Pigmentation Anomalies
Impaired development of the pigmentation of
the iris can lead to a congenital difference in coloration between the left and
right iris (heterochromia). One iris containing varying pigmentation is referred to as iris bicolor. Iso-lated heterochromia
is not necessarily clinically significant (simple hetero-chromia), yet it can
be a sign of abnormal changes. The following types are differentiated:
❖ Fuchs’ heterochromic cyclitis (etiology unclear): This refers torecurrentiridocyclitis (simultaneous inflammation of several
portions of the uvealtract) in adults, with precipitates
on the posterior surface of the cornea without formation of posterior synechiae
(adhesions between the iris and lens). The eye is free of external irritation. This disorder is often associated with
complicated cataract and increased intraocular pressure (glaucoma).
❖ Sympathetic heterochromia: Inunilateral impairment of
the sympatheticnerve supply, the affected iris is significantly lighter.
Heterochromia withunilaterally lighter pigmentation of the iris also occurs in
iridocyclitis, acute glaucoma, and anterior chamber hemorrhage (hyphema).
❖ Melanosis of the iris: This refers todark
pigmentationof one iris.
Aside from the difference in coloration
between the two irises, neither sym-pathetic heterochromia nor melanosis leads
to further symptoms. The only form of heterochromia that leads to abnormal
changes is Fuchs’ hetero-chromic cyclitis. The possible complications involved
require specific treat-ment.
Albinism (from the Latin albus = white) is a congenital metabolic diseasethat
leads to hypopigmentation of the eye. The following types are differen-tiated:
❖ocular albinism (involving only the eyes) and
❖oculocutaneous albinism (involving the eyes, skin, and hair).
In albinism the iris is light blue because of the melanin
deficiency resulting from impaired melanin synthesis. Under slit-lamp
retroillumination, the irisappears
reddish due to fundus reflex (Fig. 8.6). Ophthalmoscopy will detect choroidal vessels (Fig. 8.7). Associated
foveal aplasia results in significant
reduction in visual acuity and
nystagmus. Most patients are also
photophobic because of the missing filter function of the pigmented layer
of the iris.
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