Ashley Behrens

Evaluation of corneal flap dimensions and cut quality using the Automated Corneal Shaper microkeratome.

PURPOSE To evaluate flap dimensions and cut deterioration with repeated blade use in an automated microkeratome. METHODS The Automated Corneal Shaper (Chiron-Adatomed, Munich, Germany), 160-microm plate attached, was used to make a corneal flap in 90 pig cadaver eyes, reusing blades up to five times. Flap diameter was measured by planimetry and thickness was calculated by ultrasound pachymetry. Scanning electron microscopy of stromal beds and blade cutting edges was performed to assess cut deterioration after repeated blade use. RESULTS Mean flap central thickness was 125 +/- 32 microm. Mean vertical flap diameter was 7.6 +/- 0.4 mm. No correlation was found between thickness and diameter (r = 0.15, P = .45). Progressive thinning of the flap was observed in the direction of the flap hinge. Smooth cuts (using new blades) with periodic chatter lines at the keratectomy edge and in the stromal bed were observed with scanning electron microscopy. Increasing tissue remnants on the stromal bed and decreasing cut quality occurred with repeated blade use. Blades showed larger tissue remnants, nicks, and even folds on the cutting edge proportional to the number of times blades were used. CONCLUSION Satisfactory cut quality and reproducibility were obtained after a single use of stainless steel blades in the Automated Corneal Shaper microkeratome. Cut quality was degraded dramatically by repeated use of blades.

Evaluation of corneal flap dimensions and cut quality using a manually guided microkeratome.

BACKGROUND To evaluate reproducibility of corneal flap dimensions and cut quality with repeated blade use with a manually guided microkeratome in pig eyes. METHODS Corneal flaps were created using a manually guided microkeratome (Model One, Moria) with an intended 130-microns cut depth in 130 enucleated pig eyes. Flap thickness was calculated by pachymetry and diameter was estimated by means of applanation lenses compared to planimetry. Histology and scanning electron microscopy of samples and blades were performed to evaluate the keratectomy surface and blade cutting edge after repeated use of the blades. RESULTS Mean flap central thickness was 135 microns (SD, 37 microns). The mean diameter of 8.4 mm (SD, 0.4 mm) correlated significantly (P < .001) to the intended diameter (r = .79). Mean difference from the intended diameter was 0.8 mm (SD, 0.3 mm; range, 0.04 to 1.4 mm). Scanning electron microscopy showed even and smooth cuts with chatter lines at the keratectomy edge using new blades. After repeated blade use, increasing cut irregularity, folds, and tissue remnants on the corneal bed surface, and nicks and tissue remnants at the cutting edge of the blades were observed. CONCLUSION Reproducible flap dimensions were obtained using the Moria One microkeratome on pig eyes. The cut surface was regular and smooth with a new blade, but surface quality deteriorated considerably after repeated use of the same blade.

Orientation teeth in non-mechanical laser corneal trephination for penetrating keratoplasty: 2.94 µm Er:YAG v 193 nm ArF excimer laser

BACKGROUND/AIMS “Orientation teeth” at the donor trephination margin and correspondent “notches” at the host margin facilitate graft orientation and avoid “horizontal torsion” induced by asymmetric suture placement. In this study the quality and reproducibility of these structures created by non-mechanical laser corneal trephination were compared using two laser emissions. METHODS The procedure was performed in 20 enucleated pigs’ eyes using open metal masks with eight “orientation teeth/notches” (0.3 × 0.15 mm, base × height), an automated globe rotation device, and either a 193 nm ArF excimer laser or a Q switched 2.94 μm Er:YAG laser. “Teeth/notches” were analysed by planimetry and scanning electron microscopy (SEM). RESULTS Mean size was 0.30 (0.027) × 0.16 (0.017) mm for “teeth” and 0.30 (0.035) × 0.15 (0.021) mm for “notches” (excimer), and 0.31 (0.022) × 0.16 (0.015) mm and 0.30 (0.031) × 0.14 (0.021) mm respectively (Er:YAG). Overall, variability of notches was higher than that of teeth. By SEM, comparable cut regularity and sustained ablation profile were observed with both lasers. However, the corneal surface at the cut edge appeared slightly elevated (⩽35 μm) in the Er:YAG group. CONCLUSION Orientation teeth/notches resembling those obtained with the excimer laser can be created using the Q switched Er:YAG laser, with potential advantages of lower costs, convenient equipment size, and solid state safety.

Morphometric analysis of deposits in granular and lattice corneal dystrophy: histopathologic implications for phototherapeutic keratectomy.

Objective: To quantify the distribution and size of deposits in granular and lattice corneal dystrophies and to estimate the impact of these findings on the potential benefit of phototherapeutic keratectomy (PTK) as primary treatment in these corneal disorders. Methods: Central histologic sections of consecutive corneal buttons (34 granular dystrophy specimens of 27 patients (mean age 53 ± 12 years) and 20 lattice dystrophy specimens of 20 patients (mean age 50 ± 17 years) obtained from central penetrating keratoplasty were examined by light microscopy using Masson trichrome and Congo Red stains. Localization and anterioposterior diameter of the most superficial, the deepest, and the largest deposits were quantified in the central and the two peripheral thirds of the specimens. Bowman layer status and thickness of the epithelium were recorded. The clear central corneal zone size before and after a hypothetical superficial PTK (100-μm ablation) was calculated. Results: Central deposits in granular dystrophy were mostly superficial (mean distance from the epithelium 28 ± 19 μm) and associated with Bowman layer and epithelial changes. In lattice dystrophy, deposits were mostly midstromal (mean distance from the epithelium 79 ± 54 μm, P < 0.001) with a larger scatter, showing minor superficial involvement. After a fictitious PTK, a significant increase in mean clear central zone was achieved (P = 0.004). This increase in mean clear central zone was more pronounced in granular (from 484 ± 389 μm to 1451 ± 1954 μm) than in lattice (from 258 ± 183 μm to 846 ± 784 μm) dystrophy (P = 0.004). Deposits were completely removed in 22% of the granular dystrophy samples. In both dystrophies, a clear central “pinhole” greater than 1 mm in diameter was achieved in around one third of corneas. Conclusion: According to the histopathologic corneal deposit size and distribution, PTK may be an effective treatment to increase visual acuity in patients with granular dystrophy more than in those with lattice dystrophy, to delay or even avoid penetrating keratoplasty.

Lens opacities after nonmechanical versus mechanical corneal trephination for keratoplasty in keratoconus

Purpose: To compare the lens opacity formation after penetrating keratoplasty (PKP) using nonmechanical excimer laser corneal trephination and mechanical motor trephination. Setting: University Eye Clinic, University of Erlangen‐Nürnberg, Erlangen, Germany. Methods: Ninety‐six patients with keratoconus (96 eyes) and clear crystalline lenses were randomly assigned to the nonmechanical trephination (NMT) group (n = 46; 35 men; mean age 38.2 years ± 10.8 [SD]) or the mechanical trephination (MT) group (n = 50; 35 men; mean age 34.4 ± 9.0 years). Suturing and postoperative treatment were identical. Dilated pupil biomicroscopy and slitlamp lens photography were performed preoperatively and postoperatively at 3 month intervals. Opacities were identified as cortical, nuclear, and posterior subcapsular and graded from 1 (mild) to 3 (severe). Results: Mean follow‐up in the NMT/MT group was 3.2 ± 1.3 years/3.4 ± 1.1 years. Overall, incident opacities appeared in 23.9%/32.0% of eyes (4.3%/6.0% cortical; 19.6%/26.0% posterior subcapsular; 0%/0% nuclear) (P = .833). All cortical opacities in both groups were grade 1; posterior subcapsular opacities were grade 1 in 66.6%/61.5% of eyes and grade 2 in 22.2%/30.8% of eyes. One patient in each group presented grade 3 posterior subcapsular opacities. No differences between trephination methods were seen in a 5 year Kaplan–Meier cumulative risk of lens opacity formation (P = .763 cortical, P = .530 posterior subcapsular). Conclusion: In addition to its optical advantages, nonmechanical corneal trephination appears to have no adverse impact on cataract formation after PKP for keratoconus.

Thermal load of laser aperture masks in nonmechanical trephination for penetrating keratoplasty with the Er:YAG laser: comparison between stainless steel and ceramic masks.

Abstract Purpose: Thermal effects on the laser aperture mask may play a major role in the thermal loading of the cornea during nonmechanical trephination in penetrating keratoplasty. The purpose of this study was to assess the temperature increase on the laser mask using the 2.94-µm Er:YAG laser in order to find suitable parameters for avoidance of thermal damage to the cornea. Methods: Thermal load measurements were performed on donor (7.5 mm trephination diameter, 0.7 mm thickness, central hole 3.0 mm) and recipient (7.5 mm trephination diameter, 0.7 mm thickness, outer diameter 13.0 mm) aperture masks. The masks were either mounted on a thermal isolator or fixed directly on porcine corneal samples. Temperature increase was measured either under static conditions in the ablation area (setup 1) and at the opposite side of the mask (setup 2) or in the ablation area under dynamic conditions, rotating the whole globe to simulate a constant trephination speed with the mask positioned directly on a porcine cornea (setup 3). We used the NWL Er:YAG solid-state laser in a 1.3-mm free-running spot mode focused on the trephination margin (half of the beam on the mask and half of it on the cornea) with a pulse energy of 200 or 400 mJ and 18CrNi10 stainless steel versus three different types of ceramic masks (silicium carbide, silicium nitrite, aluminum oxide). Temperature was assessed using an infrared pyrometer with automatic data acquisition software for a personal computer. Results: Overall, the temperature rise ranged between 43.6 K (metal donor mask at the trephination area with 400 mJ pulse energy) and 3.3 K (silicium carbide recipient mask at the opposite side of the mask with 200 mJ pulse energy). With all setups and both energy levels, the heating of the metal mask was significantly higher (P<0.02) than the heating of the three types of ceramic masks. The silicium carbide masks revealed the lowest temperature rise. Comparing the three setups, the temperature rise was maximal under static conditions in the ablation area and minimal at the opposite side, with the dynamic setup ranging in between. Temperature rise was significantly greater (P<0.04) in donor masks than in recipient masks for each mask material and both energy levels. Conclusion: The physical characteristics of silicium carbide masks seem superior to those of metal masks with regard to minimizing the thermal load of the epithelium or superficial stroma during Er:YAG laser trephination of the cornea for penetrating keratoplasty.

Free-running erbium:YAG laser for nonmechanical trephination in penetrating keratoplasty: first results of experimental trephination of human donor corneas

Abstract · Background: A study was carried out to evaluate the potential suitability of a free-running erbium:YAG 2.94-µm laser for trephination of human corneas in penetrating keratoplasty. · Methods: Two human donor corneas were placed in an artificial anterior chamber and moved with an automated rotation device (one rotation per minute). An erbium:YAG laser beam (pulse duration 400 µs, repetition rate 2/s, energy density 2.5 and 15.0 J/cm2) was focused on the outer edge of a round ceramic mask placed on the human donor corneas for ablation of tissue. · Results: With a fluence of 15.0 J/cm2, perforation was achieved after 500 pulses. Perpendicular central cut edges with mild stromal ridges and, by light microscopy, a 12 to 45-µm area of stromal thermal effects and focal endothelial changes up to 200 µm central to trephination were observed. · Conclusions: The erbium:YAG laser could be a promising ”low-cost alternative” to the excimer laser for nonmechanical trephination in penetrating keratoplasty. Further studies will have to focus on reduction of thermal damage and on wound healing.

Flap quality in single versus multiple use of the same blade in the Flapmaker microkeratome.

PURPOSE We evaluated experimentally the variability of cut thickness, flap diameter, and cut quality produced by the Flapmaker corneal microkeratome (IOLTech), with single and repeated use of the same cutting blade. METHODS Keratectomy was performed with twelve cutting heads (8.5-mm diameter, 160-microm cutting depth) on 47 corneas and with six cutting heads (8.0-mm diameter, 180-microm cutting depth) on 18 freshly enucleated swine eyes in a repeated manner. Ultrasonic pachymetry was determined at the initial, central, and final microkeratome pass zones, first before the flap was created and subsequently after the flap was reflected. Flap diameter was measured by planimetry. After the procedure stromal portions were submitted for scanning electron microscopy. RESULTS On the first blade use, mean central flap thickness was 145 +/- 32 microm and mean vertical flap diameter was 8.4 +/- 0.26 mm with the 8.5-mm blades. With the 8.0-mm blades, mean central flap thickness was 155 +/- 23 microm and mean vertical flap diameter was 8.0 +/- 0.27 mm. Scanning electron microscopy disclosed smooth cut surfaces when new blades were used, but with repeated blade use, increasingly prominent stromal bed folds were observed. CONCLUSIONS The evaluated blades produced reproducible flap size and thickness and good cut quality with single use, but after the first use, cut quality markedly deteriorated. Repeated use of Flapmaker cutting blades is not recommended.