Keratoconus

Keratoconus (conical cornea) (Fig. 5.18) is a noninflammatory
bilateral (85%) ectatic condition of
cornea in its axial part. It usually starts at puberty
and progresses slowly.
Etiopathogenesis. It is still not clear. Various theories
proposed so far label it as developmental condition,
degenerative condition, hereditary dystrophy and
endocrine anomaly. Essential pathological changes
are thinning and ectasia which occur as a result of
defective synthesis of mucopolysaccharide and
collagen tissue.
Clinical features. Symptoms. Patient presents with a
defective vision due to progressive myopia and
irregular astigmatism, which does not improve fully
despite full correction with glasses.
Signs. Following signs may be elicited:
1. Window reflex is distorted.
2. Placido disc examination shows irregularity of
the circles (Fig. 5.18B).
3. Keratometry depicts extreme malalignment of
mires.
4. Photokeratoscopy reveals distortion of circles.
5. Slit lamp examination (Fig. 5.18C) may show
thinning and ectasia of central cornea, opacity at
the apex and Fleischer's ring at the base of cone,
folds in Descemet's and Bowman's membranes.
Very fine, vertical, deep stromal striae (Vogt lines)
which disappear with external pressure on the
globe are peculiar feature.
6. On retinoscopy a yawning reflex (scissor reflex)
and high oblique or irregular astigmatism is
obtained.
7. On distant direct ophthalmoscopy an annular
dark shadow (due to total internal reflection of
light) is seen which separates the central and
peripheral areas of cornea (oil droplet reflex).
8. Munson's sign, i.e. localised bulging of lower lid
when patient looks down is positive in late stages.
Morphological classification. Depending upon the
size and shape of the cone. the keratoconus is of
three types:
Nipple cone has a small size (<5mm) and steep
curvature.
Oval cone is larger (5-6 mm) and ellipsoid in
shape.

Complications. Keratoconus may be complicated by
development of acute hydrops due to rupture of
Descemet's membrane. The condition is characterised
by sudden development of corneal oedema associated
with marked defective vision, pain, photophobia and
lacrimation.
Associations. Keratoconus may be associated with :
Ocular conditions e.g. ectopia lentis, congenital
cataract, aniridia, retinitis pigmentosa, and vernal
keratoconjunctivitis (VKC).
Systemic conditions e.g., Marfan's sysndrome,
atopy, Down's syndrome, Ehlers-Danlos
syndrome, osteogenesis imperfecta and mitral
valve prolapse.
Treatment. Falling vision may not be corrected by
glasses due to irregular astigmatism.
Contact lenses (rigid gas permiable) usually
improve the vision in early cases.
In later stages penetrating keratoplasty may be
required.
Intacs, the intracorneal ring segments, are
reported to be useful in early cases.