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Sayoko Eileen Moroi, Matthew G J Trese, David Reed, Morgan Renner, Vikas Gulati, Arash Kazemi, Jay McLaren, Dave Musch, Carol Toris, Arthur J Sit; Assessing Concordance of Aqueous Humor Flow and IOP Changes After Timolol. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3007.
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© ARVO (1962-2015); The Authors (2016-present)
Timolol reduces intraocular pressure (IOP) by suppressing aqueous humor flow. However, the relationship between the IOP reduction and aqueous humor flow reduction after timolol is unknown. In this study of normal subjects, we tested the hypothesis of concordance between two pharmacodyanamic responses to timolol: aqueous humor flow and IOP.
Aqueous humor flow and IOP were measured in 74 participants, aged 55.0 ± 9.3 years (mean ± SD), who were part of the three-site, prospective aqueous humor dynamic study - Eye Dynamics and Engineering Network (EDEN) (ClinicalTrials.gov NCT01677507). Aqueous humor flow was measured in both eyes by fluorescein clearance. Each subject instilled timolol, 0.5% in both eyes twice per day for 1 week, then IOP and aqueous humor flow were re-measured at the end of the week. The outcome measures of changes in IOP and flow in response to timolol were examined by using paired t-tests. The relationship between the percent change in IOP and percent change in flow rate in the right eye was determined by linear regression.
There were no differences in participants’ age, sex or race between sites. Timolol decreased aqueous humor flow from 3.2 ± 1.3 µl/min to 1.9 ± 0.6 µl/min (p < 0.0001) and decreased IOP from 13.0 ± 2.9 mmHg to 11.0 ± 2.8 mmHg (p < 0.0001). The reduction in IOP was not associated with the reduction in flow (R2 < 0.01, p = 0.197, see Figure). Baseline IOP, baseline flow, sex, central cornea thickness (CCT), body mass index, neck circumference, tobacco use, blood pressure, presence of hypertension or diabetes, and systemic medications did not explain the variance in the change in flow or IOP.
In normal subjects, timolol does indeed decrease IOP and flow, but there is no concordance between the reduction of IOP and the reduction of aqueous humor flow after timolol. However, in addition to aqueous humor flow, IOP is also determined by episcleral venous pressure and outflow facility. The responses of IOP and flow to timolol are likely complex and influenced by variables of the Goldmann equation other than aqueous humor flow.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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