Biomechanical Measurement of Rabbit Cornea by a Modified Scheimpflug Device

Abstract

Purpose. To explore the probability and variation in biomechanical measurements of rabbit cornea by a modified Scheimpflug device. Methods. A modified Scheimpflug device was developed by imaging anterior segment of the model imitating the intact eye at various posterior pressures. The eight isolated rabbit corneas were mounted on the Barron artificial chamber and images of the anterior segment were taken at posterior pressures of 15, 30, 45, 60, and 75 mmHg by the device. The repeatability and reliability of the parameters including CCT, ACD, ACV, and CV were evaluated at each posterior pressure. All the variations of the parameters at the different posterior pressures were calculated. Results. All parameters showed good intraobserver reliability (Cronbach's alpha; intraclass correlation coefficient, α, ICC > 0.96) and repeatability in the modified Scheimpflug device. With the increase of posterior pressures, the ratio of CCT decreased linearly and the bulk modulus gradually reduced to a platform. The increase of ACD was almost linear with the posterior pressures elevated. Conclusions. The modified Scheimpflug device was a valuable tool to investigate the biomechanics of the cornea. The posterior pressure 15-75 mmHg range produced small viscoelastic deformations and nearly linear pressure-deformation response in the rabbit cornea.

Figure 1

The change of central corneal thickness (CCT) of rabbit eyes with the increase of posterior pressure. The ratios of the decrease of CCT were calculated as (CCT_15 mmHg − CCT_{posterior  pressure})/CCT_15 mmHg, where CCT_15 mmHg was viewed as the initial thickness of the cornea. The ratios were shown linearly with the increase of posterior pressure (R ² = 0.9928).

Figure 2

The change of rabbit corneal volume (CV) with the increase of posterior pressure. The ratios of the decrease of CV were calculated as (CV_15 mmHg − CV_{posterior  pressure})/CV_15 mmHg. The ratios were shown linearly with the increase of posterior pressure (R ² = 0.98).

Figure 3

The change of bulk modulus of rabbit corneas with the increase of posterior pressure. The cornea at posterior pressure of 15 mmHg was defined as primary condition (P ₀). The bulk modulus was calculated as ΔP/ΔV, where ΔP = (P − P ₀), ΔV = (CV_15 mmHg − CV_{posterior  pressure})/CV_15 mmHg.

Figure 4

The variation of anterior chamber depth (ACD) of rabbit eyes with the increase of posterior pressure. The increase of ACD was calculated as (ACD_{posterior  pressure} − ACD_15 mmHg). With the increase of posterior pressures, ACD gradually elevated and the change of ACD was almost linear (R ² = 0.9913).