Visual performance after photorefractive keratectomy with a 6-mm ablation zone

Investigation of contrast visual acuity with rigid gas permeable contact lenses after penetrating Keratoplasty

BACKGROUND

To investigate the effects of rigid gas permeable contact lens (RGP-CL) wear on contrast visual acuity in patients after penetrating keratoplasty.

METHODS

Nineteen patients (19 eyes), aged 30.45 ± 5.83 years, who had received penetrating keratoplasty and were successfully fitted with RGP-CLs at our hospital from July 2017 to June 2018 were included. Contrast visual acuities at 100%, 25%, and 10% with spectacles and RGP-CLs were analyzed using the Chi-square test. The wavefront aberrations at the anterior surface of the cornea before and 1 month after RGP-CL wear were compared using the matched sample t-test.

RESULTS

The mean best spectacle-corrected visual acuities were 0.390 ± 0.135 logMAR, 0.706 ± 0.182 logMAR, and 0.952 ± 0.223 logMAR at the 100%, 25%, and 10% contrast levels, respectively, which were significantly lower than the RGP-CL-corrected visions at the three levels (0.255 ± 0.133 logMAR, 0.488 ± 0.168 logMAR, and 0.737 ± 0.159 logMAR; all P < 0.001). The vision losses with RGP-CLs were 0.231 ± 0.099 logMAR and 0.466 ± 0.094 logMAR at the 25% and 10% contrast levels, respectively. The Zernike spherical aberration Z⁰₄ was reduced from 3.734 ± 1.061 μm to 2.622 ± 0.725 μm after wearing the RGP-CLs (P ≤ 0.001). The astigmatism parameters of Z^- 2₂ and Z²₂ were also reduced from 3.761 ± 2.309 μm and 3.316 ± 2.147 μm to 2.637 ± 1.722 μm and 2.016 ± 1.184 μm, respectively (P < 0.05).

CONCLUSION

For post-keratoplasty patients, RGP-CLs can help to improve visual performance, especially low contrast visual acuity. The improvement may be related to the reduction of corneal aberrations, mainly the spherical and astigmatism aberrations.

Single-step transepithelial photorefractive keratectomy in myopia and astigmatism: 18-month follow-up

PURPOSE

To evaluate the long-term quantitative and qualitative optical outcomes of 1-step transepithelial photorefractive keratectomy (PRK) to correct myopia and astigmatism.

SETTING

Bina Eye Hospital, Tehran, Iran.

DESIGN

Prospective interventional case series.

METHODS

Eyes with myopia with or without astigmatism were evaluated. One-step transepithelial PRK was performed with an aberration-free aspheric optimized profile and the Amaris 500 laser. Eighteen-month follow-up results for refraction, visual acuities, vector analysis, higher-order aberrations, contrast sensitivity, postoperative pain, and haze grade were assessed.

RESULTS

The study enrolled 146 eyes (74 patients). At the end of follow-up, 93.84% of eyes had an uncorrected distance visual acuity of 20/20 or better and 97.94% of eyes were within ±0.5 diopter of the targeted spherical refraction. On vector analysis, the mean correction index value was close to 1 and the mean index of success and magnitude of error values were close to 0. The achieved correction vector was on an axis counterclockwise to the axis of the intended correction. Photopic and mesopic contrast sensitivities and ocular and corneal spherical, cylindrical, and corneal coma aberrations significantly improved (all P < .001). A slight amount of trefoil aberration was induced (P < .001, ocular aberration; P < .01, corneal aberration). No eye lost more than 1 line of corrected distance visual acuity. No eye had a haze grade of 2+ degrees or higher throughout the follow-up.

CONCLUSIONS

Eighteen-month results indicate the efficacy and safety of transepithelial PRK to correct myopia and astigmatism. It improved refraction and quality of vision.

FINANCIAL DISCLOSURE

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

Comparative study of visual function and ocular aberrations of two different one-piece designed hydrophilic acrylic intraocular lens

PURPOSE

To determine whether the aspherical IOL, Tecnis ZCB00, can improve the visual quality by measuring visual acuity, wavefront aberrations, and contrast sensitivity.

METHODS

It was a retrospective case series. Patients who underwent phacoemulsification cataract surgery were divided into two groups. One group (Group TC) was implanted with one-piece aspherical acrylic IOL (Tecnis ZCB00, AMO); the other (Group SA) was implanted with one-piece spherical acrylic IOL (Sensar AAB00, AMO). Eighty-eight eyes were selected into this study, among them 43 eyes in 26 male cases and 45 eyes in 29 female cases. Thirty-six eyes in 23 cases were in Group TC, and 52 eyes in 32 cases were in Group SA. Three months postoperatively, aberrations were analyzed with i-Trace visual function analyzer (Tracy Technologies, USA). Contrast sensitivities were measured with Takaci-CGT-1000 contrast glare tester (Seiko, Japan).

RESULTS

All the 88 eyes underwent phacoemulsification with intraocular lens implantation, without complications during or after surgery. Three months postoperatively, the uncorrected vision acuity in Group TC was significantly better than in Group SA (P = 0.007). At the pupil size of 5.0 mm, higher-order aberrations in Group TC were significantly higher than in Group SA (P = 0.02), especially the spherical aberration (Z ₄⁰ ) (P < 0.001); at the pupil size of 4.0 mm, Z ₄⁰ in Group SA was statistically higher than in Group TC (P < 0.001); at the pupil size of 3.0 mm, higher-order aberrations such as coma (Z ₃^-1,1 ) and trefoil aberration (Z ₃^-3,3 ) in Group SA were obviously higher than in Group TC (P = 0.01). In the low spatial frequency, the contrast sensitivity and the glare sensitivity in Group TC were significantly higher than in Group SA (P < 0.05).

CONCLUSIONS

By the short-term follow-up (3 months), the aspherical acrylic IOL can reduce the higher-order aberrations (especially the spherical aberration) and increase the contrast sensitivity to improve the visual performance.

Mesopic contrast sensitivity and ocular higher-order aberrations after overnight orthokeratology

PURPOSE

To investigate mesopic contrast sensitivity and night driving ability in eyes undergoing overnight orthokeratology, and to analyze the relationship among mesopic contrast sensitivity, ocular higher-order aberrations, and myopic correction.

DESIGN

Prospective, noncomparative, consecutive case series.

METHODS

In 44 eyes of 22 subjects (mean age +/- standard deviation [SD], 24.0 +/- 3.2 years) with orthokeratology, ocular aberrations and mesopic contrast sensitivity were determined before and three months after commencement of the procedure. Mean spherical equivalent refraction +/- SD was -2.34 +/- 0.99 diopters at baseline. Mesopic contrast sensitivity with and without glare was assessed using the Mesotest II (Oculus, Wetzlar, Germany).

RESULTS

Orthokeratology significantly reduced the log mesopic contrast sensitivity from 0.25 +/- 0.08 to 0.08 +/- 0.10 without glare (P < .0001, Wilcoxon) and from 0.21 +/- 0.11 to 0.07 +/- 0.10 with glare (P < .0001). The proportion of eyes that fulfilled the German standard recommendation level for night driving was 36%. The induced changes in log mesopic contrast sensitivity showed significant negative correlation with the changes in third-order (r = -0.490, P = .0013 without glare; r = -0.362, P = .0177 with glare; Spearman rank correlation coefficient) and fourth-order root mean square (r = -0.586, P = .0001 and r = -0.306, P = .0450, respectively). Furthermore, significant correlation was found between the amount of myopic correction and the induced changes in log mesopic contrast sensitivity (r = -0.442, P = .0038 without glare; r = -0.464, P = .0024 with glare). The induced changes in higher-order aberrations significantly correlated with the amount of myopic correction (P < .0001, Pearson correlation coefficient).

CONCLUSIONS

Mesopic contrast sensitivity after overnight orthokeratology is deteriorated significantly as ocular higher-order aberrations increase, and these changes depend on the amount of myopic correction.

The relationship between anterior corneal aberrations and contrast sensitivity in conventional LASIK

PURPOSE

To evaluate the changes of anterior corneal aberrations before and after laser in situ keratomileusis (LASIK) and to assess the correlation between contrast sensitivity and anterior corneal aberrations.

METHODS

Right eyes of 51 patients including 6 males and 45 females undergoing conventional LASIK from September 2000 to July 2003 were enrolled. The calculation of anterior corneal aberrations before and after LASIK was obtained by analyzing the corneal topography from TMS-1 by using VOL-CT Version 6.23 software. Contrast sensitivity was measured after LASIK with an MCT 8000 under daytime and nighttime settings and with glare conditions. The differences of the Zernike coefficients and root mean square (RMS) of anterior corneal aberrations before and after LASIK were analyzed. The changes of contrast sensitivity at 1.5, 3, 6, 12, and 18 cpd were added separately for daytime and nighttime contrast sensitivity with and without glare after LASIK and were correlated with the changes of anterior corneal aberrations.

RESULTS

Vertical coma, RMS of coma-like RMS of spherical-like, RMS of trefoil-like and RMS of higher-order anterior corneal aberrations increased significantly after LASIK surgery. There were no significant correlations between the changes of anterior corneal aberrations and the changes of contrast sensitivity at daytime and nighttime, with and without glare. Contrast sensitivity at daytime and nighttime decreased at each spatial frequency after LASIK.

CONCLUSIONS

LASIK surgery induces changes of the anterior corneal aberrations. However, changes in anterior corneal aberrations did not correlate with the changes of contrast sensitivity at daytime and nighttime, with and without glare.

Contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes

PURPOSE

To investigate the relation between contrast sensitivity function and ocular higher-order wavefront aberrations in normal human eyes.

STUDY DESIGN

Prospective observational case series.

PARTICIPANTS

Three hundred seven eyes of 161 normal subjects, ranging in age from 15 to 60 years (30.9+/-8.0 [mean +/- standard deviation]).

METHODS

Ocular higher-order aberrations were measured for a 4-mm pupil using the Hartmann-Shack wavefront analyzer. The root-mean-square of the third- and fourth-order Zernike coefficients was used to represent comalike and spherical-like aberrations, respectively. We measured contrast sensitivity, low-contrast visual acuity (VA), and letter contrast sensitivity. From the contrast sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated. Pupil diameter in a photopic condition was recorded using a digital camera.

RESULTS

Multiple linear regression analysis revealed that comalike aberration (P = 0.002) was significantly associated with AULCSF, but spherical-like aberration (P = 0.200), age (P = 0.185), and photopic pupil diameter (P=0.252) were not. Comalike aberration showed a significant correlation with low-contrast VA (P<0.001), but spherical-like aberration (P = 0.293), age (P = 0.266), and pupil diameter (P = 0.756) did not. Comalike aberration was found to be significantly associated with letter contrast sensitivity (P<0.001), but spherical-like aberration (P=0.082), age (P = 0.370), and pupil diameter (P = 0.160) were not.

CONCLUSIONS

In normal human eyes, comalike aberration of the eye significantly influences contrast sensitivity function.

Response of the Cornea for up to Four Years After Photorefractive Keratectomy for Myopia

PURPOSE

To analyze the long-term corneal topographic changes 4 years after myopic photorefractive keratectomy (PRK).

METHODS

This study comprised 15 patients (30 eyes) who had PRK surgery with a scanning-spot excimer laser (Chiron Technolas 217C; Bausch & Lomb, Dornach, Germany) and were followed up to 4 years after surgery. The eyes were subdivided into three groups according to the preoperative spherical equivalent refraction. Corneal topographic maps were obtained for all eyes with a Placido disc topographer. Preoperative and follow-up topographical data were imported into a custom software program, which computed the average composite corneal maps and difference maps for each study group to quantify the anterior corneal changes following laser ablation. The software delineated three concentric zones of the corneal surface to characterize the regional corneal remodeling following the surgery.

RESULTS

A significant central corneal steepening (approximately 0.25 D, P < .001) was calculated between the 1- and 4-year postoperative maps in all study groups. A significant steepening (P < .001) of the corneal periphery was also noted for the lower myopic ablations whereas a peripheral flattening (P < .001) was observed for the deeper ablations between 1 and 4 years after surgery.

CONCLUSIONS

The anterior corneal surface was observed to remodel for up to 4 years after surface ablation, steepening a mean of approximately 0.25 D.

Precision of Higher Order Aberration Repeatability With NIDEK OPD-Scan Retinoscopic Aberrometry

PURPOSE

To evaluate repeatability of the total high order aberrations with a retinoscopic wavefront sensor.

METHODS

This prospective case series analyzed 12 eyes from 6 patients who underwent wavefront measurement using retinoscopic aberrometry with the NIDEK Optical Path Difference Scan (OPD-Scan). Four consecutive wavefront measurements of each eye were taken by two trained examiners for 5.8+/-0.8-mm and 8.2+/-0.6-mm pupils (P=.002, Wilcoxon test). Total high order aberrations out to the eighth order were assessed including third order coma, third order trefoil, fourth order quadrafoil, fourth order secondary astigmatism, and fourth order spherical aberrations. Differences between measurements of all of the variables were analyzed. A P value <.05 was considered statistically significant.

RESULTS

Repeatability analysis of the root-mean-square of total higher order aberrations, coma, trefoil, quadrafoil, secondary astigmatism, and spherical aberrations for both dilated and nondilated pupils did not show a statistically significant difference among all repeated measurements, except for trefoil and secondary astigmatism (analysis of variance and the Friedman test). The repeatability of total higher order aberrations was 0.15 microm for nondilated pupils and 0.18 microm for dilated pupils. Except for trefoil measurements, all high order aberrations showed reproducibility >0.15 microm when Zernike coefficients were analyzed individually.

CONCLUSIONS

The NIDEK OPD-Scan aberrometer measures total higher order astigmatism and most individual aberrations with acceptable repeatability. However, measurement of trefoil with this instrument is less repeatable.

Visual quality after wavefront-guided LASIK for myopia

This study evaluated the visual quality after wavefront-guided laser in situ keratomileusis (LASIK) for treating myopia. Thirty-two eyes with moderate myopia (-5.78 - -2.17D) and 25 eyes with high myopia (-7.78 - -6.17D) were prospectively reviewed. The contrast sensitivity (CS), glare and the total higher order aberrations (HOA) were measured before and 1 week, 1 month and 2 months after LASIK. The pupil diameter was measured at day- and night-time illumination. The CS and glare at all spatial frequencies were not reduced after wavefront-guided LASIK (p<0.05) and the difference between the moderate and high myopia group was not significant. No significant correlation was found between the amounts of myopia and the postoperative CS (p>0.05). The area under the log contrast sensitivity function (AULCSF) showed no correlation with the total HOA (r2=-0.071, p=0.612, between the daytime AULCSF and the total HOA with a 4 mm entrance pupil, r2=-0.176, p=0.260, between the nighttime AULCSF and the total HOA with a 6 mm entrance pupil). There was no decrease in CS and glare after wavefront-guided LASIK for myopia. In conclusion, wavefront-guided LASIK based on the individual ablation patterns is a good option for refractive surgery to improve the visual quality in both moderate and high myopia cases.

Conservation of corneal tissue with wavefront-guided laser in situ keratomileusis

PURPOSE

To determine whether corneal tissue can be conserved with wavefront-guided ablation compared to conventional surgery with a larger ablation zone for attempted prevention of glare and halo.

SETTING

Department of Ophthalmology, Ilsan Paik Hospital, Inje University, Korea.

METHODS

This prospective study was composed of 2 parts: First, 40 eyes of 20 patients were studied to determine whether a larger optical ablation could be beneficial in prevention of glare after conventional laser in situ keratomileusis (LASIK) surgery. One eye in each patient was treated with a 6.00 mm optical zone, and the other with a 6.25 mm optical zone. Second, 20 eyes of 10 patients with a higher-order root mean square (RMS) value of 0.3 or greater were evaluated to learn whether a wavefront-guided ablation could be as effective as a larger conventional optical ablation. One eye in each patient was treated by conventional LASIK surgery with a 6.25 mm optical zone, and the other eye was treated by wavefront-guided LASIK surgery with a 6.00 mm optical zone. All patients were analyzed with a WASCA analyzer (Carl Zeiss Meditec) preoperatively, and 1 month and 3 months after surgery.

RESULTS

Higher-order aberrations including coma, spherical aberration, and higher-order RMS were statistically significantly increased after conventional surgery with both a 6.00 mm and 6.25 mm optical zone. High-order aberrations including comaer- and spherical aberration after conventional surgery with 6.25 mm zone were statistically significantly increased. However, coma and higher-order RMS did not show a statistically significant increase between pre-LASIK and post-LASIK in wavefront-ablated eyes with a 6.00 mm optical zone.

CONCLUSION

Wavefront ablation showed less increase of coma and higher-order RMS regardless of a smaller optical zone. This finding might provide a clinical clue for an advantage of wavefront-guided ablation from the standpoint of corneal tissue conservation.

Low contrast visual acuity in pseudophakic patients implanted with an anterior surface modified prolate intraocular lens

PURPOSE

To determine whether implantation of a new intraocular lens (IOL) with a modified prolate anterior surface, designed to reduce the positive spherical aberration of the pseudophakic eyes, results in improved contrast sensitivity assessed in terms of low contrast visual acuity (VA).

METHODS

We carried out an intraindividual study of 12 patients with bilateral cataracts, randomized to receive a prolate anterior surface IOL (Tecnis Z9000, Pharmacia) in one eye and a biconvex spherical surface IOL (CeeOn 911 A, Pharmacia) in the other. High and low contrast VA was assessed under photopic conditions, before and after pupil dilation.

RESULTS

After mydriasis, the Technis Z9000 provided significantly better low contrast VA at contrast levels < or = 25%. No significant difference was found under normal pupil conditions.

CONCLUSION

Our results confirm the hypothesis that the spherical aberration of the eye after cataract surgery can be reduced by an anterior prolate surface IOL.

Influence of wavefront aberration and corneal subepithelial haze on low-contrast visual acuity after photorefractive keratectomy

PURPOSE

To assess low-contrast visual acuity (LCVA) after photorefractive keratectomy in relation to ocular higher-order wavefront aberration and corneal subepithelial haze.

DESIGN

Prospective, cross-sectional analysis.

METHODS

Photorefractive keratectomy was performed in 51 eyes of 27 subjects with myopic refractive error of -2.0 to -10.5 diopters. Ocular higher-order wavefront aberrations for a 4-mm pupil were measured using Topcon Hartmann-Shack wavefront aberrometer, and the extent of corneal subepithelial haze was quantified with Nidek TSPC-3 hazemeter before and 1 month after photorefractive keratectomy. Low-contrast visual acuity was recorded with Vector Vision CSV-1000LanC10% chart. Total higher-order, third-order (coma-like), and fourth-order (spherical-like) aberrations of the eye were determined. The influence of wavefront aberration and corneal subepithelial haze on LCVA was analyzed.

RESULTS

Total higher-order, third-order, and fourth-order aberrations significantly increased by surgery (P < .001, Wilcoxon signed rank test). Photorefractive keratectomy induced a significant increase in corneal haze (P < .01), but no case presented severe corneal haze (grade 3 or greater by Fantes grading). By surgery, LCVA was reduced significantly (P < .001). The logarithm of the minimal angle of resolution LCVA showed a significant correlation with total higher-order aberration (Spearman rank correlation coefficient, r(s) = 0.642, P < .0001). Both third-order (r(s) = 0.618, P < .0001) and fourth-order aberrations (r(s) = 0.552, P < .0001) also significantly correlated with logarithm of the minimal angle of resolution LCVA. There was no correlation between the degree of corneal haze and logarithm of the minimal angle of resolution LCVA (r(s) = 0.094, P = .523).

CONCLUSIONS

In eyes with mild to moderate corneal haze after photorefractive keratectomy, deterioration of LCVA is mainly attributable to increases in wavefront aberration, and not to corneal haze.

Using the Freiburg Acuity and Contrast Test to measure visual performance in USAF personnel after PRK

PURPOSE

Photorefractive keratectomy (PRK) may be an alternative to spectacle and contact lens wear for United States Air Force (USAF) aircrew and may offer some distinct advantages in operational situations. However, any residual corneal haze or scar formation from PRK could exacerbate the disabling effects of a bright glare source on a complex visual task. The USAF recently completed a longitudinal clinical evaluation of the long-term effects of PRK on visual performance, including the experiment described herein.

METHODS

After baseline data were collected, 20 nonflying active duty USAF personnel underwent PRK. Visual performance was then measured at 6, 12, and 24 months after PRK. Visual acuity (VA) and contrast sensitivity (CS) data were collected by using the Freiburg Acuity and Contrast Test (FrACT), with the subject viewing half of the runs through a polycarbonate windscreen. Experimental runs were completed under 3 glare conditions: no glare source and with either a broadband or a green laser (532-nm) glare annulus (luminance approximately 6090 cd/m) surrounding the Landolt C stimulus.

RESULTS

Systematic effects of PRK on VA relative to baseline were not identified. However, VA was almost 2 full Snellen lines worse with the laser glare source in place versus the broadband glare source. A significant drop-off was observed in CS performance after PRK under conditions of no glare and broadband glare; this was the case both with and without the windscreen. As with VA, laser glare disrupted CS performance significantly and more than broadband glare did.

CONCLUSIONS

PRK does not appear to have affected VA, but the changes in CS might represent a true decline in visual performance. The greater disruptive effects from laser versus broadband glare may be a result of increased masking from coherent spatial noise (speckle) surrounding the laser stimulus.

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.

The Effect of LASIK on Best-Corrected High-and Low-Contrast Visual Acuity

PURPOSE

To evaluate the effects of laser in situ keratomileusis (LASIK) and LASIK with concurrent astigmatic keratectomy (LASIK/AK) on high- and low-contrast visual acuity.

METHODS

The setting was a university refractive surgery practice. Patients were recruited from those undergoing LASIK or LASIK/AK for myopia (>1.00 D spherical equivalent) between May 1996 and August 1997. All subjects were at least 21 years of age. Testing occurred preoperatively and 3 and 6 months after LASIK. Main outcome measures were best spectacle-corrected, high- and low-contrast visual acuity.

RESULTS

For all subjects, there was a significant effect of surgery on nondilated low-contrast visual acuity (repeated measures two-way analysis of variance, p < 0.0001). Tukey's posthoc analysis showed that preoperative low-contrast visual acuity scores were significantly different from 3-month [0.08 logarithm of the minimum angle of resolution (logMAR)] and 6-month (0.11 logMAR) scores for patients undergoing LASIK and LASIK/AK. Under dilated conditions, there was a significant effect of surgery for high- and low-contrast visual acuity (analysis of variance, p < 0.0001 for both). Only changes in low-contrast visual acuity were clinically meaningful [LASIK, visual acuity reduction of 0.1 logMAR (1 line); LASIK/AK, visual acuity reduction of 0.15 logMAR (1.5 lines)]. When considering high and low myopes separately (LASIK only), the level of myopia had a significant effect on the visual acuity after surgery (analysis of variance, p = 0.01). Preoperative, dilated, low-contrast visual acuity scores for high myopes were significantly different from 3-month (0.14 logMAR) and 6-month (0.13 logMAR) scores. No differences were noted for low myopes.

CONCLUSIONS

Clinically meaningful postoperative changes in low-contrast visual acuity were noted in patients undergoing LASIK and LASIK/AK under natural and dilated conditions. Postoperative, dilated, low-contrast visual acuity scores were significantly worse than preoperative scores for high myopes, but remained unchanged for low myopes.

The usefulness of Vistech and FACT contrast sensitivity charts for cataract and refractive surgery outcomes research

AIM

To investigate the repeatability and sensitivity of two commonly used sine wave patch charts for contrast sensitivity (CS) measurement in cataract and refractive surgery outcomes.

METHODS

The Vistech CS chart and its descendant, the Functional Acuity Contrast Test (FACT), were administered in three experiments: (1) Post-LASIK and age matched normal subjects; (2) Preoperative cataract surgery and age matched normal subjects; (3) Test-retest repeatability data in normal subjects.

RESULTS

Contrast sensitivity was similar between post-LASIK and control groups and between the Vistech and FACT charts. The percentage of subjects one month post-LASIK achieving the maximum score across spatial frequencies (1.5, 3, 6, 12, 18 cycles per degree) were (50, 33, 13, 13, 0 respectively) for FACT, but only (0, 0, 13, 4, 0 respectively) for Vistech. A small number of cataract patients also registered the maximum score on the FACT, but up to 60% did not achieve the minimum score. Test-retest intraclass correlation coefficients varied from 0.28 to 0.64 for Vistech and 0.18 to 0.45 for FACT. Bland-Altman limits of agreement across spatial frequencies were between +/-0.30 and +/-0.85 logCS for Vistech, and +/-0.30 to +/-0.75 logCS for FACT.

DISCUSSION

The Vistech was confirmed as providing poorly repeatable data. The FACT chart, likely because of a smaller step size, showed slightly better retest agreement. However, the reduced range of scores on the chart due to the smaller step size led to ceiling (post-LASIK) and floor (cataract) effects. These problems could mask subtle differences between groups of patients with near normal visual function as found post-refractive or cataract surgery. The Vistech and FACT CS charts are ill suited for refractive or cataract surgery outcomes research.

Patient satisfaction and visual symptoms after laser in situ keratomileusis

PURPOSE

To examine preoperative risk factors for decreased satisfaction and symptoms of glare, halos, and/or starbursts after laser in situ keratomileusis (LASIK).

DESIGN

Retrospective, case-control study.

PARTICIPANTS

Participants were 604 previously myopic patients who underwent LASIK at least six months prior to completing the questionnaire.

METHODS

Questionnaires about satisfaction and night vision symptoms were mailed to 2100 patients from the Northeastern Eye Institute, UCLA, and the University of Pittsburgh. Preoperative and postoperative ocular variables were collected from the medical charts of the 841 subjects who returned the questionnaire.

MAIN OUTCOME MEASURES

Responses to various satisfaction and night vision symptom questions were compared to demographic and preoperative ocular variables using multivariate logistic regression.

RESULTS

The questionnaire return rate was 42.9%. The mean age for all subjects was 43.0 +/- 10.6 years, and 63% of the subjects were women. Overall, 97% of the subjects would recommend LASIK to a friend. Among subjects who would not recommend LASIK to a friend, a significantly larger percentage reported that they experienced glare, halos, or starbursts (13 of 16 (81.3%) vs. 206 of 388 (53.1%), chi(2) = 4.9, p = 0.03). Also, subjects with flatter preoperative minimum corneal curvature values were more likely to report that they would not recommend LASIK to a friend (OR = 0.71, 95% confidence interval (CI) = (0.52, 0.96), p = 0.03). The median score for satisfaction with vision was 100%, or the maximum value of 127 mm on the visual analog scale. Increasing age was significantly associated with dissatisfaction with vision after LASIK (OR = 1.68, 95% CI = (1.10, 2.56), P = 0.02). Halos were reported by 30%, glare by 27%, and starbursts by 25% of all subjects. Subjects who reported starbursts had a significantly flatter preoperative minimum corneal curvature (43.54 +/- 1.60 D versus 43.92 +/- 1.69 D, t = 2.15, p = 0.03). Also, subjects who had surgical enhancement were more likely to experience glare, halos, and/or starbursts (OR = 2.14, 95% CI = (1.33, 3.46), p = 0.002).

CONCLUSIONS

Most subjects are satisfied with their vision after LASIK. Our study suggests, however, that certain factors are associated with decreased satisfaction and night vision symptoms after LASIK. Some of these factors include: increasing age, flatter preoperative minimum corneal curvature, and surgical enhancement.

Quality of vision after laser in situ keratomileusis: influence of dioptric correction and pupil size on visual function

PURPOSE

To determine the influence of pupil size and the amount of ablation on visual performance and on the patient's perception of glare or halo after laser in situ keratomileusis (LASIK).

SETTING

Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.

METHODS

This study included a random cross-section of 50 eyes of 32 patients with "uniform" topography at least 6 months after LASIK and 51 eyes of 28 patients who had normal corneas. Each LASIK patient completed a survey rating adverse effects such as symptoms of night glare and halo. Pupil diameter and best spectacle-corrected visual acuity (BSCVA) were measured under photopic and scotopic conditions. Contrast sensitivity was measured with an MCT 8000 (Vistech Consultants, Inc.) under daytime and nighttime and with night glare conditions. A Technomed C-scan (Technomed Technology) was performed, and the potential corneal visual acuity (PCVA) was calculated after the settings for the pupil size were changed to the values measured under bright-light or dim-light conditions.

RESULTS

No significant difference was found between the post-LASIK and normal cornea groups in photopic or scotopic BSCVA (P>.05). In cases of moderate myopia, the post-LASIK group had decreased PCVA and contrast sensitivity (P<.05). In cases of high myopia, the post-LASIK group had decreased contrast sensitivity at spatial frequencies of 1.5 cycles per degree (cpd) under daytime conditions and 3 cpd under nighttime conditions (P<.05). Glare or halo symptoms did not correlate with scotopic BSCVA, PCVA, or nighttime contrast sensitivity with or without glare (P>.05). Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity under scotopic or photopic conditions (P>.05). In moderate myopia, the amount of attempted correction of the spherical equivalent (SE) was correlated with halo symptoms (P<.05; adjusted r(2) = 0.17). In high myopia, the amount of attempted astigmatism correction was correlated with the development of glare symptoms (P<.05; adjusted r(2) = 0.16).

CONCLUSIONS

There was a decrease in contrast sensitivity in post-LASIK eyes. The amount of attempted correction of the SE or astigmatism was correlated with the development of glare and halo symptoms. Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity in post-LASIK patients with "uniform" topography who had scotopic pupils not larger than 7.0 mm.

Fourier analysis of corneal astigmatic changes following photorefractive keratectomy

The purpose of this study was to evaluate the corneal irregular astigmatism following photorefractive keratectomy (PRK) for myopia. The corneal topography of 30 eyes of 26 patients was measured with the TMS-1 videokeratoscope before and 1 month after PRK. Axial dioptric data were decomposed into four components; A0 (Sphericity), C1 x 2 (Asymmetry), C2 x 2 (Regular astigmatism), and C3 (higher-order irregularity) for the central 3 and 6 mm zone by Fourier series harmonic analysis. Post-operative topographies were divided into those with an irregular and those with a homogeneous pattern, and the Fourier components were compared. In the 6 mm zone, A0 was significantly decreased (P < 0.001), and C1 x 2, C2 x 2, and C3 were significantly increased (P = 0.001, 0.005, 0.002, respectively). In the 3 mm zone, A0 decreased (P < 0.001) and C1 x 2 increased (P < 0.001) significantly. C1 x 2 was correlated with the post-operative corrected visual acuity (P < 0.001, r = 0.647). The irregular pattern group had a larger C1 x 2 component (P < 0.001). The treatment displacement was not correlated with any component. In conclusion, irregular topography due to intraoperative drift or asymmetrical wound healing may play a more important role in the post-operative corneal optical property than mild treatment displacement.

Outcomes After Laser in situ Keratomileusis Retreatment in High Myopes

PURPOSE

To evaluate the refractive and visual performance after laser in situ keratomileusis (LASIK) retreatment.

METHODS

A retrospective study was performed on 33 eyes of 23 patients who underwent LASIK (Bausch & Lomb Technolas 217C) retreatment for residual myopia with or without astigmatism. Parameters evaluated were uncorrected and best spectacle-corrected visual acuity, spherical equivalent refraction, contrast sensitivity, glare acuity, and pachymetry, preoperatively and at 1, 3, and 6 months postoperatively.

RESULTS

The mean spherical equivalent refraction before primary LASIK was -9.89 +/- 4.00 D and before retreatment was -2.85 +/- 2.17 D. Although contrast sensitivity and glare acuity decreased significantly after primary LASIK (P<.05), no significant change in these parameters was observed after retreatment. Smaller ablation zones were associated with decreased contrast sensitivity and glare acuity after primary LASIK as well as following retreatment. Contrast sensitivity and glare acuity following primary LASIK were significantly better in eyes with ablation zones > or = 5 mm than those with < 5 mm (P<.05). Eyes in which the ablation zone was the same as that for primary LASIK had significantly better contrast sensitivity than those with different ablation zones (increased or decreased) during retreatment. Attempted refractive correction during primary LASIK and retreatment had a significant negative correlation with contrast sensitivity and glare acuity following primary LASIK as well as retreatment.

CONCLUSION

The ablation zones following primary LASIK and retreatment should be > or = 5.00 mm and remain unchanged to improve visual performance.

Night vision disturbances after corneal refractive surgery

A certain percentage of patients complain of "glare" at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, "night vision disturbances." The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.

Mesopic Contrast Sensitivity Function After Excimer Laser Photorefractive Keratectomy

PURPOSE

To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia.

METHODS

Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes.

RESULTS

Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P < .01) in contrast sensitivity for the PRK patients in comparison with the control group under mesopic conditions for each spatial frequency tested (1.5, 3, 6, 12, and 18 c/deg), although no significant contrast sensitivity differences were observed between PRK and control groups at the photopic (85 cd/m2) level (P > .01 for all frequencies).

CONCLUSION

Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.

Risk factors for self-reported visual symptoms with Intacs inserts for myopia

OBJECTIVE

Potential risk factors and visual performance measures were evaluated for relationship to self-report of clinical visual symptoms after the refractive procedure for placement of Intacs microthin prescription inserts for myopia.

DESIGN

Retrospective nonrandomized comparative study.

PARTICIPANTS/INTERVENTION

Patients were participants in the U.S. Food and Drug Administration phase III KeraVision prospective clinical trials.

MAIN OUTCOME MEASURES

Study participants (n = 263) were retrospectively classified into one of three outcome groups on the basis of postoperative self-reported visual symptoms and/or request for Intacs inserts removal through month 24. Differences between outcome groups in visual acuity, refractive error, corneal geometry, corneal topography, type of preoperative corrective lens wear, and demographic variables were evaluated with multivariate logistic regression.

RESULTS

Clinical trial participants who had preoperative mean keratometry >45 diopters (D) (adjusted odds ratio [OR], 0.43; 95% confidence interval [CI], 0.21, 0.85, P = 0.02), manifest refractive astigmatism of 0.75 D or 1.00 D (adjusted OR, 0.52; 95% CI, 0.25, 1.08, P = 0.08), measured uncorrected visual acuity > or =2 lines better than that predicted by their respective cycloplegic refractive error (adjusted OR, 0.39; 95% CI, 0.14, 1.12, P = 0.08) and/or had worn soft contact lenses (adjusted OR, 0.58; 95% CI, 0.32, 1.04, P = 0.07) tended to be less likely to report postoperative clinical visual symptoms with Intacs inserts. Risk of clinical visual symptoms and request for Intacs inserts removal approximately doubled for each 0.50 D of additional postoperative defocus equivalent (crude OR, 1.86; 95% CI, 1.39, 2.48, P = 0.00). Controlling for postoperative defocus and important preoperative risk factors, subjects who reported significant clinical visual symptoms were more likely to have had preoperative uncorrected visual acuity that was worse than that predicted by their respective cycloplegic refractive error (adjusted OR, 1.84; 95% CI, 0.98, 3.42, P = 0.06). Risk of reporting clinical visual symptoms was increased with mesopic pupil diameter > or =6.5 mm (adjusted OR, 1.76; 95% CI, 0.96, 3.24, P = 0.07). Within the group of patients who reported postoperative clinical visual symptoms, 71 of 122 (58%) had ceased reporting them by month 24.

CONCLUSIONS

Adjusting for important risk factors simultaneously, this study suggested that certain preoperative characteristics may increase or decrease the likelihood, depending on the characteristic, of refractive surgery candidates to report significant clinical visual symptoms with Intacs inserts.

Quantitative topographic irregularity as a predictor of spectacle-corrected visual acuity after refractive surgery

PURPOSE

To evaluate a new topographic index called topographic irregularity as a quantitative predictor of corrected vision after refractive surgery.

METHODS

We defined topographic irregularity as the summed difference at all points between a topographic refractive corneal power map and its best-fit spherocylinder. We prospectively studied 107 eyes of 107 patients 3 months after a variety of refractive procedures. Topographic irregularity was calculated from topographic maps, and the correlation between topographic irregularity and spectacle-corrected visual acuity was determined using both high-contrast and low-contrast acuity charts. This correlation was compared with correlations for the surface regularity index and the surface asymmetry index. Next, we analyzed 54 of these topographic maps to create a regression scale relating surface regularity index, surface asymmetry index, and topographic irregularity to predict spectacle-corrected visual acuity. This scale was then used to predict spectacle-corrected visual acuity on the remaining 53 postoperative patients.

RESULTS

The correlation of topographic irregularity with spectacle-corrected visual acuity (R(2) =.36) was comparable to the correlation for the surface regularity index (R(2) =.36) and stronger than for the surface asymmetry index (R(2) =.11) when spectacle-corrected visual acuity was measured with high-contrast eye charts. Topographic irregularity correlated more strongly with spectacle-corrected visual acuity (R(2) =.42) than either the surface regularity index (R(2) =.28) or the surface asymmetry index (R(2) =.14) when spectacle-corrected visual acuity was measured with low-contrast eye charts. Using the regression scale, prediction of high-contrast and low-contrast spectacle-corrected visual acuity from topographic irregularity was superior to or comparable to predictions using the surface regularity index and the surface asymmetry index.

CONCLUSIONS

Topographic irregularity has a closer correlation with spectacle-corrected visual acuity than existing topographic indexes. Topographic irregularity is also an accurate predictor of spectacle-corrected visual acuity and may be a more sensitive tool for evaluating postoperative visual performance than current topographic measures.