Dimitri T. Azar

Success of monovision in presbyopes: Review of the literature and potential applications to refractive surgery*

The monovision concept of correcting one eye for distance and the other for near may be utilized in presbyopes undergoing refractive surgery. We have performed a systematic review of published literature to evaluate the factors influencing monovision success, and to determine the visual outcome in patients with monovision. Articles in MEDLINE and published bibliographies reporting monovision prescription for correction of presbyopia were systematically identified and reviewed. Pertinent data were abstracted and, when feasible, statistically analyzed. The mean success rate was 73%. The success in monovision correlated with distance correction on dominant eye, alternating dominance, less than 50 seconds of are stereoacuity reduction, and less than 0.6 prism diopter of distance esophoric shifts. Monovision resulted in significant reduction of binocular contrast sensitivity function at spatial frequencies higher than 4 cycles per degree, and 2-6% reduction in task performance, but resulted in minimal reduction of binocular visual acuity, peripheral vision, visual field width and binocular depth of focus. The published literature indicates that monovision is an effective and reasonable therapeutic modality for correcting presbyopia. Proper patient selection and clinical screening are essential for monovision success.

Objective Measurement of Corneal Light Scattering after Excimer Laser Keratectomy

PURPOSE To obtain objective measurements of corneal light scattering after excimer laser keratectomy, and to evaluate the relation of light scattering to clinical haze grading and visual acuity. METHODS The authors measured best-corrected visual acuity, subjective clinical haze grade, and corneal light-scattering index in patients undergoing photorefractive keratectomy (PRK) (n=26), and phototherapeutic keratectomy (n=8), preoperatively and postoperatively at 1,3,6,9, and 12 months or later. Corneal light scattering was correlated with visual acuity and clinical haze grade. RESULTS Corneal light scattering increased after PRK and was reduced after phototherapeutic keratectomy. Corneal light scattering index showed a stronger positive correlation with logMAR visual acuity (r=0.57) than clinical haze grading (r=0.34). Corneal light-scattering index (P<0.05 at 1 and 3 months) and clinical haze grading (P<0.05 at 6, 9, and 12 months) were significantly higher in eyes undergoing PRK with ablation depths of more than 80 microns. CONCLUSIONS Excimer laser surgery affects corneal light scattering. Ablations with depths greater than 80 microns produce significantly higher levels of haze than those less than 80 microns. Objective measurement of corneal light scattering may be useful in monitoring the outcome of excimer keratectomy.

Microkeratome-assisted posterior keratoplasty

Microkeratome-assisted posterior keratoplasty is a new surgical technique that may be valuable in treating patients with corneal decompensation secondary to endothelial dysfunction. A hinged anterior stromal flap is fashioned in the host cornea using a microkeratome, and the diseased posterior stroma and endothelium are resected. A complementary donor stromal button is prepared using a microkeratome and an artificial anterior chamber. The donor button is transplanted and secured with sutures, and the flap is repositioned. The flap can be lifted later to remove the sutures or to correct residual refractive errors using an excimer laser. This technique may allow the use of infant corneal donor tissue and may improve the outcomes of posterior keratoplasty.

Corneal light scattering with stromal reformation after laser in situ keratomileusis and photorefractive keratectomy

Objective: To correlate corneal light scattering with keratocyte and extracellular matrix reformation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Setting: Wilmer Ophthalmological Institute, Johns Hopkins University, Baltimore, Maryland, USA. Methods: Sixteen pigmented rabbit eyes were randomly divided Into 2 groups. Group 1 (n=8) had a 5.0 mm, ‐10.0 diopter (D) LASIK treatment and Group 2 (n=8), a 6.0 mm, ‐10.0 D surface PRK treatment after mechanical epithelial debridement. The stromal surface exposed at surgery was stained with dichlorotriazinylaminofluQrescein (DTAF) solution. Slitlamp biomicroscopic and objective measurement of corneal light scattering using a scatterometer were performed 1 and 2 days and 1, 2, 3, 4, 8, and 12 weeks after surgery. In each group, 2 corneas were harvested at 1 week and 1 month and 4 corneas were harvested at 12 weeks. Tissue sections were examined by light and fluorescence microscopy. The percentage of newly formed stromal tissue was calculated and correlated with the scatterometry index. Results: In Group 1, corneas remained clear and healed without significant scarring throughout the study. In Group 2, subepithelial scarring was noted. Extracellular matrix reformation peaked at 1 month and showed a slight regression thereafter. The percentage of extracellular matrix reformation was strongly correlated with the scatterometry index (r = .86, P < .001). Conclusions: In this study, significant subepithelial stromal tissue reformation followed PRK. The percentage of extracellular matrix reformation correlated well with the objective corneal light scattering measurements.

Corneal light scattering after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE To compare corneal light scattering after laser in situ keratomileusis and photorefractive keratectomy in rabbit eyes. METHODS For laser in situ keratomileusis, a 5-mm, -10-diopter spherorefractive resection was performed on the stromal bed under a corneal flap. Corneal light scattering was objectively measured for 12 weeks, and compared to corneal light scattering after photorefractive keratectomy (5 mm, -10 diopters). RESULTS Corneal light scattering was significantly lower in the laser in situ keratomileusis group than in the photorefractive keratectomy group at all time points after surgery (P < .01 at weeks 1 through 6, and P = .03 at week 12). CONCLUSIONS In this experimental study, laser in situ keratomileusis resulted in significantly less corneal light scattering than photorefractive keratectomy.

Prospective, randomized vector analysis of astigmatism after three-, one-, and no-suture phacoemulsification

Purpose: To compare surgically induced astigmatism and visual outcomes after three‐, one‐, and no‐suture phacoemulsification. Setting: Johns Hopkins Hospital, Baltimore, Maryland, and Manhattan Eye, Ear, and Throat Hospital, New York, New York, USA. Methods: This prospective, randomized study followed 131 patients treated with phacoemulsification with a 5.5 mm self‐sealing scleral tunnel and implantation of a 5.5 mm poly(methyl methacrylate) posterior chamber lens. Radial 10‐0 nylon sutures were used in the three‐ and one‐suture groups. Results: Mean astigmatism was greatest in the first postoperative week in all groups and stabilized after 8 weeks. The percentage of patients with with‐the‐rule (WTR) astigmatism increased from baseline in the one‐ and three‐suture groups and decreased in the sutureless group. Mean uncorrected Snellen acuity was significantly better in the no‐ and one‐suture groups than in the three‐suture group at 1 week. There were no significant differences in uncorrected acuity at other times. No statistically significant differences in the surgically induced spherical equivalent were noted among the three groups during the 1 year follow‐up. There was significantly less surgically induced keratometric astigmatism in the one‐suture group at 4 (P = .03) and 8 (P = .007) weeks postoperatively. At all follow‐ups, the sutureless group had the greatest proportion of patients with significant ATR astigmatic shift (1 week, 17%; 4 weeks, 32%), and the lowest proportion of patients with significant WTR astigmatic shift (10% after 1 week). At 4 weeks, the percentage of patients with significant WTR shift in the one‐suture group dropped to that in the sutureless group (10%); however, those in the one‐suture group had less ATR astigmatic shift (16%). Conclusion: Sutureless and one‐suture surgery resulted in a low percentage of WTR induced astigmatism 4 weeks postoperatively. Compared with sutureless surgery, the one‐suture surgery resulted in less ATR shift.

Simple device for objective measurements of haze following excimer laser ablation of cornea

We have developed a simple instrument for making objective measurements of haze that develops following excimer laser ablation of the cornea. It consists of an appropriately modified slit-lamp microscope, with a fiber optic pickup, a filter system for wavelength selection, and a photomultiplier detector. The scattered intensity at 120 degree(s) from the forward direction is determined. Preliminary tests were made by measuring the haze following a deep photorefractive ablation on a rabbit cornea under conditions which ensured that rather severe haze would develop. The VISX Model 20/20 laser system was set to produce a 6.0 mm diameter, -15 D correction, with a central depth of 236 micrometers . Measurements were made on the normal cornea prior to ablation and at various times up to 114 days post-ablation and are compared to slit-lamp photographs. Scattering peaked two weeks post-ablation at a value approximately 40X that of the normal (unablated) cornea and gradually decreased to approximately 11X the normal value at 114 days.