Peripheral refraction in pseudophakic eyes measured by infrared scanning photoretinoscopy

Impact of Peripheral Refractive Errors in Mobility Performance

Purpose

The purpose of this study was to investigate the functional effects of peripheral refractive errors on mobility performance through a stair negotiation task.

Methods

Twenty-one young, normal sighted subjects navigated through an obstacle with steps, wearing spectacles that altered only their peripheral refraction. Lenses were used to induce positive defocus (+2 diopters [D] and +4 D), negative defocus (-2 D and -4 D), or astigmatism (+1.75 D and -3.75 D, axis 45 degrees) in the periphery. Feet trajectories were analyzed, and several gait assessment parameters were obtained. Statistical tests were conducted to determine significant performance differences between the lenses. Peripheral refraction in each subject was measured using a scanning Hartmann-Shack wavefront sensor to assess the impact of intrinsic peripheral refraction on the experiment.

Results

Statistically significant differences in performance appeared when peripheral errors were superimposed. Crossing time with respect to plano lenses increased by 6.2%, 7.6%, 19.2%, and 29.6% for the -2 D, +2 D, -4 D, and +4 D lenses, respectively (P < 0.05 in the last 3 cases). Subjects exhibited slower walking speeds, increased step count, and adopted precautionary measures. High-power positive defocus lenses had the biggest impact on performance, and differences were observed in distance to steps between induced positive and negative defocus.

Conclusions

In this laboratory-based study without an adaptation period, peripheral refractive errors affected stair negotiation, causing cautious behavior in subjects. Performance differences among types of peripheral defocus may result from magnification effects and intrinsic peripheral refraction. These results highlight the importance of understanding the effects of induced peripheral errors by myopia control and intraocular lenses.

Peripheral defocus of monofocal intraocular lenses

PURPOSE

To quantify the angular dependence of monofocal intraocular lens (IOL) power.

SETTING

Ophthalmic Biophysics Laboratory, Kallam Anji Reddy campus, L V Prasad Eye Institute, Hyderabad, India.

DESIGN

Laboratory study.

METHODS

Experiments were performed on IOLs from 2 different manufacturers (APPALENS 207, Appasamy Associates and SN60WF, Alcon Laboratories, Inc.). IOL powers ranged from 17 to 25 diopters (D). The IOLs were mounted in a fluid-filled chamber, and the on-axis and off-axis powers were measured using a laser ray tracing system over the central 3 mm zone with delivery angles ranging from -30 to +30 degrees in 5-degree increments. The position of the best focus was calculated for each IOL at each angle. The angular dependence of IOL power was compared with theoretical predictions.

RESULTS

Peripheral defocus increased significantly with increasing incidence angle and power. The peripheral defocus at ±30 degrees increased from 5.8 to 8.5 D when the power increased from 17.5 to 24.5 D for APPALENS 207 and from 4.9 to 7.4 D when the power increased from 17 to 25 D for SN60WF. The mean difference between the measured and theoretical tangential power at ±30 degrees was 0.50 ± 0.16 D for the APPALENS 207 and -0.40 ± 0.10 D for the SN60WF, independent of IOL power.

CONCLUSIONS

IOLs introduce a significant amount of peripheral defocus which varies significantly with IOL power and design. Given that peripheral defocus is related to lens power, replacement of the crystalline lens (approximately 24 D) with an IOL will produce a significant difference in peripheral defocus profile after surgery.

Peripheral Vision in Patients Following Intraocular Lens Implantation: A Systematic Review and Meta-Analysis

PURPOSE

To update the literature on peripheral optics and vision following intraocular lens (IOLs) implantation.

METHODS

We investigated how current IOLs influence peripheral visual function, peripheral optical quality, and visual perception and performance, in patients following cataract surgery. Peripheral vision is described as vision outside the central foveal region of the eye (beyond 4-5° of eccentricity). We systematically searched PubMed, Cochrane Central Register of Controlled Trials, Embase, and gray literature for relevant references. Randomized controlled trials and observational studies were eligible for inclusion. Finally, 47 studies with a total of 5963 participants were eligible for this review, of which 15 were included in the meta-analysis.

RESULTS

Regarding visual fields, the meta-analysis showed that the pooled estimate of mean deviation (MD) measured with perimetry tests (standard automated perimetry [SAP], short-wavelength automated perimetry [SWAP], and frequency doubling technology [FDT]) appears to be lower than the mean of healthy age-matched controls, regardless of IOL design. Results for pooled estimate show that localized defects (pattern standard deviation [PSD]) were higher than those in the healthy age-matched controls for FDT. We also collected evidence demonstrating that pseudophakia increases peripheral astigmatism and a myopic shift from 20° onward, leading to decreased peripheral image quality compared with that in phakic eyes. Patient-reported outcomes on peripheral vision showed a pooled score estimate of 95.19, indicating high satisfaction, and for the Steps & Stairs questions, a pooled score estimate at 0.23, indicating no to little difficulty seeing steps and stairs.

CONCLUSIONS

Peripheral image quality is degraded in eyes after cataract surgery. Nevertheless, whether this degradation leads to impaired visual function in the periphery requires further investigation.

Inverted meniscus intraocular lens as a better optical surrogate of the crystalline lens

Current intraocular lenses (IOLs) are designed to substitute the cataractous crystalline lens, optimizing focus at the fovea. However, the common biconvex design overlooks off-axis performance, leading to a reduced optical quality in the periphery of the retina in pseudophakic patients compared to the normal phakic eye. In this work, we designed an IOL to provide better peripheral optical quality, closer in that respect to the natural lens, using ray-tracing simulations in eye models. The resulting design was a concave-convex inverted meniscus IOL with aspheric surfaces. The curvature radius of the posterior surface was smaller than that of the anterior surface by a factor that depended on the IOL power. The lenses were manufactured and evaluated in a custom-built artificial eye. Images of a point source and of extended targets were directly recorded at various field angles with both standard and the new IOLs. This type of IOL produces superior image quality in the whole visual field, being a better surrogate for the crystalline lens than the commonly used thin biconvex intraocular lenses.

Peripheral vision and hazard detection with average phakic and pseudophakic optical errors

The impact of peripheral optical errors induced by intraocular lenses was evaluated by simulating the average phakic and pseudophakic image qualities. An adaptive optics system was used to simulate the optical errors in 20° nasal and inferior visual field in phakic subjects. Peripheral resolution acuity, contrast sensitivity and hazard detection were evaluated. Pseudophakic errors typical for monofocal designs had a negative effect on resolution acuity and contrast sensitivity and the hazard detection task also showed increased false positive and misses and a longer reaction time compared to phakic optical errors. The induced peripheral pseudophakic optical errors affect the peripheral visual performance and thereby impact functional vision.

Peripheral image quality in pseudophakic eyes

The purpose of this work was to evaluate peripheral image quality in the pseudophakic eye using computational, physical, and psychophysical methods. We designed and constructed a physical model of the pseudophakic human eye with realistic dimensions using a corneal phantom and a board-only camera that was pivoted around an axis that matched the anatomical center of a human retina, assuming a radius of curvature of 12 mm, while it was submersed in a 23.4 mm long water filled chamber to emulate human ocular axial length. We used this optical setup to perform direct recording of the point spread function (PSF) and the associated retinal images for a commercial intraocular lens (IOL). Additionally, psychophysical tests were carried out to investigate the impact of the off-axis astigmatism in peripheral visual performance, where spectacle-induced astigmatism simulated the pseudophakic conditions in healthy subjects. Our findings using the physical eye model confirm the existence of large amounts of astigmatism in the periphery of the pseudophakic eye. The psychophysical tests revealed a significant reduction of detection sensitivity in the peripheral visual field. The latter suggests that off-axis astigmatism in patients implanted with IOLs may have performance and safety implications for activities requiring efficient peripheral vision.

Off-axis astigmatism in the isolated chicken crystalline lens

The chicken eye was previously found to have little off-axis astigmatism which is not explained by its special corneal shape but rather by the optical properties of the crystalline lens. To learn more about lens design, we studied off-axis astigmatism in the chicken lens in situ and compared it to a glass lens of similar power but with homogenous refractive index. After euthanasia, enucleated eye balls were cut in the equatorial plane right behind the scleral ossicles. The anterior segment was placed in a water-filled chamber. Several thin laser beams were projected in two perpendicular meridians through the lens under various eccentricities and the focal lengths were determined. Off-axis astigmatism across the horizontal visual field was determined as the differences in power in the two meridians. The same procedure was used for the glass lens. On-axis, the chicken crystalline lens had slightly more power in the vertical than in the horizontal meridian (-2.8±0.7D (SEM)). Astigmatism flipped sign and increased with eccentricity to reach +6.1±2.1D (SEM) at 33.5deg off-axis, as expected from off-axis astigmatism. Even though this value appears high, it was still 2.5 times lower than in the glass lens. A ZEMAX model of a lens with a homogeneous index and with surface profiles taken of the natural chicken lens revealed even higher levels of off-axis astigmatism. Obviously, the natural chicken lens displays much less off-axis astigmatism than a glass lens with similar power. Since its shape does not explain the low off-axis astigmatism, it must be due to a refined internal refractive index structure.

Eye shape using partial coherence interferometry, autorefraction, and SD-OCT

PURPOSE

Peripheral refraction and retinal shape may influence refractive development. Peripheral refraction has been shown to have a high degree of variability and can take considerable time to perform. Spectral domain optical coherence tomography (SD-OCT) and peripheral axial length measures may be more reliable, assuming that the retinal position is more important than the peripheral optics of the lens/cornea.

METHODS

Seventy-nine subjects' right eyes were imaged for this study (age range, 22 to 34 years; refractive error, -10 to +5.00). Thirty-degree SD-OCT (Spectralis, Heidelberg Engineering, Heidelberg, Germany) images were collected in a radial pattern along with peripheral refraction with an autorefractor (Shin-Nippon Autorefractor) and peripheral axial length measurements with partial coherence interferometry (IOLMaster, Zeiss). Statistics were performed using repeated-measures analysis of variance in SPSS (IBM, Armonk, NY), Bland-Altman analyses, and regression. All measures were converted to diopters to allow direct comparison.

RESULTS

Spectral domain OCT showed a retinal shape with an increased curvature for myopes compared with emmetropes/hyperopes. This retinal shape change became significant around 5 degrees. The SD-OCT analysis for retinal shape provides a resolution of 0.026 diopters, which is about 10 times more accurate than using autorefraction (AR) or clinical refractive techniques. Bland-Altman analyses suggest that retinal shape measured by SD-OCT and the partial coherence interferometry method were more consistent with one another than either was with AR.

CONCLUSIONS

With more accurate measures of retinal shape using SD-OCT, consistent differences between emmetropes/hyperopes and myopes were found nearer to the fovea than previously reported. Retinal shape may be influenced by central refractive error, and not merely peripheral optics. Partial coherence interferometry and SD-OCT appear to be more accurate than AR, which may be influenced by other factors such as fixation and accommodation. Autorefraction does measure the optics directly, which may be a strength of that method.