Ocular dimensions of the Chinese adolescents with keratoconus

Background: Adolescent KC is a special segment of the general KC population because an adolescents's eyes are still susceptible to blurred vision and optical defocus during the sensitive period of ocular and visual development. In the present study, we evaluated the ocular dimensions of 53 KC adolescents. Methods: One hundred and six KC eyes of 53 (42 boys and 11 girls) KC adolescents (age 15.5 +/- 1.7 years, range 11 to 18) were involved in this retrospective study. The eye with more severe KC (Severe Group) of each patient was compared with their less affected eye (Mild Group). Optical axial length (OAL) was measured by optical coherence biometry (IOL-master). Central corneal thickness, anterior chamber depth (ACD), flat keratometry value, steep keratometry value, and maximum keratometry value were assessed with an anterior segment analyzer (Pentacam HR). Anterior segment length (ASL) was manually measured from the 25 scheimpflug images captured by the Pentacam HR with the mean value recorded. The posterior segment length (PSL) was calculated with the formula PSL = OAL-ASL. Results: The mean ACD, OAL, ASL, and PSL values of the Severe Group were 3.51 +/- 0.32 mm, 24.76 +/- 1.24 mm, 4.01 +/- 0.30 mm and 20.76 +/- 1.15 mm. While those of the Mild Group were 3.36 +/- 0.29 mm, 24.97 +/- 1.40 mm, 3.94 +/- 0.35 mm and 21.03 +/- 1.31 mm. The Severe Group has significantly higher ACD (t = 4.539, P < 0.001) value but lower OAL (t = -3.120, P = 0.003) and PSL (t = -4.537, P < 0.001) values when compared with those of the Mild Group. For the Severe Group, the Kmax values were significantly correlated with the SE values (R = -0.385, P = 0.004), the ACD values (R = 0.375, P = 0.006), the ASL values (R = 0.308, P = 0.025) and the PSL values (R = -0.317, P = 0.021), but not with the OAL values (R = -0.220, P = 0.114). In the Mild Group, the Kmax values were negatively correlated with the SE (R = -0.577, P < 0.001), OAL(R=-0.533, P < 0.001), and PSL (R = -0.523, P < 0.001) values, but not with ACD (R = -0.110, P = 0.434) or ASL (R = -0.182, P = 0.192) values. Conclusions: For adolescent KC, the more keratoconic eyes may be characterized by deeper ACD but shorter OAL and PSL, when compared with the less affected ones.