Contrast sensitivity and laser in situ keratomileusis

One year follow-up of contrast sensitivity following conventional laser in situ keratomileusis and laser epithelial keratomileusis

PURPOSE

To determine the effect of conventional laser in situ keratomileusis (LASIK) and laser epithelial keratomileusis (LASEK) for myopia on contrast sensitivity (CS) using the Pelli-Robson and Vector Vision CSV-1000E CS tests.

METHODS

A prospective, comparative study was conducted on 36 eyes of 36 patients with myopia undergoing LASIK (18 eyes) and LASEK (18 eyes). Surgery was performed using the Technolas 217z laser (Bausch & Lomb). CS was recorded preoperatively and at 3, 6 and 12 months postoperatively.

RESULTS

No statistically significant difference was found in LogMAR uncorrected visual acuity post-LASIK (-0.02 ± 0.16) and LASEK (-0.04 ± 0.14). Using the Pelli-Robson, CS was significantly lower in the LASIK group 3 and 6 months postoperatively. No significant postoperative reduction in CS was observed in either treatment group. Using the CSV-1000E test, CS was significantly reduced post-LASIK at 3 (p = 0.05) and 6 (p = 0.05) cycles/degree under photopic conditions. No significant postoperative change occurred in the LASEK group under photopic or scotopic conditions. There was no significant difference in postoperative CS between the LASIK and LASEK groups at 3, 6, 12 or 18 cycles/degree using the CSV-1000E test.

CONCLUSION

One year postoperatively, there was no difference in CS between both treatment groups using the Pelli-Robson and CSV-1000E tests. CS was reduced postoperatively in the LASIK group at the lower spatial frequencies under photopic conditions. No postoperative change was detected in CS following LASIK or LASEK using the Pelli-Robson test.

Effect of laser in situ keratomileusis on vision analyzed using preoperative optical quality

PURPOSE

To evaluate the effect on vision of laser in situ keratomileusis (LASIK) based on preoperative optical quality.

SETTING

Universitat Politècnica de Catalunya, Terrassa, and Barcelona Institute of Ocular Microsurgery, Barcelona, Spain.

DESIGN

Comparative case series.

METHODS

The relative change in optical quality and visual acuity were evaluated in eyes that had LASIK for myopia. The optical quality was assessed before and 3 months after surgery using parameters provided by a double-pass system. Patients were classified into 4 groups by preoperative optical quality: low (Group 1), moderate (Group 2), high (Group 3), and very high (Group 4).

RESULTS

The study evaluated 25 patients (50 eyes). The optical quality parameters improved postoperatively in Group 1 and Group 2, with the improvement ranging from 15% to 21% and from 13% to 17%, respectively. The preoperative and postoperative optical quality in Group 3 was similar. The optical quality in Group 4 worsened significantly by percentages ranging from -20% to -26%. Although visual acuity had the same trend, there were no statistically significant changes.

CONCLUSION

The changes in optical quality after LASIK surgery depended on the patient's preoperative optical quality; visual acuity showed the same trend, although no change was significant.

Contrast Sensitivity After LASIK, LASEK, and Wavefront-guided LASEK With the VISX S4 Laser

PURPOSE

To evaluate the changes in contrast sensitivity and glare after corneal refractive surgery for moderate myopia.

METHODS

The study comprised 267 eyes of 149 patients who underwent LASIK, laser epithelial keratomileusis (LASEK), or wavefront-guided LASEK with the VISX STAR S4. Contrast sensitivity was measured with VCTS 6500 before surgery and at 2 and 6 months postoperatively. Glare was evaluated using questionnaires and the ALC glare test at last follow-up. Contrast sensitivity at 2 and 6 months was compared with preoperative contrast sensitivity in each group. Glare sensitivity in each group was compared to normal controls.

RESULTS

Contrast sensitivity did not change after LASIK (P > .05). Contrast sensitivity of 3 and 6 cycles per degree (cpd) at 2 months increased after LASEK (P < .05) and contrast sensitivity of 6, 12, and 18 cpd at 2 months and 3, 6, 12, and 18 cpd at 6 months improved in wavefront-guided LASEK (P < .05). Glare test and questionnaires did not show any significant difference between the groups.

CONCLUSIONS

Wavefront-guided LASEK induced significant increases in contrast sensitivity of moderate myopes at high spatial frequencies under mesopic conditions by 6 months. Glare was not affected by the different refractive procedures.

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.