Real-World Impact of IOP on RNFL Loss

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In a cohort of real-world patients, the rate of glaucoma progression, as reflected in loss of retinal nerve fiber layer (RNFL) thickness, was related to levels of intraocular pressure (IOP) during follow-up.¹ Fast glaucoma progression was uncommon in eyes that had very low IOPs (all measures below 15 mm Hg). However, a substantial number of eyes with fast progression had all visits with IOPs at levels that sometimes are assumed to be safe, such as 18 or 21 mm Hg.

“Certain levels of IOP over time were effective in preventing RNFL loss,” said Felipe A. Medeiros, MD, PhD, at Duke Eye Center in Durham, North Carolina. “Our data provide rates of change according to levels of IOP and disease severity, which can help guide clini­cians’ decisions in setting target IOP.”

Largest longitudinal SD-OCT results to date. This retrospective cohort study included 14,790 eyes of 7,844 glaucoma patients and suspects listed in the Duke Glaucoma Registry. Those included in the study had at least six months of follow-up, two good quality spectral-domain optical coherence tomography (SD-OCT) scans with the Spectralis platform (Heidelberg), and two IOP measures with Goldmann applanation tonometry. All evaluations were conducted between January 2009 and September 2019.

Rates of RNFL change. Overall, each increase of 1 mm Hg in mean IOP was associated with approximately 0.051 μm/year faster RNFL loss, even after adjusting for variables of age, sex, race, central corneal thickness, baseline disease severity, and follow-up time. Research­ers also assessed the relationship over time between three levels of IOP (21, 18, and 15 mm Hg) and slow, moderate, and fast progression as shown on SD-OCT. (Rates of progression were defined as follows: slow = slower than –1.0 μm/year; moderate = between –1.0 and –2.0 μm/year; and fast = faster than –2.0 μm/year.)

Eyes progressing at fast rates had relatively lower frequency of visits with “satisfactory” IOP measures. For example, 20% of fast-progression eyes had an IOP below 18 mm Hg in all visits, whereas 40% had an IOP above 18 mm Hg for more than half of visits. Only 9% of eyes with fast progression had stricter control—that is, IOP below 15 mm Hg at all visits.

Of note, a higher frequency of visits with an IOP below 18 mm Hg translated into slower RNFL change over time. However, this was not sufficient to prevent moderate or fast progression in all cases.

Other findings. Patients with primary open-angle glaucoma had faster rates of change than glaucoma suspects, but slower change than other glaucoma types. Older age and thicker baseline RNFL were also associated with faster rates of RNFL loss over time.

Clinical implications. “These findings indicate that certain levels of IOP may not be as safe as some clini­cians think,” Dr. Medeiros said. “It is very important to adequately assess the rates of change over time and adjust the target pressure in order to effectively pre­vent deterioration.”

—Miriam Karmel

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1 Jammal AA et al. Ophthalmology. Published online June 20, 2020.

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Relevant financial disclosures—Dr. Medeiros: Carl Zeiss: C,S; Heidelberg: S.

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