346 PEDIATRICS AND STRABISMUS

may not have good stereopsis (usually not unless straightened by age 2 years) but have absence of binocular vision (lost after 3 months). Often have large latent phoria; may have amblyopia.

Etiology: end result of strabismus surgery (74%), anisometropia (6%), macular lesion (1%), primary genetic inability to bifixate (1% of population; 14% of first-degree relatives of ET patients).

Thirty-seven percent of patients are orthophoric, 63% have microstrabismus as determined by cover test (mostly postoperative strabismus patients). Patients have a 3-degree macular scotoma (not suppression) in the nonfixating eye, diagnosed by 4 pD baseout test.

Treat amblyopia and anisometropia; alignment is already stabilized by extramacular NRC. Monofixation is best result after infantile ET correction and is a good predictor of long-term alignment.

Signs and Symptoms

CARTILAGE IN EYE Patau’s syndrome (trisomy 13), PHPV, teratoma

DECREASED VA (ACQUIRED, NEW ONSET) Myopia (usually develops between age 6 to late teens, compared with hyperopia, which typically increases up to age 6, then plateaus), hydrocephalus, tumor, neurodegenerative disease, infection/inflammation, toxins, and previously undiscovered decreased VA

DECREASED VA (CONGENITAL) WITH A ‘‘NORMAL’’ FUNDUS Achromatopsia, CSNB, and Leber’s congenital amaurosis (all may have paradoxical pupils)

EYE DISEASE WITH DEAFNESS Usher’s syndrome (RP), Wolfram syndrome (optic atrophy).

EYE-POPPING REFLEX Pronounced widening of the PF after abrupt decrease in ambient light or after loud noises. Present in 75% of infants within 3 weeks of birth.

FACE TURN Nystagmus null point, nerve palsy, and astigmatism

FORCED DUCTIONS POSITIVE Brown’s syndrome, congenital fibrosis, blowout fracture, thyroid eye disease, and fat adherence syndrome

FOVEAL HYPOPLASIA Albinism, aniridia, and PHPV

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HETEROCHROMIA IN CHILDREN Congenital Horner’s syndrome, JXG, and Waardenburg’s syndrome (autosomal dominant [AD], eyelid abnormalities, white forelock, sensorineural hearing loss)

INCREASED FUSIONAL AMPLITUDES Intermittent strabismus and congenital CN IV palsy

LEUKOCORIA Larval eosinophilic granuloma (Toxocara), embryonal meduloepithelioma, uveitis, Coats’ disease, organizing hemorrhage, cataract or PHPV (leading cause at birth), ON coloboma, retinoblastoma (average age 18 months) and retinopathy of prematurity (stage 5), idiopathic, and assorted other causes (congenital retinal folds, hamartoma, hemangioma, Norrie’s disease, FEVR).

MITOCHONDRIAL DNA INHERITANCE Leber’s optic atrophy, exerciseinduced myopathy, Leigh’s syndrome, Kearns-Sayre syndrome, NARP (neurogenic muscle weakness, ataxia, and RP), and infantile lactic acidosis

NYSTAGMUS AND DECREASED VA CSNB, albinism, Leber’s amaurosis, and achromatopsia.

STRABISMUS, THREE PRIMARY ETIOLOGIES:

Childhood: brainstem, central, vestibular (signal problem)

Restrictive: myopathic, compressive, thyroid (muscle problem, tendon spared), orbital pseudotumor

Paralytic: neuropathic (peripheral/central), cranial nerve, neuromuscular junction, myasthenia

VIOLATES HERRING’S LAW DVD, aberrant regeneration, Duane’s syndrome

VIOLATES SHERRINGTON’S LAW Duane’s syndrome

X-LINKED DISORDERS Adrenoleukodystrophy (optic atrophy), Aicardi’s dominant optic neuropathy (XLD), Alport’s syndrome (85% X-linked), choroideremia (XLR), Hunter’s (XLR), incontinentia pigmenti (XLD), Lenz microphthalmia syndrome, Lowe’s syndrome (XLR), megalocornea (XLR), Norrie’s disease, ocular albinism (Nettleship-Falls syndrome), Fabry’s disease (XLR), X-linked CSNB, X-linked retinoschisis (XLR), X-linked RP

Exam and Imaging

EVALUATION, STRABISMUS Consider family history of strabismus or amblyopia, birth and developmental history, red reflex history, age of onset,

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348 PEDIATRICS AND STRABISMUS

abnormal head position, and constant or intermittent strabismus. Check stereopsis prior to VA or cover testing; do W4D; look at facial structure, angle kappa, EOM, A or V pattern, and oblique dysfunction; and measure alignment in primary and secondary positions.

STEREOACUITY In order not to disrupt fusion, check stereopsis first, then check VA and alignment. The Titmus test stereo fly plate tests about 3000 seconds of arc at 40 cm; lateralization clues can give false-positive results. Randot circles range from 400 to 20 seconds of arc at 40 cm.

VISUAL ACUITY (VA) TESTING May test F/F (patient able to fix and follow) or preferential looking (Teller cards) in infants; then central, steady, and maintained VA (CSM; fixation maintained after cover is removed from the opposite eye), tumbling E, Landolt C, Allen figures, Snellen’s chart, etc.

CYCLOPLEGIC REFRACTION 1 drop anesthetic (removes stinging and disrupts epithelium to improve absorption), 1% Cyclogyl (2 doses, or 3 doses for dark irides), with 2.5% phenylephrine; wait 30 to 40 minutes. Cycloplegics are parasympatholytic; thus, there may be anticholingergic side effects (fever, flushing, delirium, etc.). Use with caution, especially with Down syndrome. Phenylephrine is an alpha-stimulating sympathomimetic; thus, it may raise blood pressure and decrease pulse rate. Retinoscopy exam improved by occluding the opposite eye.

ALIGNMENT Place plastic prisms in the frontal plane; place glass prisms in plane perpendicular to deviation.

Hirschberg: corneal light reflection; 1 mm deviation ¼ 7 degrees ¼

15 pD.

Krimskey: prism placed over the fixating eye until deviation is neutralized; modified-Krimskey if prism is held over the nonfixating eye.

Bruckner: pupillary light reflection brighter in strabismic eye (do not confuse with leukocoria).

Angle kappa: misalignment of visual and anatomic axis, is not strabismus. If positive angle kappa, the patient looks like XT; light deviates nasally from slight temporal rotation of the globe from temporally displaced fovea relative to optical axis. If negative angle kappa, the patient looks like ET (Hirschberg deviates temporally).

COVER TESTING Two diagnostic tests (CT, alternate cover test [ACT]), two quantitative tests (simultaneous prism cover test [SPCT], prism and cover). If alternating tropia, there is less concern for amblyopia.

Cover test (CT): reveals tropia.

Alternating cover test (ACT): shows phoria and tropia by dissociating the eyes. If there is no movement, consider orthophoria.

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Simultaneous prism cover test (SPCT): simultaneously place a prism for the amount of tropia on one eye, and cover over the other eye; test reveals tropia without phoria. Useful in discerning small tropias with large phorias.

Prism and cover: uncovers tropia and phoria.

ACCOMMODATIVE CONVERGENCE/ACCOMMODATION (AC/A) RATIO

Normally about 5 pD convergence per D of accommodation. Child can neutralize high AC/A by fusional divergence. Can roughly determine that a high AC/A ratio exists if the measured ET’ (near) is 10 pD more than measured ET (distance).

Heterophoric method (clinical use; test distance varies; uses prisms): pupillary distance (cm) þ [(pD near pD distance) (D near D distance or D of accommodation)]. Usually larger than gradient method.

Gradient method (research use; test distance remains constant; uses lenses): (pD with lens pD without lens) D of lens. AC/A is due to proximal convergence.

MOTILITY Ductions deal with monocular movements; versions deal with binocular conjugate or disconjugate movements. May describe normal motility as full ductions and conjugate versions, or draw cardinal fields of gaze and note underaction or overaction from 3 to þ3. Urest measurements are more objective and noted as the distance from the corneal light reflection in primary gaze when looking up, down, left, and right (stated in degrees if light reflection is on the cornea or millimeters if past the cornea).

A pattern: more XT in downgaze and reading position or more ET in upgaze, as in bilateral superior oblique overaction (SOO). A and V patterns are defined as >15 pD difference from upto downgaze.

V pattern: opposite from above, usually inferior oblique overaction (IOO; hyperdeviation is greater in its field of action)

MADDOX ROD Place over one eye, and have patient view a point source of light. Align the rod bars vertically so that the patient sees a horizontal line. If the patient sees a red and white line that is vertically separated, neutralize the vertical deviation with a prism to obtain the hypertropic amount. The test vertically dissociates the patient and is inaccurate for horizontal deviation because horizontal amplitudes are so large.

DOUBLE MADDOX ROD Use two Maddox rods (preferably one white and one red), placing one over each eye, and ask patient to make the lines parallel. Test measures ocular torsion, and the degrees of torsion are obtained from the angle between the Maddox rods’ axes. (Torsion may also be seen with the indirect ophthalmoscope. The fovea should be level with the upper third of the optic disk. If it is higher, then excyclotorsion is present; if it is lower, then incyclotorsion is most likely present.)

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350 PEDIATRICS AND STRABISMUS

SENSORY TESTS XT gives crossed diplopia in all tests except afterimage. Tests for diplopia: Maddox rod, red glass, Bagolini lenses, and W4D. Haploscopic tests: major amblyoscope, Lancaster red-green, and afterimage. Tests for suppression: W4D, Bagolini lenses and 4D base-out prism.

Afterimage: most dissociative; uniocular test for ARC. Do not perform with eccentric fixation. Flashes each fovea separately; flash the suppressed eye in the vertical plane (tends to be a horizontal macular scotoma), and flash fellow eye horizontally. Interpretation is opposite of Bagolini: ET þ ARC ¼ crossed, XT þ ARC ¼ uncrossed.

Bagolini striated lenses: least dissociative test; best for ARC with ET. Patients recognize and report their scotoma while viewing a light 15 inches away through striated lenses (can smear ocular lubricant on glasses): streak OS at 45 degrees (up and left), streak OD at 135 degrees (up and right). This produces a line of light perpendicular to the striations, and the normal eye sees an X. Examiner can simultaneously evaluate the ocular alignment.

If the strabismic patient sees an X, then ARC is present. If ARC is not present, then the ET patient sees an uncrossed image, like a V with the bottom cut off, and the XT patient sees a crossed image, like an X crossed high.

Suppression causes a break in the streak or no streak. Most patients with the monofixation syndrome (if they are directed to it) see their macular scotoma as a gap in the nonfixating eye’s light streak.

Base-in prism test for XT: increasing base-in prism before nonfixating eye moves the object of regard across the hemiretinal line onto the nasal retina out of the large scotoma and causes sudden recognition of diplopia. If ARC is present, images appear apart; for NRC, images are ‘‘kissing.’’

Euthyscope: a retinoscope with an aperture that tests fusional vergence amplitudes. Macular testing: photostressing the retina with macular area shielded bleaches out the peripheral retina and relies only on macular area to fuse (weak fusion capability). Photostressing retina with extramacular area shielded bleaches out the macula and relies only on the peripheral retina to fuse (strong fusional capability).

4D base-out prism: test for microstrabismus or monofixation syndrome; the normal response is movement of the contralateral eye away

from the prism followed by a refixation movement. With the prism OD: no movement ¼ suppression OD; OS moves but no refixation ¼ suppression OS; OS moves and refixates ¼ normal.

Major amblyoscope: best ARC test; if the objective angle ¼ subjective angle, then NRC is present. If subjective angle ¼ 0, then harmonious ARC (compensated) is present; if subjective angle is not 0, then patient has unharmonious ARC.

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Red glass test: dissociative test for suppression versus ARC. With red lens placed over right eye, patient fixates on point source of light. If the eyes are straight, patient should have retinal rivalry and see red or white alternately. ET patients have uncrossed diplopia, and XT shows crossed diplopia.

Worth four-dot test (W4D): dissociative test for testing suppression, monofixation, or ARC with ET. With glasses with red lens on right eye and green lens on left eye, patient views a flashlight that has two red, two green, and one white point sources of light. Light is viewed at a distance (subtends 0.125 second of arc on the macula) and then nearby (subtends 6 seconds of arc, an extramacular test). If the patient sees two red lights ¼ suppressing OS; if three green ¼ suppressing OD; four lights ¼ normal or if strabismic, then ARC is present; five lights ¼ diplopia; >5 lights ¼ functional issues. If distance is normal, then near test is not needed. In ET, the suppression scotoma is small (5 degrees); thus, patient should suppress W4D at a distance but have a fusion response in near test because extramacular has adapted with ARC.

VISUAL EVOKED POTENTIALS (VEPs) Can document 20/20 VA by age 6 to 8 months.

DEVELOPMENTAL AND VISUAL ACCOMPLISHMENTS See Table 9–4

TABLE 9–4

Developmental and Visual Accomplishments

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