• corneal resistance factor;
  • hysteresis;
  • penetrating keratoplasty


Background:  To compare corneal hysteresis (CH) and corneal resistance factor (CRF) in eyes 1 year following penetrating keratoplasty (PK) with that of normal eyes using the Ocular Response Analyser.

Methods:  Prospective case comparison of 166 normal right eyes and 34 unilateral post-PK eyes presenting to a teaching hospital in Birmingham, UK. The CH, CRF and Goldmann-correlated intraocular pressure, of each eye was measured using the Ocular Response Analyser. The central corneal thickness (CCT) was measured using an ultrasonic pachymeter.

Results:  The mean CH was 10.6 ±2.0 mmHg, standard deviation (SD) and CRF was 10.2 ± 2.0 mmHg (SD) in normal eyes and 8.9 ± 3.3 mmHg and 8.1 ± 3.3 mmHg in post-PK eyes, respectively. The mean CCT was 541.8 ± 36.1 µm in normal eyes and 556.0 ±69.2 µm in post-PK eyes. The Goldmann-correlated intraocular pressure was 16.1 ± 3.1 mmHg and 12.4 ± 2.9 mmHg in normal eyes and post-PK eyes, respectively. The CCT was found to be higher in post-PK eyes compared with normal eyes but the difference was not statistically significant (P > 0.5).

Conclusion:  Reduced biomechanical measures were found in post-PK eyes despite a higher mean CCT. This may be due to the altered corneal structure following PK.