III. ECTATIC CORNEAL CONDITIONS
It is conical bulge in the central or paracentral or paracentral part of the cornea due to structural weakness in corneal tissue.
Type of patient:
It is more common in:
- Positive family history (10% of cases are autosmal dominant).
- Patients with atopic diseases as spring catarrhal.
* Gradual painless drop of vision due to:
- Myopia both axial and curvature.
- Irregular astigmatism because of the irregular bulge of cornea.
- Opacities at the apex of the cone.
* It is bilateral in 85% of cases, starting in one eye.
* It starts around puberty.
1. Early signs:
a. Retinoscopy shows spinning or scissoring of red reflex.
b. By ophthalmoscopic examination a tear droplet red reflex is seen.
c. Distorted image of Placido disc and keratoscope.
d. Corneal topography for earliest diagnosis.
2. Opacities at the apex of the cone due to folds of Descemet's membrane (the vertical stria of Vogt). Also there are opacities in Bowman’s membrane.
3. Fleischer's ring at the base of the cone. It occurs due to hemosiderin deposition in the epithelium.
4. The central part of cornea becomes thinner and bulges as a small cone. This can be seen by:
* Profile view in advanced cases.
* Notching of the lower lid on down looking (Munson's sign).
* Slit lamp: Thin apex of the cone and deep anterior chamber.
Acute hydrops of keratoconus:
- Acute rupture of Descemet’s membrane occurs in the centre of the cone leading to acute corneal edema.
- The patient will complain of marked acute drop of vision and pain.
- These cracks heal within 4 months, but scarring of the central cornea occurs.
- This condition is treated by hypertonic saline and bandage contact lens.
- After absorption of edema, keratoplasty is done the central part of cornea will be scarred.
The causes of corneal ectasia are:
A. Inflammatory conditions: - Anterior staphyloma.
B. Non inflammatory: - Keratoconus.
- Keratoglobus (stationary total spherical
bulge of the cornea since birth).
1. Rigid gas permeable contact lens to replace the power of the irregular corneal surface by the power or the regular surface or the contact lens.
2. Penetrating keratoplasty if the patient is intolerant to contact lenses, or if there are central opacities.
N.B. Glasses are tried, but they usually fail to correct irregular astigmatism. They can be used in the early cases.
NB. Intracorneal rings are used to stretch the conical cornea. They are very recent and still under investigations.