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 Effect of Laser in situ Keratomileusis on Low Contrast Vision

PURPOSE

To determine the effects of laser in situ keratomileusis (LASIK) on low contrast visual acuity.

METHODS

Thirty eyes of 15 LASIK patients with myopia and astigmatism were evaluated preoperatively, and 1 and 3 months postoperatively. High contrast visual acuity (HCVA), low contrast visual acuity (LCVA), and contrast threshold were determined.

RESULTS

Mean spherical correction (SE) was -3.24 +/- 1.90 D; 16 eyes had a mean SE between -1.00 and -3.00 D, and 14 eyes were between -3.25 and -6.50 D. There was no significant change in HCVA observed at 1 and 3 months in any eye. There was a decrease in LCVA in eyes with a correction >3 D SE at 1 month (P=.04), which returned to normal at 3 months (P=.13). There was an increase in the contrast threshold at 1 month (P=.016). When eyes were divided into groups, those with >3D SE correction had an increase in contrast threshold at 1 month (P=.002); no change was seen in eyes with <3D SE correction (P=.15). At 3 months, contrast threshold was similar to baseline values in all eyes (P=.226).

CONCLUSION

LASIK transiently decreased low contrast visual function in patients with greater than 3.00 D of myopic correction.

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.

Contrast Sensitivity After Posterior Chamber Phakic Intraocular Lens Implantation for High Myopia

PURPOSE

To evaluate contrast sensitivity after posterior chamber phakic intraocular lens (PIOL) implantation for the correction of high myopia.

METHODS

Twenty eyes of ten patients had a posterior chamber phakic intraocular lens (Staar ICL) implanted to correct high myopia. Mean preoperative myopia was -14.10+/-2.70 D. Follow-up was 24 months for all patients. Contrast sensitivity was tested with best spectacle-corrected visual acuity preoperatively and 3, 6, 12, 18, and 24 months postoperatively.

RESULTS

Contrast sensitivity increased after surgery in all spatial frequencies. Normal values were achieved for low and intermediate spatial frequencies (3 and 6 c/deg). However, in spite of the improvement, values were still below normal for high spatial frequencies (12 and 18 c/deg). When the first postoperative examination was not considered, there were no statistically significant differences in contrast sensitivity values at different postoperative periods.

CONCLUSION

Contrast sensitivity increased after posterior chamber phakic intraocular lens implantation (Staar ICL) in all spatial frequencies when compared to preoperative contrast sensitivity (best spectacle-corrected).

Improvement in photorefractive corneal laser surgery results using an active eye-tracking system

PURPOSE

To study the advantage of modern eye-tracking systems for photorefractive surgery.

SETTING

Department of Ophthalmology, University of Zurich, Zurich, Switzerland.

METHODS

Photorefractive surgery (photorefractive keratectomy and laser in situ keratomileusis) for myopia and myopic astigmatism was performed in 40 eyes with a commercially available medical excimer laser system. The eyes were selected retrospectively from a larger group of patients treated at 1 clinic. In 20 eyes, the ablation was centered on the entrance pupil using the active, video-based, eye-tracking system (sampling frequency 50 Hz) of the laser. During laser treatment in the nontracker group (20 eyes), the active eye-tracking system was switched off and centration was done manually by the surgeon. Preoperatively and 1 and 3 months after surgery, the patients had a standard ophthalmic examination as well as wavefront analysis by means of a custom-designed wavefront analyzer.

RESULTS

After surgery, the visual acuity was significantly better (P <.05) in patients treated with the eye tracker. The increase in coma-like (relative increase factor 0.4) and spherical aberrations (relative increase factor 1.1) was significantly smaller in these patients than in those in the nontracker group (spherical equivalents of 3.9 and 5.1, respectively; P <.05). The refractive outcome, however, was not significantly different in sphere and cylinder.

CONCLUSION

The use of active eye tracking appeared to improve the optical and visual outcomes but did not affect the refractive outcome after photorefractive laser surgery.

Contrast sensitivity evaluation after laser in situ keratomileusis

OBJECTIVE

To determine the effects of laser in situ keratomileusis (LASIK) on best-corrected visual acuity (BCVA) and contrast sensitivity.

DESIGN

Prospective, observational case series.

PARTICIPANTS

One hundred twelve eyes, in 65 patients with myopia and myopia with astigmatism, who underwent LASIK. TESTING AND MAIN OUTCOME MEASURES: Best-corrected visual acuity using the Snellen visual acuity chart and contrast sensitivity using the CSV 1000 (Vector Vision, Dayton OH) was tested before surgery and 1 week, 1 month, and 3 months after surgery in patients who underwent LASIK.

RESULTS

Contrast sensitivity was depressed for patient eyes with spherical equivalence (SE) between -1.25 diopters (D) and -13.75 D, at 12 cycles/degree for at least 3 months and at 18 cycles/degree for 1 week after LASIK. For patient eyes with SE between -1.25 D and -6.00 D, contrast sensitivity was depressed only at 12 cycles/degree for at least 3 months after LASIK. For patient eyes with SE between -6.00 D and -13.75 D, contrast sensitivity was depressed at 6, 12, and 18 cycles/degree 1 week after LASIK but returned toward preoperative levels by 1 month after surgery. Despite the slight decreases in contrast sensitivity, all scores were still within the range of normal values except for 12 cycles/degree for 3 months and 18 cycles/degree at 1 week after surgery in the high myopia group. Although highly myopic patients, compared with patients with low myopia, had slightly less BCVA before surgery, both groups maintained their preoperative BCVA at all postoperative visits.

CONCLUSIONS

Based on this study, we conclude that LASIK has little effect on BCVA and contrast sensitivity for up to 3 months after surgery.

Prediction of letter contrast sensitivity using videokeratographic indices

PURPOSE

To analyze the relationship between corneal topography and letter contrast sensitivity.

METHOD

Experiments were conducted on 59 eyes of 51 patients who had best spectacle-corrected visual acuity of 20/20 or better and no ocular pathology except for the corneal shape. Thirty-nine eyes had an abnormal topographic pattern resulting from keratoconus, and the other 20 eyes showed a normal topographic pattern. Videokeratography was performed with the TMS-2 videokeratoscope, and the surface regularity index, surface asymmetry index, and coefficient of variation of power were obtained for each subject. Letter contrast sensitivity was measured with the CSV-1000LV with spectacle correction. The correlation between the number of correct letters and topographic indices was calculated.

RESULTS

The abnormal topography group had a significantly greater loss of letter contrast sensitivity (median = 20 letters) than the normal control (median = 23 letters; P =.0001). There were statistically significant correlations between number of correct letters and the coefficient of variation of power (r = -.77; P =. 001), number of correct letters and surface regularity index (r = -. 76, P =.001), and the number of correct letters and surface asymmetry index (r = -.64; P =.001). The linear regression equation between number of correct letters and the coefficient of variation of power was the number of correct letters = -0.05 x the coefficient of variation of power + 23.2.

CONCLUSIONS

Our results suggest that subtle visual deteriorations, which are barely detected by contrast sensitivity testing, can be predicted objectively by the corneal topographic indices.

Wavefront-guided Laser in situ Keratomileusis: Early Results in Three Eyes

PURPOSE

Wavefront optical aberrations induced by refractive corneal surgery correction of myopia are probably the reason for deterioration of visual performance in some eyes after surgery. Customized photoablation of the cornea to correct both the sphero-cylindrical refractive error as well as individual optical aberrations may improve postoperative visual acuity and visual performance.

METHODS

In 3 eyes of 3 patients the wavefront deviations were measured by means of an aberrometer of the Tscherning-type. Based on these measurements an ablation pattern was determined and applied during a LASIK procedure using a Wavelight Allegretto scanning spot excimer laser with a spot size of 1 mm and a laser repetition rate of 200 Hz. The 3 eyes are part of a prospective study on wavefront-guided LASIK started in July 1999.

RESULTS

At 1 month after LASIK, all 3 eyes had gained up to 2 lines of best spectacle-corrected visual acuity. Best spectacle-corrected visual acuity improved to 20/10 in all 3 eyes, uncorrected visual acuity was 20/10 in two eyes, and 20/12.5 in 1 eye 1 month postoperatively. The wavefront deviations were reduced by 27% on average. At 3 months, best spectacle-corrected visual acuity was 20/10 in 2 eyes and 20/12.5 in 1 eye.

CONCLUSION

Wavefront-guided LASIK is a feasible approach in refractive corneal surgery. Optimized ablation patterns may further improve the visual results.

Role of clearance and treatment zones in contrast sensitivity: significance in refractive surgery

PURPOSE

To evaluate the relationship between contrast sensitivity, surgical treatment zone, and clearance (ablation or clear zone-pupil diameter) in photorefractive keratectomy (PRK) and radial keratotomy (RK).

SETTING

Saint Louis University Eye Institute, St. Louis, Missouri, and Hunkeler Eye Center, Kansas City, Missouri, USA.

METHODS

Thirteen patients had PRK and 20, RK. Contrast sensitivity was measured with the Stereo Optical F.A.C.T. (F.A.C.T.) and VectorVision CSV-1000 (VV) charts. Pupils were measured with the Rosenbaum card.

RESULTS

In the PRK group, VV contrast sensitivity at 6 and 12 cycles per degree (cpd) correlated with the ablation zone (r2 = 0.18 and 0.22, respectively), while visual acuity and F.A.C.T. contrast sensitivity did not correlate. In the RK group, both VV and F.A.C.T. contrast sensitivity at 6 cpd correlated with clearance (r2 = 0.29 and 0.12, respectively). Pupils were larger with the VV test than with the F.A.C.T. chart because ambient chart luminance was less in the former.

CONCLUSION

Contrast sensitivity is likely a more sensitive indicator of visual function than acuity in refractive surgery. The VV system unmasks aberrations from the transition zone of ablated and unablated cornea in PRK. Larger samples are needed to determine the critical ablation clearance of the pupil to avoid loss of visual function.

Contrast sensitivity after laser in situ keratomileusis

PURPOSE

To evaluate the effect on contrast sensitivity function of laser in situ keratomileusis (LASIK) for the correction of myopia.

SETTING

Alicante Institute of Ophthalmology, University of Alicante, Spain.

METHODS

Fourteen eyes of 10 patients had LASIK to correct myopia ranging from 6.00 to 19.50 diopters (D). Mean preoperative myopia was 10.39 D +/- 3.69 (SD). Contrast sensitivity was tested preoperatively and 1, 3, and 6 months postoperatively using the CVS-1000E contrast sensitivity unit (VectorVision).

RESULTS

Contrast sensitivity decreased 1 month postoperatively; the decrease was significant only at the low and intermediate spatial frequencies of 3 and 6 cycles per degree (cpd) (P = .034 and .030, respectively). Starting from the first month, there was rapid recovery of contrast sensitivity and at the third month, no statistically significant decrease at all spatial frequencies. Six months after surgery, there was an increase in contrast sensitivity values at 3, 12, and 18 cpd, although the changes were not significant.

CONCLUSION

Although LASIK decreased contrast sensitivity values at low and intermediate spatial frequencies for 1 month after surgery, these values rapidly returned to the preoperative values at 3 months. The improvement at certain frequencies at 6 months suggests that LASIK can improve the quality of vision in eyes with moderate and high myopia.

Effects of flurbiprofen and indomethacin on acute cystoid macular edema after cataract surgery: functional vision and contrast sensitivity

We examined the effect of acute cystoid macular edema (CME) on contrast sensitivity. Eyedrops were instilled into the surgically treated eye f1p4 times daily for two days preoperatively and for three months postoperatively. Angiographic and clinical CME were measured, as were contrast sensitivity and Snellen acuity. Jaeger visual acuity equivalents were calculated and digital imaging techniques used to simulate visual function. We found that angiographic CME reduces functional vision as measured by contrast sensitivity and visual acuity over a large range of sizes. In patients treated with the flurbiprofen vehicle, those without CME had higher mean contrast sensitivity scores than those with CME; this increased over time. Those treated with flurbiprofen and indomethacin had slightly higher contrast sensitivity scores than vehicle-treated patients; this also increased over time, most notably in the higher spatial frequencies. Flurbiprofen treatment improved contrast sensitivity in patients with and without CME significantly at 12 cycles per degree. Flurbiprofen-treated patients with CME in general had higher contrast sensitivity scores than vehicle-treated patients. In this population of patients having cataract surgery, treatment with flurbiprofen or indomethacin reduced the loss of functional vision associated with CME.