Progressive blindness

LEBER'S OPTIC NEUROPATHY

Leber's optic neuropathy is a familial disorder of maternal inheritance with a tendency to affect males significantly more than females. It is classified as a mitochondrial disorder due to DNA mutation (page 503). Pathology Light source

Loss of ganglion cells in the retina

Demyelination and axonal loss in the optic nerve (papillomacular bundle)

The layers of the retina

Demyelination and axonal loss in the optic nerve (papillomacular bundle)

Ganglion cells

Bipolar cells

Clinical features

Onset of visual loss in late teens/early twenties.

- The first symptom is blurring of vision

- Both eyes are simultaneously affected (rarely one eye months before the other).

- Central vision is lost with large bilateral scotomata. Characteristically, blue/yellow colour discrimination is affected before red/green. The optic disc initially appears pink and swollen with an increase in small vessels, eventually becoming pale and atrophic.

Visual impairment progresses with peripheral constriction of the fields. Complete visual loss seldom occurs. Occasionally vision can marginally improve.

Associated symptoms and signs of a more generalised nervous system disorder occur in a proportion of cases - dementia, ataxia, progressive spastic paraplegia - and confusion with multiple sclerosis may arise. Diagnosis is based on family history. In contrast to bilateral optic neuritis, 'leakage' occurs with fluorescein angiography. Several mitochondrial DNA mutations are detected in the peripheral blood. Treatment: No treatment is effective.

The layers of the retina

Ganglion cells

Bipolar cells

gfjsry.»- — Pigment layer

RETINITIS PIGMENTOSA

A hereditary disorder of the retina which may be inherited as an autosomal dominant, recessive or X-linked disorder. All layers of the retina are affected. Posterior pole cataracts and glaucoma are occasionally associated.

Loss of rods, degeneration of cones. ~ ~ Bipolar and ganglion cells are also affected. Pigment migrates to superficial layers

■The optic nerve may show some gliosis, but often is remarkably normal.

Clinical features

Onset of visual loss in childhood. Both eyes are simultaneously affected. Initially there is a failure of twilight vision. The patient has difficulty in making his/her way as darkness falls (nyctalopia). The retina around the macular area is first affected resulting in a characteristic ring scotoma. This gradually spreads outwards; eventually only a small 'tunnel' of central vision is left. Finally, complete blindness occurs. The majority of patients are completely blind by 50 years of age.

The fundal appearance is diagnostic as a result of the superficial migration of pigment.

The electroretinogram - recording the electrical activity of the retina - is eventually lost.

---Clumping pigment]

(corpuscular appearance)

---Pale optic disc

Attenuated vessels

---Clumping pigment]

(corpuscular appearance)

---Pale optic disc

Attenuated vessels

Treatment

None. Vitamins and steroids have been tried unsuccessfully. Associated conditions in retinitis pigmentosa

Several conditions are associated with retinitis pigmentosa:

- Hypogonadism/obesity/mental deficiency - Laurence Moon syndrome

- Spinocerebellar ataxia - Friedreich's ataxia

The association with neuropathy and ataxia (NARP), or progressive external ophthalmoplegia and heart block (Kearns-Sayre syndrome) are due to mitochondrial disease (page 462)

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