Nomogram for spherical RGP contact lens fitting in patients with pellucid marginal corneal degeneration (PMCD)

To present a nomogram for spherical rigid gas-permeable (RGP) contact lens fitting in patients with pellucid marginal corneal degeneration (PMCD).

Retrospective review of the medical records of 24 patients diagnosed with PMCD who underwent an RGP contact lens trial at the Bausch & Lomb contact lens center between April 1995 and March 2002 at L.V. Prasad Eye Institute in Hyderabad, India. Data collected included age and sex of patients, duration of presenting symptoms, associated ocular conditions, presenting visual acuity, and degree of astigmatism. For the purpose of analysis, the astigmatism was classified into four groups: group 1, less than 5.00 diopters (D); group 2, 5.00 to 10.00D; group 3, 10.00 to 15.00D; and group 4, 15.00 to 20.00D. The final lens parameters, the patient's comfort level, and the duration of follow-up were analyzed.

Forty eyes of 24 patients were fitted with RGP contact lenses during the study period. Sixteen were male patients and eight were female patients. The age of the patients ranged from 13 to 59 years, with a mean of 35.5 years. Twenty-two (91.7%) patients had typical inferior PMCD, whereas the other two (8.3%) had superior PMCD. The mean corneal curvature was 7.1 mm (range, 5.9-7.8 mm) in group 1, 6.9 mm (range, 6.6-7.9 mm) in group 2, 7.5 mm (range, 6.5-7.8 mm) in group 3, and 7.9 mm (range, 6.8-7.8 mm) in group 4. The mean base curve of the final fitting lens was 6.3 mm (range, 5.7-7.8 mm) in group 1, 6.8 mm (range, 5.9-7.8 mm) in group 2, 7.5 mm (range, 6-8.2 mm) in group 3, and 7.2 mm (range, 6.6-7.8 mm) in group 4. The mean lens diameter of the final fitting lens was 8.7 mm (range, 8.6-10.6 mm) in group 1, 9.5 mm (range, 8.8-10.5 mm) in group 2, 10.2 mm (range, 8.8-11.5 mm) in group 3, and 10.4 mm (range, 8.8-11.3 mm) in group 4. The common fluorescein patterns were central touch with midcentral peripheral pooling in 14 (35%) and dumbbell pattern in seven (17.%). The final visual acuity range with an RGP lens in the four astigmatism groups was 20/40 to 20/20 in group 1, 20/30 to 20/20 in group 2, 20/40 to 20/20 in group 3, and 20/200 to 20/50 in group 4. Twenty-one patients were comfortable with an RGP lens, and the mean duration of follow-up was 13 months. Three patients discontinued lens wear. In one patient, the lens was not stable, and the other two experienced discomfort with their lenses.

Spherical rigid gas-permeable lenses are a good option for patients even with advanced PMCD. In patients with astigmatism of less than 10D, a lens with a base curve of 6.0 to 7.0 mm and a diameter of 8.0 to 9.5 mm seems to be a good initial lens for trial, and for patients with astigmatism of more than 10D, a lens with a base curve of 7.0 to 7.5 mm and a diameter of 10.0 to 10.5 mm seems to be a good initial lens.