Refractive Surgery

PURPOSE:
The purpose of the study was to determine the integrity of human eyes after refractive procedures.

METHODS:
Whole human globes underwent either radial keratotomy (RK) with eight incisions, automated lamellar keratoplasty (ALK), photorefractive keratectomy (PRK), or excimer laser assisted in situ keratomileusis(LASIK). Eyes then were subjected to quantitatively increasing levels of trauma until rupture occurred.

RESULTS:
All eyes operated on required less energy to rupture as compared with that of control eyes. The mean number of trials required for rupture is as follows (energy doubled with each successive trial): normal, 4.29; LASIK, 3.80; ALK, 3.67; PRK, 3.60; and RK, 2.83. The level of energy required to rupture normal, ALK, PRK, and LASIK eyes was not significantly different. All RK eyes ruptured at incisions. Most ALK, PRK, and LASIK eyes ruptured near the flap edge or limbus. Most normal eyes ruptured with both corneal and scleral involvement. Age of tissue donors at the time of death and time elapsed between death and procedure were not significantly different between groups (P = 0.88 and 0.79, respectively).

CONCLUSIONS:
The energy required to rupture ALK,PRK, and LASIK eyes is not significantly different from that for normal eyes. The RK eyes ruptured with significantly less energy than did normal eyes. All RK eyes ruptured at incision sites.

Authors' abstract, Ophthalmol
Houston, TX

Refractive Surgery

PURPOSE: We present the clinicopathologic correlations of two case and two other clinical cases of topical anesthetic abuse keratopathy that were originally diagnosed as Acanthamoeba keratitis because of ring keratitis presentation and characteristic history.

METHODS: Four patients who were referred to us with suspected Acanthamoeba keratitis are included. Each was initially treated for amoebic keratitis, by using established protocols, and only later was the true origin (topical anesthetic abuse) uncovered. The clinical and surgical histories, pathologic analysis of the corneal specimens, and follow-up of < or = 4 years are included.

RESULTS: Our four cases show another cause for ring infiltration of the cornea. Two cases resulted in corneal transplantation and multiple other medical or surgical treatments in an attempt to restore vision but had poor outcomes of finger-counting vision. Two other cases responded to intensive medical treatments with return of useful vision. Evaluation of the surgical specimens revealed a previously unpublished finding of near total cell death within the corneal stroma.

CONCLUSION: Topical anesthetic abuse resulting in sight-threatening keratitis may be seen as a masquerade syndrome in many cases. Because of the often poor outcome, we must be aware of this entity, prevent abuse, and be vigilant in our prohibition of topical anesthetic for any therapeutic use.

Authors' abstract, Cornea
National Naval Medical Center,
Bethesda, Maryland

Refractive Surgery

PURPOSE: To analyze the results after laser-assisted in situ keratomileusis (LASIK) treatment for positive cylinder at the flattest meridian.

SETTING: Instituto de la Vision, Buenos Aires, Argentina.

METHODS: A prospective, nonrandomized study was conducted. Patients were divided into three groups: (1) simple hyperopic astigmatism (SHA); 15 eyes with a mean preoperative cylinder of +3.37 diopters (D) +/- 1.62 (SD); compound hyperopic astigmatism (CHA); 75 eyes with a mean preoperative cylinder of +3.34 +/- 1.39 D; (3) mixed astigmatism (MA); 73 eyes with a mean preoperative cylinder of +3.45 +/- 2.15 D. In all eyes, treatment of the cylinder was performed at the flattest meridian by LASIK using the Chiron-Technolas Keracor 116/117 laser. The following parameters were analyzed over time: uncorrected visual acuity; best corrected visual acuity; correction of the spherical equivalent and the cylinder; lines of visual acuity gained and lost.

RESULTS: Six months after the procedure, refractive cylinder was reduced to +0.58 +/- 1.22 D in the SHA group, +0.12 +/- 1.23 D in the CHA group, and -0.11 +/- 1.28 D in the MA group. Uncorrected visual acuities were 20/20 or 20/25 in 66.7, 60.4, and 76.5% of the groups, respectively.

CONCLUSIONS: Use of the LASIK technique with the Keracor laser to treat positive cylinder at the flattest meridian corrected simple and compound hyperopic astigmatism and mixed astigmatism with good predictability and safety. This treatment has not produced a hyperopic refractive change at the opposite meridian.

Authors' abstract, JCRS
Instituto de la Vision,
Buenos Aires, Argentina.

Refractive Surgery

PURPOSE:
To determine the degree of corneal thickness variability that may be encountered during routine radial keratotomy (RK) surgery.

SETTING:
Office refractive surgical suite. Laurel Eye Clinic, Brookville, Pennsylvania.

METHODS:
This study statistically analyzed variability in corneal thickness measured at the optical zone in 140 consecutive eight-incision RK cases. Pachymetry measurements were assessed at each of the eight circumferential optical zone locations and then evaluated in regard to intra-patient variation by location and inter-patient variation in location thickness patterns. Covariants such as central corneal thickness and differing optical zone size were also analyzed.

RESULTS:
Mean corneal thickness (adjusted for optical zone and central thickness) between the three superior locations and the three inferior locations varied by 10 microns. In more than 10% of cases, this adjusted difference was greater than 30 microns. Central corneal thickness and differing optical zone sizes had a significant effect on the results.

CONCLUSION:
Corneal thickness measured at the optical zone during eight-incision RK varied significantly by incision location, bringing into question the notion that one blade depth setting is adequate for all incisions.

Authors' abstract, JCRS
San Diego, CA

Refractive Surgery

PURPOSE:

We report preliminary results of a new procedure for correcting high astigmatism after penetrating keratoplasty.

METHODS:

The procedure entails full-thickness trephination along the original donor-recipient junction with careful suturing in a combined interrupted and running fashion. Four eyes of four patients with severe astigmatism and myopia after penetrating keratoplasty underwent the procedure.

RESULTS:

High preoperative cylinder ranging from 4.50 to 16.00 D (mean 9.00 D) was reduced to 0.50 to 3.50 D (mean 1.90 D) at the last examination (between 3 to 6 months). Spherical equivalent myopia ranging from -2.00 to -10.25 D (mean -4.90 D) was essentially unchanged at plano to -9.00 D (-4.70 D) at the last examination. Overall, there was a mean refractive cylinder reduction of 7.10 D (79%).

CONCLUSION:

Retrephination after penetrating keratoplasty appears to be an acceptable alternative for correcting high astigmatism, and had only a small effect on the level of myopia.

Authors' abstract, JRS
Anheuser-Busch Eye Institute,
St. Louis, MO

Refractive Surgery

BACKGROUND:

The correction of astigmatism with photorefractive keratectomy has been recommended in simple and myopic astigmatism. Therefore in this study the excimer laser was used to correct compound hyperopic and mixed astigmatism.

METHODS:

We present a prospective clinical study of photorefractive keratectomy in 30 eyes of 24 patients with compound hyperopic astigmatism with a mean spherical equivalent of +4.30 D and mean astigmatism of 2.33 D (group I) and in 17 eyes of 15 patients with mixed astigmatism with a mean spherical equivalent refraction of +0.46 D and mean astigmatism of 4.75 D (group II). The excimer laser used in this study was an MEL 60 (Aesculap-Meditec). In both groups an 18-month follow-up study was performed.

RESULTS:

In the compound hyperopic astigmatism group after 18 months, 14 of 17 treated eyes (82.3%) were within +/-1.00 D, and 11 (64.7%) were within 60.50 D of the intended correction. In the mixed astigmatism group after 18 months, 10 of 11 eyes (90.9%) were within +/-1.00 D, 8 eyes (72.7%) were within +/-0.50 D of the intended correction. In regard to the stability the 1 year regression of spherical equivalent in the compound hyperopic astigmatism group is 0.78 D and in the mixed astigmatism group 0.37 D. At 18 months, spectacle corrected visual acuity in the compound hyperopic astigmatism group was unchanged or improved in 14 eyes (87.5%); 2 eyes (12.5%) had lost one line. In the mixed astigmatism group at 18 months, spectacle corrected visual acuity was unchanged or improved in 9 eyes (81.8 %); 2 eyes (18.1%) lost one line. Preoperatively, the mean uncorrected visual acuity was 20/100 in the compound hyperopic astigmatism group and the mixed astigmatism group. At 18 months, 14 eyes (93.3%) in the compound hyperopic astigmatism group had an uncorrected visual acuity of 20/40 or better; 4 (26.6%) eyes had an uncorrected visual acuity of 20/20 or better. In the mixed astigmatism group, 9 (81.8%) eyes had an uncorrected visual acuity of 20/40 or better; 4 (36.3%) eyes had an uncorrected visual acuity of 20/20 or better.

CONCLUSION: Photorefractive keratectomy is an efficient and relatively safe procedure for reducing or eliminating compound hyperopic and mixed astigmatism up to 6.00 D.

Authors' abstract, JRS
Klinikum St. Marien,
Amberg, Germany