Intraocular pressure (IOP) at elevated levels, along with consequent visual field (VF) defect, has long been diagnostic for glaucoma. A few previous studies have looked at the association between IOP and VF worsening throughout disease progression and noticed that for every 1mm Hg decrease in IOP from baseline, there was a resulting 10% risk reduction of VF worsening. Another noted that VF worsening was unlikely to occur, but only if the maximum IOP is kept below 18mm Hg. To further examine these associations, a recent study observed treated glaucoma patients’ IOP and VF data and found that although IOP is linked to worsening VF in eyes at the advanced stage, those with less severe glaucoma only experienced a higher risk of VF worsening at a higher IOP.
Researchers gathered data from the Wilmer Eye Institute, including 1,446 eyes of 869 glaucoma patients (18 or older) treated between 1998 and 2012. Participants each had at least five longitudinal reliable VF tests and IOP measures on record to be analyzed in the study. Glaucoma severity was measured using the mean deviation of VF at baseline.
For all eyes, the mean rate of change of VF mean deviation over the years was -0.31 dB/yr. When comparing patients with mild/suspect glaucoma to those with moderate or advanced glaucoma at baseline, the latter had a faster rate of VF MD loss over time (-0.28 dB/yr vs. -0.42 dB/yr). Patients with mild/suspect disease with treated IOPs below 21 mmHg did not appear to have increased VF worsening. However, this is not the case for patients with treated IOPs beyond this value.
“For eyes with moderate/advanced disease, at mean treated IOPs below 21, a 1mm Hg increment in mean treated IOP did result in a statistically significant higher rate of VF worsening (-0.02 dB/yr per 1mm Hg increment in IOP),” the researchers explained in their paper. “Above a threshold of 21mm Hg, both eyes with mild/suspect and moderate/advanced disease show higher rates of VF worsening with higher levels of mean treated IOP. However, the influence of a 1mm Hg treated IOP increment was much more profound in eyes with moderate/advanced glaucoma compared to eyes with mild/suspect glaucoma.”
Even at the same treated IOP levels, eyes with moderate or advanced glaucoma tend to progress much quicker than those with mild disease. Based on the current study results, “at a treated IOP of 25, on average eyes with mild disease will take 1.5 years to lose 1dB of VF whereas for an eye with advanced disease the time it takes to lose a similar amount of field is 0.3 years,” the authors conclude. Patients with mild or suspect disease will face a very minimal risk of progressive loss of VF if treated IOP is kept below 20. Even for those with advanced glaucoma, although risk of VF loss is largely inevitable, staying under this recommended maximum level may help decelerate visual damage.
Yohannan J, Boland MV, Ramulu P, et al. The association between intraocular pressure and visual field worsening in treated glaucoma patients. Wilmer Eye Institute. 2021. [Epub ahead of print].