Relationship between optic nerve head and retinal nerve fiber layer with central corneal thickness in primary open angle glaucoma: A three-dimensional optical coherence tomography study.

206 Öztürker, Optic Nerve Head, Retinal Nerve Fiber Layer and Corneal Thickness in Glaucoma / doi: 10.14744/hnhj.2018. 54366 plementary connective tissue layer, the structural change of the cornea may reflect the change of lamina cribrosa. In some studies, the corneal thickness was found to be correlated with the anterior scleral thickness in POAG[8] and the scleral bed was thin in excavated optic nerves. [9] Biomechanical properties of the cornea are believed to reflect the structural vulnerability of the eye and increase glaucoma susceptibility. Therefore, it has been suggested that corneal thickness has an effect on ONH resistance as well as on IOP measurement. The purpose of this study was to determine whether thin corneas are associated with specific ONH parameters and peripapillary retinal nerve fiber layer (RNFL) thickness. The assessment of the relationship between biomechanical properties of the cornea and optic nerve may provide an additional insight in understanding the advanced damage in glaucomatous eyes with thin corneas. Materials and Methods The study was a retrospective, cross-sectional study on documented patients with POAG in glaucoma practice. The study and data collection confirmed to all local laws and complied with the principles of the Declaration of Helsinki. In total, 144 eyes of 144 patients (79 female, 65 male) with newly diagnosed POAG were included in the study. All eyes had open-angle observed by gonioscopy, and the patients fulfilled at least two of the following criteria: glaucomatous optic neuropathy, IOP >21 mmHg on at least three occasions, and glaucomatous visual field defects. Eyes were divided into two groups on the basis of their median central corneal thickness (CCT) and classified into thick cornea group (Group 1) and thin cornea group (Group 2). Group 1 represented 82 eyes with CCT ≥540 μm and Group 2 represented 62 eyes with CCT <540 μm. Each patient underwent a complete ophthalmic examination with glaucoma diagnosis confirmed by at least two visual fields with standardized reliability indices (Humphrey stat pac 2 parameters of <5% probability for mean deviation, and either corrected pattern standard deviation of <5% probability or glaucoma hemifield test “outside normal limits”). Visual field was tested using the 30-2 Swedish interactive threshold algorithm standard strategy of the Humphrey Field Analyzer (Carl Zeiss Meditec AG, Jena, Germany). Inclusion criteria were best corrected visual acuity not worse than 20/60, refractive errors ≤±3.0 D sphere and ≤±1.5 D cylinder, and good OCT image quality. Exclusion criteria were secondary glaucoma, history of previous ocular surgery, corneal or retinal diseases, and systemic comorbidities that may affect the visual field. IOP was measured using Goldmann applanation tonometry, and at least two IOP measurements were applied. CCT was measured with Nidek ultrasonic pachymetry UB1000. ONH with RNFL imaging was performed by the Topcon 3D SD-OCT 2000 (Topcon Corporation, Tokyo, Japan). Eyes were dilated with 0.5% tropicamide, and OCT images were obtained by the same technician. Images with signal strength >40 were used for analyses. For each eye, average, superior, and inferior peripapillary RNFL thicknesses were evaluated and automatically calculated by OCT using existing software. 3D SD-OCT 2000 (software Version 8.00; Topcon Corporation) automatically detects the disk center by referring to the infrared reflectance image. On the basis of the inputted refractive information, the software adjusts the circle diameter for the circle scan and corrects papillary diameter, area, and volume, while also calculating magnification compensation, which enables accurate scanning. The machine automatically detects the edge of the optic disk as the end of the retinal pigment epithelium/choriocapillaris. Among the parameters measured by ONH analysis, the following were examined: optic disc area, cup area, cup-disc area ratio, horizontal cup-disc ratio, vertical cup-disc ratio, cup volume, rim area, and rim volume. SPSS 11.5 for Windows was used for statistical analysis. All OCT parameters were compared with the two groups as defined according to the corneal thickness value. Significance between groups was determined using independent-samples T-tests. Pearson correlation analysis was used for the correlation coefficient regarding relationship to CCT.