Stiles-Crawford Effect Research Articles

Visual Axis and Stiles-Crawford Effect Peak Show a Positional Correlation in Normal Eyes: A Cohort Study.

The purpose of this study was to locate the visual axis and evaluate its correlation with the Stiles-Crawford effect (SCE) peak. Ten young, healthy individuals (20 eyes) were enrolled. An optical system was developed to locate the visual axis and measure SCE. To locate the visual axis, 2 small laser spots at 450 nm and 680 nm were co-aligned and delivered to the retina. The participants were asked to move a translatable pinhole until these spots were perceived to overlap each other. The same system assessed SCE at 680 nm using a bipartite, 2-channel (reference and test) Maxwellian-view optical system. The peak positions were estimated using a two-dimensional Gaussian fitting function and correlated with the visual axis positions. Both the visual axis (x = 0.24 ± 0.35 mm, y = -0.16 ± 0.34 mm) and the SCE peak (x = 0.27 ± 0.35 mm, y = -0.15 ± 0.31 mm) showed intersubject variability among the cohort. The SCE peak positions were highly correlated in both the horizontal and vertical meridians to the visual axes (R2 = 0.98 and 0.96 for the x and y coordinates, respectively). Nine of the 10 participants demonstrated mirror symmetry for the coordinates of the visual axis and the SCE peak between the eyes (R2 = 0.71 for the visual axis and 0.76 for the SCE peak). The visual axis and SCE peak locations varied among the participants; however, they were highly correlated with each other for each individual. These findings suggest a potential mechanism underlying the foveal cone photoreceptor alignment.

Mitochondria in cone photoreceptors act as microlenses to enhance photon delivery and confer directional sensitivity to light.

Mammalian photoreceptors aggregate numerous mitochondria, organelles chiefly for energy production, in the ellipsoid region immediately adjacent to the light-sensitive outer segment to support the high metabolic demands of phototransduction. However, these complex, lipid-rich organelles are also poised to affect light passage into the outer segment. Here, we show, via live imaging and simulations, that despite this risk of light scattering or absorption, these tightly packed mitochondria “focus” light for entry into the outer segment and that mitochondrial remodeling affects such light concentration. This “microlens”-like feature of cone mitochondria delivers light with an angular dependence akin to the Stiles-Crawford effect (SCE), providing a simple explanation for this essential visual phenomenon that improves resolution. This new insight into the optical role of mitochondria is relevant for the interpretation of clinical ophthalmological imaging, lending support for the use of SCE as an early diagnostic tool in retinal disease.

Invited Session II: Retinal mechanisms mediating vision: Mitochondria in cone photo-receptors act as microlenses to enhance photon delivery and confer directional sensitivity to light

Mitochondria are cellular organelles chiefly intended for energy production. Mammalian photoceptors aggregate numerous mitochondria in the ellipsoid region immediately adjacent to their light-sensitive outer segments to support the high metabolic demands of phototransduction. However, these complex, lipid-rich organelles are also poised to affect the passage of light into the outer segment, an essential step in the transduction of physical energy into cellular signals. Here we show, via live-imaging and computational modeling, that despite this risk of light scattering or absorption, such tightly packed mitochondria concentrate light for entry into the outer segment. Intriguingly, this "microlens"-like feature of cone mitochondria delivers light with an angular dependence akin to the Stiles-Crawford effect (SCE), providing a simple explanation for this essential visual phenomenon that improves resolution. Given the pivotal role that photoreceptor mitochondria play in multiple retinal degenerative diseases, this new insight into their optical properties provides critical information for the accurate interpretation of non-invasive ophthalmic imaging results and lends support for using SCE as an early diagnostic tool.

Planar polarity in primate cone photoreceptors: a potential role in Stiles Crawford effect phototropism

Human cone phototropism is a key mechanism underlying the Stiles-Crawford effect, a psychophysiological phenomenon according to which photoreceptor outer/inner segments are aligned along with the direction of incoming light. However, such photomechanical movements of photoreceptors remain elusive in mammals. We first show here that primate cone photoreceptors have a planar polarity organized radially around the optical center of the eye. This planar polarity, based on the structure of the cilium and calyceal processes, is highly reminiscent of the planar polarity of the hair cells and their kinocilium and stereocilia. Secondly, we observe under super-high resolution expansion microscopy the cytoskeleton and Usher proteins architecture in the photoreceptors, which appears to establish a mechanical continuity between the outer and inner segments. Taken together, these results suggest a comprehensive cellular mechanism consistent with an active phototropism of cones toward the optical center of the eye, and thus with the Stiles-Crawford effect.

The integrated Stiles-Crawford effect: understanding the role of pupil size and outer-segment length in foveal vision

The integrated Stiles-Crawford effect: understanding the role of pupil size and outer-segment length in foveal vision

Subjective measurement of the Stiles-Crawford effect of the first kind with variation in accommodation.

To measure the Stiles-Crawford effect of the first kind (SCE-I), corresponding to central vision, with innovative technology to evaluate changes in the directionality and photoreceptor alignment with accommodation. A uniaxial Maxwellian system (spot size in pupil 0.5mm diameter) was employed, incorporating a spatial light modulator to flicker at 2Hz between two 2.3° fields corresponding to test (peripheral pupil) and reference (pupil centre) positions. Participants determined thresholds at 13 positions along the horizontal pupil meridian by indicating if the test field was brighter or dimmer than the reference field. Thresholds were determined by a staircase procedure after four reversals at each pupil location. After pupil dilation, seven emmetropes were tested at 0 D to 6 D accommodation stimulus levels in 2 D intervals. Data were fit by the Gaussian function, both when the fits were unforced or forced to pass through the sensitivity expected for the reference point. Directionality (ρ) and peak location values were determined for unforced and forced fits. Regression slopes for ρ as a function of accommodation stimulus were not significant. There was a tendency for to shift temporally with increasing accommodation across the 6 D stimulus range. This was not significant for regression fitting (-0.059mm/D, R2 =0.06, p=0.20), but a paired t-test for 0 and 6 D stimuli showed a weakly significant change of 0.62mm (p=0.05). The differences between the two fitting approaches were small and non-significant. Directionality did not change with accommodation, but the pupil peak location showed a significant temporal shift of approximately 0.62mm with 6 D accommodation stimulus. It is possible that substantial changes in the directionality and a shift in the direction of peak location might occur at very high levels of accommodation.

Subjective measurement of the Stiles-Crawford effect with different field sizes.

The Stiles-Crawford effect of the first kind (SCE) is the phenomenon in which light entering the eye near the center of the pupil appears brighter than light entering near the edge. Previous investigations have found an increase in the directionality (steepness) of the effect as the testing location moves from the center of the visual field to parafoveal positions, but the effect of central field size has not been considered. The influence of field size on the SCE was investigated using a uniaxial Maxwellian system in which stimulus presentation was controlled by an active-matrix liquid crystal display. SCE directionality increased as field size increased from 0.5° to 4.7° diameter, although this was noted in four mild myopes and not in two emmetropes. The change with field size was supported by a geometric optics absorption model.

Assessing Photoreceptor Status in Retinal Dystrophies: From High-Resolution Imaging to Functional Vision

PurposeTo describe the value of integrating phenotype/genotype data, disease staging, and evaluation of functional vision in patient-centered management of retinal dystrophies.Methods(1) Cross-sectional structure-function and retrospective longitudinal studies to assess the correlations between standard fundus autofluorescence (FAF), optical coherence tomography, visual acuity (VA), and perimetry (visual field [VF]) examinations to evaluate photoreceptor functional loss in a cohort of patients with rod-cone dystrophy (RCD); (2) flood-illumination adaptive optics (FIAO) imaging focusing on photoreceptor misalignment and orientation of outer segments; and (3) evaluation of the impact of visual impairment in daily life activities, based on functional (visual and mobility) vision assessment in a naturalistic environment in visually impaired subjects with RCD and subjects treated with LuxturnaⓇ for RPE65-related Leber congenital amaurosis before and after therapy.ResultsThe results of the cross-sectional transversal study showed that (1) VA and macular sensitivity were weakly correlated with the structural variables; and (2) functional impairment (VF) was correlated with reduction of anatomical markers of photoreceptor structure and increased width of autofluorescent ring. The dimensions of the ring of increased FAF evolved faster. Other criteria that differed among groups were the lengths of the ellipsoid zone, the external limiting membrane, and the foveal thickness. FIAO revealed a variety of phenotypes: paradoxical visibility of foveal cones; heterogeneous brightness of cones; dim, inner segment–like, and RPE-like mosaic. Directional illumination by varying orientation of incident light (Stiles-Crawford effect) and the amount of side illumination (gaze-dependent imaging) affected photoreceptor visibility. Mobility assessment under different lighting conditions showed correlation with VF, VA, contrast sensitivity (CS), and dark adaptation, with different predictive values depending on mobility study paradigms and illumination level. At high illumination level (235 lux), VF was a predictor for all mobility performance models. Under low illumination (1 and 2 lux), VF was the most significant predictor of mobility performance variables, while CS best explained the number of collisions and segments. In subjects treated with LuxturnaⓇ, a very favorable impact on travel speed and reduction in the number of collisions, especially at low luminance, was observable 6 months following injection, in both children and adults.ConclusionsOur results suggest the benefit of development and implementation of quantitative and reproducible tools to evaluate the status of photoreceptors and the impact of both visual impairment and novel therapies in real-life conditions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Testing the effect of ocular aberrations in the perceived transverse chromatic aberration.

We have measured the ocular transverse chromatic aberration (TCA) in 11 subjects using 2D-two-color Vernier alignment, for two pupil diameters, in a polychromatic adaptive optics (AO) system. TCA measurements were performed for two pupil diameters: for a small pupil (2-mm), referred to as 'optical TCA' (oTCA), and for a large pupil (6-mm), referred to 'perceived TCA' (pTCA). Also, the TCA was measured through both natural aberrations (HOAs) and AO-corrected aberrations. Computer simulations of pTCA incorporated longitudinal chromatic aberration (LCA), the patient's HOAs measured with Hartmann-Shack, and the Stiles-Crawford effect (SCE), measured objectively by laser ray tracing. The oTCA and the simulated pTCA (no aberrations) were shifted nasally 1.20 arcmin and 1.40 arcmin respectively. The experimental pTCA (-0.27 arcmin horizontally and -0.62 vertically) was well predicted (81%) by simulations when both the individual HOAs and SCE were considered. Both HOAs and SCE interact with oTCA, reducing it in magnitude and changing its orientation. The results indicate that estimations of polychromatic image quality should incorporate patient's specific data of HOAs, LCA, TCA & SCE.

ATTENUATION OUTER RETINAL BANDS ON OPTICAL COHERENCE TOMOGRAPHY FOLLOWING MACULAR EDEMA: A Possible Manifestation of Photoreceptor Misalignment.

Macular edema is a common retinal disease which may leave important anatomical and functional sequelaes. Directional fundus imaging consists of comparing on- and off-axis images to reveal angle-dependent reflectance properties of fundus structures, which may be related to misaligned photoreceptors. Here, we analyzed directional optical coherence tomography (OCT) and flood-illumination adaptive optics ophthalmoscopy images to detect evidence of misaligned photoreceptors following macular edema. Transversal, observational study. Nine patients having recovered a normal macular profile after macular edema due to retinal vein occlusion were included. For each patient, a reference OCT scan (i.e., with the incident beam normal to the fovea) was acquired, and off-axis scans were then acquired by laterally shifting the entry pupil. In addition, in four of these eyes, directional adaptive optics ophthalmoscopy documented the directional variations of cone metrics. Included patients comprised two women and seven men (age range, 19-76 years). Reference OCT scans showed patchy attenuation of the cone outer segment tips and to a lesser extent of the inner segment/outer segment lines in all, but two eyes; these. Increased intensity of the cone outer segment tips and inner segment/outer segment lines could be observed on off-axis scans. Accordingly, fusion images showed 66% average reduction of the length of cone outer segment tips attenuation. In two cases, although reference scans showed continuity of outer bands, focal attenuation was evidenced in off-axis images. Directional adaptive optics ophthalmoscopy imaging showed a strong directional variability of cone counts in these areas, ranging from near absence to roughly two-third of reference values. In each case, directional variations of cone counts paralleled those of the reflectance of outer bands. After macular edema, focal attenuations of the inner segment/outer segment and of the cone outer segment tips lines may be present on OCT. These areas may show a strong directional variability by both OCT and adaptive optics ophthalmoscopy, suggesting that misaligned photoreceptor outer segments contribute to such features. The evaluation of outer retinal damage following macular edema should therefore take into account the optical Stiles-Crawford effect to disambiguate missing from misaligned cones.

Directional light-capture efficiency of the foveal and parafoveal photoreceptors at different luminance levels: an experimental and analytical study.

A gradual drop in visibility with obliquely incident light on retinal photoreceptors is namely described by the Stiles-Crawford effect of the first kind and characterized by a directionality parameter. Using a digital micromirror device in a uniaxial flicker system, here we report on variations of this effect with luminance levels, wavelengths within the visible and near-infrared spectrum and retinal regions ranging from the fovea to 7.5° parafoveal. Results show a consistent directionality in mesopic and photopic conditions. Higher directionality is measured for longer wavelengths, and a decrease with retinal eccentricity is observed. Results are discussed in relation to an absorption model for the visual pigments taking the outer-segment packing and thickness of the neural retina into account. Good correspondence is found without enforcing photoreceptor waveguiding.

Do Müller Cells Act as Optical Fibers in the Primate Retina?

To examine whether Müller cells in the primate retina act as optical light guides. In the literature, it has been suggested that Müller cells in the primate retina act as optical fibers. I have conducted a survey of the literature for papers in support of or refuting this assumption. I show that neither histology, nor the direct observation of photoreceptors, nor the entoptic observation of the retina agree with the assumption that Müller cells in the human retina act as optical waveguides. I confirm the classic view that the inner/outer segments act together as optical waveguides and that they are the origin of the Stiles-Crawford effect of the first kind.

Adaptation to Brightness Perception in Patients Implanted With a Small Aperture

PurposeSmall apertures are successfully used to extend depth of focus in presbyopic patients implemented either as corneal inlays or intraocular lenses. The use of small apertures reduces retinal illuminance. In this study, we quantify the relative perceived brightness in the 2 eyes of patients implanted monocularly with a small-aperture inlay.DesignProspective case series.MethodsWe used a binocular adaptive optics vision simulator to determine the relative perceived brightness. Four patients implanted monocularly with the KAMRA corneal inlay (1.6 mm) and a group of control subjects participated in the study. The projected pupil on the eye implanted with the inlay alternated in diameter between 0 and 2.5 mm (effective 1.6 mm) to eliminate potential for light to project around the periphery of the inlay while the corresponding fellow eye projected pupil alternated between 0 and 3.0 mm or 0 and 4.0 mm at a frequency of 1 Hz. Alternation on both eyes was synchronized so that only 1 eye at a time had a nonblocked pupil. At equal transmittance, a flickering was perceived. Patients' task consisted of modifying the transmittance of the pupil corresponding to the fellow eye until the perceived flickering, owing to the different perceived brightness, was minimized. This equalizing transmittance (ET) value indicates the relative perceived brightness.ResultsIn the KAMRA's patients, ET was found to be greater than expected considering the difference in pupil sizes and the Stiles-Crawford effect, showing an enhanced a greater brightness perception in the eye with the small aperture in comparison with the fellow eye. Compared with the control subjects, this difference was on average bigger by a factor of ×1.42.ConclusionsPatients implanted with the small-aperture corneal inlay exhibited an enhanced brightness perception with the eye implanted, in comparison with their untreated fellow eye. The amount of this increase is much larger than what could be expected owing to the Stiles-Crawford effect and was probably attributable to a neural adaptation process. This phenomenon could explain a reported equalization of brightness between eyes in patients with unilateral inlays and implies that the expected reduction of brightness may have a less significant impact on these patients, as expected.

Analysing the impact of myopia on the Stiles-Crawford effect of the first kind using a digital micromirror device.

Photoreceptor light acceptance is closely tied to the Stiles-Crawford effect of the first kind (SCE-I). Whether the SCE-I plays a role in myopic development remains unclear although a reduction in directionality has been predicted for high myopia. The purpose of this study is to analyse the relationship between foveal SCE-I directionality, axial eye length, and defocus for emmetropic subjects wearing ophthalmic trial lenses during psychophysical measurements and for myopic subjects with their natural correction. A novel uniaxial flicker system has been implemented making use of a Digital Micromirror Device (DMD) to flicker between a 2.3 visual degrees circular reference and a set of circular test patterns in a monocular Maxwellian view at 0.5 Hz. The brightness of the test is adjusted by the duty cycle of the projected light to an upper limit of 22727Hz. The wavelength and bandwidth are set by a tuneable liquid-crystal filter centred at 550 nm. A total of four measurement series for 11 pupil entrance points have been realized for the right eye of 6 emmetropic and 10 myopic subjects whose pupils were dilated with tropicamide. Five of the emmetropic subjects wore ophthalmic trial lenses in the range of -3 to +9 dioptres to mimic hyperopic to highly myopic vision and resulting visibility plots have been fitted to a Gaussian SCE-I function. In turn, the myopic subjects wore their natural correction during the analysis of the SCE-I. All subjects had their axial eye length determined with an ultrasound device. A SCE-I directionality parameter in the range of 0.03 to 0.06/mm2 was found for the emmetropic subjects with corrected vision in fair agreement to values in the literature. The results also revealed a marked reduction in directionality in the range from 16% to 30% with every 3 dioptre increase of simulated myopia, as well as a 10% increased directionality in simulated hyperopic eyes. For both emmetropic and myopic subjects, a decrease in directionality with increase in axial length was found in agreement with theoretical expectations. The study confirms a clear link between SCE-I directionality, uncorrected defocus, and axial eye length. This may play a role for emmetropization and thus myopic progression as cone photoreceptors capture light from a wider pupil area in elongated eyes due to a geometrical scaling.

Volumetric integration model of the Stiles-Crawford effect of the first kind and its experimental verification.

The integrated Stiles-Crawford function is commonly used as apodization model for vision through the natural eye pupil. However, this method does not account for possible effects related to the retinal thickness, the large length-to-diameter aspect ratio of the photoreceptors, or the use of nonMaxwellian illumination. Here, we introduce a geometrical optics model to calculate the fraction of overlap between light at the retina and the photoreceptor outer segments where absorption triggers vision. The model, which does not account for photoreceptor waveguiding, is discussed for both Maxwellian and nonMaxwellian illumination. The integrated Stiles-Crawford effect is analyzed experimentally with a uniaxial pupil-size flicker methodology and we find that the psychophysical measurements match better to the geometrical optics predictions than direct integration of a Stiles-Crawford function.

Factors Affecting Mydriasis-Free Flicker ERGs Recorded With Real-Time Correction for Retinal Illuminance: Study of 150 Young Healthy Subjects.

A small, full-field flicker electroretinogram (ERG) recording system was recently developed to record flicker ERGs without mydriasis (RETeval). The device delivers a stimulus with constant retinal illuminance by adjusting the retinal luminance to compensate for changes in the pupillary area. The purpose of this study was to determine what factors affect the fundamental components of the flicker ERGs recorded by RETeval in young healthy subjects. Flicker ERGs were recorded with the RETeval system from 150 eyes of 150 young healthy subjects (age, 20-29 years). Univariate and multivariate linear regression analyses were performed to identify the factors that affected the implicit times and amplitudes of the fundamental component of the flicker ERGs. The independent variables included age, sex, refractive error, axial length, and pupillary area. Multivariate regression analyses indicated that a longer axial length (P = 0.03) and larger pupillary area (P = 0.008) were independent factors that were significantly associated with longer implicit times of the fundamental component of the flicker ERGs. Multivariate regression analyses also showed that the female sex (P = 0.03) was an independent factor, which was significantly associated with larger amplitude fundamental component of the flicker ERGs. These results indicate that the fundamental components of the RETeval flicker ERGs are significantly affected by the axial length, pupillary area, and sex of young healthy subjects. The results also suggest that it would be better to compensate for the Stiles-Crawford effect when flicker ERGs are recorded with natural pupils.

Compensative Retinal Response to Departures from Unit Contrast and Unit Spot-Size Ratio

The objective of this work is to show how the retina responds to the loss of luminance efficiency due to increasing departure from either unit contrast or unit spot-size ratio in a compensative fashion. The methods adopted are two-wave interference and the single mode wave guiding of a photoreceptor cone. A correlation is established between loss of luminance efficiency due to oblique incidence and contrast in the interference pattern. Similarly, a relation between the fraction of the power that is not able to be coupled to a cone due to the peripheral entry of light and the spot-size ratio departure is developed. The findings are that due to maximum departure from unit contrast, the retinal response takes the traditional Stiles- Crawford route, but with no departure the Stiles-Crawford Effect of the first kind (SCE I) becomes totally irrelevant for the retina and for intermediate situations (between unit and zero contrast) the retinal response is controlled by a modified SCE I weakened proportionate to the contrast of the interference pattern on the retina. Likewise, when the incident spotsize and the waveguide mode spot-size match, the spotsize ratio is unity, departure is zero, the coupling of power is 100% and visibility loss is zero. But with gradual enhancement in the spot-size ratio departure, the visibility loss also increases. Again, a visibility loss of 90 % corresponds to a departure of either 6-fold or 1/6-fold (equivalent to a pupil entry point of 4 mm). This suggests that a pupil entry point of 3.5 mm may point to a loss of 70-80 %, a result reached with departure from contrast also. This way of correlating the retinal response to either contrast or spot-size ratio has the advantage of employing them as potential biomarkers for early detection of diseases affecting the photoreceptors.

Uniaxial flicker analysis of the psychophysical Stiles–Crawford effects

Purpose: We report on a semi-automated system for frequency analysis of the Stiles–Crawford effect of the first kind (SCE-I) using flicker methodology designed to gain insight into the temporal dynamics of the perceived visibility for alternating pupil entrance points. We describe the system and its calibration in detail and discuss psychophysical measurement data obtained for the two authors. Methods: A uniaxial system is used for SCE-I characterization of two emmetropic subjects as a function of flicker frequency for narrow wavelength bands chosen in the range of 450–700 nm using a fibre-guided tungsten–halogen lamp as light source. The flicker is realized using two orthogonally mounted galvanometric scanning mirrors that allow linear trajectories at any angle across the pupil. A fast tuneable liquid-crystal neutral density filter is used for brightness adjustment and another liquid-crystal filter is used for wavelength adjustment at each pupil point allowing simultaneous hue-shift determination for the Stiles–Crawford effect of the second kind (SCE-II). Results: Validation of the system is realized with a CCD camera, a spectrometer and a powermeter, and the data obtained are used in the software to calibrate all subsequent human subject measurements. The psychophysical data obtained show a strong frequency dependence of the Gaussian SCE-I with a characteristic directionality parameter, ρ, that is found to increase from 0.03 to 0.06/mm2 with flicker in the range of 1–10 Hz. The simultaneously determined hue shift could not be determined beyond 1 Hz due to the longer time required for a subjective determination. Conclusion: We have reported on a fast uniaxial system for temporal characterization of the SCE-I. The psychophysical results obtained show that accurate specification of frequency in flicker analysis is mandatory when comparing SCE-I visibility and directionality curves obtained with those obtained using quasi-static bipartite fields. A uniaxial design offers unique advantages over that of common two-channel systems by completely eliminating spectral errors or brightness differences in the two branches that otherwise will impose on those of the visual system and degrade the psychophysical data. Future work with more subjects will be used to narrow the uncertainty and the causes of the effects observed.

VERY EARLY DISEASE MANIFESTATIONS OF MACULAR TELANGIECTASIA TYPE 2.

To report very early morphologic and functional alterations in patients with macular telangiectasia type 2. Patients with asymmetric disease manifestations, in whom retinal alterations characteristic for macular telangiectasia type 2 were present in one but not in the apparently unaffected fellow eye, underwent multimodal imaging and functional testing (microperimetry, visual acuity, reading ability, Amsler test). Fellow eyes not allowing the diagnosis of macular telangiectasia type 2 based on hitherto diagnostic standards consistently showed a severely reduced directional cone reflectance (Stiles-Crawford effect). Optical coherence tomography revealed an asymmetric configuration of the foveal pit with focal temporal thinning most pronounced at 1° eccentricity. Topographically related, macular pigment optical density was reduced in a small wedge-shaped temporal paracentral sector, resulting in an increased signal on fundus autofluorescence and fluorescein angiography imaging. No functional deficits were detectable in fellow eyes. Haidinger brushes were perceived in the fellow eye but not in the affected index eye with pronounced loss of macular pigment. Specific morphologic alterations precede vascular alterations and functional deficits in macular telangiectasia type 2. The described alterations indicate a primarily degenerative process with a secondary retinal vascular phenotype, and may be helpful for early identification of patients and affected family members.

Custom selection of aspheric intraocular lens in eyes with previous hyperopic corneal surgery

To determine the optimum amount of spherical aberration in intra-ocular lenses (IOLs) to maximize optical quality in eyes with previous hyperopic corneal surgery. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas. Theoretical simulation study. The amount of spherical aberration in the IOL was varied to produce residual ocular spherical aberration ranging from -0.50 to +0.50 μm. With the use of the Zernike Tool Program, the polychromatic point-spread function with Stiles-Crawford effect was calculated for 6.0 mm and 4.0 mm pupils and defocus of 0.00 diopter (D), -0.50 D, and +0.50 D. The IOL spherical aberration at which maximum image quality was achieved was determined. Stepwise multiple regression analysis was performed to assess the predictors of optimum IOL spherical aberration. Aspheric IOL implantation was simulated in 106 eyes of 80 patients; ages ranged from 40 to 59 years. With 0.00 D, -0.50 D, and +0.50 D defocus, respectively, the ranges of 25th to 75th percentiles of the optimum IOL spherical aberration were -0.12 to +0.20 μm, +0.10 to +0.42 μm, and -0.35 to -0.03 μm for the 6.0 mm pupil and -0.14 to +0.26 μm, +0.41 to +0.86 μm, and -0.74 to -0.24 μm for the 4.0 mm pupil. The amount of optimum IOL spherical aberration could be predicted on the basis of other higher-order aberrations (HOAs) of the cornea with multiple correlation coefficients up to 0.98. The amount of IOL spherical aberration producing the best image quality in eyes with previous hyperopic corneal surgery varied widely and could be predicted on the basis of the full spectrum of corneal HOAs. Supported in part by an unrestricted grant from Research to Prevent Blindness, New York, New York. No author has a financial or proprietary interest in any material or method mentioned.