98th Annual Meeting DOG 2000

P 734

Correlation of changes in pachymetry, central corneal power and spherical equivalent after myopic PRK

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

Purpose: To quantify the association between the regression of the refractive effect and the increasing postoperative corneal thickness ( D PACHY) after myopic photorefractive keratectomy (PRK).

Patients and Methods: PRK (mean attempted correction of -5.6 ± 1.7 diopters (D)) was performed using the excimer laser (MEL 60, Aesculap-Meditec). In 36 eyes (mean age 31.6 ± 6.5 years, follow-up ³ 1 year) the intended stromal ablation depth was 53 ± 17 (23 to 81) µm. The refractive regression after PRK was defined as (1) change of spherical equivalent (D SE), (2) change of keratometric central power (D KERA) and (3) change of topographic central power (D TOPO).

Results: From the first week to 12 months postoperatively corneal thickness, keratometric and topographic central power increased while SE decreased.


spherical equivalent

keratometric central power

topographic central power


529 µm

-5.62 D

43.4 D


1 week postoperatively

433 µm

0.27 D

38.8 D

39.8 D

1 month postoperatively

449 µm

0.04 D

39.1 D

39.9 D

3 months postoperatively

457 µm

-0.36 D

39.5 D

40.4 D

12 months postoperatively

470 µm

-0.79 D

39.9 D

40.8 D

1 week vs. 12 months





D PACHY correlated significantly with D KERA (r=0.63, p=0.015) and D TOPO (r=0.68, p=0.008). These correlations were more pronounced in the high myopic group (>6 D). However, D PACHY did not correlate with D SE (p=0.84). In contrast, D KERA (r=0.43, p=0.012) and D TOPO (r=0.39, p=0.02) correlated significantly with D SE.

Conclusions: As expected, the regression of the refractive effect after myopic PRK goes along with an increasing central corneal power. However, our results indicate that the increase in central corneal thickness is not exclusively responsible for this regression

Department of Ophthalmology and Eye Hospital, University Erlangen-Nürnberg, Schwabachanlage 6, D-91054 Erlangen, Germany