Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology for Primary Care 3rd edition_Wright, Farzavandi_2008
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Chapter 21
Ocular Pigmentation
Abnormalities
Albinism (Also See Chapter 6)
Albinism is a lack of melanin pigment that can occur primarily involving the eyes (ocular albinism [OA]) or systemically (oculocutaneous albinism [OCA]).
Classification of albinism
Traditionally, albinism has been classified according to clinical phenotype with 2 main categories, OCA and OA.
Recently, there has been a reclassification of the albinism subtypes. With the availability of new molecular genetic studies, the classification of albinism has shifted emphasis to genotype as opposed to phenotype alone. Hence, this has led to redefining existing phenotypic categories and the addition of new subtypes based on specific genetic mutations. The following is a brief overview of the current classification of albinism.
Oculocutaneous albinism
Oculocutaneous albinism is characterized by the reduction or absence of melanin in the skin, hair, and optic system (including the eyes and optic nerves). The lack of skin pigment not only results in a pale skin appearance but also increased risk of skin cancer. Oculocutaneous albinism is divided further into several subtypes based on the distinct genetic mutation
(Table 21 1).
The eye findings associated with OCA include nystagmus, hypopigmen tation of the iris with transillumination defects, hypopigmented fundus, foveal hypoplasia, and poor visual acuity (usually 20/80–20/400). Patients with tyrosinase positive OCA show progressive increased pigmentation,
as they are able to produce melanin. Tyrosinase negative OCA is a severe hypopigmentation disorder that tends to be static and is associated with very poor visual acuity and legal blindness. Both tyrosinase positive and tyrosinase negative oculocutaneous albinism are inherited as an auto somal recessive trait. Transillumination defects of the iris are important in
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Table 21-1. Oculocutaneous Albinism (OCA) Types
Subtypes |
Gene Position |
Affected Protein |
|
|
|
OCA 1 |
11q14-21 |
Tyrosinase |
•OCA 1A (tyrosinase-negative OCA)
•OCA 1B (yellow-mutant/Amish/xanthous, temperature-sensitive)
•OCA 1A/1B heterozygote
OCA 2 |
15q11-13 |
P protein |
• Tyrosinase-positive OCA, brown OCA |
|
|
|
|
|
OCA 3 |
9p23 |
Tyrosinase-related |
|
|
protein |
|
|
|
distinguishing true albinism from otherwise normal patients with hypopig mentation (Figure 21 1 A and B).
Ocular Albinism
Ocular albinism is characterized by changes in the optic system only, with no clinical difference in skin and hair color. Two major disorders exist in this category, OA 1 and autosomal recessive OA (Table 21 2).
Ocular albinism is hypopigmentation that is localized to the eye. Patients with OA may have brown or dark hair and will not look like the typical patient with albinism. Ocular albinism is usually inherited as X linked
or autosomal recessive trait. Typical findings of OA are transillumina tion defects of the iris, nystagmus, and hypopigmented fundus. Macular hypoplasia also can be associated with OA. In addition, strabismus is com monly seen with OCA and OA. Hemifield visual evoked potential studies show excess of decussation at the chiasm, and patients with albinism show
decreased binocularity. Decreased vision associated with albinism is related
Table 21-2. Ocular Albinism (OA) Types
Subtypes |
Gene Position |
Affected Protein |
|
|
|
OA 1 (X-linked recessive OA/ |
X p22.3-22.2 |
Unknown |
Nettleshop-Falls type) |
|
|
|
|
|
Autosomal recessive OA |
Not a distinct |
Tyrosinase in some cases; |
|
position |
P protein in some cases |
|
|
|
Ocular Pigmentation Abnormalities |
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Figure 21 1.
A, Hermansky-Pudlak syndrome with ocular albinism, but irides are brown. B, Despite brown eyes, the iris transilluminates on slitlamp examination, showing the hypopigmentation of the iris pigmented epithelium.
to macular hypoplasia. Vision tends to improve over time as pigmentation increases, especially in patients with tyrosinase positive albinism.
Hermansky Pudlak Syndrome
Hermansky Pudlak syndrome is a tyrosinase positive albinism with prolonged bleeding time secondary to abnormal platelet aggregation. Lung disease and ulcerative colitis develop at approximately 30 to 40 years of age. Because of the platelet abnormalities, patients show bruisability, increased nosebleeds, and increased bleeding after minor surgical proce dures (Figure 21 1).
Chédiak Higashi Syndrome
Chédiak Higashi syndrome is a tyrosinase positive oculocutaneous albinism associated with defective degranulation of neutrophils that fails to prevent infections secondary to defective microtubule assembly. Bacterial
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infections are dangerous in these patients and can be fatal in childhood. A severe lymphoma like syndrome may also occur.
Waardenburg Syndrome
Waardenburg syndrome is not a pigment deficiency disease, but is associated with white forelocks, hypopigmented fundus, and heterochromia secondary to hypopigmentation of all or part of the iris. Other findings include telecan thus, confluent eyebrows, and sensorineural deafness.
Nevus of Ota
Nevus of Ota is congenital melanosis of the periocular skin and eye (mela nosis oculi) that occurs unilaterally. Characteristics of melanosis oculi include increased pigmentation of the conjunctiva, sclera, and episclera. The mandible, oral and nasal mucosa, tympanic membrane, and dura may also have increased pigmentation. The condition is most commonly seen in females, often occurring in Asian or black people and almost all cases are unilateral, although bilateral cases have been reported. Skin lesions, which are simply areas of increased pigmentation, may be present at birth and often increase in pigment density during puberty. There is a slight but significant increased risk for malignant transformation of the nevus, with approximately 4% of cases evolving into melanomas. This is an important cosmetic problem because the increased pigmentation is difficult to treat with cosmetic cover ups.
Conjunctival Nevi
See Chapter 13 and Figure 13 16.
Blue Sclera
Blue sclera is caused by visibility of uveal tissue through thin sclera. The common ocular and systemic conditions associated with blue sclera are listed in Table 21 3.
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Table 21-3. Ocular and Systemic Conditions Associated With Blue Sclera
1.Myopia
2.Buphthalmos
3.Scleral staphyloma
4.Congenital ocular melanosis
5.Aniridia
6.Ehlers-Danlos syndrome
7.Marfan syndrome
8.Osteogenesis imperfecta
9.Paget syndrome
10.Pierre Robin syndrome
Chapter 22
Leukocoria: Cataracts,
Retinal Tumors, and
Coats Disease
Leukocoria—“White Pupil”
Leukocoria is defined as a white pupil and indicates an opacity at or behind the pupil. A white pupil can be the result of a cataract, an opacity of the vitreous, or retinal disease (Table 22 1). Leukocoria implies that the cornea is clear. A corneal opacity will, however, result in an abnormal red reflex and obscure visualization of the pupil. If the details of the iris and pupil are clearly seen, the opacity is behind the pupil. If, on the other hand, visualiza tion of the iris and pupil is obscured, the opacity is in front of the iris (ie, in the anterior chamber or cornea). Refer to Chapter 15 for a discussion of cor neal abnormalities. Patients with leukocoria require an immediate referral for a full ophthalmic evaluation.
Table 22-1. Differential Diagnosis of Leukocoria
Cataract (this chapter)
Coats disease (this chapter)
Coloboma of macula and optic nerve (Chapter 6)
Corneal opacity (Chapter 15)
Familial exudative vitreoretinopathy (FEVR) (Chapter 19)
Incontinentia pigmenti (Chapter 19)
Leukemia with vitreous hemorrhage (this chapter)
Medulloepithelioma and retinal tumors (this chapter)
Myelinated nerve fibers (Chapter 9)
Norrie disease (Chapter 6)
Persistent hyperplastic primary vitreous (PHPV) (this chapter)
Retinoblastoma (this chapter)
Retinopathy of prematurity (Chapter 19)
Toxocariasis (Chapter 14)
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Pediatric Cataracts
In contrast to adults, cataracts in children present a special challenge because early visual rehabilitation is critical to prevent irreversible ambly opia. Until the late 1980s, many ophthalmologists would not even attempt surgery on unilateral congenital cataracts because of the poor prognosis. Now ophthalmologists operate as early as the first week of life, and the prognosis is much improved.
Morphology of Infantile Cataracts
Infantile cataracts can be classified by the location of the lens opacity. The lens nucleus is the first part of the lens to develop and is demarcated by 2 Y sutures, one on the anterior surface and one on the posterior surface (Figure 22 1). Opacities at or within the Y sutures are termed nuclear cataracts. This indicates that the cataract was present since birth (Figure 22 2). Cataracts located peripheral to the Y sutures are called cortical cataracts. Cortical cataracts that are layered in an onionskin like pattern with clear zones between the opacities are termed lamellar, or zonular, cataracts (Figure 22 3). The visual prognosis for lamellar cataracts is rela tively good because they are acquired, and the lens is relatively clear during the early period of visual development. Cataracts are characterized as ante rior or posterior.
P
Figure 22 1.
Diagram of neonatal lens showing anterior lens epithelium and lens nucleus located between the Y-sutures and the cortex peripheral to the Y-sutures. A, anterior; P, posterior.
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Figure 22 2.
Four-week-old infant with a congenital sutural nuclear cataract. Note the anterior Y-suture is oriented upright. The peripheral clear red reflex represents clear lens cortex, whereas the central opacity involves the sutures and nucleus.
Anterior Cataracts
Anterior Polar Cataracts
Anterior polar cataracts involve the anterior capsule and anterior cortex at the center or “pole” of the lens (Figure 22 4). Typically, anterior polar cata racts are small, nonprogressive, and usually do not interfere with visual acu ity, although some will progress and eventually require surgery.
Anterior Subcapsular Cataracts
Anterior subcapsular cataracts are opacities located directly under the ante rior capsule in the anterior lens cortex.
Alport Syndrome
Alport syndrome is classically described as being associated with anterior lenticonus (anterior bowing of the anterior capsule), with or without ante rior polar subcapsular cataracts. Systemic findings include neurosensory hearing loss and hemorrhagic nephritis with late renal failure and renal hypertension. Alport syndrome is fairly common and accounts for approxi mately one sixth of familial glomerular nephritis. Only 15% of patients, however, have ocular abnormalities. Various modes of inheritance have been described, including X linked dominant (most common), autosomal