CORNEAL OPACITIES

The word 'corneal opacification' literally means loss of normal transparency of cornea, which can occur in many conditions. Therefore, the term 'corneal
opacity' is used particularly for the loss of transparency
of cornea due to scarring.

Causes
1. Congenital opacities may occur as developmental anomalies or following birth trauma.
2. Healed corneal wounds.
3. Healed corneal ulcers.

Clinical features
A corneal opacity may produce loss of vision (when dense opacity covers the pupillary area) or blurred vision (due to astigmatic effect).

Types of corneal opacity
Depending on the density, corneal opacity is graded as nebula, macula and leucoma.
1. Nebular corneal opacity. It is a faint opacity which results due to superficial scars involving Bowman's layer and superficial stroma (Figs. 1A and 2A). A thin, diffuse nebula covering the pupillary area interferes more with vision than the localised leucoma away from pupillary area. Further, the nebula produces more discomfort to patient due to blurred image owing to irregular astigmatism than the leucoma which completely cuts off the light rays.

2. Macular corneal opacity. It is a semi-dense opacity produced when scarring involves about half the corneal stroma (Figs. 1B and 2B).

3. Leucomatous corneal opacity (leucoma simplex). It is a dense white opacity which results due to scarring of more than half of the stroma (Figs. 1C and 2C).

4. Adherent leucoma: It results when healing occurs after perforation of cornea with incarceration of iris (Figs. 1D and 2D).

5. Corneal facet. Sometimes the corneal surface is depressed at the site of healing (due to less fibrous tissue); such a scar is called facet.

6. Kerectasia. In this condition corneal curvature is increased at the site of opacity (bulge due to weak scar).

Fig. 1. Diagramatic depiction of corneal opacity: A, nebular; B, macular; C, leucomatous; D, adherent leucoma.

Fig.2. Clinical photographs of corneal opacity: A, Nebular; B, Macular; C, Leucomatous; D, Adherent leucoma.

7. Anterior staphyloma. An ectasia of psuedocornea (the scar formed from organised exudates and fibrous tissue covered with epithelium) which results after total sloughing of cornea, with iris plastered behind it is called anterior staphyloma (Figs. 3 A and B).

Fig. 3. Anterior staphyloma : A, diagrammatic cross-section; B, clinical photograph.

Secondary changes in corneal opacity which may be seen in long-standing cases include: hyaline degeneration, calcareous degeneration, pigmentation
and atheromatous ulceration.

Treatment
1. Optical iridectomy. It may be performed in cases with central macular or leucomatous corneal opacities, provided vision improves with pupillary
dilatation.
2. Keratoplasty provides good visual results in uncomplicated cases with corneal opacities, where optical iridectomy is not of much use.
3. Phototherapeutic keratectomy (PTK) performed with excimer laser is useful in superficial (nebular) corneal opacities.

4. Cosmetic coloured contact lens gives very good cosmetic appearance in an eye with ugly scar having no potential for vision. Presently, this is considered the best option, even over and above the tatooing for cosmetic purpose.
5. Tattooing of scar. It was performed for cosmetic purposes in the past. It is suitable only for firm scars in a quiet eye without useful vision. For tattooing Indian black ink, gold or platinum may be used. To perform tattooing, first of all, the epithelium covering the opacity is removed under topical anaesthesia (2 percent or 4 percent xylocaine). Then a piece of blotting paper of the same size and shape, soaked in 4 percent gold chloride (for brown colour) or 2 percent platinum chloride (for dark colour) is applied over it. After 2-3 minutes the piece of filter paper is removed and a few drops of freshly prepared hydrazine hydrate (2 percent) solution are poured over it. Lastly, eye is irrigated with normal saline and patched after instilling antibiotic and atropine eye ointment. Epithelium grows over the pigmented area.