RGP insights

PMMA Lens Wear: A Probable Cause of Keratoconus

BY LORETTA B. SZCZOTKA, OD, MS
November 1999

For keratoconic patients with no documented family history and no known associated systemic disease or connective tissue disorder, the etiology of their condition is still largely unknown.

Repeated corneal trauma, such as hard contact lens wear and excessive eye rubbing, has been implicated as a direct cause of keratoconus. Proponents of this theory believe that the increased prevalence of atopic disease associated with keratoconus results in ocular itching, which precipitates vigorous eye rubbing, a form of anterior segment trauma. Several groups have reported on presumed keratoconus development from constant rigid lens movement. It has been implied that this form of repeated corneal insult, coupled with corneal hypoxia from PMMA lens wear, may be enough to produce the permanent clinical and corneal tissue changes common to keratoconus. The following case arguably supports the theory of PMMA lens induced keratoconus:

Case History

A 53-year-old female presented for a second opinion and a contact lens refitting for her presumed keratoconic condition. She was fit with PMMA lenses OU over 20 years ago. She wore them uneventfully for more than 12 years, but about 8 years ago, was advised to wear RGP lenses. Her right eye was successfully refit, but due to her inability to achieve acceptable visual acuity and physical fitting characteristics, the RGP fitting of her left eye was abandoned for her original PMMA lens. In the last 8 years, the patient has progressively noticed spectacle blur but continued to tolerate her lenses. Clinical examination OS revealed reduced best corrected spectacle acuity, distorted steep keratometric mires, a distorted retinoscopy reflex (oil drop reflex) and a full Fleisher's ring. Her right eye was correctable to 20/20 with spectacles. No distortion was noted on keratometry or retinoscopy, and no slit lamp signs of keratoconus were present.

Figure 1 shows the axial and tangential topography maps of both eyes. The right eye displays average and regular curvature readings, while the left eye has marked inferior corneal steepening, coincident flattening of the superior quadrant and a large sagging cone, which is characteristic of keratoconus.

A definite causative relationship between PMMA lens wear and keratoconus is difficult to confirm in most studies since long-term bilateral PMMA wear is typically assessed retrospectively in eyes that developed unilateral or bilateral keratoconus.

However, in this case of parallel RGP and PMMA lens wear in the same patient, the RGP-fitted right eye serves as a good control, while the left eye provides evidence implicating PMMA lens wear as a potential factor in the development of keratoconus. As a result, this patient's case provides reason to refit patients wearing PMMA lenses into lenses with higher oxygen permeability. CLS

Dr. Szczotka is an assistant professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens Service at University Hospitals of Cleveland.