Non-invasive measurement of transparency, arcus senilis, and scleral rim diameter of corneas during eye banking

Abstract

We developed a non-invasive device to quantify transparency (T), clear corneal diameter (CCD) excluding arcus senilis, and scleral rim diameter (SRD) of stored corneas. The T value (expressed in % on a relative scale), based on the modulation transfer function principle, referred to the ratio of local contrasts of a special LED backlit chart measured with and without cornea. CCD and SRD (in mm) were automatically calculated by morphologic operations. Firstly, we assessed measurement reproducibility. We then determined the agreement of T and CCD values with 3-level scores given independently by three experts on 179 scientific corneas. Thirdly, an eye bank was equipped with the device, and 358 consecutive organ-cultured (OC) corneas were tested for donor- and storage- related factors possibly influencing T and CCD. Reproducibility of T, CCD and SRD measurements was high, with intraclass correlation coefficients of 0.982, 0.886, and 0.999 respectively. Capacity to discriminate the three levels of transparency and arcus senilis was good, with T of 20.0 (10.0-33.6), 38.3 (24.3-75.4) and 57.9 (33.9-90.0) % respectively for T deemed poor, average, and good (P < 0.001), and CCD of 9.8 (7.3-10.6), 10.5 (8.2-11.5), and 11.1 (9.9-12.0) mm respectively for arcus senilis deemed prominent, moderate or absent (P < 0.001). T was correlated with neither donor age nor endothelial cell density nor storage time, but slightly worsened during OC for corneas assessed twice. In conclusion, the device, which can be easily integrated in the facilities of an eye bank, provides reliable objective measurement of T, CCD, and SRD. This could be a useful tool for standardizing quality assessment of stored corneas and consequently optimizing their selection for penetrating, endothelial or anterior lamellar keratoplasty.