High IOP variability linked to faster RNFL thinning
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High IOP variability was associated with faster rate of retinal nerve fiber thinning over time in a cohort of patients with open-angle glaucoma, according to a study published in JAMA Ophthalmology.
“Our study suggests that in addition to monitoring IOP magnitude, clinicians should consider IOP variability in the evaluation of patients with glaucoma,” Takashi Nishida, MD, PhD, of the Shiley Eye Institute at the University of California, San Diego, and colleagues wrote.
In a retrospective longitudinal study, researchers analyzed 815 eyes with preperimetric glaucoma (n = 251) and perimetric glaucoma (n = 564) from 508 patients who were enrolled in the Diagnostic Innovations in Glaucoma Study and African Descent and Glaucoma Evaluation Study from 2008 to 2020. More than half the patients were women (55.1%), and the mean age was 65.5 years. Participants self-reported as white (55.3%), Black (38.4%), Asian (4.7%) and other (1.6%).
Patients with at least four visits and 2 years of IOP and OCT measurements were analyzed. Researchers categorized eyes based on the rates of change in the retinal nerve fiber layer (RNFL) on OCT: The fast group was characterized by RNFL thinning faster than –2 µm per year, the moderate group was between –2 µm and –1 µm per year, and the slow group was thinning slower than –1 µm per year.
According to results, the mean rate of RNFL change among patients was –0.67 µm per year. The mean IOP was 14.8 mm Hg, with a peak IOP of 18.8 mm Hg. IOP fluctuation was 2.4 mm Hg, and IOP range was 7.4 mm Hg. All IOP measurements were highest in the fast progressor group.
After adjusting for mean IOP and other factors, multivariable models demonstrated that faster annual RNFL thinning was linked with higher IOP fluctuation (0.20 m per 1-mm Hg higher; P < .001) or higher IOP range (0.05 m per 1-mm Hg higher; P < .001).
“While the biological basis for this association is unknown, these results support the assessment IOP variability as well as mean IOP in patients with glaucoma to identify those at greater risk of RNFL progression,” Nishida and colleagues wrote.
Perspective
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We know from classic glaucoma studies like the Advanced Glaucoma Intervention Study (AGIS investigators) and the Collaborative Initial Glaucoma Treatment Study (Musch et al.) that higher IOP is associated with glaucoma progression, but fluctuations in IOP are currently less studied. This study is clinically useful in that it indicates we should flag diagnosed glaucoma patients with more variable IOPs as potential fast progressors. Medically treated patients were included in the study, so this applies to treated and untreated patients. The method of IOP data collection also reflects how IOP is measured by most clinicians – two or three times per year during office hours. Range and standard deviation of a set of IOPs are quick to calculate, but the study does not tell us exactly what range or SD should raise our suspicions. The average ranges and SDs these authors found for moderate and severe progressors may be useful indicators, but, as always with glaucoma, there are no magic numbers, and some fast progressors had variations in IOP that looked like the slow progressors. This study is another reminder that glaucoma is a complex disease, and clinicians should consider as much data as possible when determining a patient’s treatment plan – not just max IOP.
References:
- AGIS investigators. Ophthalmology. 2004;doi:org/10.1016/j.ophtha.2003.09.025.
- Musch DC, et al. Ophthalmology. 1999;doi:10.1016/s0161-6420(99)90147-1.
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