The Effect of Pseudoexfoliation on Choroidal Thickness in Open Angle Glaucoma

In the present study, the investigators aimed to evaluate the effect of the presence of PEX on choroidal thickness in two groups of glaucoma patients with similar degrees of damage and similar demographical characteristics. The investigators also evaluated whether there was a correlation between choroidal thickness and indicators of glaucoma severity, such as retinal nerve fiber layer (RNFL) thickness and mean deviation (MD) value, in these two glaucoma types.

MATERIALS AND METHODS The study included 30 eyes of 30 patients diagnosed with POAG and 30 eyes of 30 patients diagnosed with PEX glaucoma who presented to Glaucoma Unit of Izmir Katip Celebi University Atatürk Training and Research Hospital between August 2014 and February 2015. The control group included 30 eyes of 30 healthy individuals with similar age distribution.

Approval was obtained from the ethics committee of Izmir Katip Celebi University Medical School Atatürk Training and Research Hospital. Detailed informed consent forms were obtained from each of the patients included in the study.

The study included subjects over 18 years old who had best corrected visual acuity of 0.5 or better, transparent optic medium, at least two reliable visual field tests, and reliable spectral domain (SD)-OCT (signal strength≥7/10) and EDI-OCT images (signal strength≥6/10) Information pertaining to patients' systemic diseases and chronic medication use was recorded. Patients with diabetes mellitus, systemic arterial hypertension, renal failure, hemodialysis history, chronic medication, or smoking habit were not included.

Patients with retinal and neuro-ophthalmological diseases, amblyopia, active or previous uveitis, previous ocular trauma, intraocular surgery within last 6 months, previous trabeculectomy, or refractive error with a spherical equivalent greater than ±3.0 D were excluded from the study. In order to minimize the effect of IOP on choroidal thickness, patients with IOP higher than 21 mmHg at the time of OCT image acquisition were not included in the study.

POAG was diagnosed based on high IOP (>21 mmHg) at the time of diagnosis, typical glaucomatous optic disc and visual field changes, and normal anterior chamber angle. In contrast, PEX glaucoma diagnosis was based on high IOP (>21 mmHg) at diagnosis and typical glaucomatous optic disc and visual field changes, plus the presence of PEX material or hyperpigmentation in the anterior chamber angle and the presence of PEX material at the pupillary margins or the anterior lens on anterior segment examination after pupil dilation. The control group consisted of healthy individuals with normal anterior and posterior segment findings and IOP less than 21 mmHg.

All subjects underwent a detailed ophthalmologic examination. Axial length was measured using IOL Master (Carl Zeiss Meditec, Dublin, CA, USA) optic biometry. Visual field was assessed with Humphrey II Perimetry (Carl Zeiss Meditec, Dublin, CA, USA) SITA standard central 24-2 test. Tests with fixation loss less than 20%, false negative, and false positive response rates below 33% were considered reliable. Patients with at least two reliable visual field tests were included in the study. MD values were obtained.

Optic disc images were obtained with Cirrus 4000 HD-OCT (Carl ZeissMeditec, Dublin, CA, USA) SD-OCT device. Mean RNFL thickness and vertical cup-to-disc (c/d) ratios were noted. Choroidal imaging was done after pupil dilation using the EDI-OCT mode. The SD Cirrus HD-OCT light source was centered on 800 nm wavelength to achieve 5 μm maximal resolution in tissue. In order to minimize the effect of diurnal choroidal thickness variation on the measurements, choroidal thickness measurements of all patients were made between 09:00 and 11:00 am, after a resting period of 30 minutes. The macular field was scanned in the horizontal plane in high-resolution 1 line raster mode. Patients were asked to focus on the instrument's internal fixation light until the retinal image was acquired. Images with signal strength of 6/10 or better were eligible for assessment. Patients who had at least two reliable high-resolution foveal and choroidal imagings were included in the study.

The fovea centralis was determined by identifying the point of maximum depression in the central 500-micron-diameter area. The internal and external choroidal margins were determined manually in the section passing through the fovea centralis. These margins were drawn based on criteria defined by Boonarpha et al.[15]. The posterior edge of the hyperreflective band corresponding to the retinal pigment epithelium-Bruch's membrane complex was determined as the anterior border of the choriocapillaris. The posterior border of the choriocapillaris was demarcated as the hyperreflective band corresponding to the sclerochoroidal interface or the hyporeflective line corresponding to suprachoroidal space. In cases where these two anatomic structures could not be visualized, measurement was done using the prominent straight line corresponding to the posterior margin of the large choroidal vessels. Patients in whom choroidal margins could not be clearly distinguished were not included in the study.

High-resolution retinal choroidal images with distinct choroidal margins were transferred to ImageJ software [40]. The high-resolution EDI-OCT images were 6000 microns wide and 2000 microns high, as indicated in the manufacturer's user's manual. EDI-OCT images to be measured were opened using ImageJ software. The Scale command was selected in the Image tab of ImageJ software menu. Using the Scale menu, width (pixels) was defined as 6000 and height (pixels) as 2000. The distance to be measured was marked on the new image of 6000x2000 pixels and measurements were done using the Measure command in Analyze tab. The choroidal margins were drawn in this software according to the specified criteria, followed by manual measurements. Measurements were taken vertically at the fovea centralis and in the nasal and temporal quadrants at distances of 1500 and 2500 microns from the fovea centralis. The same researcher repeated the measurements at different times using the double-blind method, and intraobserver and intervisit measurement repeatability was assessed.

All data were analysed using SPSS software. Independent t-test was used to compare the groups. The correlation between choroidal thickness and other variables (age, axial length, vertical c/d, RNFL thickness, MD) was evaluated using Pearson correlation analysis.Repeatability analysis of study parameters measured with Cirrus 4000 HD OCT was evaluated using the coefficient of variation (CV). For CV calculation of choroidal thickness measured by Cirrus 4000 HD OCT, 10 consequential measurements were obtained by the same operator to the same eye of the subject. CV is defined as the ratio of the standard deviation to the mean: cV=σ/μ