Background: Osteogenesis imperfecta (OI) is a rare, autosomal-inherited, connective tissue disorder characterised by bone fractures, deafness and blue sclera. Additional ocular findings are decreased ocular rigidity, myopia, glaucoma, keratoconus, corneal opacity, small corneal diameter and congenital Bowman's layer agenesis.
Purpose: This cross-sectional, masked, case-control study aimed to assess whether central corneal thickness (CCT) is affected in patients with OI and to focus on the clinical significance of scleral blueness.
Materials and methods: Twenty-three children with OI (13 boys, 10 girls) and 15 age-, sex- and refraction-matched healthy control subjects (eight boys, seven girls) were assessed for CCT by ultrasound pachymetry. The CCT was compared between two different patient subgroups (type-I OI with blue sclera, n = 12; type-IV OI without blue sclera, n = 11). Mann-Whitney U-test or analysis of variance was used as indicated and only right eyes of each subject were included in statistical analysis. Results were expressed as mean +/- S.D. and statistical significance was taken as p < 0.05.
Results: Mean age and sex distribution was similar between the groups (10.1+/-2.5 vs 9.8+/-1.8 years, p > 0.05). Patients with OI had significantly lower CCT (459.5+/-24.6 microm) than in control subjects (543.6+/-21.4 microm; p < 0.001). The CCT was below 500 microm in 22 of 23 children (95.6%) with OI, 15 of which (65.2%) were below 450 microm. In contrast, CCT was over 500 microm in all eyes in the control group. Type-I OI eyes with blue sclera had significantly (p = 0.005) lower CCT readings (446.5+/-16.3 microm) than type-IV OI eyes without blue sclera (473.6+/-25.0 microm). Mean keratometric values were similar between the groups (44.2+/-1.7 vs 43.8+/-1.6 dioptre, p > 0.05). Mean cycloplegic refraction was similar between the groups (-0.32+/-0.5 vs -0.18+/-0.4 dioptre; p > 0.05), although five of 23 OI patients had myopia, and mean intraocular pressure was lower in OI patients than controls (12.7+/-1.8 mmHg vs 15.6+/-1.9 mmHg; p < 0.001).
Conclusions: The CCT is thinner and negatively correlated with the blueness of the sclera in patients with OI. The CCT readings may therefore be of utmost importance in the diagnosis of OI. An ophthalmologist should be aware of an artificially low intraocular pressure measurement in such patients. In addition, when considering a keratorefractive treatment, CCT must be evaluated carefully to avoid unexpected results or complications. Sturdy protective spectacles should be prescribed to those who are not bed bound. Possible correlation of low CCT with biochemical changes in scleral collagen or systemic parameters awaits further investigation.