Study Planning and Statement of Ethics
The study was a single-center, comparative, cross-sectional case series performed at the Department of Ophthalmology, Bozyaka Training and Research Hospital, Turkey, between April 2015 and October 2016. The study was conducted in accordance with the Tenets of the Declaration of Helsinki, with local ethical approval from the ethics committee of our hospital.
Examination Protocol and Patient Selection
All individuals included in the study were older than 50 years of age, and their demographic features were recorded. The study group consisted of newly diagnosed bilateral AMD and clinically unilateral XFS. The control group consisted of age- and sex-matched healthy subjects. All individuals underwent a comprehensive ophthalmic examination, including best-corrected visual acuity (BCVA) tests, anterior segment and posterior segment slit-lamp examination, intraocular pressure (IOP) measurement by Goldmann applanation tonometry, and a dilated fundus examination. In addition, fundus photography, fundus fluorescence angiography (FFA), and choroidal thickness (CT) measurements using the Spectralis optical coherence tomography (OCT) system (Heidelberg Engineering, Heidelberg, Germany) were performed.
Inclusion criteria for the study group were: age older than 50 years; newly diagnosed bilateral AMD and clinically unilateral XFS, where diagnosis of XFS was confirmed with slit-lamp biomicroscopy and clinically unilateral XFS was defined as the unilateral presence of detectable exfoliation material by slit-lamp examination on the anterior lens capsule or at the pupillary border after pupillary dilation, open angle in gonioscopy, IOP less than 21 mm Hg without treatment, normal optic disc appearance, and visual field test; confirmation of AMD was performed with direct and indirect fundus examination, OCT, and FFA; and no previous treatment for AMD.
Exclusion criteria for the study group were patients with PEX glaucoma or any type of glaucoma, congenital, or acquired retinal disorder, previous ocular surgery, or ocular trauma; patients with a history of any inflammatory ocular disease such as anterior or posterior uveitis; patients with any coexisting systemic disease including systemic hypertension, diabetes mellitus, and cardiovascular disease (due to the possible influence on CT), and patients with a history of any chronic drug use, including sildenafil, analgesics, antihistamines, and decongestants; any retinal disease, including diabetic retinopathy, retinal vessel occlusion, polypoidal choroidal vasculopathy (PCV), or central serous chorioretinopathy that may confound the evaluation of the retina other than AMD; patients with clinically bilateral XFS syndrome; concomitant or previous therapy to treat AMD including oral supplements of vitamins and minerals, intravitreal injections, laser photocoagulation, and photodynamic therapy; and patients not sufficiently cooperative for OCT measurements. Additionally, to reduce the effects of refractive error on OCT testing, patients with a refractive spherical diopter (D) greater than 5 D or with high cylinder diopter (> 3 D) were also excluded from the study.
We had estimated that at least 31 pairs of patients and controls would be required to achieve an 80% probability of detecting a mean between-group difference in SFCT of 33 μm with a standard deviation of 46 μm, and a standardized difference of 0.75 at a 5% significance level. The 33 μm difference in retinal nerve fiber layer thickness was considered based on the results of Turan-Vural et al.9 We initially examined 2,242 patients admitted to the retina clinic. Of these, 94 patients fulfilled the inclusion criteria of newly diagnosed bilateral AMD and clinically unilateral XFS in the present study. Eighteen of the 94 eligible patients were excluded from the study due to the exclusion criteria, including history of previous ocular surgery, chronic drug use, glaucoma, and retinal vascular diseases. In total, 152 eyes of 76 patients with a diagnosis of bilateral AMD and clinically unilateral XFS admitted to the retina clinic were included. Fifty-two age- and sex-matched healthy subjects were included in the study as a control group for CT measurements. Participants were divided into three groups for statistical analysis. Subjects with clinically unilateral XFS eyes, non-XFS fellow eyes, and controls were labeled as groups A, B, and C, respectively. Representative images of a patient with clinically unilateral XFS and bilateral AMD are shown in Figure 1.
Representative images including the anterior segment, color fundus, fundus autofluorescence, and optical coherence tomography of a patient with clinically unilateral pseudoexfoliation syndrome (XFS) and bilateral age-related macular degeneration (AMD). (A, C, E, and G) (Right eye): Eye with clinically unilateral XFS (arrow) and intermediate AMD. (B, D, F, and H) (Left eye): Non-XFS fellow eye with wet AMD.
Fundus Photograph Grading and Classification of AMD
All of the fundus photographs were recorded by the same physician (MOZ). Two retinal specialists (MOZ, OK) who were blinded to the data pertaining to the characteristics of the patients individually graded the photographs. All equivocal and wet AMD lesions were discussed between the specialists. AMD was diagnosed on the basis of the morphologic changes observed. Patients likely to have wet AMD subsequently underwent a FFA to confirm the diagnosis. AMD grading was performed by checking an area of 3,000 μm from the foveal center. In this area, the drusen size, number, and type were recorded. Hypopigmentation and hyperpigmentation of the retinal pigment epithelium (RPE) and signs of wet AMD including subretinal hemorrhage, serous or hemorrhagic RPE detachment, a subretinal neovascular membrane, and a subretinal fibrous scar were also recorded.
AMD was classified based on the 2013 consensus of the Beckman Initiative for Macular Research Classification Committee.10 All eyes were grouped into stages 1 to 3 based on this classification system after the examination of the color fundus photographs, OCT, and FFA. Stage 1, characterized by medium drusen (range: ≥ 63 μm to ≤ 125 μm) but without pigmentary abnormalities, was accepted as early AMD; stage 2, characterized by large drusen (≥ 125 μm) or with pigmentary abnormalities associated with at least medium drusen, was accepted as intermediate AMD; and stage 3, characterized by neovascular AMD, was accepted as late AMD.10
OCT Measurements by Enhanced Depth Imaging Spectral-Domain OCT
Choroidal imaging was performed using spectral-domain OCT (SD-OCT) in enhanced depth imaging (EDI) mode (Spectralis OCT; Heidelberg Engineering, Heidelberg, Germany). The EDI image was averaged for 100 scans using the automatic averaging and eye-tracking system. At the macula, we scanned the horizontal sections across the center of the fovea. The SFCT was defined as the distance between the inner surface of the sclera and the hyperreflective line corresponding to the RPE and was measured using the manual caliper function with the Heidelberg Eye Explorer software (version 126.96.36.199; Heidelberg Engineering, Heidelberg, Germany) (Figure 2). If the line was blurred, especially at the chorioscleral interface, the center of the line was traced and measured. If pigment epithelium detachment was present, Bruch's membrane was used as the inner margin of the choroid instead of the RPE line. If Bruch's membrane was not identified, the inner margin of the choroid was defined by the border between the hyporeflective sub-RPE fluid and the mesoreflective choroid tissue. All OCT measurements were performed at the same time of day, in the morning, to avoid diurnal fluctuations. For each eye, the SFCT was measured independently by two blinded clinicians (OK, MOZ), and the mean values were recorded. Each observer was masked to the other observer's measurements. The measurements were performed in a random order and masked fashion. Interobserver reproducibility of the CT measurements was assessed by measuring the intraclass correlation coefficient (ICC). To abolish bias, eyes with more than a 10 % difference in measurements between the clinicians were excluded from the study.
Subfoveal choroidal thickness (SFCT) measurement in a patient with age-related macular degeneration using enhanced depth imaging optical coherence tomography (EDI OCT). The SFCT measurements in the macular region were performed using horizontal EDI OCT scanning. SFCT was measured between the hyperreflective line corresponding to the retinal pigment epithelium and the inner surface of the sclera.
Statistical analyses were performed using the SPSS for Windows 17.0 software (SPSS, Chicago, IL). For each continuous variable, normality was determined by Kolmogorov-Smirnov test. Chi-squared test was used to compare categorical data, and independent sample t-test was used for the intergroup comparisons of normally distributed continuous variables. One-way analysis of variance (ANOVA) test was used to compare clinical results between the three groups. In a post-hoc analysis, the Tukey test was used to compare two groups at a time, such as XFS and non-XFS fellow eyes, XFS and healthy subjects, and non-XFS fellow eyes and healthy subjects. A P value less than .05 was considered statistically significant.