The relationship between refractive and biometric changes during Edinger–Westphal stimulated accommodation in rhesus monkeys

Abstract

Experiments were undertaken to understand the relationship between dynamic accommodative refractive and biometric (lens thickness (LT), anterior chamber depth (ACD) and anterior segment length (ASL=ACD+LT)) changes during Edinger-Westphal stimulated accommodation in rhesus monkeys. Experiments were conducted on three rhesus monkeys (aged 11·5, 4·75 and 4·75 years) which had undergone prior, bilateral, complete iridectomies and implantation of a stimulating electrode in the Edinger-Westphal (EW) nucleus. Accommodative refractive responses were first measured dynamically with video-based infrared photorefraction and then ocular biometric responses were measured dynamically with continuous ultrasound biometry (CUB) during EW stimulation. The same stimulus amplitudes were used for the refractive and biometric measurements to allow them to be compared. Main sequence relationships (ratio of peak velocity to amplitude) were calculated. Dynamic accommodative refractive changes are linearly correlated with the biometric changes and accommodative biometric changes in ACD, ASL and LT show systematic linear correlations with increasing accommodative amplitudes. The relationships are relatively similar for the eyes of the different monkeys. Dynamic analysis showed that main sequence relationships for both biometry and refraction are linear. Although accommodative refractive changes in the eye occur primarily due to changes in lens surface curvature, the refractive changes are well correlated with A-scan measured accommodative biometric changes. Accommodative changes in ACD, LT and ASL are all well correlated over the full extent of the accommodative response.

Edinger-Westphal and pharmacologically stimulated accommodative refractive changes and lens and ciliary process movements in rhesus monkeys

“…While the number of monkeys used in the current study is small, the measurements were repeated for many responses and responses of different amplitudes including repeat experiments in the same monkeys. The results are consistent between monkeys and, in agreement with prior such studies in which relatively few monkeys were used, show striking correlations between the accommodative physical changes and the optical refractive changes (Glasser, Wendt and Ostrin, 2006;Vilupuru and Glasser, 2005). The study was intended to determine the optical and physical relationships during the act of accommodation, and this can be achieved with relatively few monkeys.…”

“…Results from this study show that the lens edge and ciliary processes move centripetally with accommodation, and that these changes are linearly related to refractive changes during EW stimulated accommodation. These systematic changes in ciliary process and lens edge movement, along with systematic changes in anterior segment axial biometry (Ostrin and Glasser, 2005;Vilupuru and Glasser, 2005;Vilupuru and Glasser, 2003), and lens diameter (Glasser, Wendt and Ostrin, 2006) show that the anterior segment physical changes are highly correlated with optical changes during accommodation. …”

“…A Swan-Jacob gonioscopy lens placed on the iridectomized eye allows direct visualization of the ciliary processes, zonular fibers and adjacent lens equator. Such studies have provided important information on the accommodative mechanism and age changes that contribute to the progression of presbyopia, but have not determined the relationship between the physical movements and the accommodative refractive change.Prior studies in rhesus monkeys have related lens axial thickness and diameter changes to the accommodative refractive changes (Glasser, Wendt and Ostrin, 2006;Ostrin and Glasser, 2005;Vilupuru and Glasser, 2005), showing highly systematic physical and optical accommodative changes that occur to bring about refractive change. Because the ciliary body movements indirectly cause the refractive changes, it is equally important to understand how the ciliary body accommodative movements relate to the refractive change.…”

“…Prior studies in rhesus monkeys have related lens axial thickness and diameter changes to the accommodative refractive changes (Glasser, Wendt and Ostrin, 2006;Ostrin and Glasser, 2005;Vilupuru and Glasser, 2005), showing highly systematic physical and optical accommodative changes that occur to bring about refractive change. Because the ciliary body movements indirectly cause the refractive changes, it is equally important to understand how the ciliary body accommodative movements relate to the refractive change.…”

Edinger–Westphal stimulated accommodative dynamics in anesthetized, middle-aged rhesus monkeys

“…The optical accommodative response of the eye occurs through a contraction of the ciliary muscle, release of zonular tension around the lens equator, a decrease in lens diameter and a resulting increase in crystalline lens curvatures (Glasser and Campbell, 1998;Glasser and Kaufman, 1999;Glasser et al, 2006;Vilupuru and Glasser, 2005). The maximum amplitude of accommodation declines with advancing age, and in humans above approximately 50 years of age, the ability to accommodate is completely lost, a condition known as presbyopia (Duane, 1912;Glasser and Campbell, 1998).…”