TOPOGRAPHIC DETECTION OF PHOTOREFRACTIVE KERATECTOMY

Purpose: This study aimed to evaluate the sensitivity and specificity of subjective review of corneal topography to detect patients who have undergone photorefractive keratectomy (PRK). Methods: Topographic map s from 3 different devices were obtained from 19 patients with postope rative PRK and 9 control subjects with emmetropia and 10 control subje cts with myopia. Each image was printed in an absolute and relative sc ale (total of 228 maps) and graded for overall shape and pattern. Fift een masked reviewers independently rated each map as either postoperat ive PRK or not. Results: The overall sensitivity (ability to detect PR K) and specificity rates (ability to exclude control subjects) by revi ewers were 65% and 93%, respectively, Sensitivity was influenced indep endently by the scale (relative, 68%; absolute, 62%; P < 0.01), experi ence of reviewer (experienced, 77%; inexperienced, 53%; P < 0.001), an d device (Alcon, 67 +/- 29.9; Eyesys, 75 +/- 29.4%; and Tomey, 54 +/- 31.7%; P < 0.001), Low levels of preoperative myopia were consistently more difficult to detect than higher levels (low myopia -1.50 to -2.9 9 diopters [D] sensitivity: 53 +/- 34.5%; medium level -3.00 to -4.49 D:67 +/- 28.9%; and high level -4.50 to -6.00 D:77 +/- 21.1%; P < 0.00 01), Differences in specificity between experienced and inexperienced reviewers were obtained when maps had a homogeneous topographic patter n (97 +/- 5.6% and 85 +/- 13.7%, respectively; P < 0.05), Several cont rol topography patterns (e.g., homogeneous, focal, and keyhole) were d isproportionately more difficult to correctly identify on the Eyesys d evice. Conclusions: Topographic experience is a significant factor inf luencing the correct identification of PRK. Techniques also can be use d to enhance detection, such as the use of different devices and scale s, However, if subjective review of topography is used as the only met hod of detection, many patients with PRK will not be identified proper ly. In addition, the most prevalent preoperative myopic category in th e general population (myopia < -3.00 D) also is the most difficult to detect after treatment, This reduces the usefulness of topography as a screening tool, Other techniques are needed to improve the detection of patients with postoperative PRK.