An inherited eye disorder characterized by progressive
degeneration of the choroidea, retinal pigment epithelium, and neural
Progressive Tapetochoroidal Dystrophy.
Less than 1:100,000 in the general population.
X-chromosomal recessive transmission. Almost
exclusively men are affected, but a few female cases have been described.
The responsible gene has been mapped to Xq21.2.
A point mutation is responsible for impairment in
geranyl transferase which affects vesicle transport in retinal cells
in choroideremia. Affected males usually first note symptoms in adolescence,
experiencing night blindness and peripheral visual field loss.
Based on the clinical findings of progressive
degeneration of the choroidea, with night blindness occurring in the teenage
years. The differential diagnosis includes gyrate atrophy of the choroid,
diffuse choriocapillaris atrophy and X-linked retinitis pigmentosa.
The combination of inheritance mode, ophthalmic examination,
visual field testing, and electroretinography (ERG) helps confirm the
The ERG in affected males may initially show a
pattern of rod-cone degeneration. Fundoscopy reveals patchy areas of
chorioretinal degeneration, usually beginning in the midperipheral areas of
the fundus and manifesting as a ring scotoma. As these areas enlarge, the
disease progresses to marked loss of the retinal pigment epithelium and the
choriocapillaris, while deep choroidal vessels are preserved. Although the
function and anatomy of the central macula is preserved until late in the
disease process, affected men rarely retain any central vision beyond the
seventh decade of life. Almost one third of these patients also have
posterior subcapsular cataracts. Although choroideremia is essentially a
retinal degenerative disease, associations with other clinical findings
(severe mental retardation, agenesis of the corpus callosum, signs of
encephalopathy, (sensorineural and conductive) hearing loss, distal motor
neuropathy, and cleft lip and palate have been reported. No effective
History should demonstrate the
extent of retinal degeneration. Check for concomitant diseases as mentioned
In the presence of peripheral motor
weakness, the effects of neuromuscular blockade may be enhanced and careful
titration to effect will be necessary using a peripheral nerve stimulator.
In the presence of severe weakness of the respiratory musculature, extubation at
the end of a procedure may have to be delayed until full return of muscle
function. The presence or absence of other neurologic findings may influence
the anesthetic technique. Patients with this condition may be blind, and the
psychological considerations pertaining to this situation should be
kept in mind.
Careful dosing of neuromuscular
blockers is recommended in the presence of muscular weakness.
X-Linked Retinitis Pigmentosa: Retinitis pigmentosa is the most common
cause of inherited visual loss (approximately 1:4000 in the general
population is affected). It usually begins between the second and fourth
decade of life with night blindness and later is followed by tunnel vision.
The rate and extent of progression are highly variable. More than 70
different genetic defects have been described, all resulting in retinitis
pigmentosa. The X-linked ...