Effect of intraocular pressure level on topographic and biomechanical parameters of the cornea in keratoconus

Relevance In studying the causes of keratectasia development in keratoconus (KK), the study of the relationship between the strength characteristics of the cornea and the level of intraocular pressure (IOP) remains an urgent task, the balance between which, as is known, ensures the stability of the cornea configuration in the norm [1, 2]. Objective To study changes in the biomechanical and topographic parameters of the cornea at different levels of ophthalmotonus. Material and methods Studies of corneal parameters were conducted under experimental conditions on cadaver eyes with imitation of thinning characteristic of the "keratoconus cornea", and in clinical practice on the eyes of patients with progressive keratoconus stages I-III. Results In experimental conditions on 7 cadaver eyes with residual corneal thickness of 200–250 μm, the average increase in corneal refraction with manometrically regulated IOP above 30 mmHg was 4.9 ± 1.3 D. In clinical practice in patients with progressive keratoconus (14 eyes), as a result of prescribing instillations of an antihypertensive drug (dorzolamide + timolol) during control examinations after 1 week and then at intervals of 3 months, statistically significant results were recorded: a decrease in IOP by 2.5–6.9 mmHg, an average of 4.7 ± 2.2 mmHg; an increase in the minimum corneal thickness by 8–16 μm, an average of 11.8 ± 4.2; a 1.42-fold decrease in the new indicator we introduced – the index of the critical ratio of IOP and corneal hysteresis, indicating a decrease in the cornea's tendency to ectasia [3–5]. Conclusion The changes in corneal parameters in eyes with keratoconus, revealed in experimental and clinical conditions, indicate their undoubted dependence on the existing level of ophthalmotonus, which in turn indicates a significant stabilizing potential for reducing IOP during the progression of keratoconus. Keywords: keratoconus; intraocular pressure; corneal biomechanics; corneal thickness; refraction