Prediction of letter contrast sensitivity using videokeratographic indices

A novel tool for quantitative measurement of distortion in keratoconus

Background

Keratoconus is associated with thinning and anterior protrusion of the cornea resulting in the symptoms of blurry and distorted vision. The commonly used clinical vision tests such as visual acuity and contrast sensitivity may not reflect the symptoms experienced in keratoconus and there are no quantitative tools to measure visual distortion. In this study, we used a quantitative test based on vernier alignment and field matching techniques to quantify visual distortion in keratoconus and assess its relation to corneal structural changes.

Methods

A total of 50 participants (25 keratoconus and 25 visually normal) completed the experiment where they aligned supra-threshold white target circles in opposite field in reference to guidelines and circles to complete a square structure monocularly. The task was repeated five times and the global distortion index (GDI) and global uncertainty index (GUI) were calculated as the mean and standard deviation respectively of local perceived misalignment of target circles over five trials.

Results

Both GDI and GUI were higher in participants with keratoconus compared to controls (p < 0.01). Both parameters correlated with the best corrected visual acuity, maximum corneal curvature (K_max), topographical keratoconus classification (TKC) and central corneal thickness (CCT).

Conclusion

Our findings show that the quantitative measure of distortion could be a useful tool for behavioural assessment of progressive keratoconus.

Contrast sensitivity and higher-order aberrations in Keratoconus subjects

This study analyzes the relationship between contrast-sensitivity and higher-order aberrations (HOA) in mild and subclinical-keratoconus in subjects with good visual-acuity (VA). Keratoconus group (including subclinical-keratoconus) and controls underwent autokeratometry, corneal-tomography, autorefraction and HOA measurement. Contrast-sensitivity was tested using a psychophysical two-alternative forced-choice Gabor patches in three blocks (6, 9, 12 cycles/deg). Controls were compared to the keratoconus group and to a keratoconus subgroup with VA of 0.00 LogMar group ("keratoconus-0.00VA"). Spearman correlation tested association between HOA and contrast-sensitivity. Twenty-two keratoconus subjects (38 eyes: 28 keratoconus, 10 subclinical-keratoconus, 20 keratoconus-0.00VA) and 35 controls were included. There was a significant difference between control and keratoconus, and between control and keratoconus-0.00VA, for keratometry, cylinder, thinnest and central corneal thickness (p < 0.001). Controls showed lower HOA and higher contrast-sensitivity for all spatial-frequencies (p < 0.001). Most HOA were negatively correlated with contrast-sensitivity for all spatial-frequencies for keratoconus group and for 9 and 12 cycles/deg for keratoconus-0.00VA. Keratoconus subjects with good VA showed reduction in contrast-sensitivity and increased HOAs compared to controls. HOA and contrast-sensitivity are inversely correlated in subjects with mild keratoconus despite good VA. This suggests that the main mechanism underlying the decreased vision quality in keratoconus is the increase of HOA.

The impact of irregular corneal shape parameters on visual acuity and contrast sensitivity

BACKGROUND

To understand which irregular corneal parameters determine the visual quality in keratoconus subjects.

METHODS

The cross-sectional study examined the eyes of 44 subjects, graded from the first to third keratoconus stages by Amsler-Krumeich classification. We obtained measurements in two ways: (a) by projecting two perpendicular axes onto a cornea (first, through the central point of the cornea and keratoconus apex; second, as the perpendicular axis) to read the elevation values at points on these axes as parameters characterising the corneal surface; (b) by projecting circles with different diameters around the central part of the cornea (1, 2, and 3 mm) and reading elevation values at points equally displaced on these circles as parameters characterising an anterior surface slope. Irregular corneal shape parameters' correlations with visual acuity and contrast sensitivity were determined in order to understand which corneal slope parameter has the strongest correlation with visual acuity and contrast sensitivity.

RESULTS

Parameters characterising the corneal surface's correlations with contrast sensitivity were from r = 0.25 (p = 0.03) at 3 cpd to r = 0.47 (p < 0.01) at 9 cpd for the highest elevation and from r = 0.33 (p = 0.09) at 5 cpd to r = 0.40 (p < 0.01) at 11 cpd for the lowest elevation in all subjects together, while for visual acuity the parameters were r = 0.30 (p < 0.01) for the highest elevation and r = 0.21 (p = 0.06) for the lowest elevation in all subjects together. The correlation between contrast sensitivity and the highest and lowest corneal point in all measured cornea was stronger for subjects with a peripheral corneal apex than for those with a central apex. In keratoconus subjects, contrast sensitivity displayed a strong correlation with slope in the central part of the cornea (with a radius of 1 mm) ranging from 0.48 (p < 0.01) at 3 cpd to 0.61 (p < 0.01) at 9 cpd.

CONCLUSION

Contrast sensitivity has a higher correlation with corneal shape parameters than with visual acuity. Subjects with a peripheral corneal apex had stronger correlations with visual acuity and contrast sensitivity than did subjects with a central apex. In keratoconus subjects, the strongest correlation was for contrast sensitivity and elevation (slope) in the region within a 1 mm radius of the corneal centre in the opposite direction of the keratoconus apex (direction (ax) CB).

Deterioration of contrast sensitivity in eyes with epiphora due to lacrimal passage obstruction

Purpose

Epiphora causes deterioration in contrast sensitivity in some eye diseases. This study was conducted to investigate contrast sensitivity in eyes with epiphora caused by lacrimal passage obstruction.

Methods

This single-center, prospective case series enrolled 57 patients with unilateral lacrimal passage obstruction. The best-corrected visual acuity (BCVA), contrast sensitivity function, and lower tear meniscus of the affected and contralateral unaffected eyes were compared. The area under the log contrast sensitivity function (AULCSF) was calculated.

Results

The BCVA did not significantly differ between the affected and contralateral eyes, while the AULCSF was significantly lower in the affected eyes than that in the contralateral eyes (median 1.35, interquartile range 1.22–1.44 vs. median 1.36, interquartile range 1.28–1.46, P = 0.032). Lower tear meniscus parameters were significantly higher in the affected eyes than those in the contralateral eyes (P < 0.005).

Conclusions

The contrast sensitivity function is significantly diminished in eyes with epiphora caused by lacrimal passage obstruction.

Impact of Dry Eye on Prolonged Reading

SIGNIFICANCE

Patients with dry eye frequently report difficulty with reading. However, the impact of dry eye on reading has not been studied in detail. This study shows the unfavorable effect of dry eye on reading speed and offers mechanisms that may be responsible.

PURPOSE

The purpose of this study was to evaluate the impact of dry eye signs as well as symptoms on both short-duration out-loud and prolonged silent reading.

METHODS

This study included 116 patients with clinically significant dry eye, 39 patients with dry eye symptoms only, and 31 controls, 50 years or older. After the Ocular Surface Disease Index (OSDI) questionnaire, objective testing of dry eye (tear film stability studies, Schirmer's test, and ocular surface staining) was performed. Total OSDI score and two subscores (vision related and discomfort related) were calculated. A short-duration out-loud reading test and a 30-minute sustained silent reading test were performed. Reading speed for each test was calculated as words per minute (wpm) and compared across the three groups.

RESULTS

Patients with clinically significant dry eye read slower than controls measured with sustained silent reading test (240 vs. 272 wpm, P = .04), but not with short-duration out-loud reading test (146 vs. 153 wpm, P = .47). Patients with dry eye symptoms only did not have slower reading speed measured using either reading test as compared with controls. However, vision-related OSDI subscore independently was associated with slower reading speed (P = .02). Multivariable regression models demonstrated that each 1-point (between 0 and 6) increase in corneal staining score led to a 10-wpm decrease in sustained silent reading speed (P = .01).

CONCLUSIONS

This study demonstrates a significant negative impact of dry eye (particularly presence of corneal staining) on prolonged reading. Prolonged reading task may serve as an objective clinically relevant test to measure the impact of dry eye on vision-related quality of life.

Toric intraocular lenses in eyes with with-the-rule, against-the-rule, and oblique astigmatism: One-year results

PURPOSE

To assess 1-year clinical results of toric intraocular lenses (IOLs) in eyes having with-the-rule (WTR), against-the-rule (ATR), or oblique corneal astigmatism.

SETTING

Four ophthalmic surgical sites, Japan.

DESIGN

Prospective case series.

METHODS

One of 3 toric IOLs or 1 nontoric IOL was implanted in eyes having phacoemulsification and IOL implantation.

RESULTS

The study comprised 218 eyes (155 patients). Based on the suggestion of an online toric calculator with anterior corneal curvature data, 63 eyes received the SN6AT3 IOL with a cylinder power of 1.50 diopters [D] at IOL plane (1.50 D cylinder IOL) 55 eyes the SN6AT4 IOL with a cylinder power of 2.25 D at IOL plane (2.25 D cylinder IOL), and 58 eyes the SN6AT5 IOL with a cylinder power of 3.00 D at IOL plane (3.00 D cylinder IOL) (all Acrysof IQ toric), and 42 eyes received the SN60WF IOL (nontoric IOL). One hundred ninety-four eyes (89.0%) completed 1-year of follow-up. The centroid error in predicted residual astigmatism calculated using vector analysis was close to the origin in eyes with WTR astigmatism (0.17 diopter [D] @ 174.9 ± 0.54 D), while those with ATR and oblique astigmatism were significantly shifted toward the ATR direction (P < .001). The distance from the origin was significantly smaller in the WTR group than in ATR and oblique groups (P < .05). The centroid errors were shifted toward ATR in all toric IOL groups (P < .001); however, the distance from the origin was not different between groups (P = .52). Postoperatively, the mean absolute misalignment of the IOLs was 5.92 degrees ± 5.59 (SD) at 1 day and 6.24 ± 5.87 degrees at 1 year. The results of other clinical parameters were excellent, with no significant differences between astigmatism categories or IOL models.

CONCLUSION

Based on anterior corneal curvature alone, toric IOLs undercorrected ATR and oblique astigmatism; however, 1-year clinical results of toric IOLs were highly stable and satisfactory.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Objective and subjective diagnostic parameters in the fellow eye of unilateral keratoconus

BACKGROUND

Keratoconus (KC) is usually a bilateral corneal ectatic disease. For significant asymmetric presentation (so called unilateral KC), the fellow eye has the mildest and earliest form of the disease, which is typically called forme fruste keratoconus. The aim of this study was to evaluate the sensitivity and specificity of parameters derived from a Scheimpflug imaging system (Pentacam) as well as the changes in the quality of mesopic vision in the apparently normal fellow eye (forme fruste) to detect the earliest and most sensitive parameters.

METHODS

Patients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared to subjects with normal eyes. The patients were examined using a rotating Scheimpflug imaging system (Pentacam).The following parameters were evaluated: keratometry, minimum corneal thickness, pachymetry progression index (PPI), Ambrósio relational thickness (ART), posterior elevation, back difference elevation (BDE) and multimetric D index(D index). Receiver operating characteristic (ROC) curves were analyzed by evaluating the area under the curve (AUC) to detect the sensitivity and specificity of each parameter. Mesopic vision evaluations were performed by contrast sensitivity and glare tests for each group.

RESULTS

A total of 48 patients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye and 72normal subjects were evaluated. In the clinical keratoconus eyes, the mean K, back difference elevation (BDE), pachymetric progression index maximum(PPI max), and multimetric D were significantly higher compared to the normal subjects, whereas the corneal pachymetry and Ambrósio relational thickness maximum (ART max) were significantly lower. In the forme fruste eyes, the ROC analysis showed that the AUC values of the mean K, thinnest pachymetry, ARTmax, BDE, D index, and PPI max were 0.82, 0.61, 0.88, 0. 67, and 0.64, respectively. The contrast sensitivity and glare tests were significantly affected in the forme fruste cases.

CONCLUSION

In forme fruste keratoconus eyes, the ART max is considered a highly sensitive objective parameter. Contrast sensitivity and glare is an important subjective test, which is affected in forme fruste patients.

Correlation between visual function and refractive, topographic, pachymetric and aberrometric data in eyes with keratoconus

AIM

To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus.

METHODS

Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є(2)), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices.

RESULTS

The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672) (P<0.001 for all). Root mean square (RMS) was 4.3±1.81 µm, spherical aberration (SA) was -0.4±0.67 µm, vertical and horizontal coma were -2.1±1.47 and -0.4±0.72 µm. All wavefront data (except horizontal coma), AAI, Є(2) and maximum BFS correlated significantly with the visual function (P≤0.001 for all).

CONCLUSION

In this study, CS is more affected than CDVA as a visual function. The quantity and quality of vision is significantly correlated with well-known and new topographic indices. There is not a significant correlation between visual function and pachymetric parameters. The significantly correlated indices can be used in staging keratoconus and to follow the outcome of a treatment.

Noninvasive assessment of tear stability with the tear stability analysis system in tear dysfunction patients

PURPOSE

To evaluate tear film stability in patients with tear dysfunction and an asymptomatic control group by using the novel, noninvasive Tear Stability Analysis System (TSAS).

METHODS

In this prospective case-control study, 45 patients with dysfunctional tear syndrome (DTS) were stratified into three groups (1, 2, and 3/4) based on clinical severity, with higher scores indicating more severe symptoms; 25 asymptomatic control subjects were evaluated. TSAS measurements were performed with the RT-7000 Auto Refractor-Keratometer (Tomey Corporation, Nagoya, Japan). Images of ring mires projected onto the cornea every second for 6 seconds were captured and analyzed. Focal changes in brightness were calculated as numerical ring breakup (RBU) values, and the elapsed time when the cumulative values (RBU sum) exceeded a threshold was defined as the ring breakup time (RBUT).

RESULTS

RBUTs in the DTS groups were all significantly lower than those in the control subjects, with the lowest values found in DTS 3/4. RBUT was significantly shorter in DTS 3/4 than in DTS 1 (P<0.001). The change in RBU sum over a 6-second period in the DTS groups combined or between the individual groups was statistically significant (P<0.001), as was the difference between the 1- and 6-second values. For distinguishing between asymptomatic controls and DTS, the sensitivity and specificity of a 5.0-second RBUT cutoff were 82.0% and 60.0%, respectively.

CONCLUSIONS

The TSAS may be a useful, noninvasive instrument for evaluating tear stability and for classifying DTS severity.

Higher-order wavefront aberration and letter-contrast sensitivity in keratoconus

AIMS

To evaluate the relation between higher-order aberration of the eye and contrast sensitivity function in eyes with keratoconus.

METHODS

In 22 eyes of 14 patients with keratoconus (age 30.5+/-8.4 years, means+/-SD) and 26 eyes of 13 normal controls (age 29.2+/-6.7 years), ocular higher-order wavefront aberration for a 6-mm pupil was measured with the Hartmann-Schack aberrometer (KR-9000 PW, Topcon). The root mean square (RMS) of third- and fourth-order Zernike coefficients was used to represent higher-order aberrations. The letter-contrast sensitivity was examined using the CSV-1000LV contrast chart (Vector Vision).

RESULTS

In the keratoconus group, the letter-contrast sensitivity showed significant correlation with third-order (Spearman's correlation coefficient r=-0.736, P<0.001) and fourth-order aberrations (r=-0.464, P<0.05). There was borderline correlation between log MAR BSCVA and third-order (r=0.413, P=0.070) and fourth-order aberrations (r=0.394, P=0.086). In the normal group, the letter-contrast sensitivity had no significant correlation with third-order (r=-0.170, P=0.411) and fourth-order aberrations (r=-0.088, P=0.673), and log MAR best spectacle-corrected visual acuity (BSCVA) showed no correlation with third-order (r=0.063, P=0.762) and fourth-order aberrations (r=-0.282, P=0.165).

CONCLUSIONS

In eyes with keratoconus, there is significant correlation between contrast sensitivity and ocular higher-order wavefront aberrations.

Penetrating Keratoplasty for Keratoconus: The Nexus Between Corneal Wavefront Aberrations and Visual Performance

PURPOSE

To compare the visual and optical performance after penetrating keratoplasty (PK) for keratoconus to normal patients and to examine the relationship between corneal wavefront aberrations and visual performance in patients with PK.

METHODS

Visual performance testing, with optimal refractive correction, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity with and without glare, and high contrast visual acuity. Corneal first surface wavefront aberrations were calculated from EyeSys topography data using VOL-Pro software v7.00 for a 4.0-mm pupil as a 10th order Zernike expansion and converted into single value metrics. Normal patients were compared to patients with PK using analysis of variance, and linear regression was used to compare wavefront aberration metrics to visual performance.

RESULTS

Patients with PK (n=14, age 41.6 +/- 7.0 years) and normal patients (n=14, age 36.7-9.0 years) were of similar age (F(1, 26) = 2.54, P = .12). Normal patients saw significantly better on all visual performance measures and had better optical performance for total higher order root-mean-square corneal wavefront aberration (mean-SD): PK, 0.67 +/- 0.41 microm; normal, 0.09 +/- 0.02 microm (F(1,26) = 28.41, P < .001) and across all Zernike orders and modes. Wavefront aberrations in PK eyes were dominated by trefoil 0.35 +/- 0.27 microm, coma 0.47 +/- 0.37 microm, spherical aberration 0.17 +/- 0.10 microm, and tetrafoil 0.12 +/- 0.07 microm. The relationships between corneal wavefront aberration and visual performance metrics were strongest for LCVA = 0.30-0.98 Pupil fraction for wavefront (tessellation) -0.04 Half width at half height, R2=0.75.

CONCLUSIONS

In this series, patients with PK had poorer visual performance compared to normal patients, which is due to increased corneal wavefront aberrations. Outcomes research in corneal transplantation should include measurement of wavefront aberrations and visual performance in the contrast domain.

Simulation of Machine-Specific Topographic Indices for Use Across Platforms

PURPOSE

The objective of this project is to simulate the current published topographic indices used for the detection and evaluation of keratoconus to allow their application to maps acquired from multiple topographic machines.

METHODS

A retrospective analysis was performed on 21 eyes of 14 previously diagnosed keratoconus patients from a single practice using a Tomey TMS-1, an Alcon EyeMap, and a Keratron Topographer. Maps that could not be processed or that contained processing errors were excluded from analysis. Topographic indices native to each of the three devices were recorded from each map. Software was written in ANSI standard C to simulate the indices based on the published formulas and/or descriptions to extend the functionality of The Ohio State University Corneal Topography Tool (OSUCTT), a software package designed to accept the input from many corneal topographic devices and provide consistent display and analysis. Twenty indices were simulated. Linear regression analysis was performed between each simulated index and the corresponding native index. A cross-platform comparison using regression analysis was also performed.

RESULTS

All simulated indices were significantly correlated with the corresponding native indices (p < 0.01), with a mean R of 0.84, ranging from 0.42 to 0.99. Cross-platform comparisons were nonsignificant for specific indices and devices.

CONCLUSION

Topographic indices native to three devices were successfully simulated. Cross-platform comparisons may be limited for specific indices.

Normal values for a clinical test of letter-recognition contrast thresholds

PURPOSE

To investigate the contrast thresholds (CTs) in normal subjects using a high-luminance, letter-recognition task under clinically relevant testing conditions.

SETTING

Texas Tech University Health Sciences System, Lubbock, Texas, USA.

METHODS

Sixty normal subjects aged 20 to 49 years with a best corrected visual acuity of 20/20 or better in both eyes participated. M & S Technologies software was used to display black-on-white Sloan letters at contrast levels of 25%, 20%, 15%, 12%, and 10% through 1% in 1% decrements. The effects of age, sex, optotype size, eye dominance, ambient illumination level (bright = 625 - 630 lux; dim = <3 lux), and direction of approach to threshold were analyzed using a multivariate, ordinary, least-squares analysis.

RESULTS

Age and sex did not influence CTs. Ascending versus descending testing was not statistically significant (P>.5). The effects of room illumination and eye dominance were significant (P<.01). Significant differences were found between 20/30 and 20/50, 20/30 and 20/70, and 20/50 and 20/70 optotype sizes (P<.01 for all comparisons).

CONCLUSIONS

A commercially available, computer-based test of CTs was easy to administer and apparently easy for inexperienced subjects to perform. The results suggest criteria for detecting visual problems concerned with familiar but complex spatial-image shapes. This information might be used to assess the effects of treatments such as laser refractive surgery on recognition contrast. Further study is warranted.

Contrast and glare testing in keratoconus and after penetrating keratoplasty

AIM

To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus.

METHODS

All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA.

RESULTS

Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F(2,48) = 6.16; p<0.01, post hoc Sheffé p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures.

CONCLUSIONS

PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain.

Assessing the severity of keratitis sicca with videokeratoscopic indices

PURPOSE

To determine the correlation between the regularity indices of the Tomey TMS-2N computerized videokeratoscopy (CVK) instrument (Tomey, Waltham, MA) with conventional measures of dry eye symptoms and disease.

DESIGN

A retrospective, clinic-based, case-control study.

PARTICIPANTS

A total of 16 eyes of 16 asymptomatic normal subjects and 74 eyes of 74 patients with reports of ocular irritation.

METHODS

Corneal surface regularity and potential visual acuity indices of the Tomey TMS-2N CVK instrument were evaluated in patients with ocular irritation symptoms and in normal subjects.

MAIN OUTCOME MEASURES

The surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity index (PVA), and irregular astigmatism index (IAI) of the Tomey TMS-2N were compared between normal and dry-eye patients. Severity of dry-eye symptoms was assessed with a validated questionnaire. Schirmer 1 test (without anesthesia), biomicroscopic meibomian gland evaluation with a composite severity score (MGD score), fluorescein tear break-up time (TBUT), and corneal fluorescein staining were performed. The correlations between CVK indices of the Tomey TMS-2N and the symptom severity score, Schirmer 1 test, MGD score, TBUT, and corneal fluorescein staining score were studied.

RESULTS

Dry-eye patients had greater mean symptom severity scores, lower Schirmer 1 test scores, greater MGD scores, more rapid TBUT, and greater total corneal fluorescein staining scores (P < 0.001 for all parameters). The SRI, SAI, and IAI were all significantly greater in dry-eye patients than normal subjects. These were 0.46 +/- 0.36 (normal) versus 1.09 +/- 0.76 (dry) for the SRI (P = 0.0017), 0.30 +/- 0.15 (normal) versus 0.90 +/- 1.09 (dry) for the SAI (P = 0.0321), and 0.42 +/- 0.28 (normal) versus 0.56 +/- 0.24 (dry) for the IAI (P = 0.0321). The PVA index was significantly lower in the dry-eye patients (0.89 +/- 0.13) than normal eyes (0.68 +/- 0.23; P = 0.0008). The SRI, SAI, and IAI were positively correlated with total and central corneal fluorescein staining scores (P < 0.00001 for all indices). An SRI (> or =0.80), SAI (> or =0.50), and IAI (> or =0.50) had sensitivities in predicting total corneal fluorescein staining (score > or = 3) of 89%, 69%, and 82%, respectively. The specificity of these indices was 80%, 78%, and 82%, respectively. In all 90 eyes, the mean SRI was greater in subjects older than 50 years (P = 0.012) compared with younger patients, whereas no age effect was noted in the dry-eye patients. The SRI and PVA index showed better correlation with symptoms of blurred vision than the best-corrected visual acuity.

CONCLUSIONS

Patients with ocular irritation have an irregular corneal surface that may contribute to their irritation and visual symptoms. Because of their high sensitivity and specificity, the regularity indices of the Tomey TMS-2N have the potential to be used as objective diagnostic indices for dry eye, as well as a means to evaluate the severity of this disease.

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.