High Myopia May Slow IOP Recovery After Ocular Compression

Eye doctor measuring the patient intraocular pressure
Cropped photo of a blonde woman undergoing the air puff test performed by an ophthalmologist
Researchers noted a positive trend between the IOP drop rate and outflow facilities.

This article is part of Optometry Advisor’s conference coverage from the 2021 meeting of the American Academy of Optometry, held in Boston from November 3 to 6, 2021. The team at Optometry Advisor will be reporting on a variety of the research presented by the primary eye care experts at the AAO. Check back for more from the AAO Optometry 2021 Meeting..

There is a positive trend between rate of intraocular pressure (IOP) drop and outflow facilities, according to study results presented at the American Academy of Optometry 2021 meeting in Boston. The investigators hypothesized that IOP recovery could be related to aqueous outflow facilities. They first tested this in porcine eyes, and then conducted a clinical study. IOP regulation appeared weaker in eyes with high myopia, according to the research.  

The investigation used 9 freshly enucleated porcine eyes to establish baseline outflow facility using a constant-flow infusion method (flow rates used: 4 uL/min, 6 uL/min, 8 uL/min, and 10 uL/min). IOP decay was regularly monitored until baseline IOP was achieved. 

Investigators used rebound tonometry to measure IOP in 45 young adults. The participants were separated into 2 groups, those with high myopia (HM) had a spherical equivalent of -6.00 D or worse, or an axial length 26 mm or longer. The other group included participants without HM. Ocular compression was used to elevate IOP. Rebound tonometry was performed repeatedly in 30-second intervals during the 2 minute compression phase and 10-minute recovery phase. 

The average outflow facilities of 9 porcine eyes was 0.3893 uL/min/mm Hg. The researchers found that outflow facilities of individual porcine eyes varied from 0.2256 uL/min/mm Hg to 0.5610 uL/min/mm Hg. Eyes with higher outflow facilities were associated with faster IOP reduction, but the association was not significant (r2=0.11, P =.376). 

There were 25 HM and 20 non-HM and both groups had similar ages (HM: 24.0±2.6 years; non-HM: 24.1±2.8 years, P =.941). Baseline IOP was higher in patients with HM (15.3±3.2 mm Hg) than without HM (13.7±3.0 mm Hg). However, they were similar statistically (P =.089). 

Immediately after ocular compression, the 2 groups’ peak of IOP elevation was similar (HM: 25.3±5.8 mm Hg; non-HM: 22.1±5.0 mm Hg, P =.053). Both groups demonstrated a decrease in IOP during the 2-minute compression phase. The reduction rates were similar (HM: 1.84 mm Hg/min; non-HM: 1.32 mm Hg/min, P =.055). IOP dropped below the baseline after ocular compression. According to investigators, HM took more time (5.5 minutes) than non-HM (4 minutes) for IOP to return to its baseline level. 

The researchers say additional study is needed to confirm the positive trend between rate of IOP reduction and outflow facilities. 

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Lam A, Xu FY, Zuo B, Do CW. Intraocular pressure variation during and after transient increase in applied pressure: an evaluation of outflow facility. Poster presented at: American Academy of Optometry 2021 Annual Meeting;  November 5, 2021; Boston. Board #147.