This study compares the rates of visual loss before and after cataract surgery. While intraocular pressure parameters improved, surprisingly, cataract surgery was associated with increasing visual field loss. Previous papers have quantified the effect of cataract vs. glaucoma on the visual field. Overall, they suggest generalized loss with cataract, focal loss with glaucoma, and unmasking of mild visual field loss with cataract surgery.
The current manuscript uses a previously published pointwise exponential model to determine the independent effect of cataract vs glaucoma on visual field decay. Their model fits the mathematical behavior of individual perimetry test locations and separates into slow components and fast components. The model demonstrates cataract surgery altering the slow component, which indicates that increasing cataract creates slow decay of the visual field. In converse, glaucoma creates fast decay.
This innovative study and analysis of visual field decay is important, and could help clinicians determine whether their patient's cataract or glaucoma is creating their visual complaints. One important caveat is that patients with cataract and glaucoma may have visual dysfunction from both conditions progressing simultaneously, and several previous studies suggest slow and fast rates of glaucoma decay.
Patients with progressive glaucoma may be interested in cataract surgery when compared to traditional glaucoma surgery because it is less invasive and has mild IOP lowering effect. Therefore, this population may be enriched with glaucoma patients with current progression, which are likely to have future glaucomatous progression. Table 3 shows significant slow decay even after cataract surgery. Is this related to posterior capsular opacification or another reason? Finally, if the hypothesis is that cataract surgery slows the apparent rate of glaucomatous visual field decay, the study should consider controlling for factors known to be associated with visual field progression to determine whether cataract surgery is still significant such as preoperative IOP, age, previous disc hemorrhage, and baseline mean deviation of the visual field (MD). In summary, this innovative study helps distinguish between different mechanisms of visual field loss and that cataract surgery may not be protective against glaucomatous progression.