“In Latin a bulla (plural: bullae) was a ‘bubble, stud or knob.’ It referred to any rounded protrusion, particularly one that was hollow or cystic.

Bullae: More than one bulla, a bulla being a blister more than 5 mm (about 3/16 inch) in diameter with thin walls that is full of fluid.”¹ Thus reads the etymology and medical definition of this unusual condition.

This particular scleral lens patient has both keratoconus and Fuchs’ dystrophy. A Descemet stripping automated endothelial keratoplasty (DSAEK) procedure was performed on the right eye several years ago. The left eye was only monitored, as the condition was not as severe.

Large epithelial bullae may appear under conditions of hypoxia, in this case due to the presence of a scleral contact lens. In Fuchs’ dystrophy, the corneal endothelium cannot maintain the cornea in its normal dehydrated state. The same may be seen in cases of endothelial trauma that may result from complications of intraocular surgery.² In either case, aqueous fluid is absorbed through the corneal stroma into the epithelium, resulting in these blisters. While normally painful, the scleral lens in this case apparently provided a bandage effect, as the patient complained only of poor vision.

A paper by Isozaki and Chiu³ points out that while bullae may be apparent while in the fluid reservoir of the scleral lens, they quickly disappear after lens removal. Further, they do not reappear after lens removal, and the cornea returns to its normal state. Separation of the epithelium is apparent at the level of the basement membrane.³

Treatment includes discontinuing scleral contact lens wear and the application of topical hyperosmotic agents such as sodium chloride 5% hypertonic solution.⁴

To avoid this complication, some recommendations include:⁴

1. Avoid fitting patients in scleral lenses who have endothelial cell counts less than 800 cells/mm²
2. Use high-Dk materials
3. Fit the thinnest lens practicable
4. Reduce corneal and limbal clearances to below 200µm
5. Fenestrate the lens

If these strategies do not ameliorate the condition, then a surgical option such as DSAEK may be the best choice.

REFERENCES

1. Shiel Jr. WC. Medical Definition of Bullae. Medicinenet. Available at https://www.medicinenet.com/bullae/definition.htm . Accessed Dec. 18, 2020.
2. Roat, MI. Bullous Keratopathy, Merck Manual Professional Version, May 2020.
3. Isozaki VL, Chiu GB. Transient corneal epithelial bullae associated with large diameter scleral lens wear: A case series. Cont Lens Anterior Eye. 2018 Oct;41:463-468.
4. Fadel D, Scleral Lens Issues and Complications: Their Recognition, Etiology and Management. Dougmar Publ. Group, Inc. Aug. 2020. pp.142-143.