Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

FIGURE 4-9. Patient prefers to fix with the left eye (left figure). Occluding left eye forces fixation to right eye (center figure), and when the occluder is removed (right figure), the patient maintains fixation with the nonpreferred eye, indicating no amblyopia.

preference in 50% to 70% of cases, even if the vision is equal to within a 2 Snellen lines difference.63,64 This high overdiagnosis rate in children with small-angle strabismus occurs because they have monofixation syndrome. These patients have peripheral fusion but suppress one fovea, so they show strong fixation preference even if vision is equal. The overdiagnosis of amblyopia in patients with small-angle strabismus can be rectified by using the vertical prism test, which disrupts peripheral fusion and temporarily breaks down the monofixation syndrome.

VERTICAL PRISM TEST (INDUCED TROPIA TEST,

10 DIOPTER FIXATION TEST)

The vertical prism test is used in preverbal children with straight eyes or small-angle strabismus to accurately diagnose amblyopia.62,63 It is performed by placing a 10 to 15 PD prism base-up or base-down in front of one eye, thereby inducing a vertical tropia (Fig. 4-10). With the induced vertical strabismus, fixation preference can be determined as shown in Figure 4-11. In Figure 4-11A, a base-down prism is placed over the right eye. The right eye is fixing because both eyes move up as the right eye fixates through the prism. In Figure 4-11B, the prism is placed over the left eye, but the patient still fixates with the right eye, evidenced by the fact that both eyes are in primary

eye with a plus lens rather than occluding one eye. Blurring one eye induces less nystagmus than occlusion. Use the minimum amount of plus necessary to force fixation to the fellow eye. The vertical prism test can identify which eye is fixing. Usually, a5.00 D lens is sufficient to blur distance vision enough to force fixation to the fellow eye. Linear presentation of optotypes is difficult for patients with nystagmus because the optotypes tend to run together, so try a single optotype presentation. Also, take a binocular visual acuity measurement in addition to a monocular acuity in patients with nystagmus because binocular vision is usually better than monocular vision. To assess the best functional visual acuity potential in a patient with nystagmus, test binocular vision while allowing the patient to adopt their preferred face turn or head tilt.

VISION SCREENING

Early detection and treatment of pediatric ocular disease is critical. Diseases such as congenital cataracts, retinoblastoma, and congenital glaucoma require early treatment during infancy. Delay in diagnosis may result in irreversible vision loss and, in the case of retinoblastoma, even death. Patients with congenital cataracts treated during the first weeks of life have a relatively good prognosis, whereas surgery performed after 2 to 3 months of age is considered late and is associated with a poor visual outcome. It is, therefore, imperative to perform effective vision screening for all children from newborn infants to older children.

Vision screening examinations should start at birth and continue as part of routine checkups for primary care physicians. The acronym I-ARM (inspection—acuity, red reflex, and motility) can be a helpful reminder of the essential parts of a pediatric screening examination. Table 4-4 summarizes the I-ARM screening eye examination for neonates, babies, and children. The most important test for the newborn is the red reflex test. If an abnormal red reflex is present, then an immediate referral to an ophthalmologist is required. Infant screening examinations take less than a minute, but this brief exam is quite powerful. If performed properly, it can detect the vast majority of eye pathology, including the important diagnoses mentioned previously. Guidelines for visual acuity referral are presented in Table 4-5.

Red Reflex

The red reflex test is the single best vision screening exam for infants and young children. It is best performed using the Brückner modification, which is simply a simultaneous bilateral red reflex. Use the direct ophthalmoscope and view the patient’s eyes at a distance of approximately 2 feet from the patient. Use a broad beam so that both eyes are illuminated at the same time. Dim the room lights and have the child look directly into the ophthalmoscope light. Start with the ophthalmoscope on low illumination then slowly increase the illumination until a red reflex is seen. You will observe a red reflex that fills the pupil and a small (approximately 1 mm) white light reflex that appears to reflect off the cornea (Fig. 4-12). The white light reflex is actually a reflex coming from just behind the pupil and is called the “corneal light reflex” or the “Hirschberg reflex.” Thus, the Brückner test gives both a red reflex and the corneal light reflex simultaneously.

Blockage of the retinal image or large retinal pathology will result in an abnormal red reflex. A cataract can either block the

TABLE 4-5. Abnormal Red Reflex: Symmetry Is the Key.

FIGURE 4-12. Normal Brückner test with symmetrical red reflex and centered corneal light reflex.

red reflex or reflect light to give a white reflex. Retinoblastoma has a yellowish-white color and will produce a yellow reflex. Anisometropia (difference in refractive error) will result in an unequal red reflex. Strabismus will cause a brighter red reflex in the deviated eye, and the corneal light reflex will be decentered. The key sign of a normal exam is symmetry. See Figure 4-13 and Table 4-5 for examples of abnormal red reflexes.

AMBLYOPIA TREATMENT

Early treatment of amblyopia is critical for best visual acuity results. The basic strategy for treating amblyopia is to first provide a clear retinal image, and then correct ocular dominance if dominance is present, as early as possible during the period of visual plasticity (birth to 8 years). Correction of ocular dominance is accomplished by forcing fixation to the amblyopic eye through patching or blurring the vision of the sound eye.

Clear Retinal Image

Patients with bilateral hypermetropia ( 5.00 D) should receive the full hypermetropic correction, as amblyopic eyes do not fully accommodate. Patients who are given partial correction of their high hypermetropia often show very slow or no improvement

A

B

FIGURE 4-13A,B. Abnormal reflex. (A) Cataract: left eye. (B) Anisometropia: brighter reflex in right eye.

in their amblyopia. Patients with large astigmatism ( 2.50 D) will also have amblyopia secondary to the astigmatism or develop meridional amblyopia. Prescribe the full astigmatic correction to provide a clear retinal image. It is important to consider correcting astigmatisms of 2.50 to 3.00 or more in small children, even if the astigmatism is bilateral. Table 4-6 lists guidelines for prescribing spectacles in children. In general, if the patient has anisometropic amblyopia and straight eyes, this author initially prescribes just glasses and waits to start patch-

C

FIGURE 4-13C. (C) Strabismus: esotropia with brighter reflex from deviated left eye. (Note: This is the author’s youngest son. The author subsequently performed strabismus surgery on him, and the eyes have remained straight.)

ing of the good eye. Most anisometropic amblyopes will respond to glasses alone with no or minimal part-time occlusion of the good eye.19

Children with media opacities, such as a visually significant cataract, should have immediate surgery with visual rehabilitation using a contact lens or intraocular lens. Early treatment is critical; infants with a congenital cataract should undergo surgery within the first month of life, even as early as the first week.

TABLE 4-6. When Should Spectacles Be Prescribed in Children?

Correct Ocular Dominance

OCCLUSION

Patching or occlusion therapy is based on covering the sound eye to stimulate the amblyopic eye. Strabismic patients without binocular fusion can be treated with full-time occlusion; however, full-time occlusion may result in reverse amblyopia in children under 4 to 5 years of age. To prevent reverse amblyopia, do not use full-time occlusion for more than 1 week per the child’s age in years without reexamining the vision of the good eye. For example, a 2-year-old child receiving full-time occlusion should be examined every 2 weeks. In children less than 1 year of age, part-time occlusion may be preferable to avoid reverse amblyopia.

Amblyopic patients with essentially straight eyes (tropias8 PD) and peripheral fusion (e.g., anisometropic amblyopia and microtropia monofixators) are best treated with part-time patching (3 to 4 h/day) or no occlusion. For anisometropic amblyopia, initially prescribe spectacle correction and follow the patient each month for visual acuity improvement. If vision does not improve on monthly follow-ups, then part-time patching is started. Part-time occlusion or penalization therapy is preferred because these methods help to preserve fusion. If vision does not improve with part-time occlusion, then full-time occlusion should be tried.

PENALIZATION

Penalization is a method for blurring the sound eye to force fixation to the amblyopic eye. Penalization actually switches ocular suppression, which can be demonstrated by a Polaroid vectographic chart or by the Worth 4-dot test. Penalization only works if fixation is switched from the sound eye to the amblyopic eye.59 Blurring of the sound eye can be achieved by various methods. Optical penalization is based on over-plussing (prescribing more plus sphere than needed) the sound eye to force fixation to the amblyopic eye for distance targets; the patient will usually use the sound eye for near targets. Optical penalization works well for mild amblyopia; however, some children will look over the tops of their glasses to use their sound eye. Atropine penalization is a stronger form of penalization and is useful even in dense amblyopia so long as the patient has significant hypermetropia of the good eye.38 Atropine at 0.5% or

1% is placed in the sound eye each day, optical correction is removed from the sound eye, and the amblyopic eye is given full optical correction. If the patient switches fixation to the amblyopic eye under these conditions of penalization, then penalization will improve vision.59

Cyclopentolate can be used as an in-office test to predict if penalization will work.59 The in-office test consists of providing the amblyopic eye with full optical correction while deadening the sound eye with cyclopentolate and removing optical correction from the sound eye. If fixation switches to the amblyopic eye under these conditions, then the patient will improve with atropine penalization. Atropine penalization usually requires3.00 or more hypermetropia in the sound eye to obtain significant blur to switch fixation. It is important to note that blurring the sound eye to a visual acuity lower than the amblyopic eye does not guarantee a switch in fixation to the amblyopic eye. Penalization in young children may result in reverse amblyopia (decrease vision in the previously good eye), so patients 4 years of age or younger should be followed closely when undergoing atropine penalization therapy.50,59

OCCLUSIVE CONTACT LENS

Occlusive contact lens can be used in treating amblyopia. A study by Eustis and Chamberlain15 showed 92% of patients improved at least 1 line of Snellen acuity, but complications limited the usefulness. Complications included conjunctival irritation and poor contact lens fit, and one patient even learned to decenter the lens to peek around the occlusive contact lens. There was a high recurrence to pretreatment visual acuity, as 55% showed recurrence of amblyopia. The authors concluded that occlusive contact lenses should only be considered as a last resort and that these patients require close follow-up.15

BILATERAL LIGHT OCCLUSION

A preventive treatment of amblyopia may be the use of bilateral light occlusion. Studies on dark-rearing have shown that bilateral total light occlusion prolongs the sensitive period of visual development. In several animal studies, researchers have shown that animals placed in total darkness for several months (or the human equivalent to several years) do not develop dense amblyopia and their visual development is minimally affected.9,10,11,40 A study by Hoyt22 on neonates with hyperbilirubinemia treated