Influence of biometric parameters and the effects of laser peripheral iridotomy and argon iridoplasty on angle closure in Caucasian subjects

The purpose of this study was, first, to evaluate the intraocular pressure characteristics in eyes with occludable anterior chamber angles and the influence of Peripheral Anterior Synechiae (PAS). Second, to further investigate the hypothesis that smaller values for Angle Opening Distance (AOD), Angle Recess Area (ARA), Trabecular-Iris Space Area (TISA) and Trabecular-Iris Angle (TIA), are associated with greater diurnal intraocular pressure fluctuation and extent of PAS. Third, to additionally investigate the effect of Laser Peripheral Iridotomy (LPI) and Argon Laser Peripheral Iridoplasty (ALPI), in treated eyes versus untreated, on the diurnal intraocular pressure fluctuation, the angle parameters aforementioned and the corneal endothelial cell density, polymegethism and pleomorphism. 40 Caucasian patients with a gonioscopic diagnosis (less than 180 degrees posterior pigmented trabecular meshwork visible) of bilateral Primary Angle Closure (PAC), Primary Angle Closure Suspect (PACS) or a combination of both conditions and no ocular co-morbidity were recruited. After recruitment one eye was randomized to receive LPI and the fellow remained untreated as a control eye. Three months after LPI, those eyes in which the anterior chamber angle remained occludable were further randomized into either receiving ALPI or no further treatment. The follow up visits were set at 1 day, 1 week, 1.5 months, 3 months and 6 months after LPI. For ALPI, the treated eyes were assessed at 1 day, 1 week, 1.2 months and 2.5 months. Intraocular pressure (IOP) was measured hourly from 9.00 am to 4.00 pm with Goldmann applanation tonometry by the same examiner at the baseline and final visit. Diurnal intraocular pressure (DIOP) fluctuation was defined as the difference between the maximum and minimum IOP during that period. iii Angle parameters were measured using the novel non-contact three-dimensional AS-OCT (CASIA) in dark (0.3-0.5 lux) and light (170-200 lux) conditions at every follow up visit. AOD, ARA, TISA and TIA were quantified in 8 different sections of the angle (Superior, Superior-Nasal, Nasal, Inferior-Nasal, Inferior, Inferior-Temporal, Temporal and Superior-Temporal) and at 500 and 750m from the scleral spur. All the scans were acquired and evaluated by the same examiner. Measurements of DIOP in eyes with PAS were 1.5 mmHg (p=0.043) higher than in eyes without PAS. DIOP fluctuation varied from 1.50 mmHg to 14.50 mmHg (mean 5.99 mmHg, SD 2.70 mmHg). There was a statistically significant relationship between this fluctuation and the majority of angle parameters in Superior and Superior-Nasal sections, showing standardized coefficients from -254 to -438, demonstrating an inverse relationship between angle parameters and DIOP in these sections. Additionally, the higher contribution to the multiple predictor models also demonstrated negative standardised coefficients showing a similar inverse relationship between magnitude of fluctuation and angle dimensions. These models were statistically significant (p<0.05) for AOD 750 (light), ARA 750 (light and dark), TISA 500 (light), TISA 750 (light), TIA 500 (light) and TIA 750 (light and dark). The circumference of PAS (measured in degrees) and DIOP showed a statistically significant association (calculated using single factor or univariate regression) at every time measurement of the DIOP. There was a statistically significant widening effect of the parameters found in the Inferior-Temporal section of the angle of those eyes treated with LPI, but no effect was found on the diurnal intraocular pressure fluctuation. After ALPI, the parameters found in Superior, Inferior-Temporal and Superior-Temporal significantly increased 2.5 months after the treatment when compared to the untreated eye. Additionally, ALPI was associated with a reduction in the diurnal intraocular pressure fluctuation of 1.60 mmHg (SD 0.78 mmHg) that was of borderline statistical significance (p=0.056). There was not a clear effect on the endothelial cells density, polymegethism or pleomorphism after the LPI or ALPI treatments. Substantial changes in IOP occur throughout the day in patients with occludable anterior chamber angles. Narrower angle parameters and the presence of PAS are associated with greater diurnal fluctuation.