All patients underwent a clinical ophthalmic examination including visual acuity, slit lamp examination, gonioscopy, anterior chamber depth, and axial length (IOL Master; Carl Zeiss Meditec Inc., Dublin, CA), central corneal thickness (CCT; Pachmate DGH 55, DGH Technology, Inc., Exton, PA), visual fields (Humphrey automated white-on-white, 24-2 SITA-standard; Carl Zeiss Meditec), and dilated funduscopy.
The night before (10 PM) the fluorophotometric scans, participants self-administered from 3 to 6 drops of fluorescein sodium 2% (Minims; Bausch & Lomb, Kingston-upon-Thames, UK) topically into both eyes at 5-minute intervals depending on their ages (age, ≤25 years, 5 to 6 drops; age 26–35 years, 4 drops; >35 years of age, 3 drops).
17 Fluorophotometry was performed in both eyes with a scanning ocular fluorophotometer from 9 AM to 12 noon (FM-2, Fluorotron Master ocular fluorophotometer; OcuMetrics, Mountain View, CA). The aqueous flow rate was determined using dedicated software provided with the fluorophotometer (Appendix). Duplicate or triplicate scans were collected and repeated at 1-hour intervals for four measurements to determine the aqueous flow rate (
F t). Following each set of scans, IOP was measured using pneumotonometry (Model 30 Classic; Reichert Ophthalmic Instruments, Depew, NY); IOP was recorded as the arithmetic mean of a total of 12 measurements per eye: 3 measurements every hour alternating between eyes. Patients with IOP >21 mm Hg on the screening day may have had IOP of 21 mm Hg or less thereafter.
Tonographic outflow facility (
C) was performed with an electronic Schiøtz tonographer (model 720; Berkeley Bioengineering, Inc., San Leandro, CA) at 10 AM. The facility of outflow was measured from the rate of decay of IOP in the supine position during application of a recording Schiøtz tonometer over a period of 4 minutes with a standard 5.5-g weight.
18 The
R values of the curve at every 30-second time point were manually entered into the McLaren tonography computer program.
19 The program fits a second-degree polynomial by least-squares to the nine data points and determines by extrapolation the best-fit values for time 0 and time 4 minutes.
Uveoscleral outflow was calculated using Goldmann's equation
20 with an assumed episcleral venous pressure of 8, 9, 10, or 11 mm Hg.
19,21 F t is the rate of aqueous humor formation,
C is the tonographic facility of outflow, IOP is the intraocular pressure,
P v is the episcleral venous pressure, and
F u is the uveoscleral outflow.
Only one randomly (Excel random number generator; Microsoft, Redmond, WA) chosen eye per participant was included in the data analysis, when both eyes fulfilled the inclusion criteria.