Nagy ZZ, Munkácsy G, Krueger RR. Changes in mesopic vision after photorefractive keratectomy for myopia. J Refract Surg. 2002 May-Jun;18(3):249-52.

Abstract:

PURPOSE: To evaluate the mesopic functions of excimer laser treated eyes with different treatment diameters and different laser beam delivery systems.

METHODS: In Group 1, 38 eyes were treated with the Aesculap Meditec MEL 60 ArF scanning laser beam excimer laser. The treatment diameter was 5.0 mm. In Group 2, 38 eyes were treated with the Aesculap Meditec MEL 70(G-Scan) flying spot excimer laser; the chosen treatment diameter was 6.5 mm. In Group 3, there were 38 eyes with no treatment; vision was corrected only with spectacles (control group). All eyes had 20/20 best spectacle-corrected visual acuity before surgery, as did the control group. Measurements were carried out preoperatively and at 12 months following surgery. All eyes exhibited normal corneal wound healing, and subepithelial haze was <0.5 according to Hanna's scale. Mesopic functions (mesopic vision and glare sensitivity) were tested with the Mesoptometer II.

RESULTS: The average preoperative refractive error in Group 1 was -3.40 D; in Group 2, -3.38 D; in Group 3, -3.44 D. In Group 1, 34% of the treated eyes met the night driving requirements (recognition at 1:5 contrast level), whereas in Group 2, 85%, and in Group 3, 95% of the eyes fulfilled this criteria. When contrast vision was tested under glare conditions in Group 1, 31.6%; in Group 2, 80%; and in Group 3, 94.7% of the eyes identified the target orientation (Landolt ring) at contrast level 1:5.

CONCLUSIONS: The unoperated spectacle wearers had better results in all tested functions. The larger 6.5-mm treatment diameter with the use of the flying spot laser beam delivery system resulted in better mesopic function and contrast vision under mesopic conditions than the smaller 5.0-mm diameter.

Full text excerpts:

Patients with larger than 6.5-mm mesopic pupil diameter were also excluded.

The mean pupil size under photopic conditions in Group 1 was 2.4 ± 0.06 mm, under mesopic conditions it was 5.8 ± 0.4 mm. In Group 2, the mean pupil size under photopic conditions was 2.42 ± 0.05 mm, under mesopic conditions it was 5.9 ± 0.32 mm.

As PRK has been accepted as a standard refractive procedure, the resulting quality of vision has become an important issue in refractive surgery. In the early
days of PRK, high contrast visual acuity and performance was usually the only parameter tested, although from the start patients reported visual impairment under mesopic and glare conditions. In practice, especially night car driving causes problems. Refractive surgeons attributed the decrease of low-contrast vision to the size of the ablation zone and to the corneal wound healing processes (subepithelial haze) following excimer PRK; the role of ablation zone diameter has been studied. With pupil dilation, the presence of a special refractive ring can be verified using retroillumination. Using videokeratography, surface irregularities can also be verified.