS fixing." OD fixing means that the patient entered the test with the OD viewing (occluder passes from OS to OD) and vice versa. This difference immediately suggests a paretic strabismus.

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The Simultaneous Prism and Cover Test

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The simultaneous prism and cover test is not without difficulties. First, the ocular shift must be studied behind a prism immediately after it has been moved into place. However, with practice, the apparent displacement of the eye due to the prism is easily distinguished from the actual shift of the eye.

The test does not work unless the occluder is placed before the fixating eye and the prism before the deviating eye. These patients typically have small deviations, making it difficult to tell which is the deviating eye. Also, the fixation of many of these patients can rapidly alternate. The correct performance of the test the first time sets up circumstances for incorrect performance with the next prism chosen for a patient who alternates easily. When the occluder goes before one eye, fixation is switched to the fellow eye and will remain there unless there is strong preference for the first eye. The examiner then must change the prism and occluder to opposite hands or, more easily, can occlude the other eye for a moment, switching fixation back to the original eye.

The simultaneous prism and cover test should be used when the deviation is less than 20 prism diopters on the prism and alternate cover test, when stereoacuity is 67 seconds or less, and on all postoperative patients with strabismus. It need not be used if the cover test indicates orthophoria.

The importance of this test should be well understood. The tropic components of these deviations have been observed to measure only up to 8 prism diopters. This is the angle of deviation with which the patient does everyday casual binocular seeing. In a routine workup, the patient would have tropia on the cover test. The amount of shift would be only 8 prism diopters or 4°, but measurements are not taken on the cover test. The examiner would then do the usual prism and alternate cover test, measure 20 prism diopters of deviation, and assume that this is the measure of the patient's tropic deviation. This large measurement may cause an examiner to recommend surgery, whereas the actual tropic component that this patient has is only 8 prism diopters, which is not a cosmetic problem in most patients.

Alternate Methods of Measuring the Deviation

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In infants and uncooperative patients, Hirschberg estimates may have to be performed. Although Hirschberg recommended specific landmarks, such as the pupillary margin, as having certain values, it is probably more accurate to estimate the decentration of the reflex in millimeters, using a point symmetrical to the reflex in the fixating eye. This can be multiplied by 15 prism diopters, and the result is close to a measured deviation.

When estimating by either method, it is imperative to shine the light in line with the examiner's viewing eye. To keep the light in line, the examiner can hold the muscle light against his or her cheek and frequently repeat the measurement.

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Versions (Binocular Eye Movements)

Versions should be checked in the nine diagnostic or cardinal positions of gaze that are outlined in Table 1. This has already been accomplished during cover testing in five of these nine positions. Examination of the oblique positions can be performed by gross observation as the patient follows a near target into these positions.

The findings may be graded according to the scheme an examiner is most familiar with. Many clinicians use the designation for overaction of an individual muscle as +1 to +4, and underaction of an individual muscle as -1 to -4. This notation can be used for recording individual ductions. It is simple and convenient to limit reference to the findings as an underaction or overaction of an oblique muscle. Notice that the indirection of any oblique can be expressed as overaction of the yoke muscles (always a vertical rectus). "Underaction" and "overaction" are descriptions of the position of the eyes; these terms do not imply the etiology of the deviation (e.g., paresis, hypertrophy, contracture).

In clinical practice, there is a need to simplify the recording of examinations. For example, overaction of the superior oblique muscles in both eyes may be written as 2+ O.A.S.O.O.U.

Ductions (Monocular Eye Movements)

If versions are not full, ductions should be rested in all fields of action of the individual eye. Recognition and quantification of duction deficits are important in diagnosing paretic and restrictive extraocular muscle disorders.

It is not uncommon for congenital esotropes to have limited abduction. Non-ophthalmologists frequently interpret this as sixth cranial nerve paralysis, even to the point of ordering inappropriate radiologic procedures. Patching of one and then the other eye usually results in improvement of ductions within hours or days at most. Even without patching, ductions improve with age in these patients. If the child does not allow manual covering of each eye, occluder patches will frequently work.

A chair that swivels is useful in observing ductions and versions. To check right gaze (medial rectus OS or lateral rectus OD), the infant should sit on the caregiver's lap with the infant's legs extending to the left and the chair should be turned to the left, holding the target to the far right. The infant will turn the head maximally to the right, but then must use maximum dextroversion of the eyes. Manual attempts to hold the child's head straight are invariably frustrating, with resistive movements and prompt lack of interest in the target. Noisy targets (such as jangling keys) held at close range work best.

Color Vision

The H-R-R pseudoisochromatic plates are an excellent test series. When using these tests, the examiner can detect yellow-blue as well as red-green defects and results provide a rough quantitative capability. The directions enclosed with this test are explicit and will not be reviewed here. The test is dependent upon the child's knowing numbers. However, a form of the Ishihara color test that uses circle and square shapes in place of numbers is available.

The Farnsworth D-15 color chips may be used for those patients who fail the H-R-R. According to experts, only patients with functionally significant defects fail the former test, whereas the latter is a rigid screening tool. Neither of these tests discriminates anopes (total color defectives) from anomalies (partial color defectives). This requires testing with an anomaloscope, which is well beyond the range of routine examination.¹⁴

Near Points of Accommodation and Convergence

These tests not only measure accommodation, but also may provoke and reveal a latent esotropia at the near point in patients with a high AC/A ratio. Convergence is assessed by having the child accommodate on a near target and then bringing the target as close to the eyes as possible, while observing the convergence. An alternate cover test can be performed at this time to attempt to elicit an exophoria at near fixation.

Stereoacuity

Stereoacuity is the most fundamental sensory test and is widely used by pediatric ophthalmologists. A stereoacuity of 60 seconds or better correlates with bifoveal fusion. In a review of 100 patients in his AOS thesis on monofixation syndrome, Parks found that both esotropes and exotropes with central suppression never had a stereoacuity better than 70 seconds. A score below 67 seconds virtually proves bifoveal fixation.^15,16

The Titmus Test

The Titmus, or stereo Fly, test is used frequently. Unfortunately, the Titmus test had been designed prior to the discovery of Parks' correlations. It would be helpful to have a fourth row of animal images with 60 seconds disparity, since the animal presentation is more suitable for very young children than the series of nine stereo circles.

The Titmus test is sensitive to light and a better score can be obtained by ensuring good illumination. The test is also sensitive to the distance maintained from the eyes, which must be respected if accuracy is desired. Although allowing a child to touch the test will deface it sooner, the improved cooperation is well worth the expense of replacement.

Showing the House Fly picture test to a 2- to 6-year-old child will frequently produce a giggly or frightened response, especially if the child has been told that the fly is wearing "magic" glasses. This can be taken as evidence that the fly appears as three-dimensional. The examiner should ask the patient to pick up the wings with his or her fingers. It is also useful to ask the child to place a finger under the wing. As a credibility check, the examiner may turn the book sideways so that the fly cannot be seen stereoscopically (the disparity is now vertical).

A positive response to the larger figures proves at least peripheral fusion. A response below 67 seconds of arc (7, 8, and 9 on the circle test) proves bifoveal fusion. Of course, it would be possible for a patient with bifoveal fixation to test less than 67 seconds by failing to understand the test or becoming bored with it. For patients scoring 67 seconds or less, it is wise to search for central suppression in one eye with the Worth 4 dot test, Bagolini lenses, red-green perimetry, Polaroid vectograph, or the 4-diopter prism test. These are the five tests used in the Parks' study of monofixation syndrome. Other sensory tests require more elaborate equipment and are beyond the scope of routine examination.

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Tests for Central Suppression

Worth 4 Dot Test
The Worth 4 dot test, used as a test for fusion, has been traditionally performed at both distance and near. A standard, 6-m distant test subtends 1.25°, whereas a near test subtends 6° (33 cm with a hand held flashlight). If a patient has a central suppression zone in the deviating eye (usually 3° to 5°), the results would indicate a monocular response to the 1.25° test and a fusion response to the 6° test, simply because the latter projection falls outside the scotoma.

The angle subtended by the dots can be varied by changing the distance between the handheld flashlight and the patient. In this manner, the size of the suppression of the scotoma can be defined by noting the distance at which the red or green lights appear or disappear.

Testing includes using only the handheld flashlight and omitting the standard distance test. The child wears red-green glasses. An effective method is to present the handheld flashlight test object at 10 ft and to ask "How many lights do you see?" Corroboration of the response may be obtained by asking "What color are the lights?"

If a monocular response is obtained (two red lights or three green lights), slowly bring the light closer to the child, asking the child to tell you if the other colored lights appear. The flashlight is brought to within 12 inches of the face.

Patients with central suppression (monofixation syndrome) will report the appearance of all four lights at a distance commensurate with their suppression scotoma.16 Patients who continue to report a monocular response up to about 12 inches have total suppression of one retina. It is useful to know that normal bifixating patients may give a monocular response between 10 ft to 20 ft on the basis of retinal rivalry.

Bagolini Lenses
Commercially available Bagolini lenses can be placed in a trial frame (over the distance corrections, if any) so that the striations are at right angles to each other. The examiner is not required to remember the position of the striations because the reflected streaks can be seen as the patient sees them when the examiner is positioned in front of the child. A handheld muscle light is used, and the child is asked to draw the lines with his finger in the air just as he sees them.

Children with bifoveal fusion see a perfect cross (X). If central suppression is present, the central scotoma in the deviating eye appears as a break in the line corresponding to that eye (-/-). Usually, the examiner must call the attention of the patient to the break. He can receive some reassurance that he is not "talking the patient into something not seen" by eliciting that the break is in the line corresponding to the deviating eye. A child with rapid alternation readily switches his suppression from eye to eye as fast as the fixation is switched. If total suppression of the deviating eye occurs, the patient will see only one line [ / ] or the other [ \ ].¹⁸

This test requires a more mature patient than determination of stereoacuity and the Worth 4 dot test. The advantage, however, is that it simulates casual seeing, since the dissociation is minimal.

Polaroid Vectograph
Children with central or total suppression of one eye will delete letters on the AO Polaroid vectograph. The patient wears special Polaroid glasses (polarized vertically in one eye and horizontally in the other). The slide is also projected in a polarized fashion, so that some letters on the vision chart are presented to the OD only, some to the OS only, and some to both. Illiterate children who can count can also perform the test by counting the letters seen. The test is exquisitely sensitive, having the fewest false negatives of any of the five tests used to explore for scotomas in the classic Parks monofixation study.¹⁶ Distance stereoacuity testing can also be performed using the B-VAT II, which is discussed in the section on assessment of visual acuity.

The 4-Diopter Prism Test
The 4-diopter prism test should be mentioned as a fast and inexpensive sensory determination that can be performed by the physician. Its mechanism and its numerous pitfalls have been outlined well and at length in the literature.¹⁹ This test is the least reliable of the group for identifying total regional suppression, but does have some merit.

The sensory testing described in this section is directed toward proving total suppression, central suppression, or no suppression of the deviating eye. This represents an assay of whether the child has no binocularity, peripheral binocularity only, or bifoveal binocularity. The first has a poor prognosis for maintaining alignment, whereas the second and third have excellent prognoses. These decisions can be reached before the third birthday in almost all cases and often can be made before the second birthday. A 4-prism diopter base out prism is placed quickly over the right eye while the patient fixates on a light source or distance target. The examiner observes the movements of the left eye, then repeats the test on the left eye. When bifoveal fusion is present, placing the prism over the right eye produces levoversion of both eyes and a subsequent convergent fusional movement of the left. Absence of a secondary fusional movement of the left eye indicates a foveal suppression scotoma in the eye. A foveal suppression scotoma in the right eye would preclude any initial shift in either eye, as the prism shifts the image within the scotoma. The child may be asked to identify a "jump" of the fixation target in the direction of the apex of the prism to substantiate the test.

Fusional Vergences

Fusional vergences measure the ability of a child to converge or diverge behind a changing prism to maintain fusion. Its endpoint is the "make" or "break." If fusional vergences are demonstrated, binocularity exists. Monofixators (patients with peripheral fusion only) tend to have fusional vergences in the normal range. Although it is true that children with large scotomas often have fusional vergences that are inferior to those with small scotomas, the range in all groups is uniform and good. This generalization is especially valuable since the monofixation syndrome can be identified by the other sensory tests long before the child is old enough to give "make" and "break" responses.

Fusion, even if only of the monofixating type, provides the child with stereopsis and a self-regulating mechanism for holding the eyes straight, thus improving the prognosis for continued alignment.

The test can be done with either a prism bar or a rotary prism. Accommodative targets are used. The speed with which an examiner advances the rotary prism or prism bar affects the endpoint and its reproducibility.

The "breakpoint" can be grossly observed even before the child can put into words what is seen. The problem with performing this test on very young children is not "discovering the endpoint" as much as it is having the youngsters maintain their fixation while holding this distracting instrument in front of them.

Double Maddox Rod Testing

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External Exam

General inspection of the child's overall appearance and body habitus may provide an immediate diagnosis in some specific syndromes. Obvious external features such as ptosis, blepharophimosis, and lid and iris colobomas should be noted. The pupils can be checked for reactivity to light and near targets and for the presence of an afferent pupillary defect. The latter is diagnosed with a swinging flashlight test. As the light is directed from the normal eye to the eye with the afferent defect in the visual pathway, both pupils will dilate. This indicates an abnormality in the afferent limb of the pupillomotor response.

Slit Lamp Examination

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Tonometry

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Refraction and Retinoscopy

Manifest refraction is useful when prescribing glasses in older children, but a cycloplegic retinoscopy should be performed on every child at the initial visit. It is not unusual to find an unsuspected refractive error requiring treatment in a child presenting for a totally unrelated reason. Furthermore, the knowledge garnered by the ophthalmologist performing retinoscopy in the infant and pediatric age groups is useful for refining technique and for establishing one's own standards. This allows the physician to make appropriate decisions as to prescribing glasses and refractive trends over time.

Adequate cycloplegia can be obtained with combinations of cyclopentolate 2%, tropicamide 1% and phenylephrine. Atropine refraction is generally not necessary, but cyclogel 1% or 2% must be incorporated in the formula that is used. The combination formulated by Caputo and Schnitzer provides cycloplegia and mydriasis even in children with dark irides.²⁰ This formula combines 10 mL of 2% cyclopentolate with 2.5 mL of 1% tropicamide and 2.5 mL of 10% phenylepherine. Care should always be taken to avoid over dosage of these agents.

In most cases, individual handheld trial lenses are used in retinoscopy. Care must be taken to remain "on axis," which may require frequent changes of position by the examiner. A Welch Allyn (Skaneateles Falls, NY) 3.5-volt streak retinoscope provides an excellent light source and beam for

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Autorefractors are useful in children, particularly in detecting the axis of astigmatism. The handheld Retinomax K-Plus instrument produced by Nikon (Tokyo, Japan) is light weight and easy to use in infants and children since it requires only brief fixation. This instrument is portable and can be easily taken to the operating room for refraction during examinations under anesthesia. In addition, it provides a simple method of performing keratometry even in very young, minimally cooperative children. This information is essential in determining intraocular lens power for implantation in pediatric cataracts. In older, more cooperative children, standard methods of keratometry can be employed.

Photoscreening Devices

Recently, photoscreening cameras have become available for detecting amblyogenic factors. These cameras have been found to be useful for pediatricians and others interested in screening preverbal children.²¹ The cameras typically use eccentric flash photorefraction. The most commonly used device provides an instant two meridian photograph of the retinal reflex on Polaroid film.⁶ With a properly taken photograph, strabismus, asymmetric and abnormal refractive errors, and media opacities are detected. These cameras may prove useful for mass vision screening programs. Some require ophthalmologists to interpret the photographs. This technology provides an accurate, reliable method of detecting amblyogenic factors in undilated children. The major limitation of these cameras is the frequency of off-center fixation (29%) that requires a second photograph to be taken. This becomes less likely as the photographer becomes more experienced in using the camera.

Ophthalmoscopy

Ophthalmoscopy is an important part of the eye examination that is usually performed last. The reason for this is that indirect ophthalmoscopy is dependent upon satisfactory dilation of the pupil, and therefore time is allotted for dilation. In addition, children are generally most unhappy with this segment of the examination and are uncomfortable with the light source. Nevertheless, indirect ophthalmoscopy should be performed at the initial visit and when indicated in subsequent examinations. Often, the assistance of the caregiver to firmly restrain the child on the lap against the chest is required to successfully complete this examination. A lid retractor or wire lid speculum may be required if the lids cannot be held open with the examiner's finger tips. Scleral depression is not routinely used unless the periphery of the retina cannot be visualized in infants at risk for developing retinopathy of prematurity. Direct ophthalmoscopy and other slit lamp methods of retinal evaluation are performed when indicated and when cooperation permits.

Summary

Proper performance of the pediatric eye examination is a challenging and rewarding experience. It is advantageous to use the technological advances presently available to achieve optimal results (Table 2).¹⁰ The importance of flexibility of the examiner as to the sequence of the exam in the different pediatric age groups cannot be over emphasized. In particular, the establishment of a rapport with both the child and the guardian, and recognition that the cooperation of both is necessary, are goals for which the pediatric ophthalmologist must strive.

References

1. Simons K. Preschool vision screening: Rationale, methodology and outcome. Ophthalmol. 1996;41:3.
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