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R A Applegate

Publications and source records attributed to R A Applegate.

46 records · Page 3Linked to original sources
PubMedDate not supplied

Corneal aberrations and visual performance after radial keratotomy.

BACKGROUND: Refractive surgery and videokeratography have allowed us to study the effects on visual performance of relatively large changes in corneal aberration structure induced by surgical changes in corneal shape. METHODS: We quantified in one eye of nine normal and 23 radial keratotomy patients, the area under the log contrast sensitivity function (AULCSF) and corneal first surface wavefront variance for two artificial pupil sizes (3 and 7 mm). Contrast sensitivity was measured with sine-wave gratings at six spacial frequencies. Wavefront variance was derived from videokeratographs using Zernike polynomials. RESULTS: For normals eyes there were no significant changes over time. For eyes that had radial keratotomy, there were significant pupil size-dependent changes. For the 3 mm pupil, there were significant surgery-induced changes in the corneal wavefront variance which became large (approximately 30 times preoperative values) at 7 mm. Significant correlated changes in AULCSF for the 7 mm pupil but not for the 3 mm pupil occurred immediately following surgery and remained. CONCLUSIONS: Radial keratotomy, like photorefractive keratectomy, shifts the distribution of aberrations from third order dominance (coma-like aberrations) to fourth order dominance (spherical-like aberrations). Radial keratotomy-induced aberrations and loss in contrast sensitivity are reduced with increasing clear zone diameter. Radial keratotomy induces an increase in the optical aberrations of the eye and the increase for large pupils (7 mm) but not small (3 mm) is correlated to a decrease in contrast sensitivity.

Contrast Sensitivity↗
PubMedDate not supplied

Corneal first surface optical aberrations and visual performance.

PURPOSE: Wavefront analysis has demonstrated that refractive surgery-induced corneal first surface aberrations are large, are dominated by symmetric aberrations (spherical-like aberrations), and are correlated to measures of visual performance. It is not clear whether the correlation between corneal first surface aberrations and visual performance can be generalized to other corneal conditions where large asymmetric aberrations (coma-like aberrations) may dominate the aberration structure. The purpose of the research reported here was to determine the general utility of corneal first surface wavefront analysis in predicting visual performance. METHODS: Patients were 13 normals and 78 patients with a variety of corneal conditions including surgically removed pterygia, penetrating keratoplasty, keratoconus, radial keratotomy, laser in situ keratomileusis, and others. Videokeratographs were taken for all patients and used to calculate corneal first surface wavefront variance for 3 and 7 mm pupils. Similarly, visual performance was quantified by measurements of contrast sensitivity and high and low contrast acuities through both 3 and 7 mm pupils. RESULTS: Statistically significant correlations existed between all three measures of visual performance and the corneal wavefront variance. All relationships were stronger for the 7 mm diameter-pupil condition than the 3 mm pupil. CONCLUSION: Regardless of the cause, corneas with increased wavefront variance showed a quantifiable decrease in visual performance that was pupil size dependent.

Adolescent↗
PubMedDate not supplied

Limits to vision: can we do better than nature?

Non-invasive wavefront sensing of the human eye provides the necessary information to design corrections which minimize the monochromatic optical errors of the eye beyond simple sphere (defocus) and cylinder (astigmatism). These "ideal" corrections must move with the eye, maintaining proper alignment with the eye's optics. Viable modes of correction include contact lenses, refractive surgery and intraocular lenses. Will these "ideal" corrections lead to better vision? If so, how much better? Here we explore the limits imposed by the optical and neural design of the eye. For larger pupil sizes (>3 mm diameter) "ideal" corrections improve the optical quality of the retinal image beyond the limits imposed by photoreceptor spacing. Photoreceptor spacing limits visual acuity to between 20/8 and 20/10. Correcting the higher order aberrations will provide images with higher contrast and crisper edges. When perfected, "ideal" corrections will provide for high contrast visual acuity between 20/8 and 20/10.

Contrast Sensitivity↗
PubMedDate not supplied

Anterior corneal optical aberrations induced by photorefractive keratectomy for hyperopia.

PURPOSE: Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye. METHODS: Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests. RESULTS: Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error. CONCLUSIONS: The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.

Cornea↗
PubMedDate not supplied

Schematic eye models for simulation of patient visual performance.

PURPOSE: To determine if model eyes can simulate the visual performance of normal human eyes under conditions of varying low myopic blur, pupil size, and contrast. METHODS: High and low contrast Bailey-Lovie logMAR visual acuity (VA) of three normal eyes of three subjects were measured for four artificial pupil sizes and ten levels of myopic defocus. Simulated visual acuities were then determined for three model eyes--the Indiana Eye with no spherical aberration, the Indiana Eye with average spherical aberration, and the Kooijman Eye--by generating optically aberrated VA charts for each testing condition using Visual Optics Lab software by Sarver and Associates, Inc, and having the subjects read high resolution printouts of these charts using a 3-mm pupil and optimal spectacle correction. The correlation between real VA and simulated VA was then plotted and a regression line calculated. RESULTS: Slopes for the Indiana Eye, Indiana Eye with spherical aberration, and Kooijman Eye were 0.98, 0.98, and 1.01 for high contrast, and 0.92, 0.67, and 0.75 for low contrast, respectively. The r2 values were 0.73, 0.74, and 0.77, for high contrast, and 0.69, 0.40, and 0.50 for low contrast, respectively. Under low contrast conditions the Indiana Eye VA was significantly closer to the real VA than that of the other two models (P<.0003). CONCLUSION: Visual performance can be simulated by eye models. The simple single surface Indiana Eye with no spherical aberration best modeled both high and low contrast visual acuity.

Adult↗
PubMedDate not supplied

The importance of pupil size in optical quality measurements following radial keratotomy.

This review considers the importance of pupil size when specifying the optical quality or visual performance of eyes following radical keratotomy. The experimental evidence presented includes measurements both before and after radial keratotomy of the eye's: 1) corneal curvature; 2) optical aberrations; 3) modulation transfer function; 4) visual acuity as a function of test beam entry; and 5) disability glare. Together these five lines of evidence demonstrate that pupil size is a key factor influencing both the optical quality of the eye and visual performance.

Cornea↗