Effects of change in intraocular pressure on axial eye length and lens position

Abstract

Purpose To quantify the biometric changes of ocular dimensions with mechanical elevation of intraocular pressure (IOP) in vivo, to get a better understanding of the elastic properties of the human ocular structures that may play a role in the pathogenesis of various diseases such as myopia or glaucoma. Methods Changes in IOP were induced by a suction cup in 18 eyes under cycloplegia. Axial eye length (AEL) and anterior chamber depth (ACD) were measured with non-invasive laser interferometry during elevation of the IOP 10 and 20 mmHg over baseline values and after a 10-min resting period. Results IOP elevation of 10 and 20 mmHg respectively caused a significant increase of AEL of 23 lm (95% confidence interval: 14-34 lm) and 39 lm (confidence interval (CI): 28-51 lm). After mechanical oculopression, which resulted in an IOP reduction of -5.1 mmHg (CI: À6.3 to À4.0 mmHg) vs baseline, a significant shortening of À7 lm (CI: À13 to 0 lm) was observed. The change in AEL correlated with the change in IOP (r ¼ 0.66, P ¼ 0.005). Furthermore, a significant increase in ACD of 30 lm (CI: 24-36 lm) was detected with IOP reduction after oculopression, but no change was seen during IOP elevation. Conclusions Biometric changes of the human eye as a response to IOP changes were assessed in vivo. The correlation between change in AEL and IOP found emphasizes the need of in vivo ocular rigidity measurements in the human eye.

The short-term influence of exercise on axial length and intraocular pressure

“…Previous studies in humans have shown that reductions in IOP (either mechanically or pharmacologically induced) are associated with short-term decreases in AXL, suggesting a mechanical contraction/expansion of the globe with changes in IOP. 5,6 Our findings of a reduction in AXL accompanying the reduced IOP following a short period of dynamic exercise are consistent with these previous findings.…”

“…36 Changes in aqueous fluid dynamics in the eye could also potentially be involved in the anterior chamber variations observed, particularly considering that previous studies have also found reductions in IOP to be accompanied by increases in ACD. 5 Our findings may have implications for longer-term refractive error development. A number of recent studies have noted a link between outdoor activities and refractive error development with the majority of these studies suggesting that greater amounts of time spent on outdoor activities are associated with reduced chances of developing myopia.…”

“…The development of precise optical techniques for the measurement of AXL has shown that a range of different physiological factors can lead to short-term changes in this biometric parameter. Changes in accommodation, [1][2][3] imposed defocus, 4 alterations in IOP 5,6 and water loading 7 have all been found to be associated with short term changes in human AXL. Significant diurnal variations in AXL have also been documented.…”

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“…Intraocular pressure (IOP) has been hypothesized to be one of several factors implicated in the pathogenesis of myopia [5]. Elevated IOP is said to impose scleral stress and creep, resulting in axial eye elongation with scleral stretch [6].…”

The Influence of Light Exposure and Seasonal Changes on Short-Term and Longer-Term Changes in Axial Length of the Human Eye

“…These measurements were also collected at least 1 -2 hours after waking, to avoid the potential confounding effects of over-night corneal swelling and anterior segment changes (Read et al, 2008) influencing the axial length measurements. Accommodation (Drexler et al, 1998;Woodman et al, 2011;Woodman et al, 2012), imposed defocus , alterations in IOP (Leydolt et al, 2008), water drinking , supine posture (Mallen & Kashyap, 2007;Malihi & Sit, 2012) and exercise (moderate intensity) ) also cause short-term axial length changes. Hence, before each measurement session, participants were asked to view a distance target binocularly (seated and watching television at a 5 m distance) with their optimal distance correction for a period of 10 minutes, to avoid the influence of any previous activities upon the measurements.…”