Detection of the early keratoconus based on corneal biomechanical properties in the refractive surgery candidates

Abstract

Context:Subclinical keratoconus is contraindication to refractive surgery. The currently used methods of preoperative screening do not always allow differentiating between healthy eyes and those with subclinical keratoconus.Aim:To evaluate biomechanical parameters of the cornea, waveform score (WS), and intraocular pressure (IOP) as potentially useful adjuncts to the diagnostic algorithm for precise detection of the early keratoconus stages and selection of refractive surgery candidates.Settings and Design:Department of Ophthalmology and prospective cross-sectional study.Patients and Methods:Patients enrolled in the study were diagnosed with refractive disorders. We assessed parameters of corneal biomechanics such as corneal hysteresis (CH), corneal resistance factor (CRF), Goldman-correlated IOP (IOPg), corneal compensated IOP, WS, and keratoconus match index (KMI). They were classified into one of three groups based on the predefined KMI range: Group 1 (from 0.352 to 0.757) – 45 eyes, Group 2 (from −0.08 to 0.313) – 52 eyes, and Group 0 - control group (from 0.761 to 1.642) – 80 eyes.Results:In both study groups, IOPg, CRF, and CH were decreased when compared to control (P < 0.0001). In control group, there was positive correlation between CH and KMI (P < 0.05), with no correlations in any of the two study groups. CRF correlated positively with KMI in control (P < 0.0001) and in Group 2 (P < 0.05).Conclusions:CH and CRF, together with WS and IOPg, consist a clinically useful adjunct to detect subclinical keratoconus in patients referred for refractive surgery when based on KMI staging.

Comparison between Corneal Biomechanics in Normal and Keratoconic Corneas Using Ocular Response Analyzer

“…There is no statistical difference regarding corneal compensated intraocular pressure (IOPcc) (14.17 ± 3.44 and 14.23 ± 2.01 mm Hg respectively with p value = 0.942). and this is in agreement with results of Pniakowska and Jurowski (21) , who found that Goldmann correlated intraocular pressure (IOPg) values were found lower in keratoconus group than normal and found also that there is no statistical difference in mean IOPcc observed between Group 2 and control group (P > 0.05).…”

“…Also (21) stated that mean values of CRF (P < 0.0001 and P < 0.0001 respectively) were significantly lower in keratoconic eyes than in the control group…”

Corneal Biomechanical Properties in Patients with Acromegaly

“…27 Ayrıca, Pniakowska ve ark.nın refraktif cerrahi adaylarında kornea biyomekanik özelliklerine göre erken keratokonusu saptamak için planladıkları çalışmalarında, KH ve KRF'nin refraktif cerrahi için başvuran hastalarda subklinik keratokonusu saptamak için klinik olarak yardımcı parametreler olabileceklerini belirtmişlerdir. 28…”

Keratoconus Screening in Primary Eye Care – A General Overview

“…Corneal biomechanical metrics are statistically significant between keratoconic and healthy corneas using both ORA 71,[75][76][77] (keratoconus showed lower CH and CRF value) and Corvis 71,[78][79][80] (keratoconus showed higher deformation amplitude), which could be useful to detect subclinical keratoconus. 81 Unfortunately, data provide for these devices have not proven to be a definitive keratoconus diagnostic value (able to differentiate between keratoconus, forme fruste and normal eyes) 71 because a substantial overlap exists with normal corneas, 82,83 and further research is necessary to obtain valid cut-off values to use in combination with more clinical data. 20,72,75,77,80,84,85 In summary, further clinical validation is necessary to inderstand the meaning of these biomechanical parameters obtainied with ORA and Corvis before they can be used in clinical practice.…”