Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Retinal Disease_Wright, Spiegel, Thompson_2006

FIGURE 12-2. Typical peripheral lattice degeneration may demonstrate linear white lesions as well as hyperpigmentation. Atrophic holes or flap tears may be associated with lattice.

the posterior pole and an optic nerve crescent. The crescent and tessellation are usually seen on the same side of the nerve. Although these findings in an adult are often secondary to intermediate myopia, in a child they are often the harbinger of a staphyloma, an area of ectasia with thinning of the retina, choroid, and sclera. As pathological myopia progresses, the tessellated area becomes thinned, and eventually excavated (Fig. 12-3). There may be pigment clumping around the edges or within the otherwise hypopigmented area of the staphyloma.

Many types of staphylomas have been described, depending on their location. The most visually significant are those affecting the macula. The presence of a staphyloma is a poor prog-

FIGURE 12-1A–C. (A) Left fundus of a 13-year-old girl. The spherical equivalent is 14.00 D. Note that the scleral cresent is most prominent in a somewhat atypical inferonasal location. Tessellation of the posterior pole and a decreased foveal reflex are also present. There is a Bergmeister’s papilla on the disc. (B) Right fundus of the same patient, with a spherical equivalent 8.00 D. Note the correlation of the size of the crescent with the refraction. (C) Myopic disc demonstrates a crescent on one side, with “supertraction” on the other. The small black dot seen on the disc is an artifact caused by visualization of the “Allen dot” of the fundus camera that occurs when a highly myopic eye is photographed.

FIGURE 12-3. A peripapillary staphyloma. Note the choroidal vessels diving into the excavation of the staphyloma. The ectasia may occur around the nerve, nasal to the disc, or temporal to the disc. It may also involve the macula, and, because it may increase over time, the prognosis for central vision is poor.

nostic sign. Most of these eyes have best corrected acuities of less than 20/20 early in life and continued loss of vision with increasing age. Almost 50% of eyes with staphylomas are legally blind by the fifth decade of life.8 “Lacquer cracks” (Fig. 12-4A,B) may develop in or near the macula. These linear, whitish lesions represent breaks in Bruch’s membrane. In one study, 4.3% of eyes with an axial length greater than or equal to 26.5 mm exhibited lacquer cracks; the youngest patients seen to have this abnormality were in their late teens.9 Lacquer cracks themselves usually do not affect acuity; however, they are a poor prognostic sign for the retention of good vision and may be associated with an acquired blue-yellow color deficit.27 Focal retinal degeneration, hemorrhages, and subretinal neovascular membranes associated with the lacquer cracks are probably responsible for the poor prognosis.

Retinal hemorrhages, particularly in the macula, are not uncommon in pathological myopia and are of two main types. In the first, an acute hemorrhage occurs, unrelated to a subretinal net, causing a severe reduction in acuity but resolving over weeks with vision returning to its previous level. These spontaneous

FIGURE 12-5. Multiple Fuch’s spots in the macula with a recent hemorrhage as well. The prognosis for good vision in this eye is very poor. (Courtesy of G.F. Judisch, Iowa City, IA.)

(Fig. 12-5); this may be followed by atrophy. Visual loss is severe and may be irreversible in these cases.63

Large and small areas of chorioretinal atrophy are seen in some eyes (Fig. 12-6). These areas may coalesce as patients

FIGURE 12-6. Geographic atrophy around the optic nerve and in the posterior pole.

become older resulting in large areas of atrophy with somewhat scalloped edges. Even in eyes without macular hemorrhage, the macula may show hyperpigmentation and pigment mottling that is already apparent in childhood.7

In later life, eyes with pathological myopia may show marked thinning of all layers of the eye, especially in areas of staphyloma. The choroid in particular becomes thin and sclerotic.

CLINICAL ASSESSMENT

It is of the utmost importance to do a cycloplegic refraction as part of the evaluation of myopia, certainly in all children, and even in adult myopes. Many patients have been over-minussed over years of manifest refractions. Children can accommodate up to 15 diopters with ease, but by the age of 40 years, only about 3 diopters can be easily performed. Overcorrection in adulthood may cause asthenopia and even accommodative esotropia or the breakdown of esophorias because of greater difficulty in accommodating over the extra minus with advancing age.37

In older children and adults, a cycloplegic subjective refraction can be done, with or without the duochrome test; 1% cyclopentolate hydrochloride should be used. In younger children, the results of cycloplegic retinoscopy should be prescribed. On subsequent visits, cycloplegic retinoscopy while the child is wearing the glasses can be done to refine the prescription and eliminate vertex distance errors. In patients of all ages with moderate to high levels of myopia, refraction over the patient’s existing glasses may give a more accurate final prescription than using a phoropter or trial frames. Because accommodation may play a role in the development of myopia, at the very least, myopic patients should not be “over-minussed” as this induces extra accommodative effort at all distances.

A careful family history should be taken with special emphasis on presence or absence of early-onset refractive errors, retinal detachment, hyperextensibility, cleft palate or bifid uvula, arthritis, best corrected vision below the level necessary to obtain a driver’s license, or ectopia lentis. Answers to these questions may point to a more serious ocular or systemic syndrome than isolated simple myopia.

It is important to remember the natural history of physiological myopia when evaluating a new patient. Children are

rarely highly myopic before the age of 9 years (although there is evidence that Asian children may develop higher degrees of myopia at younger ages than other ethnic groups). High myopia in children younger than this should prompt a detailed review of systems, birth history asking specifically about prematurity, retinopathy of prematurity either treated or untreated, or other risk factors, and a systemic evaluation for associated syndromes. Intraocular pressure should always be measured at least once, because myopia in infancy can be a presenting sign of congenital glaucoma. Hearing testing should be done in young children presenting with myopia, because several syndromes have deafness as a feature.

SYSTEMIC ASSOCIATIONS

In addition to the types of myopia listed earlier, which are usually isolated, there are special subsets of myopia that fit imperfectly into one of the groups. Unilateral high myopia with increased axial length may occur as a part of a hemihypertrophy syndrome, with myelinated nerve fibers, or as an isolated finding. Myopia related to retinopathy of prematurity (ROP) may be caused by an abnormally spherical lens, increased axial length, or both. Premature infants who develop ROP have a much higher risk of developing myopia than those who did not have ROP, in both Asian and western populations.60 The prevalence has been found to increase between 3 and 12 months of age on cycloplegic refraction but to remain stable thereafter.49 A higher prevalence of eyes with more than 8.00 diopters of myopia was found in those treated with cryotherapy versus those who were not treated. Whether this is attributable to the cryotherapy itself or to the opportunity to measure refraction in eyes that otherwise would have developed retinal detachments because of worse, more myopiogenic ROP is unknown.49

Myopia may be the presenting sign of several systemic syndromes. Stickler’s syndrome, a defect in collagen synthesis caused by mutations in the COL2A1 gene (type 1)1 and COL11A1 gene (type 2),53 may present with nystagmus in early childhood as a result of defocus severe enough to cause deprivation, at times in the 15.00 to 20.00 diopter range. In patients with lower degrees of myopia, presentation may be later, when it is noted that the child holds near objects excessively close. Other associated features are early-onset arthritis,

hearing loss, flat midface, and cleft palate or bifid uvula. The vitreous is optically empty, with broad veils visible on indirect ophthalmoscopy. It is autosomal dominant.

Kneist dysplasia and spondyloepiphyseal dysplasia (SED) congenita are more severe autosomal dominant manifestations of Col2A1 mutations.66 Some forms are lethal in the neonatal period. Kneist dysplasia patients resemble Stickler patients, but in addition suffer from dwarfism and scoliosis. Patients with SED congenita have dwarfism with barrel chests, hearing loss, joint disease, and high myopia with a predisposition to retinal detachment. Knobloch syndrome is autosomal recessive and may be associated with an unusual posterior scalp lesion that can overlay an occipital encephalocele. It has been mapped to chromosome 21q22.3.57 Myopia is also more prevalent in certain ocular disorders such as retinitis pigmentosa, congenital stationary night blindness, Aland eye disease, and gyrate atrophy.

INHERITANCE

The inheritance of myopia is complex, probably because there are many “myopias” with different etiologies. Autosomal dominant, recessive, and sporadic cases of isolated myopia have been reported.7,33,59 Many pedigrees give the appearance of a complex trait, that is, the frequency is increased within a family relative to the general population, but the inheritance does not follow simple Mendelian laws; this may occur when more than one gene is involved, and/or when there are environmental factors necessary for the expression of the trait.

Some studies have demonstrated that children who have two myopic parents are more likely to become myopic than those with only one, or neither.38 Axial length is longer in children of myopic parents, even before they develop myopia.72 In a study of children 6 to 12 years old, the rates of myopia were 12.2% of the children with two myopic parents, 8.2% of those with one myopic parent, and 2.7% of those without myopic parents.72 Another study found that children with two myopic parents were 6.42 times more likely to become myopic than children without myopic parents.43 Such studies support the idea that a predisposition is inherited. A similar study done in Hong Kong did not find a correlation with parental myopia, however.12 Even a U.S. study that sought to find a strong predictor of juvenile myopia found that neither refraction at school entry, refrac-

tion in infancy, nor parental myopia had both high sensitivity and specificity.38 The genetic contribution may be difficult to elucidate because environmental factors, such as nearwork and accommodation, may also play a role and may be similar in members of the same family.4,73 In addition, it is likely that several different genes for corneal shape, axial length, lens shape, and perhaps eye growth are inherited from each parent, making inheritance of even emmetropia complex to understand. Sorsby found that in refractively normal families there is a mild correlation (0.30) between the midparent refraction (average of the two parents’ refractions) and that of offspring.59 A reevaluation of Goldschmidt’s data by Guggenheim et al.19 found a much higher correlation (0.65) for the midparent/offspring refractions in children with high myopia than in those with refraction near emmetropia, which may suggest autosomal dominant transmission in some cases. Sorsby also found that the concordance in refraction between monozygotic twins was high, 0.71, but not perfect.

Some pedigrees have been reported that appear to represent autosomal dominant inheritance of isolated high myopia. At least two genetic loci have been found, demonstrating genetic heterogeneity.70,71 Genetic heterogeneity between high and low myopia has also been reported.46

TREATMENT AND PREVENTION

The treatment of myopia consists of managing both the visual acuity loss and the complications that may arise. Treatment of the blurred vision in myopia has had a long and checkered history. Everything from physical exercise to palming the eyes to having myopic students study in green rooms has been advocated at one time or another.31,65 These trials have been uniformly unimpressive in improving acuity.

Prevention

Sight-saving classes, exercises, undercorrection, cycloplegic therapy, contact lenses, pinhole glasses, and many other therapies have been aimed at preventing or slowing the progression of myopia. Surgery has been advocated to retard the progression of staphylomas in pathological myopia. A few of these therapies deserve mention.

There is evidence from several studies that atropinization during childhood slows or prevents an increase in myopia5,25; however the effects may not be long lasting.55 One study that standardized final refractions of atropine and control groups at 20 years of age did find a long-term benefit, with those in the atropine group having a mean refraction of 2.79 diopters whereas those in the control group averaged 3.78.26 The longterm effects of chronic dilation, including the effect of increased ultraviolet exposure, are not known. Also, the need for bifocals to read during atropine therapy is inconvenient, and patient and parent acceptance is often a problem.55 The muscarinic antagonist pirenzipine retards axial myopia in nonhuman primates61 and is currently being tested in clinical trials for use in human children. The rationale for use is that, in animal studies, atropine blocks myopia development even when the optic nerve is severed, meaning the mechanism cannot be lack of accommodation alone. Pirenzipine acts on the same receptors as atropine, yet the mydriasis and cycloplegia are minimal, theoretically producing the same pharmacological or transmitter effect without the side effects.

Undercorrection and near adds have had mixed results, but overall there is little evidence that the chance for benefit warrants the increased expense and effort for most myopes. One study showed no difference in myopic progression over 3 years between children who wore their correction full time, part time, or not at all.41

A trial of timolol maleate eyedrops in children with physiological and intermediate myopia showed that there was no significant difference in progression of myopia between the control and timolol groups; some children on topical timolol maleate actually had greater increases in myopia, although axial lengths did not increase more than the control group.23 The author concluded that timolol maleate has no role in the treatment of these children.

In patients with pathological myopia, however, timolol or other ocular antihypertensives may be beneficial.7 Scleral reinforcement with various materials also has good results in some hands, and given the poor prognosis in young patients with increasing staphylomas, may be indicated in certain patients.7,62 Scleral shortening may be useful in cases of detachment secondary to macular hole formation.39 Activities such as weight lifting, deep sea diving, and sports or hobbies that involve straining or raising intrathoracic pressure should be avoided.