Association between corneal volume change and corneal biomechanical property before and after small incision lenticule extraction in myopia

Background

The relationship between corneal central thickness (CCT) and corneal biomechanical property does not reflect the effective amount of ablated tissue because CCT measures only the change in a single point.Corneal volume (CV) is a representative parameter of corneal morphology, and it can fully reflect corneal thickness and tissue distribution.

Objective

This study was to investigate the correlation between volumetric corneal changes and corneal biomechanical properties after small incision lenticule extraction (SMILE).

Methods

A prospective series cases-observational study was carried out.This study protocol was approved by Ethic Committee of Tianjin Eye Hospital, and written informed consent was obtained from each patient prior to entering the cohort.Sixty-seven right eyes of 67 myopia or myopic astigmatism patients who received SMILE in Tianjin Eye Hospital from June 2014 to July 2015 were included in this study.Before and 3 months after surgery, the CV at 3, 3-5, 5-7 and 7-10 mm (CV3, CV3-5, CV5-7, CV7-10) was measured by Pentacam anterior segment analysis system, and corneal hysteresis (CH) and corneal resistance factor (CRF) were obtained by ocular response analyzer (ORA). The changes of CV (ΔCV), CH (ΔCH) and CRF (ΔCRF) were calculated, and the correlations between ΔCV and ΔCH or ΔCRF were analyzed.

Results

CV3, CV3-5 and CV5-7 values after SMILE were significantly lower than those before SMILE (t=36.24, 20.38, 16.17, all at P< 0.001). The CH values before and after SMILE were (10.06±1.11)mmHg and (8.10±1.05)mmHg (1 mmHg=0.133 kPa), and the CRF values before and after SMILE were (10.40±1.38)mmHg and (6.91±1.19)mmHg, respectively, showing significant reduces after SMILE than before SMILE (t=16.71, 27.41, both at P<0.001). Positive correlations were seen between the CV values at different corneal areas and CH value or CRF value.Moderate positive correlations were found between CV3 and CH or CRF (r=0.571, 0.569; both at P<0.001) before surgery, and 3 months after surgery, a weak positive correlation was seen between ΔCV3 and ΔCH (r=0.394, P<0.001) or a moderate positive correlation between ΔCV3 and ΔCRF (r=0.501, P<0.001).

Conclusions

The CV value is gradually increased from the central cornea to periphery cornea.The CV change is associated with CH and CRF changes after SMILE, and CV3 probably is a useful parameter for the evaluation of corneal biomechanics after refractive surgery.