Contrast and glare testing in keratoconus before and after penetrating keratoplasty
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.
Method: 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), F2,48 = 6.16; p<0.01, post hoc SheffeŽ 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 confou and 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.
Abbreviations: CS, contrast sensitivity; GLLVCA, low contrast visual acuity glare loss; GLPRCS, 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
Br J Ophthalmol 2004;88:653-657. doi: 10.1136/bjo.2003.027029
K Pesudovs, P Schoneveld, R J Seto, D J Coster
Accepted for publication 22 August 2003
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