Toshifumi Mihashi

Compensation of corneal horizontal/vertical astigmatism, lateral coma, and spherical aberration by internal optics of the eye.

Both the anterior surface of the cornea and the internal optics (the posterior cornea, crystalline lens) contribute to the aberration of a wavefront passing through the eye. Artal, Guirao, Berrio, and Williams (2001) reported that the wavefront aberrations produced by the internal optics offset, or compensate for, the aberrations produced by the cornea to reduce ocular wavefront aberrations. We have investigated the wavefront aberrations of the cornea, internal optics, and complete eye on both the population and individual level to determine which aberrations are compensated and probable paths leading to that compensation. The corneal and ocular aberrations of 30 young subjects at relaxed accommodation were measured with the Topcon Wavefront Analyzer, which simultaneously measures refraction, corneal topography (videokeratoscope), and wavefront aberrations (Hartmann-Shack sensor). We found strong evidence for compensation of horizontal/vertical (H/V) astigmatism (Zernike term Z5) lateral coma (Z8) and spherical aberration (Z12). H/V astigmatism compensation is scaled for each individual, suggesting that it is actively determined by a fine-tuning process. Spherical aberration shows no individual compensation, suggesting that is a passive result of genetically determined physiology. Lateral coma shows individually scaled compensation, some of which may be attributable to eccentricity of the fovea.

Wavefront aberrations measured with Hartmann-Shack sensor in patients with keratoconus.

OBJECTIVE To compare the ocular wavefront aberrations of normal and keratoconic eyes and to describe the characteristics of the higher-order aberrations in eyes with keratoconus. DESIGN Prospective case control and observational study. PARTICIPANTS Thirty-five keratoconic eyes and thirty-eight normal controls. METHODS Higher-order aberrations in refraction were measured with a wavefront sensor, and those aberrations resulting from the cornea were evaluated by videokeratographic data. MAIN OUTCOME MEASURES Coma-like (S(3 + 5)), spherical-like (S(4 + 6)), and total (S(3 + 4 + 5 + 6)) higher-order aberrations in both refraction and the cornea. RESULTS The mean +/- standard deviation of S(3 + 5) (1.88 +/- 1.16), S(4 + 6) (0.70 +/- 0.55), and S(3 + 4 + 5 + 6) (2.03 +/- 1.23) in refraction (6-mm diameter, root mean square, micro m) were significantly higher in the keratoconic eyes than in normal controls (0.26 +/- 0.10, 0.19 +/- 0.10, 0.34 +/- 0.11, respectively; Mann-Whitney U test, P = 0.001). Coma-like aberrations were 2.32 times larger than spherical-like aberrations in keratoconic eyes. CONCLUSIONS The increase of ocular higher-order aberrations in keratoconic eyes results from an increase of corneal higher-order aberrations. Coma-like aberrations were dominant compared with spherical-like aberrations in keratoconic eyes. Wavefront sensing will enable us not only to evaluate the quality of vision but also to differentiate keratoconic eyes from normal eyes by analyzing the characteristics of the higher-order aberrations.

Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis

OBJECTIVE To assess the relation between magnitude of refractive correction and changes in higher order wavefront aberrations of the cornea after laser in situ keratomileusis. DESIGN Prospective, consecutive, nonrandomized comparative trial (self-controlled). PARTICIPANTS One hundred eyes of 53 patients with myopia (-2.0 to -13.0 diopters) were included. INTERVENTION Laser in situ keratomileusis was performed. Videokeratography measurements were conducted before and 1 month after surgery. MAIN OUTCOME MEASURES The videokeratography data were used to calculate the higher order wavefront aberrations of the cornea for both small (3 mm) and large (6 mm) pupils. RESULTS For a 3-mm pupil, the surgery significantly increased coma-like (2.4 +/- 1.3-fold, P < 0.001, paired t test) and spherical-like (1.8 +/- 0.9-fold, P < 0.001) aberrations. For a 6-mm pupil, both coma-like (4.4 +/- 3.3-fold, P < 0.001) and spherical-like (9.4 +/- 5.2-fold, P < 0.001) aberrations were significantly increased by surgery. The amount of achieved correction showed significant correlations with the changes in coma-like (Pearson correlation coefficient r = 0.446, P < 0.001) and spherical-like (r = 0.348, P < 0.001) aberrations for a 3-mm pupil, and coma-like (r = 0.566, P < 0.001) and spherical-like (r = 0.693, P < 0.001) aberrations for a 6-mm pupil. The eyes that lost 2 or more lines of baseline spectacle-corrected visual acuity showed significantly larger induced increases in coma-like (P = 0.003, Mann-Whitney U test) and spherical-like (P = 0.009) aberrations for a 3-mm pupil than those that either improved or remained within 1 line of spectacle-corrected visual acuity CONCLUSIONS Laser in situ keratomileusis, performed using the current algorithms, increases higher order wavefront aberrations of the cornea, dependent on the amount of refractive correction.

Effect of tear film break-up on higher-order aberrations measured with wavefront sensor.

PURPOSE To investigate whether optical wavefront aberrations vary with tear film break-up. DESIGN Observational case series. METHODS Higher-order aberrations were examined for 20 eyes of 20 normal subjects with a Hartmann-Shack wavefront sensor before and after tear film break-up. RESULTS Higher-order aberrations for photopic vision (central 4 mm diameter) after tear film break-up increased 1.44 fold compared to higher-order aberrations before tear film break-up (P =.001, paired t-test). Higher-order aberrations after tear film break-up for scotopic vision (central 6 mm diameter) were also 1.23 times higher than those before break-up (P =.005, paired t-test). CONCLUSION Wavefront sensing enabled us to evaluate the induced irregular astigmatism caused by tear film break-up quantitatively. Wavefront aberrations should be measured carefully to avoid the effects of tear film break-up, especially in wavefront-guided refractive surgery.

Wavefront Analysis in Eyes With Nuclear or Cortical Cataract

PURPOSE To compare the higher-order aberrations of the oculus (whole eye) and cornea in eyes with mild cortical or nuclear cataract and to estimate the effect of ocular higher-order aberrations on the loss of contrast sensitivity using wavefront analysis. DESIGN Observational case series. METHODS Six eyes of four patients with mild nuclear cataract, 18 eyes of 14 patients with mild cortical cataract, and nine eyes of nine normal patients were examined. Wavefront aberrations of the oculus and cornea for central 6 mm diameter were measured using the Hartmann-Shack (HS) aberrometer. Higher-order aberrations were calculated with Zernike polynomials up to sixth order. The relationship between average lens density (ALD) measured by the Scheimpflug camera and the ocular total higher-order aberration (OTHA) was investigated. The relationship between contrast sensitivity (CS) and the OTHA or ALD was also examined. RESULTS The OTHA was significantly larger in cataracts compared with normal subjects, while corneal total higher-order aberration did not differ between cataracts and normal subjects. The polarity of spherical aberration was negative in all eyes with nuclear cataract while positive in all eyes with cortical cataract. The correlation between ALD and OTHA was not significant in eyes with cataracts. The CS highly correlated with OTHA while it moderately correlated with ALD. CONCLUSIONS The HS aberrometer is useful to objectively evaluate the deterioration of images in eyes with mild cataract and it revealed that the polarity of spherical aberration was different between nuclear and cortical cataract. It was also suggested that in mild nuclear or cortical cataract, not only light scattering, but also optical aberration of the lens contributes to the loss of contrast sensitivity.

Wavefront analysis of higher-order aberrations in patients with cataract ☆

Purpose: To determine local refractive changes and higher‐order aberrations in patients with nuclear or cortical cataract. Setting: Osaka University Medical School, Osaka, Japan. Methods: Wavefront analysis of both ocular and corneal aberrations was performed with the Hartmann‐Shack aberrometer in 2 patients, a 22‐year‐old woman with bilateral developmental nuclear cataract and a 68‐year‐old woman with mild bilateral cortical cataract. Results: Case 1 showed a delay in the wavefront that caused a myopic shift in the central pupillary area in both eyes, associated with the nuclear cataract. The spherical‐like aberration (right eye, 36%; left eye, 21%) was greater than the coma‐like aberration in both eyes. Case 2 showed an advancement of the wavefront that caused a hyperopic shift, especially in the lower temporal pupillary area, that was associated with the cortical cataract. The coma‐like aberration (right eye, 63%; left eye, 52%) was greater than the spherical‐like aberration in both eyes. The polarity of the third‐order spherical aberration was negative in Case 1 and positive in Case 2. Corneal higher‐order aberrations were small and had a different distribution than ocular higher‐order aberrations in both patients. Conclusions: The Hartmann‐Shack aberrometer was useful in detecting local refractive changes and higher‐order aberrations in patients with mild cataract. The polarity and the absolute value of ocular higher‐order aberrations may be useful parameters to characterize eyes with cataract.

Serial Measurements of Higher-Order Aberrations after Blinking in Patients with Dry Eye

PURPOSE To study the sequential postblink changes in ocular higher-order aberrations (HOAs) in patients with dry eye. METHODS A wavefront sensor was used to measure HOAs sequentially for 30 seconds in 20 eyes of 20 patients with dry eye. The 20 eyes were classified into two groups, with or without superficial punctate keratopathy (SPK) in the central cornea. During the measurement, subjects were required to blink every 10 seconds. The aberration data were analyzed in the central 4-mm diameter for coma-like, spherical-like, and total HOAs up to sixth-order Zernike polynomials. Total HOAs, as well as fluctuation index (FI) and stability index (SI) of the total HOAs over time were compared between the two groups. The sequential changes in coma-like aberration, spherical-like aberration, and total HOAs were also investigated. RESULTS The total ocular HOAs were significantly (P = 0.001) greater in dry eyes with central SPK than in dry eyes without central SPK. The sequential pattern of the total ocular HOAs had higher initial and consistently higher values in dry eyes with central SPK, whereas that of dry eyes without central SPK showed consistently lower total HOAs that were similar to the pattern of normal eyes. CONCLUSIONS Increased HOAs in dry eye at least partially result from SPK above the optical zone. The low tear volume in dry eye may not cause sequential increases in HOAs after blinking. Sequential measurement of HOAs may be useful for evaluating the sequential changes in optical quality in patients with dry eye.

Higher-Order Aberrations Due to the Posterior Corneal Surface in Patients with Keratoconus

PURPOSE This study was designed to investigate higher-order aberrations (HOAs) due to the posterior corneal surface in keratoconic eyes compared with normal eyes. METHODS We studied 24 normal and 28 keratoconic eyes. The anterior/posterior corneal heights and pachymetric data were obtained with a rotating Scheimpflug camera. HOAs for 6 mm pupils were calculated from the differences between the height data and the best-fit sphere, using an original program for each corneal surface. The reference axes of the measurements were aligned with the primary line of sight. The HOAs were expanded with normalized Zernike polynomials. For each pair of standard Zernike terms for trefoil, coma, tetrafoil, and secondary astigmatism, one value for the magnitude and axis was calculated by Zernike vector analysis. RESULTS The mean total corneal HOAs (root mean square [microm]) from the anterior/posterior surfaces were significantly (P < 0.001) higher in keratoconic (4.34/1.09, respectively) than in control eyes (0.46/0.15). The mean magnitude of each Zernike vector terms for trefoil, coma, and spherical aberration from the anterior/posterior surfaces was significantly (P < 0.001) higher in keratoconic (0.77/0.19, 3.57/0.87, -0.44/0.17) than control eyes (0.09/0.04, 0.33/0.07, 0.25/-0.07), respectively. The mean axes by vector calculation for coma due to the anterior (63.6 degrees ) and posterior surfaces (241.9 degrees ) were in opposite directions. CONCLUSIONS Corneal HOAs on both corneal surfaces in keratoconic eyes were higher than in control eyes. Coma from the posterior surface compensated partly for that from the anterior surface. Residual irregular astigmatism in patients with keratoconus wearing rigid gas permeable contact lenses can be estimated by measuring the HOA from the posterior corneal surface.

Light scattering and optical aberrations as objective parameters to predict visual deterioration in eyes with cataracts

Purpose: To predict the visual deterioration of eyes with cortical (CC) or nuclear (NC) cataract from objective data on ocular higher‐order aberration (HOA) and forward (FLS) and backward light scattering (BLS). Setting: Osaka University Medical School, Osaka, Japan. Methods: Twenty‐two eyes with mild NC, 41 eyes with mild CC, and 11 normal eyes were examined. Higher‐order aberrations were calculated with the Zernike polynomials up to the fourth order from the values obtained by wavefront analysis using the Hartmann‐Shack aberrometer. Forward light scattering was calculated from the size of the aberrometer spot images for the central 4 mm, and backward light scattering (BLS) was calculated from the optical density of the Scheimpflug images. The relationship between the area under the log contrast sensitivity function (AULCSF) curve and HOAs, FLS, and BLS was examined. Results: Area under the log contrast sensitivity function was moderately correlated with the HOAs, FLS, and BLS. Multiple linear regression analysis revealed that the AULCSF was predicted by the linear combination of these variables (R2=.484, P<.001). Area under the log contrast sensitivity was predicted by BLS and HOA (R2=.555) in the NC group and by FLS and HOAs (R2=.540) in the CC group. Conclusions: Loss of contrast sensitivity was predominantly due to BLS and HOA in eyes with NC and FLS and HOA in eyes with CC. Higher‐order aberrations, FLS, and BLS, variables that are obtained objectively, can be used to predict quantitatively the visual deterioration in cataractous eyes.

Effect of Aging on Ocular Light Scatter and Higher Order Aberrations

PURPOSE To study the effect of aging on ocular light scatter and higher order aberrations in humans. METHODS Seventy-six eyes of 76 normal subjects who had refractive errors but no ocular disease were studied. Their age ranged from 4 to 69 years (mean 34.8 +/- 5.8 yr). Both light scatter and total higher order aberrations were simultaneously and quantitatively measured by a Hartmann-Shack sensor for the central 4-mm-diameter pupil. Higher order aberrations were calculated from the Zernike polynomials up to the 4th order. The amount of light scatter was estimated by using the diameter of the point spread functions (PSFs) of the Hartmann images. A correction was made for the effect of the aberrations on the width of the images. Linear regression analysis was performed to investigate the effect of aging on light scatter and total higher order aberrations. RESULTS A significant correlation was found between scatter and age (Spearman rank correlation coefficient, r = 0.501, P = .001). Also, the total higher order aberrations increased significantly with age (r = 0.323, P = .005). The total higher order aberration and scatter index were not statistically significantly correlated (r = 0.184, P = .112). CONCLUSIONS These results indicate that scatter was better correlated with age than higher order aberrations.