Scleral thickness in human eyes

Abstract

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 (0.50±0.11 mm) to the ora serrata (0.43±0.14 mm) and the equator (0.42±0.15 mm), and then increased to the midpoint between posterior pole and equator (0.65±0.15 mm) and to the posterior pole (0.94±0.18 mm), from where it decreased to the peri-optic nerve region (0.86±0.21 mm) and finally the peripapillary scleral flange (0.39±0.09 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.

Figure 1. Transected human globe demonstrating the points of scleral measurements.

Figure 2. Histophotograph showing the peripapillary scleral flange (white double arrows) which functions as “bridge” between the sclera just outside of the optic nerve meninges (long black arrow) and the lamina cribrosa of the optic nerve head (yellow arrows), and which forms the anterior border of the orbital cerebrospinal fluid space (black asterisk).

Figure 3. Scleral Thickness at Different Measurement Points in Human Enucleated Eyes.

Figure 4. Scatterplot showing the correlation between axial length and the scleral thickness measured at the midpoint between the posterior pole and the equator in human globes (correlation coefficient = 0.48; P<0.001).

Blue Circles The association was not statistically significant (P = 0.23), if only non-axially elongated eyes (axial length ≤26 mm) were included.

Figure 5. Scatterplot showing the correlation between axial length and the scleral thickness measured at the posterior pole in human globes (correlation coefficient = 0.61; P<0.001).

Figure 6. Scatterplot showing the correlation between the thickness of the peripapillary scleral flange and the central lamina cribrosa thickness in adult human non-glaucomatous eyes (P = 0.03; correlation coefficient: 0.23); equation of the regression line: Central Lamina Cribrosa Thickness (um) = 263×(Thickness of the Peripapillary Scleral Flange (mm))+303 um.