Corneal surface regularity and the effect of artificial tears in aqueous tear deficiency

Abstract

Purpose To evaluate corneal surface regularity and the effect of artificial tears on the regularity of the corneal surface in dry eye. Design A prospective, clinic-based, case-control study. Participants A total of 64 eyes of 33 normal subjects and 42 eyes of 22 patients with aqueous tear deficiency were evaluated. Methods Indices of the TMS-1 corneal topography instrument (Tomey Technology, Cambridge, MA) were used to evaluate corneal surface regularity and potential visual acuity (PVA) in patients with aqueous tear deficiency dry eye before and after the instillation of artificial tears and in normal subjects. The TMS-1 topographic maps were classified into round, oval, symmetric bow-tie, asymmetric bow-tie, and irregular patterns. Main outcome measures The surface regularity index (SRI), surface asymmetry index (SAI), PVA index, and topographic pattern of the TMS-1 were compared between normal and dry eyes and in dry eyes before and after the instillation of artificial tears. Results The SRI and SAI were significantly elevated and the PVA was significantly reduced in dry eye patients compared with normal subjects: 0.31 ± 0.22, 0.30 ± 0.16, and 20/17.89 ± 20/3.04, respectively, in normal subjects and 1.28 ± 0.73, 1.05 ± 1.17, and 20/33.45 ± 20/13.99, respectively, in patients with dry eye ( P < 0.001 for all indices). The average amount of astigmatism was also increased in dry eyes (2.10 ± 1.96 prism diopters) compared with normal eyes (1.13 ± 0.53 prism diopters, P = 0.02). In dry eyes, the SRI and SAI were positively correlated with corneal fluorescein staining scores ( P = 0.005 for SRI and P = 0.016 for SAI). The mean PVA was not significantly different from the mean actual corrected visual acuity. The dry eyes had a significantly lower percentage of symmetric bow-tie patterns and a greater percentage of irregular patterns on topographic maps than normal eyes. After the instillation of artificial tears, the SRI, SAI, and mean astigmatism all decreased significantly ( P < 0.001 for SRI, P < 0.002 for SAI, P = 0.04 for astigmatism) and the PVA improved ( P < 0.001) in dry eyes. An irregular topographic pattern was observed in 45.24% of dry eyes, and this decreased to 30.95% after the instillation of artificial tears ( P < 0.005). Conclusions Patients with aqueous deficiency have an irregular corneal surface that may contribute to their visual difficulties. The SRI and SAI could be used as objective diagnostic indices for dry eye as well as for evaluating the severity of this disease and the effect of artificial tears. Artificial tears have the secondary benefit of smoothing the corneal surface in dry eye.