Correlation Between Corneal Biomechanics and Anterior Segment Parameters in Healthy Saudi Females

Background: The ocular response analyzer (ORA) can measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated IOP (IOPg) and corneal compensated intraocular pressure (IOPcc). 1 Anterior segment parameters such as central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) can be measured by Pentacam which is a Scheimpug imaging device. 2 Many studies 3-10 investigated the correlation between corneal biomechanics and anterior segment parameters in healthy eyes and demonstrated a strong correlation between CH, CRF with CCT. Hwang et al 2013 7 found that CV was positively correlated with CH, but not CRF. However, Çevik et al 2016 10 reported positive correlations between CH, CRF, and CV and negative correlations between CH, CRF and both of posterior steep and average posterior 𝐾 values. Hwang et al 2 did not show a signicant association between CA and all the biomechanical properties. Conversely, Montard et al 4 reported a negative association between CA with CH and CRF. Therefore, there is still debate regarding evaluation of this relation. Up to our knowledge, the correlation between corneal biomechanics and anterior segment parameters in healthy eyes is never investigated in Saudi Arabia. The purpose of this study was conducted to evaluate the correlation between corneal biomechanics measured with ORA and anterior segment parameters assessed with Oculus Pentacam HR in healthy Saudi females. Methods: This study was a prospective, non-randomized, cross-sectional, observational and quantitative study. The study included 129 eyes of 129 healthy Saudi females from King Saud University, Riyadh, Saudi Arabia. The mean age was 19.87 ± 1.328 (18 – 29 years). All subjects underwent a comprehensive ophthalmologic examination including refraction, visual acuity measurement, slit-lamp biomicroscopic examination, IOP measurement with an air puffer tonometer, and funduscopy. In addition, anterior segment parameters were measured with Oculus Pentacam

The ocular response analyzer (ORA) can measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated IOP (IOPg) and corneal compensated intraocular pressure (IOPcc). 1 Anterior segment parameters such as central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) can be measured by Pentacam which is a Scheimp ug imaging device. 2 Many studies 3-10 investigated the correlation between corneal biomechanics and anterior segment parameters in healthy eyes and demonstrated a strong correlation between CH, CRF with CCT. Hwang et al 2013 7 found that CV was positively correlated with CH, but not CRF. However, Çevik et al 2016 10 reported positive correlations between CH, CRF, and CV and negative correlations between CH, CRF and both of posterior steep and average posterior values.
Hwang et al 2 did not show a signi cant association between CA and all the biomechanical properties. Conversely, Montard et al 4 reported a negative association between CA with CH and CRF. Therefore, there is still debate regarding evaluation of this relation. Up to our knowledge, the correlation between corneal biomechanics and anterior segment parameters in healthy eyes is never investigated in Saudi Arabia.
The purpose of this study was conducted to evaluate the correlation between corneal biomechanics measured with ORA and anterior segment parameters assessed with Oculus Pentacam HR in healthy Saudi females.

Study Design
This study was a prospective, non-randomized, cross-sectional, observational and quantitative study. This study got the approval of institutional review board (IRB) of College of Applied Medical Science, King Saud University, Riyadh, Saudi Arabia (CAMS 021-3940, approved date: 21/11/2018). It is adherent to the tenets of the Declaration of Helsinki 2013. All the participants signed comprehensive consent after explaining all procedures of the study.

Subjects
The study included 129 eyes of 129 healthy Saudi females from King Saud University, Riyadh, Saudi Arabia from January to March 2019. The mean age was 19.87 ± 1.328 years (18-29 years). The inclusion criteria were bestcorrected visual acuity of 20/20; IOP of 21 mmHg and normal ocular appearance. Exclusion criteria were participants who have a history of intraocular surgery, refractive surgery, and contact lens use within 2 weeks, the presence of corneal abnormalities such as keratoconus, corneal scarring that would preclude accurate ORA and IOP measurements, or a diagnosis of "glaucoma suspect" or glaucoma. Besides, eyes with IOPcc or IOPg of 21 mmHg were excluded in this study. All subjects underwent a comprehensive ophthalmologic examination including refraction by auto-refractometry (NIDEK ARK-510A), visual acuity measurement, biomicroscopic examination, IOP measurement with an air puff tonometer, and funduscopy. One eye from each participant was selected randomly.

Measurement of Corneal Biomechanics
Corneal biomechanical parameters were measured with ORA (Reichert Ophthalmic Instruments). First, the patient was instructed to set properly and xate on the green light, and they were informed that they will only sense a very gentle puff of. The device reported the following parameters that were analyzed: CH, CRF, IOPg, and corneal IOPcc for each ≥ ≤ > patient. The ORA examination was performed at least 3 times. The average values of three measurements were recorded for analysis.

Statistical Analysis
All data was analyzed using a Statistical Package for the Social Sciences (SPSS) version 22.0 software (SPSS Inc., Chicago, II, USA). Quantitative variables were reported as mean ± standard deviation (± SD) and range. Associations between corneal biomechanical parameters and anterior segment parameters were analyzed by Pearson's Correlation coe cients. P < 0.05 was considered a statistically signi cant.

Discussion
This study aimed to assess the correlation between corneal biomechanics and anterior segment parameters in healthy Saudi females. This study demonstrated a signi cant positive correlation between CCT and each of CH, CRF,  Our study found no association between corneal biomechanics and age in adult Saudi females. This result matched with Lim et al, 6 Buey et al 2014, 11 Kamiya et al, 12 and Chang et al. 13 However, this nding disagreed with Çevik et al 10  Correlation between corneal resistance factor (CRF) and central corneal thickness (CCT) for all eyes Figure 3 Correlation between Goldmann correlated IOP (IOPg) and central corneal thickness (CCT) for all eyes