Scleral Thickness in Human Eyes

Citation: Vurgese S, Panda-Jonas S, Jonas JB ( Scleral Thickness in Human Eyes Sujiv Vurgese. 0 1 Songhomitra Panda-Jonas. 0 1 Jost B. Jonas 0 1 Demetrios Vavvas, Massachusetts Eye & Ear Infirmary, Harvard Medical School, United States of America 0 Ethics Statement The Medical Ethics Committee II of the Medical Faculty Mannheim of the Ruprecht-Karls University Heidelberg approved 1 Department of Ophthalmology, Medical Faculty Mannheim, Ruprecht-Karls-University Heidelberg , Heidelberg , Germany Purpose: To obtain information about scleral thickness in different ocular regions and its associations. Methods: The histomorphometric study included 238 human globes which had been enucleated because of choroidal melanomas or due to secondary angle-closure glaucoma. Using light microscopy, anterior-posterior pupil-optic nerve sections were measured. Results: In the non-axially elongated group (axial length #26 mm), scleral thickness decreased from the limbus (0.5060.11 mm) to the ora serrata (0.4360.14 mm) and the equator (0.4260.15 mm), and then increased to the midpoint between posterior pole and equator (0.6560.15 mm) and to the posterior pole (0.9460.18 mm), from where it decreased to the peri-optic nerve region (0.8660.21 mm) and finally the peripapillary scleral flange (0.3960.09 mm). Scleral thickness was significantly lower in the axially elongated group (axial length .26 mm) than in the non-axially elongated group for measurements taken at and posterior to the equator. Scleral thickness measurements of the posterior pole and of the peripapillary scleral flange were correlated with lamina cribrosa thickness measurements. Scleral thickness measurements at any location of examination were not significantly (all P.0.10) correlated with corneal thickness measurements. Scleral thickness was statistically independent of age, gender and presence of glaucoma. Conclusions: In non-axially elongated eyes, the sclera was thickest at the posterior pole, followed by the peri-optic nerve region, the midpoint between posterior pole and equator, the limbus, the ora serrata, the equator and finally the peripapillary scleral flange. In axially elongated eyes, scleral thinning occurred at and posterior to the equator, being more marked closer to the posterior pole and the longer the axial length was. Within the anterior and posterior segment respectively, scleral thickness measurements were correlated with each other. Posterior scleral thickness was correlated with lamina cribrosa thickness. Scleral thickness measurements at any location of examination were not significantly correlated with corneal thickness or with age, gender and presence of absolute secondary angler-closure glaucoma. - . These authors contributed equally to this work. The sclera forms the outer layer of the ocular globe and serves to stabilize size and shape to the eye. Stability of the globe shape is of utmost importance for the optical system which heavily depends on constant distances between cornea, lens and retina. The thickness of the sclera is a major factor in providing a firm structure to the globe [15]. Although previous studies have already measured the scleral thickness in human eyes [625], these studies included relatively few globes, and quantitative information on differences in scleral thickness between various ocular regions and its association with the size of the globe, gender and lamina cribrosa thickness have been scarce so far. We, therefore, conducted this study to measure the scleral thickness in different regions of the eye and to correlate the measurements with data of the globe diameters, thickness of the lamina cribrosa and gender. the study protocol. In agreement with the approval by the ethics committee, informed consent was not obtained since the globes had been enucleated up to 30 years before the study was initiated. The study included globes of white patients which had been enucleated due to painful absolute glaucoma or because of malignant choroidal melanomas. In the glaucomatous group, vision was completely or almost completely lost. The whole study population was divided into globes with an axial length longer than 26 mm (axially elongated group) and into globes with an axial length of equal to or less than 26 mm (non-axially elongated group). The reason to use a value of 26 mm as cut-off point between the axially elongated group and the non-axially elongated group was that in preceding clinical and population-based studies the equivalent of an axial length of about 26.0 to 26.5 mm marked the start of a high myopia associated increase in the optic nerve head size as well as an increase in the prevalence of myopic retinopathy [2628]. In the tumor group, the malignant choroidal melanomas did not infiltrate the trabecular meshwork, neither directly or indirectly by migrating cells. The parapapillary region was free of tumor. Visual acuity depended on the degree of cataract, vitreous opacities, and foveal involvement by the tumor. At the time when the eyes were enucleated, no other treatment modalities such as endoresection of the tumor or radiologic brachytherapy were available or were thought not to be suitable for tumor removal with respect to its location and size. Some of the eyes had been included in previous studies on different topics [7,8]. Immediately after enucleation, the globes were fixed in a solution of 4% formaldehyde and 1% glutaraldehyde. Using anatomical landmarks such as the insertion of the oblique muscles, the 12 oclock position of the globes was marked at the limbus. The axial length and the horizontal and vertical diameters of the globe were measured with a caliper. The globes were then processed for histological sectioning. The direction of the histologic cut depended on the location of the tumor in the group of eyes with a malignant choroidal melanoma, and it was horizontal in the glaucoma group. Otherwise the preparation of the globes did not vary between the glaucomatous eyes and the non-glaucomatous eyes or between the axially elongated and the non-axially elongated eyes. The globes were prepared in routine manner for light microscopy. A pupil-optic nerve section was cut out of the fixed globes. The segments were dehydrated in alcohol, imbedded in paraffin, sectioned for light microscopy, and stained by the Periodic-Acid-Shiff (PAS) method. For all eyes, one section (thickness: 8 mm) running through the central part of the optic disc was selected for further evaluation. We measured the thickness of the sclera at the: limbus ora serrata equator midpoint between the posterior pole and the equator posterior pole (Fig. 1) outside of the optic nerve head after merging of the optic nerve sheaths with the sclera (Fig. 2), and at the border optic disc in the peripapillary scleral flange, before merging of the optic nerve sheaths with the sclera (Fig. 2). Additionally, we measured the sagittal, horizontal and vertical diameter of the globe. In subg (...truncated)