An ocular surface prosthesis for keratoglobus and Terrien's marginal degeneration

This case report describes the challenges in fitting corneas using the prosthetic replacement of ocular surface ecosystem (PROSE) device in a unique case of bilateral keratoglobus (KG) with Terrien's marginal degeneration (TMD).

KG and TMD are uncommon corneal ectatic conditions, characterized by protrusion and thinning of the cornea. Optical correction with spectacles is limited, as this may not provide the best-corrected visual acuity because of irregular corneal astigmatism. Corneal gas-permeable lenses can provide optimal vision, but they have poor fitting characteristics in advanced stages. The PROSE device has the advantage of masking the irregularity of the cornea with a tear lens and a contact lens power that provides a smooth refractive surface. This case report describes the fitting aspects of the PROSE device in a case diagnosed with KG and TMD. A generous vault allows the PROSE device to sink into the conjunctiva more, causing impingement, but a PROSE with higher vault is required as corneal clearance decreases with wear time. Corneal thickness measurements during the trial can give a better idea of corneal edema expected after prescribing the PROSE device. Optical coherence tomography is a useful tool for measuring diurnal changes in the corneal thickness and vault over a period in such challenging cases.

Modification of not only the vault but also the haptic and total diameter of the device is required to achieve an optimal fit. Though challenging, successful fitting of the scleral lens in ectatic corneas is attainable, with the aid of anterior imaging and spline technologies.