PURPOSE: To characterise the baseline parameters and tomographic features prior to hydrops in patients with keratoconus. METHODS: Of the 190 patients diagnosed with hydrops, during the study period between 2015 and 2022, 55 eyes of 55 patients who had corneal tomography in both eyes prior to developing hydrops were included in this study. Comparison of clinical and tomography parameters between the eyes was performed. RESULTS: The mean age was 22.07 ± 7.9 (16-29) years. The right eye was affected in 27 patients and the left eye in 28 patients. Thirty-four were males. The mean of mean keratometry values, Km (defined as the average of flat and steep keratometry) prior to hydrops episode was 62.4 ± 6.7 (58.9-67.8) dioptres(D). The mean of maximum keratometry values (denoted as Kmax) was 76.7 ± 12.65 (69.1-85) D. Mean thinnest pachymetry was 285.4 ± 74.8 (234-328) microns. The mean intraocular pressure was 11.7 ± 2.9(10-13.25) mm Hg. The mean log MAR uncorrected distance visual acuity at the clinic visit prior to hydrops was 1.6 ± 0.43 (1.3-2). Of the 55 eyes that had hydrops,50 (90.9%) eyes were using contact lenses. There was a statistically significant difference in the uncorrected distance visual acuity, steep keratometry, flat keratometry, and corneal thickness at the thinnest point between the eyes with hydrops, compared to contralateral fellow eyes (p value <
0.001). Multivariate analysis showed a statistically significant effect of crosslinking in preventing hydrops
however, this effect was not seen in eyes with paracentral cones. CONCLUSION: The study characterises the demographic and tomographic features in eyes prior to developing hydrops. These parameters could be taken into consideration in the management of keratoconus patients. A hydrops risk scoring system can be developed from a larger subset of tomography data from hydrops eyes.