Epithelial Downgrowth
Definition: Epithelial downgrowth is the proliferation and extension of surface squamous epithelium through a wound to line the inner tissues and cavities of the eye.
Etiology: Squamous epithelium enters the eye through poorly apposed or poorly healed surgical wounds or a traumatic breech in the eyewall. Usually the epithelial cells enter through a gap in cornea.
Incidence/Prevalence: The incidence of epithelial downgrowth after penetrating keratoplasty in one series was 0.2%. Cataract surgery was the most common predisposing surgical procedure accounting for about 86% of cases in a 30 year study. Penetrating keratoplasty accounted for 12% of the cases. The incidence in cataract surgery has fallen precipitously with smaller wounds and better attention to wound closure. Epithelial downgrowth also occurs after evisceration.
Clinical Findings: The clinical findings may be subtle and are often unrecognized. Two basic types have been emphasized. The diffuse type is associated with sheets of epithelium that cover the trabecular meshwork and iris. If the trabecular meshwork is covered then elevated intraocular pressure is usually abrupt in onset and unresponsive to therapy. A smooth iris membrane may be visible. The diffuse type has a poor prognosis. The cystic type of epithelial downgrowth is more benign.
Histopathology: Stratified squamous epithelium that is quite similar to normal corneal epithelium can usually be identified on the posterior corneal surface. Sometimes, the wound responsible can be traced in sections. 
In the case shown above, severe dry eye disease resulted in a corneal ulcer. The ulcer eventually worsened and perforated. A conjunctival flap (arrow 2) was pulled over the defect, which now shows marked thinning (arrow 3) which resulted in a perforation. 
Epithelial downgrowth was not recognized clinically and the patient eventually had phthisis bulbi and was eviscerated. Epithelial downgrowth is evident lining the posterior surface of the cornea (arrow 3) and iris (arrow 4). Click on the photo to compare the epithelium of the cornea to that of the downgrowth (arrow 3) and that of the flap (arrow 2).
The relentless epithelium has grown on the surface of the iris and resulted in anterior synechiae. The downgrowth (arrow 2) is evident adjacent to both the iris and Descemet's membrane (arrow 5). Arrow 4 features typical iris blood sheathing of loose collagen permitting the clear identification as iris.
The stratified squamous epithelium (arrow lit) can be seen lining gliotic retina (arrows 6) that has previously detached (no photoreceptors are visible).
Stratified squamous epithelium (arrow 9) can also be seen on the surface of ciliary processes adjacent to the non pigmented ciliary epithelium of ciliary processes (8).
Treatment: Complete excision of the membrane is necessary. In the diffuse type many authors have called for radical block excision with cornea-scleroplasty. Some authors report success with simple excision.
Prognosis: The diffuse type often results in phthisis and enucleation. The recurrence rate is about 50% even after excision.
References:
1. Weiner MJ et al. Epithelial downgrowth. Br J Ophthalmol 1989;73:6-11.
2. Sugar et al Arch Ophthalmol 1977.
3. Ghaiy et al. 2005 Arch Ophthal 9: 1268
