Diurnal visual changes in radial keratotomy: implications for visual standards. Refractive Surgery Study Group

Multifocal Corneal Excimer Femtosecond Laser in situ Keratomileusis following Radial Keratotomy: A Case Report with Six Months of Follow-Up

We report the case of a 46-year-old female patient who was referred to our clinic (Orasis Eye Clinic, Reinach, Switzerland) seeking improvement of her distance and near visual acuity. Radial keratotomy (RK) was performed at a younger age on both eyes to correct -5 D myopia. The patient underwent a bilateral same-session multifocal corneal excimer femtosecond laser (Supracor) keratomileusis correction. We introduce a new correction approach, possibly suitable for presbyopic patients previously treated with RK, and we present several potential novel advantages such as enhanced near, intermediate vision, and improvement in quality of life. This is the first report of a bilateral excimer laser treatment attempt of presbyopia following RK.

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.

Normal values for the Pelli-Robson contrast sensitivity test

PURPOSE

To define normal values for the Pelli-Robson contrast sensitivity test in different age groups.

SETTING

University Eye Clinic of Kuopio, Kuopio, Finland.

METHODS

Contrast sensitivity was measured with the Pelli-Robson contrast sensitivity test in 87 persons (60 women and 27 men) with a mean age of 34.5 years +/- 20.8 (SD) (range 6 to 75 years). Results were studied by age group (years): 6 to 9, 10 to 19, 20 to 29, 30 to 39, 40 to 49, 50 to 59, and 60 and older. Of 163 eyes, both were healthy in 76 persons and 1 was healthy in 11. Study participants consisted of members of the staff of the Kuopio University Hospital Eye Clinic, medical students at the Kuopio University, and patients of the Strabismus and General Ophthalmology Units of the Eye Clinic and their accompanying persons. Two test distances were used: 1 m and 3 m. Eyes were tested individually; thereafter, the test was done binocularly.

RESULTS

There were significant differences in logarithmic contrast sensitivity values among the age groups except on the test of the left eye at 1 m. The P values for the right eye at 1 m and 3 m, left eye at 1 m and 3 m, and both eyes at 1 m and 3 m were 0.003, 0.002, 0.19, 0.043, 0.037, and 0.003, respectively. The mean test results in 1 eye varied from 1.68 in the 60 year and older group to 1.84 in the 20 to 29 and 30 to 39 year groups. Binocularly, the variation was from 1.73 in the 40 year group to 1.99 in the 30 year group.

CONCLUSIONS

The Pelli-Robson contrast sensitivity test is a quick and reliable method in a clinical setting. Normal values of the test can be of help in evaluating cataract patients or patients having refractive surgery.

Diurnal stability of refraction after implantation with intracorneal ring segments

PURPOSE

To investigate diurnal changes in visual acuity and refraction in myopic eyes implanted with intracorneal ring segments (ICRS).

SETTING

University of California San Diego Shiley Eye Center, La Jolla, California, and Emory University Vision Correction Center, Atlanta, Georgia, USA.

METHODS

This prospective study involved 2 groups of patients who had ICRS (Intacs) implantation and a follow-up of at least 6 months. The first group included 102 eyes of 51 bilaterally treated patients; the second group, 32 eyes of 16 unilaterally treated patients. Examinations including visual acuity, manifest refraction, and videokeratography were done in the morning and evening at least 9 hours apart on a single day. Refractive changes were analyzed by power vectors; multivariate statistics were used to determine the significance of change in any component of the spectacle prescription.

RESULTS

In the bilateral treatment group, 97 eyes (95%) were within 1 line of spectacle-corrected visual acuity from morning to evening. The mean change in manifest refraction was -0.14 +0.08 x 4 and in spherical equivalent, -0.10 diopters (D) (sigma = 0.3; range -0.750 to +0.875 D). Ninety-six eyes (94%) had a change in refraction within 0.50 D of spherical equivalent. There was no significant change in corneal power (P =.20). In the unilateral treatment group, there was no significant difference between treated and untreated eyes in changes in spectacle-corrected visual acuity, manifest refraction, or corneal power and toricity (P.05).

CONCLUSION

No clinically significant diurnal variation in visual acuity or manifest refraction was observed after ICRS implantation or in untreated paired eyes. Moreover, the data suggest less diurnal change in visual acuity and refraction after ICRS implantation.

Visual performance requirements for post-PRK police recruits

BACKGROUND: New Zealand Police regulations (1996) allow the unaided visual acuity requirement of 6/12 to be achieved following refractive surgery (except radial keratotomy or keratoplasty) provided applicants also achieve normal (95 per cent confidence limit data from the literature): glare disability, contrast sensitivity, and low luminance visual acuity, one year or more after treatment. METHODS: To confirm the limits adopted, 80 young normal adults were subjected to the tests in the regulations. To examine the operation of the current standards, the results of 34 post-photorefractive keratectomy (post-PRK) police applicants are reported. Glare disability was the loss of high contrast visual acuity (VA) with the Mentor Brightness Acuity Tester at medium intensity. Contrast sensitivity (CS) was examined using both Melbourne Edge Test thresholds and the VA difference between high and low contrast Bailey-Lovie charts. Low luminance VA was measured using high contrast Bailey-Lovie charts viewed through a one per cent transmittance filter. RESULTS: The 95 per cent confidence limits found for normal performance were as follows. Glare disability: no more than 10 letters worse than VA without glare. Contrast sensitivity: no more than 12 letters difference between high contrast and low contrast letter acuity together with an edge contrast threshold of not less than 20 dB (CS = 100). These results were close to the values adopted for the current standard. The 95 per cent confidence limit for low luminance VA was a loss of 24 letters (almost five lines) and not the three lines of loss estimated from the literature. Two of the 34 post-PRK applicants failed. One was unable to achieve 6/6 acuity with best refraction. The second could not meet the low luminance VA limit (loss no more than three lines). No failures have been due to glare disability or poor contrast sensitivity even though one applicant had obvious corneal haze.