Biomechanical and Morphological Differences between the Sclera Canal Ring and a Peripheral Sclera Ring in the Porcine Eye

Aim: To investigate a possible association between the biomechanical load and unload behaviour and the elastin content of the sclera canal ring (SCR) and a superiorly localized sclera ring (SPS) in the porcine eye. Methods: Two sclera rings were trephined from each of 40 porcine eyes, one containing the SCR and the other an SPS. The load and the unload curves were measured in the extension range of 0–2.0 mm by a biomaterial tester. Hysteresis was determined from the area enclosed by the loading and unloading curve. Histochemical staining with resorcin-fuchsin and morphometric analysis of paraffin-embedded sections of both rings were performed to detect the area occupied by elastin fibres. Results: At 1 mm extension, the mean load of the SCR was 0.89 8 0.22 N and that of the SPS 1.13 8 0.19 N, which was not significantly different between both rings (p 1 0.05). Mean hysteresis in the SCR was 1.55 8 0.30 N ! mm and 1.90 8 0.18 N ! mm in the SPS, which was significantly different between both rings (p = 0.01). Mean sclera thickness was 986 _ m in the SCR (range: 900–1,060 _ m) and 971 _ m in the SPS (range: 800–1,200 _ m) without a statistically significant difference between both sclera rings (p = 0.78). The area occupied by elastin fibres was 15.5 8 3.4% in the SCR and 4.5 8 1.5% in the SPS, which was significantly different between both rings (p = 0.0001). Conclusion: Hysteresis in the SCR was significantly lower than in the SPS, indicating a higher elasticity of the SCR in the porcine eye. This effect could be explained by a higher content of elastin in the surrounding ring of the peripapillary optic nerve head providing reversible contraction in cases of intra-ocular pressure variations