97th DOG Annual Meeting 1999

K178

CORRELATION BETWEEN REFRACTIVE, KERATOMETRIC AND TOPOGRAPHIC ASTIGMATISM AFTER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA

N. X. Nguyen, A. Langenbucher, A. Walter, B. Seitz

Purpose: To check for mutual agreement of three different methods of assessment of astigmatism after photorefractive keratektomy (PRK). Patients and Methods: 47 eyes of 28 patients (age 32.7*6.6 years) following PRK using an 193 nm excimer laser (MEL 60, Aesculap-Meditec) were included in this study. 37 eyes were treated for pure myopia (-4.9 ± 2.4 D) and 10 eyes for myopic astigmatism (sphere -2.0 to -7.0 D, cylinder -1.0 to -3.0 D). The stromal ablation depth was 57.3±18.2 (range 16 to 92) µm. Preoperatively and at each postoperative examination, subjective refractometry (RA), keratometry (KA) (Zeiss, Oberkochen) and topography analysis (TMS-1, Tomey, Erlangen) were performed. The axes of topographic and keratometric cylinders were corrected periodically (180º) with respect to the refractive cylinder axis.

Results: Pre- und postoperatively, the absolute astigmatism values correlated highly significantly between all three methods (p<0.0001). After a mean follow-up of 17.5±12.0 months the difference between RA und KA was -0.4±0.4 D (p<0.0001), between RA and TA it was -0.7±0.5 D (p<0.0001), between KA and TA it was -0.3±0.3 D (p<0.0001). In eyes treated for pure myopia, no difference between pre- and postoperative RA was detected (p=0.5).

time

RA (D)

KA (D)

TA (D)

preop

0.6 ± 0.6

1.1 ± 0.6

1.3 ± 0.5

postop

0.5 ± 0.4

0.9 ± 0.5

1.2 ± 0.5


The axes of both topographic and keratometric astigmatism correlated highly significantly with the refractive cylinder axis (r = 0.9, p<0.0001).

Conclusion: In the long-term follow-up after myopic PRK, the difference between refractive and keratometric astigmatism does not differ from the preoperative value indicating an even corneal surface. However, topographic analysis produces higher astigmatism values in a systematic manner before and after PRK.

Department of Ophthalmology, University of Erlangen-Nürnberg, Schwabachanlage 6, D-91054 Erlangen, Germany (Chairman: Prof. G. O. H. Naumann).

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