RETINITIS PIGMENTOSA

This primary pigmentary retinal dystrophy is a
hereditary disorder predominantly affecting the rods
more than the cones.
Inheritance
Most common mode is autosomal recessive, followed
by autosomal dominant. X-linked recessive is the least
common.
Incidence
It occurs in 5 persons per 1000 of the world
population.
Age. It appears in the childhood and progresses
slowly, often resulting in blindness in advanced
middle age.
Race. No race is known to be exempt or prone to it.
Sex. Males are more commonly affected than
females in a ratio of 3:2.
Laterality. Disease is almost invariably bilateral
and both the eyes are equally affected.
Clinical features
(A) Visual symptoms
1. Night blindness. It is the characteristic feature
and may present several years before the visible
changes in the retina appear. It occurs due to
degeneration of the rods.
2. Dark adaptation. Light threshold of the peripheral
retina is increased; though the process of dark
adaptation itself is not affected until very late.
3. Tubular vision occurs in advanced cases.
(B) Fundus changes (Fig. 11.18)
1. Retinal pigmentary changes. These are typically
perivascular and resemble bone corpuscles in
shape. Initially, these changes are found in the
equatorial region only and later spread both
anteriorly and posteriorly.
2. Retinal arterioles are attenuated (narrowed) and
may become thread-like in late stages.
3. Optic disc becomes pale and waxy in later stages
and ultimately consecutive optic atrophy occurs
(Fig. 11.19).
4. Other associated changes which may be seen are
colloid bodies, choroidal sclerosis, cystoid macular
oedema, atrophic or cellophane maculopathy.
(C) Visual field changes (Fig. 11.20)
Annular or ring-shaped scotoma is a typical feature
which corresponds to the degenerated equatorial zone
of retina. As the disease progresses, scotoma
increases anteriorly and posteriorly and ultimately only central vision is left (tubular vision). Eventually
even this is also lost and the patient becomes blind.
(D) Electrophysiological changes
Typical electrophysiological changes appear early in
the disease before the subjective symptoms or the
objective signs (fundus changes) appear.
1. Electro-retinogram (ERG) is subnormal or
abolished.
2. Electro-oculogram (EOG) shows absence of light
peak.
Associations of retinitis pigmentosa
I. Ocular associations. These include myopia, primary
open angle glaucoma, microphthalmos, conical cornea
and posterior subcapsular cataract.
II. Systemic associations. These are in the form of
following syndromes:
1. Laurence-Moon-Biedl syndrome. It is
characterised by retinitis pigmentosa, obesity,
hypogenitalism, polydactyly and mental
deficiency.
2. Cockayne’s syndrome. It comprises retinitis
pigmentosa, progressive infantile deafness,
dwarfism, mental retardation, nystagmus and
ataxia.
3. Refsum’s syndrome. It is characterised by retinitis
pigmentosa, peripheral neuropathy and cerebellar
ataxia.
4. Usher’s syndrome. It includes retinitis pigmentosa
and labyrinthine deafness.
5. Hallgren’s syndrome. It comprises retinitis
pigmentosa, vestibulo-cerebellar ataxia, congenital
deafness and mental deficiency.
Atypical forms of retinitis pigmentosa
1. Retinitis pigmentosa sine pigmento. It is
characterised by all the clinical features of typical
retinitis pigmentosa, except that there are no
visible pigmentary changes in the fundus.
2. Sectorial retinitis pigmentosa. It is characterised
by involvement of only one sector of the retina.
3. Pericentric retinitis pigmentosa. In this condition
all the clinical features are similar to typical retinitis
pigmentosa except that pigmentary changes are
confined to an area, immediately around the
macula.
4. Retinitis punctata albescens. It is characterised
by the presence of innumerable discrete white
dots scattered over the fundus without pigmentary
changes. Other features are narrowing of
arterioles, night blindness and constriction of
visual fields.
Treatment
It is most unsatisfactory; rather we can say that till
date there is no effective treatment for the disease.
1. Measures to stop progression, which have been
tried from time to time, without any breakthrough
include: vasodilators, placental extracts,
transplantation of rectus muscles into
suprachoroidal space, light exclusion therapy,
ultrasonic therapy and acupuncture therapy.
Recently vitamin A and E have been
recommended to check its progression.
2. Low vision aids (LVA) in the form of ‘magnifying
glasses’ and ‘night vision device’ may be of
some help.
3. Rehabilitation of the patient should be carried
out as per his socio-economic background.
4. Prophylaxis. Genetic counselling for no
consanguinous marriages may help to reduce the
incidence of disease. Further, affected individuals
should be advised not to produce children.