Comparison of the optical image quality in the periphery of phakic and pseudophakic eyes.

PURPOSE: The natural lens may provide some compensatory optical effect in the periphery. When it is substituted by an IOL during cataract surgery, the quality of the peripheral optics will be modified. We compared the peripheral image quality in the eyes of patients with one eye implanted with a monofocal IOL and the fellow eye still with the natural precataract lens. METHODS: We used a scanning peripheral Hartmann-Shack wavefront sensor to measure the central 80° of visual angle along the horizontal meridian. Twelve patients with ages ranging between 65 to 81 years were evaluated. The results of the phakic and pseudophakic eyes were compared using the spherical equivalent, astigmatism, higher order aberrations, and the Strehl ratio. The statistical differences at each angle between the two eyes were evaluated. RESULTS: In the eyes implanted with IOLs, the peripheral mean spherical equivalent was slightly more myopic than in the phakic eyes, although the differences were only significant for some angles. Astigmatism increased much faster in the periphery for the pseudophakic eyes as compared with the phakic eyes. The mean values were significantly different from 9° and 17° outwards at the temporal and nasal retina, respectively. As an example, at 30°, eyes implanted with IOLs presented 1.5 diopters (D) of additional astigmatism. The higher order aberrations were not significantly different between the two groups. CONCLUSIONS: Eyes implanted with monofocal IOLs present more astigmatism in the periphery than the healthy older eyes. This suggests that the crystalline lens provides a beneficial effect to partially compensate off-axis astigmatism. The degradation of the peripheral retinal image may reduce the pseudophakic patient's performance in common visual tasks.

Evaluating the peripheral optical effect of multifocal contact lenses.

PURPOSE: Multifocal soft contact lenses have been used to decrease the progression of myopia, presumably by inducing relative peripheral myopia at the same time as the central image is focused on the fovea. The aim of this study was to investigate how the peripheral optical effect of commercially available multifocal soft contact lenses can be evaluated from objective wavefront measurements. METHODS: Two multifocal lenses with high and low add and one monofocal design were measured over the ±40° horizontal field, using a scanning Hartmann-Shack wavefront sensor on four subjects. The effect on the refractive shift, the peripheral image quality, and the depth of field of the lenses was evaluated using the area under the modulation transfer function as the image quality metric. RESULTS: The multifocal lenses with a centre distance design and 2 dioptres of add induced about 0.50 dioptre of relative peripheral myopia at 30° in the nasal visual field. For larger off-axis angles the border of the optical zone of the lenses severely degraded image quality. Moreover, these multifocal lenses also significantly reduced the image quality and increased the depth of field for angles as small as 10°-15°. CONCLUSIONS: The proposed methodology showed that the tested multifocal soft contact lenses gave a very small peripheral myopic shift in these four subjects and that they would need a larger optical zone and a more controlled depth of field to explain a possible treatment effect on myopia progression.

Optical quality of emmetropic and myopic eyes in the periphery measured with high-angular resolution.

PURPOSE: On average, myopic eyes present a relative hyperopia in the peripheral retina. This has been associated with the possibility that by modifying the peripheral refraction, the progression of central myopia could be controlled. The authors explored how refractive errors and optical aberrations interact in the formation of the retinal image in the periphery, in eyes with different central refractions. METHODS: The authors used a fast and high-angular resolution scanning wavefront sensor to measure the optical image quality of the eye in the horizontal meridian (± 40°) in 202 eyes of 101 subjects, 54 males and 47 females with an average age (std) of 27.5 (± 7.2) years and an average foveal refraction (std) of -0.8 (± 1.3 D) of which 64 were non-myopes (refraction ± std: 0.01 ± 0.46 D) and 37 myopes (-2.12 ± 1.08 D). They evaluated the relationship between peripheral optical properties and central refraction using different metrics. RESULTS: The authors observed a significant tendency to a relative hyperopia in the periphery of the myopic eyes. The relative peripheral refraction (RPR) was significantly different between the emmetropic and myopic eyes from 15°-40° temporal retina and from 20°-40° nasal retina. The mean RPR metric correlated with the central refraction of the subject (r = -0.552 / -0.560 [OD / OS]). The image quality presented only minor differences between the various refractive groups at angles of 30°-40° when the central refraction was corrected. CONCLUSIONS: Peripheral overall blur is mostly influenced by the interaction of defocus and oblique astigmatism, and at larger eccentricities is similar for the different refractive groups. This could argue against the hypothesis that a relative peripheral hyperopia could drive eyes toward myopia.

Comparison of two scanning instruments to measure peripheral refraction in the human eye.

To better understand how peripheral refraction affects development of myopia in humans, specialized instruments are fundamental for precise and rapid measurements of refraction over the visual field. We compare here two prototype instruments that measure in a few seconds the peripheral refraction in the eye with high angular resolution over a range of about ±45 deg. One instrument is based on the continuous recording of Hartmann-Shack (HS) images (HS scanner) and the other is based on the photorefraction (PR) principle (PR scanner). On average, good correlations were found between the refraction results provided by the two devices, although it varied across subjects. A detailed statistical analysis of the differences between both instruments was performed based on measurements in 35 young subjects. Both instruments have advantages and disadvantages. The HS scanner also provides the high-order aberration data, while the PR scanner is more compact and has a lower cost. Both instruments are current prototypes, and further optimization is possible to make them even more suitable tools for future visual optics and myopia research and also for different ophthalmic applications.

Fast scanning peripheral wave-front sensor for the human eye.

We designed and built a fast scanning peripheral Hartmann-Shack (HS) wave-front sensor to measure the off-axis wave-front aberrations in the human eye. The new instrument is capable of measuring the optical quality over the central 80° horizontal visual field in 1.8 seconds with an angular resolution of 1°. The subject has an open field of view without any moving elements in the line-of-sight and the head is kept in place by a head-chin rest. The same efficiency, reliability and measurement quality as the current static HS sensor were found but with much higher acquisition speed and comfort for the patients. This instrument has the potential to facilitate and improve future research on the peripheral optical quality of the eye in large groups of subjects.