Evaluation of corneal biomechanics before and after up-to-date keratoplasty in patients with bullous keratopathy

Abstract

Aim - to study biomechanical properties of the cornea in patients with bullous keratopathy before and after keratoplasty. Ocular response analyzer (ORA, Reichert) indices were studied in 37 patients (37 eyes) with bullous keratopathy before and after surgery - in 1, 2, and 6 months and then in 1, 2, 3, and 5 years. The following keratoplasty modifications were performed: ultrathin Descemet's stripping automated endothelial keratoplasty (UTDSAEK) - in 17 cases, microkeratome-assisted posterior keratoplasty (MAPK) - in 13 cases, half top-hat penetrating keratoplasty (HTH PK) - in 7 cases. Corneal hysteresis (CH) and corneal resistance factor (CRF) values were significantly decreased in non-operated bullous keratopathy eyes as compared to healthy ones (p<0.05). By the 6-month follow-up these parameters have been found to be partially recovered and stabilized in all groups, however, still lower than normal (p<0.05). Differences between the groups were never statistically reliable, not at any time after surgery. Moreover, in eyes with bullous keratopathy, the mean corneal-compensated intraocular pressure (IOPcc) exceeded the mean Goldman-related IOP (IOPg) by 2.4 mmHg. One month after keratoplasty the difference between IOPcc and IOPg was 2.7, 4.3, and 3.6 mmHg in the MAPK, UTDSAEK, and HTH PK group, respectively; in 6 months - 2.6; 2.4 and 3.6 mmHg, respectively (p<0.05). In the fellow healthy eyes the two IOP measurements were not statistically different. Chronic edema of the cornea results in alteration of its viscoelastic properties. It has been shown that CH and CRF values decrease significantly in the eye involved as compared to the fellow healthy eye. After keratoplasty, regardless of the exact modification, these parameters partially recover, but remain lower than normal for at least 5 years as it was in our study. Neither before the surgery (when the cornea is chronically swollen), nor after, does corneal thickness correlate with its biomechanical indices. Postoperative reduction in corneal rigidity in eyes with bullous keratopathy may be confusing and lead to underestimation of the true level of IOP, thus, causing delays in diagnosis of concomitant glaucoma.