Ocular Biometry and Genomic Association in Primary Angle Closure Disease. A Descriptive study.

Purpose: To study the ocular biometric parameters in PACD patients and to compare them with normal control subjects. To identify the role of genetic polymorphisms in PCMTD1 and COL11A1 genes in our population in PACD pathogenesis.

Materials and methods: This cross-sectional comparative study included patients with PACD age-matched normal subjects. Patients who underwent prior laser iridotomy or intraocular surgery and those using miotics were excluded from the study. The comprehensive ophthalmological evaluation included slit lamp biomicroscopy, applanation tonometry, gonioscopy, and optic disc evaluation. PACD patients were classified as per the International Society for Geographical and Epidemiological Ophthalmology (ISGEO) classification into PACS, PAC, and PACG. Ocular biometry was performed for parameters like AXL, ACD, lens thickness (LT), central corneal thickness (CCT), and mean keratometry (K) values using the Partial Coherence Interferometry biometer. Variables like relative lens position (RLP) and lens axial length factor (LAF) were calculated from the above parameters. Genotyping was done for PACD patients and control subjects to look for PCMTD1, NM_001286783.1:c.215G>A and COL11A1, NM_080629.2:c.2386C>G genetic polymorphism.

Results: A total of 200 eyes of 100 PACD patients and the same number of control subjects were included in the study. PACD patients had significantly shorter AXL (21.68 mm vs. 23.25 ± 0.63 in controls, p < 0.05), short anterior chamber depth (2.33 ± 0.5 mm vs. 2.97 ± 0.92, p < 0.05), and increased Lens thickness (4.45 ± 0.41 mm vs. 4.11 ± 0.45 mm, p = 0.00). The Relative lens position (2.10 ± 0.2 vs. 2.16 ± 0.17, p < 0.03), Lens axial length factor (2.06 ± 0.21 vs. 1.76 ± 0.2, p = 0.00), Mean keratometry (D) (45.73 ± 1.64 vs. 44.33 ± 1.37, p = 0.00) were significantly different. Central corneal thickness (µ) (516.15 ± 34 vs. 511.9 ± 35.28, p = 0.8) was insignificant. Among the subgroups of PACD, PACG patients had steeper corneas when compared to PACS and PAC (46.67 ± 2.45 vs. 45.55 ± 1.54 vs. 45.64 ± 1.1, p < 0.01), while other parameters were not significant. Genotyping of PCMTD1, NM_001286783.1:c.215C>T, and COL11A1, NM_080629.2:c.2386C>G polymorphism yielded no significant association with PACD.

Discussion: Though association studies have identified several candidate genes, these are either not extended to other populations or controversial. In our research, ocular biometric parameters vary in primary angle closure disease patients, with corneal curvature being the only exemption in the studied variable without significant differences. We also found that the allelic frequency for PCMTD1, NM_001286783.1:c.215C>T was 95.75% and 4.25% for C and T, respectively, which is different from available data (97% and 3% for C and T in South Asians). For COL11A1, NM_080629.2:c.2386C>G, we found a % allelic frequency of 96% and 4% for C and G, respectively. The study subjects with heterozygous genotypes of PCMTD1 and COL11A1 showed an Odds Ratio of 1.48 (95% CI: 0.53-4.04), p=0.46 and 1.31 (95% CI: 0.47-3.68), p=0.8 when compared to controls, which were not significant.

Conclusion: Ocular biometric parameters vary significantly in PACD patients compared to normal subjects. Except for corneal curvature, there was no significant difference among PACS, PAC, and PACG.