Raymond P. Gailitis

Factors That Affect Corneal Flap Thickness With the Hansatome Microkeratome

PURPOSE To evaluate factors that influence corneal flap thickness with the Hansatome microkeratome. METHODS One hundred thirty-two eyes of 70 patients underwent laser in situ keratomileusis (LASIK). Corneal flap thickness was measured by subtracting the intraoperative corneal bed pachymetry measurement from intraoperative total corneal pachymetry. Variables examined included plate thickness, ring size, blade use, temperature, humidity, barometric pressure, age, average keratometric power, and preoperative corneal thickness. RESULTS Mean flap thickness using a 180-microm plate was 143 +/- 19 microm (range 61 to 207 microm). Mean flap thickness using a 160-microm plate was 119 +/- 20 microm (range 83 to 159 microm). The difference was statistically significant (P < .05). Mean flap thickness using a 180-microm plate and the same blade on the right and left eye was 151 +/- 21 microm (range 113 to 200 microm) and 137 +/- 21 microm (range 91 to 191 microm), respectively. The 14-microm difference was statistically significant (P < .001). There was a slight negative correlation of flap thickness with humidity. There was a positive correlation with preoperative corneal thickness (pachymetry). CONCLUSION The Hansatome tended to cut thinner flaps than anticipated based on the plate used. Flaps cut on the first eye were thicker than the second eye using the same blade. Thicker corneas tended to lead to thicker flaps. There was no correlation between flap thickness and microkeratome ring size, temperature, barometric pressure, patient age, or average keratometric power.

A Prototype Erodible Mask Delivery System for the Excimer Laser

PURPOSE The authors developed an erodible mask delivery system for the argon-fluoride 193-nm excimer laser, which offers the possibility of correcting hyperopia and astigmatism as well as myopia. METHOD Masks were made of polymethylmethacrylate on a quartz window, with intended corrections for myopia and hyperopia of 2.5 and 5 diopters (D). Ablations using the mask and control ablations using an expanding diaphragm were performed in 30 eyes of 15 pigmented rabbits with an Excimed UV200 laser (Summit Technology, Inc, Waltham, MA). The rabbits were followed for 134 days with regular biomicroscopy and retinoscopic examination by two observers. RESULTS Ablations with the mask to correct myopia were successful and produced stable corrections, although the higher-power mask produced undercorrections. Hyperopic masks produced paradoxic myopic corrections, possibly due to the lack of a transition zone at the edge of the mask. Corneas ablated with the mask had less sub-epithelial haze than those ablated with the diaphragm at all examinations. Results of histopathologic examination showed epithelial hyperplasia over the ablation zone in all eyes. Dichlorotriazinyl aminofluorescein collagen staining showed subepithelial new collagen in all eyes, but there was no relation between the depth of ablation at any point on the cornea and the amount of new collagen deposited there. CONCLUSIONS Myopic ablations are feasible with the erodible mask, although additional calibration is needed. Hyperopic ablations were unsuccessful with the current design. Corneas ablated with the mask may be clearer than corneas ablated with the diaphragm, possibly due to a smoother ablated surface. Regression of effect after laser ablation in the rabbit model is likely due more to epithelial hyperplasia than to stromal remodeling.

Current Status of Synthetic Epikeratoplasty

Many of the deficiencies with human tissue epikeratoplasty might be improved by the use of a suitable synthetic lenticule. Potential biomaterials for epikeratoplasty include collagen (types I, III, or IV), collagen-hydrogel copolymers, bioactive synthetics, and coated hydrogels. The biomaterial must be engineered to achieve strict specifications of optical clarity, support of epithelial migration and adhesion, permeability to solutes, and stability to corneal proteases. Attaching synthetic lenticules to the cornea without cutting Bowmans layer by adhesives, laser welding, or direct adhesion may also improve the efficacy of synthetic epikeratoplasty.

Comparison of LASIK outcomes with the Alcon LADARVision4000 and the VISX STAR S2 excimer lasers using optimized nomograms.

PURPOSE To evaluate the difference in clinical outcomes between LASIK patients treated with the Alcon LADARVision4000 laser and the VISX STAR S2 laser using optimized nomograms. METHODS Data from 572 LASIK surgeries of two groups that were sequentially performed by one surgeon were retrospectively reviewed. The first group of 286 eyes were the last cases performed with the VISX STAR S2 laser. Following these surgeries, a second group of 286 eyes were the first cases performed with the Alcon LADARVision4000 laser, after an initial 50-eye adaptation period. Treatments were guided by the Refractive Surgery Consultant software. RESULTS For myopic eyes 3 months postoperatively, the percentage of eyes with uncorrected visual acuity (UCVA) > or = 20/20, accuracy of treatment within +/- 0.5 D, and loss of > or = 2 lines of best spectacle-corrected visual acuity (BSCVA) for the LADARVision4000 and STAR S2, respectively was: 89% vs 63%, 84% vs 80%, and 0.8% vs 3.8%. For hyperopic eyes 3 months postoperatively, the percentage of eyes with UCVA > or = 20/20, accuracy of treatment within +/- 0.5 D, and loss of > or = 2 lines of BSCVA for the LADARVision4000 and STAR S2, respectively was: 74% vs 33%, 69% vs 74%, and 2% vs 18.5%. CONCLUSIONS Although good results are evident for both platforms, superior results were observed with the Alcon LADARVision4000 laser.

Corneal refractive surgery using an ultraviolet (213 nm) solid state laser

The authors demonstrate the use of a frequency multiplied Q-switched Nd:YAG laser to generate the fifth (213 nm) and the fourth (266 nm) harmonic frequencies to ablate porcine corneas and synthetic collagen materials. This new strategy is discussed for corneal refractive surgery using a solid state laser. The potential for spatially resolved refractive correction based on a 213 nm solid state laser is reviewed in light of new corneal imaging technology that can detect localized refractive errors of the eye. Finally, the authors discuss remaining problems that need to be addressed before this technology can be applied to clinical investigation.

Comparison of laser phacovaporization using the Er:YAG and the Er:YSGG laser

Future advances in cataract surgery aim to remove the crystalline lens through a small opening such that the capsular bag, once devoid of lens epithelial cells, may be refilled with a clear polymer which may exhibit the elastic properties of a young lens and restore accommodation. Several different lasers are currently being investigated for laser cataract surgery including the excimer, pulsed visible and short infrared, and mid infrared lasers. Taking advantage of the strong water absorption peak at 2.94 micrometers , we have investigated the laser tissue interaction of the Er:YAG (2.94 micrometers ) and Er:YSGG (2.79 micrometers ) which have water absorption coefficients of 13,000 cm-1 and 7,000 cm-1, respectively. We have devised a delivery system which measures the ablation time versus radiant energy through a known thickness on a lens nucleus in free air for these two wavelengths. The current presentation compares the ablation rates versus radiant exposure of these two lasers in human lens nuclei. We also show the histopathology from ablated lenses of these two different wavelengths at different radiant exposures. Integration with fiberoptics and clinical applications is discussed.