Comparing Aqueous Flow in Glaucoma Cases by Fluorophotometry Versus Pneumatonography

Abstract

Purpose : Aqueous flow (Fa) is a pharmacological target to reduce IOP and treat glaucoma. The current method of measurement is fluorophotometry (Fa_Fl) which takes two or more hours to complete. A quicker method was proposed in 1950 by W. Morton Grant, who calculated Fa via a Schiøtz tonometer to collect steady state pressure (P₀) and tonographic outflow facility (C). This method has not been applied to pneumatonography nor to eyes with glaucoma or ocular hypertension. We hypothesize that Fa calculated by Grant’s method (Fa_Gr= CxP₀) via pneumatonography will align with Fa_Fl in patients under baseline and with timolol treatment.

Methods : Subjects with either ocular hypertension (OHT) or open-angle glaucoma (OAG) were enrolled in a multicenter, prospective, randomized crossover trial of latanoprost and timolol (ClinicalTrials.gov Identifier NCT04412096) as part of Eye Dynamics and Engineering Network 2 (EDEN2). Fa_Fl was measured twice, at baseline and after one week treatment with timolol. At each visit, fluorophotometry, pneumatonography and tonometry were performed on the study eye. This yielded Fa_Fl, C and P₀, with Fa_Gr = CxP₀. Fa_Gr values were first compared to each other, to observe effects of timolol, and then to Fa_Fl values to determine any correlation. Values were analyzed using paired t-tests and Gardner-Altman plots.

Results : Preliminary results from 16 subjects (8 OHT, 8 OAG; 11 males, 5 females; 2 Asian, 4 African American, 10 White) ages 38-79 years (58 ± 11 years) are reported. Different sample sizes were analyzed based on quality of Fa_Fl and Fa_Gr. Timolol lowered Fa_Fl significantly compared to baseline (paired mean difference= -1.17, P value= 0.0004, Fig. 1a). There was not a similar timolol treatment effect using Fa_Gr calculation (paired mean difference= 0.543, P value= 0.464, Fig. 1b). Fa_Gr and Fa_Fl both at baseline were compared and are not similar (paired mean difference= -1.52, P value= 0.0164, Fig. 2).

Conclusions : In this preliminary finding, pneumatonography method is not an accurate tool to measure Fa compared to fluorophotometry nor to measure timolol induced changes in Fa. Further investigation and improvement of this outflow facility approach would enable assessment of aqueous flow in eyes that currently cannot be studied by fluorophotometry (e.g., eyes with uveitis, pseudophakia, or aphakia).

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Fig. 1: Baseline and post-timolol for Fa_Fl (a) and Fa_Gr (b)

 

Fig. 2: Comparing baseline of Fa_Gr and Fa_Fl