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Contrast and glare testing in keratoconus and after penetrating keratoplasty

Department of Ophthalmology, Flinders Medical Centre and Flinders University, Bedford Park, South Australia, 5042, Australia

Correspondence to:
Correspondence to:
K Pesudovs
Department of Ophthalmology, Flinders Medical Centre, Bedford Park, South Australia, 5042, Australia; Konrad.Pesudovs{at}flinders.edu.au

Aim: To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus.

Methods: All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA.

Results: Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F_2,48 = 6.16; p<0.01, post hoc Sheffé p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures.

Conclusions: PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain.

Keywords: contrast; glare testing; keratoconus; penetrating keratoplasty; visual acuity

Abbreviations: CS, contrast sensitivity; GL_LVCA, low contrast visual acuity glare loss; GL_PRCS, Pelli-Robson contrast sensitivity glare loss; LCL, low contrast loss; LCVA, low contrast visual acuity; PK, penetrating keratoplasty; PRCS, Pelli-Robson contrast sensitivity; VA, visual acuity