Biomechanical parameters of the fibrous capsule of the eyeball in pseudoexfoliative glaucoma in comparison with primary open-angle glaucoma

BACKGROUND: Pseudoexfoliation syndrome is currently considered as a systemic disorder of the connective tissue metabolism with the accumulation in all corneal cell layers of pseudoexfoliation syndrome deposits, which disrupt corneal morphology and biomechanics.

AIM: to study the features of biomechanical parameters of the fibrous capsule of eyes in primary open-angle glaucoma (POAG) in comparison with those in pseudoexfoliative glaucoma (PEG).

MATERIALS AND METHODS: We compared 65 eyes with POAG and 77 eyes with PEG aged under 80 years. The control group consisted of 18 healthy eyes. Biomechanical indicators were compared, such as: DA Ratio, Integr. Radius, SP-A1, SSI, BGF, biomechanically corrected intraocular pressure (bIOP) obtained with Pentacam (Oculus) and CorVis ST.

RESULTS: Patients with PEG were elder (68.013 ± 0.75 years) in contrast to POAG patients (60.03 ± 1.05 years) (p = 0.001), had a thinner central retinal thickness (CRT) — 543.99 ± 3.9 µm versus 559.33 ± 4.4 µm in those with POAG (p = 0.010). The IOP level did not differ between groups, and no correlation with CRT was detected. Indicators of corneal stiffness: DA ratio Integr. Radius did not differ between POAG, PEG and control group. The SP-A1 parameter also did not differ between POAG and PEG patients, while there were differences between PEG patients and the control group (p = 0.046). Moreover, in eyes with POAG, SP-A1 directly correlates with IOP Ро (p = 0.001) and CRT (p = 0.001), in those with PEG — p = 0.001 and p = 0.001, respectively. The SSI index in PEG was higher and amounted to 1.38 ± 0.03 versus 1.27 ± 0.03 in POAG (p = 0.013), while it correlated with age only in the case of PEG (p = 0.007). A correlation between SSI and CTR was also revealed — in POAG (p = 0.018), in PEG (p = 0.001). In PEG, BGF shows higher values (25.92 ± 2.3) than in POAG (17.71 ± 2.2; p = 0.010). BGF has no correlation with age (p = 0.094 and p = 0.737 for POAG and PEG, respectively), depends on CRT (p = 0.001 and p = 0.027, respectively), on bIOP (p = 0.001 and p = 0.001, respectively), and on SP-A1 (p = 0.009 and p = 0.001, respectively). The only parameter that was higher in PEG than in POAG was SSI, which did not correlate with the BGF indicator (p = 0.642 and p = 0.327, respectively).

CONCLUSIONS: We did not find any fundamental differences in biomechanics between PEG and POAG, which could explain the significant rates of progression of PEG. Based on our data, it is obvious that the eye with PEG differs from that with POAG being more rigid, even at similar IOP values.