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Michael Simpson, Maria Muzyka-Wozniak; Iris Characteristics Affecting Far Peripheral Vision and Negative Dysphotopsia. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4227.
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© ARVO (1962-2015); The Authors (2016-present)
Recent theoretical evaluations have found that negative dysphotopsia with intraocular lenses (IOLs) is related to a double image in the far periphery, and that there can also be a constricted total visual field (eg Holladay, Simpson, J Cat Refract Surg (in press)). Eye images are evaluated to characterize the iris surfaces that limit peripheral rays, and modeling is used to estimate limiting visual angles.
Anterior segment optical coherence tomography (OCT) preop and postop images were exported from Visante for 21 normal eyes evaluated previously (Muzyka-Wozniak J Cat Refr Surg 2016;42:563-8). ImageJ was used to manually identify features, and Matlab was used to calculate the maximum iris thickness and its distance from the pupil, the gap between the iris and IOL, etc. The average eye was modeled in Zemax to estimate limiting visual angles.
Preop and postop iris dimensions were similar, with a mean maximum thickness of 0.48±0.08 mm at 0.92 ±0.18 mm from the pupil, which did not vary systematically with pupil diameter (range 2.5-3.7mm (3.18±0.35 mm) for postop eyes). The axial pupil location (min clear iris diameter) was found to be very close to the posterior iris plane on average, and a simple wedge was used to simulate the iris shape. Mean postop values are overlaid on an example eye in Fig 1. The posterior iris surface moved from 3.32±0.31mm preop to 4.10±0.19 mm postop, with an iris-to-IOL gap of 0.51±0.16 mm, and pupil decentration of 0.23±0.16 mm nasally. The iris was implemented in Zemax as two opaque apertures (Fig 2), and raytracing the average eye with a 3.5 mm pupil, visual angles up to 93° could be focused by the IOL, but an additional peripheral image was created for visual angles above 73°.
A simple approximation for the inner iris profile is a triangle, and rays at very large angles are obstructed by the anterior iris (eg Fig 2). Raytracing with a 3.5 mm pupil shows that light from 73° that misses the IOL hits the retina more posterior than focused light from 93°. This overlap makes negative dysphotopsia unlikely (though possible for small pupils), but peripheral illumination comes from visual angles that are also imaged by the IOL. The maximum visual angle is determined by the limit of the sensitive retina, which can’t be identified in the images (and which has no measurement method).
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig 1. OCT negative marked with average distances
Fig 2. Eye model with 3.5 mm pupil
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