Color vision and contrast sensitivity testing after radial keratotomy

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.

Color vision after laser in situ keratomileusis

PURPOSE

To evaluate the effect of laser in situ keratomileusis (LASIK) on color vision.

SETTING

Department of Ophthalmology, China Medical College Hospital, Taichung, Taiwan.

METHOD

This prospective study comprised consecutive patients having LASIK. Patients were eligible for inclusion if they had a best corrected visual acuity of 20/20 or better and a normal color vision test preoperatively and an uncorrected near visual acuity of 20/40 or better postoperatively. Color vision was tested using the Farnsworth-Munsell 100-hue test (FM 100 test) preoperatively and 1 day, 1 week, and 1 month postoperatively.

RESULTS

Twenty-nine eyes of 15 patients having LASIK were enrolled in the study. The mean patient age was 29.2 years +/- 2.9 (SD). The mean preoperative spherical equivalent refractive error was -5.6 +/- 1.8 diopters, and the mean preoperative error score of the FM 100 test was 3.79 +/- 1.55. After surgery, no significant change in the error score was observed at 1 day (4.30 +/- 1.07, P =.1039, paired t test), 1 week (3.72 +/- 1.25, P =.8125, paired t test), or 1 month (3.97 +/- 1.29, P =.6149, paired t test).

CONCLUSION

Laser in situ keratomileusis did not affect color vision evaluated by the FM 100 test.

Oblique Versus Vertical-Horizontal Incision Orientation in Four-Incision Radial Keratotomy

BACKGROUND

Four-incision radial keratotomy is used for the correction of mild to moderate myopia. The traditional orientation of incisions was naturally on the horizontal and vertical meridians. We undertook a comparative study of oblique versus traditional four-incision radial keratotomy (orthogonal orientation) to show the advantage of an oblique incision orientation.

METHODS

A prospective study of two groups of 21 eyes was conducted: an orthogonal group with vertical-horizontal orientation of the four incisions, and an oblique group with four obliquely oriented incisions. Spatial contrast sensitivity, glare, and night vision tests were performed and results compared. The follow up period was 3 months.

RESULTS

Glare and contrast sensitivity were less affected with oblique orientation of incisions. There was no significant difference regarding night vision effects. We observed a decrease in induced astigmatism with oblique orientation.

CONCLUSION

The location of horizontal incisions within the palpebral fissure and the unequal lengths of horizontal and vertical incisions are responsible for ocular alterations. An oblique orientation is preferable to avoid glare, starburst, and induced astigmatism.

Contrast sensitivity in radial keratotomy

In a prospective study, contrast sensitivity function was determined before and one month postsurgery in 15 consecutive cases of radial keratotomy. The results obtained pre-operatively were compared to those of an age-matched, emmetropic reference group also comprising 15 persons. Three different test conditions were employed. High luminance background levels of 130 cd/m2, low luminance levels of 3.5 cd/m2 and low luminance levels completed with a central glare source of 7.5 lux. Using an eight-incisional radial keratotomy technique with a 3 mm optical zone, a median reduction in myopia of 3.5 diopters was observed. Corrected visual acuity was not affected by the surgery. The contrast sensitivity functions of the myopic group pre-operatively compared to the post-operative values showed no significant difference for any of the three test conditions. Compared to the reference group, the myopic group pre-operatively demonstrated a statistically significant reduced contrast sensitivity for all test conditions.

Complications of radial and transverse keratotomy

Radial keratotomy for myopia and transverse keratotomy for astigmatism are the most commonly performed refractive surgical procedures. A decade of experience with modern techniques has produced considerable literature on the complications of keratotomy. Vision-threatening complications (bacterial keratitis, traumatic rupture of the globe through weakened keratotomy scars, endophthalmitis, cataract formation from surgical trauma to the lens) are quite rare, occurring in less than 1% of eyes in published series. The most common side effects affect most patients in the first few months after surgery: pain for 24 to 48 hours, transient glare and light sensitivity, and fluctuating visual acuity. The most common persistent complications are overcorrection and undercorrection. Persistent irregular astigmatism occurs in almost all cases in the region of the incision scars, but it is rarely severe enough to reduce spectacle acuity. Most individuals have mild glare, but this is rarely disabling. Diurnal variation of refraction in visual acuity occurs commonly, but the magnitude of the fluctuation is seldom enough to require multiple pairs of spectacles. Longterm refractive stability occurs in approximately half of eyes by six months, but approximately one in four eyes will experience continued change over six months to four years. Complications, such as scarring from intersecting keratotomy incisions, irregular astigmatism resulting from multiple reoperations, and overcorrections with the attendant early onset of symptomatic presbyopia are becoming much less frequent.