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G.K. Rai, B. Gilmartin, J.S. Wolffsohn, A. Cervino; The Effect of Accommodation on IOP: Evidence for Dose Dependency . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5859.
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Literature on the relationship between accommodation and IOP is limited with the most recent study (Mauger et al., 1984 Am J Optom Physiol Opt) reporting a reduction of 1.32±0.43 mmHg after 3.5 mins of accommodation to a 4D stimulus using contact tonometry (CT) (N=30, age 22–35 yrs). We investigated the relationship further using a high resolution (0.1 mmHg) non–contact tonometer (NCT) coupled with the cardiac pulse, a fixed pace respiratory cycle (15 breathes/min) and quasi–continuous measures of accommodation responses to 3 levels of accommodation stimuli.
A modified NCT (Pulsair Keeler, UK) was coupled with a finger pulse transducer and a Labview Acquisition Program (National Instruments, USA) to trigger the air pulse at 1 of 3 locations on the cardiac cycle; peak, middle, or trough. Of the 3 locations, the middle demonstrated the least variance and a high level of correlation (r=0.90, p<0.001) with Goldmann CT (N=50, mean age 21.1±3.0 yrs). Accordingly, 5 IOP measures synchronized with the middle location were taken on the RE while the LE fixated zero (low=L), 1.50 (intermediate=I) and 4D (high=H) accommodative stimuli (presented randomly) for 3 minutes (N=40, mean age 20.6±3.0yrs). The LE was rendered functionally emmetropic with soft contact lenses and the accommodative response was measured at 1s intervals during the IOP measurement period with the portable Flexible–Ref FR–5000 (Grand Seiko Co, Ltd, Japan) monocular IR open–view autorefractor.
Mean (MN) accommodation response levels for L, I, and H stimulus levels were respectively –0.14±0.31, 1.67±0.20 and 4.15±0.36D. The corresponding distributions of IOP (mmHg) were L: MN±SD=13.95±2.09, range (RG)=10.24–19.47, median (MD)=13.51; I: MN±SD=13.34±2.05, RG=9.62–18.92, MD=12.94 and H: MN±SD =13.82±2.17, RG=9.09–20.33, MD=13.34. ANOVA indicated a significant effect of accommodation on IOP (F=4.82, p=0.016). The MN±SD and RG of the differences in IOP (mmHg) between the L to I and L to H accommodation levels were respectively 0.61±0.99 (p<0.001), RG=1.01 to –2.75 and 0.13±1.41 (p=0.56), RG=4.47 to –3.27. The % change in IOP between the L to I and L to H accommodation levels were respectively, –4.23±7.05 and –0.55±10.23 (p=0.04).
The data demonstrate that the relationship between accommodation and IOP is characterised by substantial inter–subject variation. Despite this, intermediate accommodation response levels are shown to lower IOP significantly. The dose dependency evident has instigated a series of investigations on accommodation and autoregulation within the ocular vascular system.
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