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.

Assessment of Corneal Wound Healing by Interactive Topography

INTRODUCTION

Constitutive properties of the cornea and wounds within the cornea have been measured previously by destructive methods in which a strip of cornea was removed, placed on an instrument, and stretched until broken. To assess corneal wound healing and the interaction of medication, incision patterns and other clinical issues, we present a simple, noninvasive test of corneal wound healing utilizing a videokeratoscope and Honan balloon.

METHODS

A pre-test corneal topography was performed. The Honan balloon was placed on the eye at a pressure of 30mm mercury for 5 minutes. After removal of the balloon, additional corneal topographies were performed for comparison to the baseline topography. Study eyes were divided into six groups: 15 eyes in the normal group not involved in the Honan balloon test, 15 eyes formed a control group without previous ocular surgery, 15 eyes were within 3 months of radial keratotomy (RK), 15 eyes were more than 9 months after RK, 12 eyes had previous automated in situ keratomileusis (ALK), and 12 eyes had previous penetrating keratoplasty (PK).

RESULTS

Average videokeratometric flattening was reported for all groups at intervals of 1, 2, and 3 minutes after removal of the Honan balloon. The normal group flattened by 0.04 +/- 0.10 D (range, +0.10 to -0.12 D) at 1 minute; 0.02 +/- 0.08 D (range, +0.10 to -0.10 D) at 2 minutes; and 0.02 +/- 0.06 D (range, +0.10 to -0.09 D) at 3 minutes. The control group flattened by -0.10 +/- 0.10 D (range, +0.30 to -0.30 D) at 1 minute; 0.01 +/- 0.12 D (range, +0.15 to -0.25 D) at 2 minutes; and 0.07 +/- 0.11 D (range, +0.14 to -0.18 D) at 3 minutes. The 3-month RK group flattened 0.95 +/- 0.23 D (range, 1.35 to 0.67 D) at 1 minute; 0.53 +/- 0.16 D (range, 0.71 to 0.39 D) at 2 minutes; and 0.40 +/- 0.15 D (range, 0.56 to 0.30 D) at 3 minutes. The 9-month RK group flattened 0.10 +/- 0.13 D (range, 0.23 to 0.02 D) at 1 minute; 0.10 +/- 0.12 D (range, 0.18 to -0.01 D) at 2 minutes; and 0.01 +/- 0.14 D (range 0.05 to 0.10 D) at 3 minutes. The ALK group flattened 0.65 +/- 0.42 D (range 0.98 to 0.38 D) at 1 minute; 0.27 +/- 0.19 D (range 0.39 to 0.10 D) at 2 minutes; and 0.21 +/- 0.17 D (range, 0.29 to 0.09 D) at 3 minutes. The PK group flattened 1.30 +/- 0.60 D (range, 1.75 to 0.90 D) at 1 minute; 1.18 +/- 0.43 D (range, 1.51 to 0.98 D) at 2 minutes; and 0.41 +/- 0.57 D (range, 0.88 to 0.30 D) at 3 minutes.

CONCLUSIONS

We have established normal corneal wound healing curves from preliminary data utilizing Buzard interactive topography on normal control eyes and after radial keratotomy, automated lamellar keratoplasty, and penetrating keratoplasty. Deviation from these normal curves indicates either excessive or inadequate wound healing.

Healing of reopened-and-sutured radial keratotomy wounds

We designed a study to evaluate healing in reopened-and-sutured (RAS) keratotomy wounds to determine the efficacy of reoperations in treating radial keratotomy overcorrections. Using light and transmission electron microscopy, we compared stromal scar tissue organization (transverse fibroblast orientation and collagen fiber continuity across the wound) in RAS wounds and in sutured and unsutured control wounds in 18 monkey eyes one to nine weeks after surgery. Wound healing morphology of RAS wounds varied with the interval between reoperation and termination of the experiment. Scar tissue organization was sagittal at one week postoperatively, transverse in the anterior and mid regions after four weeks, and transverse over the entire wound after nine weeks. Sutured wounds showed a similar pattern of healing, although transverse scar tissue organization was restricted to the anterior and mid regions in the late healing phases. In contrast, unsutured wounds showed a temporary, transverse scar tissue organization over the entire wound depth at two to four weeks and a progressive reorientation of the mid and posterior scar tissue sagittal to the wound at later intervals. The results suggest that reopening and suturing keratotomy incisions to treat radial keratotomy overcorrections may be effective through a myopic shift induced by sutured wound apposition and long-term wound remodeling, contraction, or both.

Photorefractive keratectomy to treat myopia and astigmatism after radial keratotomy and penetrating keratoplasty

Fifteen eyes with an initial myopia between -5.00 diopters (D) and -12.00 D were treated with radial keratotomy (RK) followed by photorefractive keratectomy (PRK) at least 6 months later and observed for 6 months to 24 months. Five eyes that had penetrating keratoplasty (PKP) were treated for residual ametropia by PRK and followed for up to two years. For the RK-treated eyes, mean pre-PRK refraction was -4.00 D sphere and + 1.25 D cylinder, which improved to -0.52 D sphere and + 0.73 D cylinder. Incidence of complications, including corneal haze, was extremely low in both the RK and PKP groups. In summary, PRK is a valuable method for correcting ametropia following RK and PKP, with risks similar to that for eyes having PRK as the initial refractive procedure.