KERATOCONUS , KERATOGLOBUS , KERATOCONUS POSTERIOR

KERATOCONUS
Keratoconus (conical cornea) (Fig. 1) 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 theoriesproposed so far label it as developmental condition,degenerative condition, hereditary dystrophy and

Refractive surgery for astigmatism

Refractive surgical techniques employed for myopia
can be adapted to correct astigmatism alone or
simultaneously with myopia as follows:
1. Astigmatic keratotomy (AK) refers to making
transverse cuts in the mid periphery of the steep
corneal meridian (Fig. 1).

Fig. 1. Astigmatic keratotomy. (A) showing flat and deep meridians of cornea; (B) paired transverse incisions to flattern
the steep meridian; (C) showing correction of astigmatism after astigmatic keratotomy.

AK can be performed
alone (for astigmatism only) or along with RK (for
associated myopia).
2. Photo-astigmatic refractive keratotomy (PARK)
is performed using 

Refractive surgery for hyperopia

In general, refractive surgery for hyperopia is not as
effective or reliable as for myopia. However, following
procedures are used:

1. Holmium laser thermoplasty has been used for
low degree of hyperopia. In this technique, laser spots
are applied in a ring at the periphery to produce central
steepening. Regression effect and induced
astigmatism are the main problems.

2. Hyperopic PRK using excimer laser has also been
tried. Regression effect and prolonged epithelial
healing are the  

Refractive surgery of myopia

Surgery to correct refractive errors has become very
popular. It should be performed after the error has
stabilized; preferably after 20 years of age.

Refractive surgery of myopia
1. Radial keratotomy (RK) refers to making deep (90 percent of corneal thickness) radial incisions in the peripheral part of cornea leaving the central 4 mm optical zone (Fig 1).

Fig. 1. Radial keratotomy. (A) configuration of radial
incisions; (B) depth of incision.

These incisions on healing; flatten the central cornea thereby reducing its
refractive power. This procedure gives very good correction in low to moderate myopia (2 to 6 D).

Disadvantages. Note: Because of its disadvantages
RK is not recommended presently. (i) Cornea is
weakened, so chances of globe rupture following
trauma are