Recent findings from a study published in the Journal of Glaucoma compared the progression patterns of peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GCIPL) thinning via guided progression analysis (GPA) of optical coherence tomography (OCT) in primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG) patients.
Give me some background first.
PXG is characterized by higher mean intraocular pressure (IOP) levels, greater diurnal fluctuations in IOP, and increased marked pressure spikes relative to POAG.
This can make PXG more difficult to manage; case in point: a previous study suggested that even with similar IOP levels, PXG can cause progressively greater glaucomatous damage than POAG.
Which brings us to …
Consequently, a South Korean research team sought to identify differences in the structural progression patterns of POAG and PXG to identify potential progression monitoring protocols and improve long-term care.
Now, talk about the study.
Investigators assessed the progression of RNFL and GCIPL thinning by GPA from the Cirrus HD-OCT machine.
They evaluated the topographic patterns of progressive RNFL and GCIPL thinning by overlaying the acquired images of the RNFL and GCIPL thickness-change maps.
Subsequently, the rates of progression of RNFL and GCIPL thinning were analyzed and compared between patients with POAG and PXG.
Who was included in the study?
Medical records review led investigators to retrospectively recruit participants aged 18 years or older who had been diagnosed with POAG or PXG between September 2008 and August 2020 at the Glaucoma Clinic of Seoul National University Hospital in Seoul, South Korea.
In total, 248 eyes of 248 patients with POAG (175 eyes of 175 patients) and PXG (73 eyes of 73 patients) were enrolled, and 156 POAG eyes and 48 PXG eyes were included in the study.
Findings?
Overall, progressive RNFL thinning was significantly more common in PXG than in POAG (p = 0.005).
The RNFL progression-frequency maps indicated that progression predominantly appeared in the superotemporal and inferotemporal areas in POAG, while it had invaded more into the temporal area in PXG.
Based on the GCIPL maps, progression was most common in the inferotemporal area in both POAG and PXG.
Tell me more.
The average progression rate of GCIPL thinning was faster in PXG than in POAG (p=0.013).
When analyzed in two halves (superior/inferior), the progression rate of the inferior half was faster in PXG than in POAG (p=0.011).
Of note, the range of IOP fluctuation was greater—even though the average IOPs during the follow-up period were not significantly different—between POAG and PXG.
Expert opinion?
According to the study authors, “Greater long-term IOP fluctuation might have caused the difference in the patterns of RNFL thinning, since long-term IOP fluctuation has been reported to be significantly related to the risk of glaucoma progression.”
“This possibility suggests that attention and effort are required not only to lower average IOP but also to reduce IOP fluctuation,” they added.
Limitations?
The number of PXG patients with long-term follow-up and progressive RNFL or GCIPL thinning was relatively small.
Additionally, investigators did not evaluate the pure natural history of untreated POAG or PXG as enrolled patients were treated for their glaucoma, and all stages of glaucoma were grouped together.
Take home.
These findings suggest that OCT GPA has clinical utility in showing progression patterns of RNFL and GCIPL thinning in POAG and PXG.
They highlighted that RNFL thinning was more common in PXG than POAG, and progression of RNFL and GCIPL thinning tended to occur in different areas based on the type of glaucoma.
Thus, understanding these differences could be helpful in monitoring patients and tailoring glaucoma treatments.
Next steps?
The study authors noted that further studies with larger cohorts and patients grouped together by glaucoma severity are warranted to more precisely understand the specific patterns of progressive RNFL and GCIPL thinning based on glaucoma type.