Scott X. Stevens

The BioMask for treatment of corneal surface irregularities with excimer laser phototherapeutic keratectomy.

PURPOSE To assess the characteristics of BioMask as a potential masking agent for use with the excimer laser. METHOD We addressed ablation rate, smoothness, ease of use, dioptric shift, treatment of standardized irregular topography, and ability of BioMask to induce dioptric change in vivo. RESULTS BioMask ablates at a rate of 0.28 microm per pulse. The BioMask conforms to the base curve of a contact lens in the excimer blank, eye bank eye, and rabbit eye with a r2 of 0.9982, 0.9844, 0.9858, respectively. We are readily able to create 20 diopters of flattening or steepening (r2 = 0.9944). Standardized irregular topography generation in the rabbit eye and then removal with BioMask was successful. The central corneal topography of the rabbit cornea showed predictable changes with various contact lens base curves with the BioMask (r2 = 0.875). CONCLUSIONS BioMask has excellent potential as an ablatable mask material in the treatment of superficial corneal scars.

Treatment of corneal surface irregularities using biomask as an adjunct to excimer laser phototherapeutic keratectomy.

Purpose. To assess the clinical changes induced by the use of BioMask as an adjunct to phototherapeutic keratectomy (PTK) using the excimer laser. Methods. A nonrandomized, prospective clinical trial was conducted. Twenty-two consecutive patients were enrolled for BioMask treatment with reduced visual acuity caused by irregular astigmatism or corneal scarring. Patients were treated with a broad-beam excimer laser using the standard PTK mode. The BioMask collagen material was applied as a liquid at 47°C and molded using custom-made, rigid, gas-permeable contact lenses. After allowing the material to cool for approximately 3 minutes, the lens was removed and the gel was ablated at a fluence of 130–140 mJ/cm 2 at a frequency of 10 Hz, until the stromal bed appeared smooth. After surgery, patients were followed at day 1, week 1, and months 1, 3, 6, 9, and 12. The main outcome measures were best spectacle-corrected visual acuity (BSCVA) and uncorrected visual acuity (UVA). Results. Comparison of the preoperative and postoperative BSCVAs showed a statistically significant change in vision (p = 0.0356). Before surgery, the mean Snellen BSCVA was 20/90, whereas after surgery, BSCVA increased to 20/60. Sixty-five percent of the patients had an improved BSCVA, with an average gain of 3.7 lines per patient (range, +2 to +10). Fifteen percent of the patients lost an average of 3.0 lines (range, −2 to −6), and 20% had no change. UVA averaged 20/180 before surgery and 20/123 after surgery, but the change was not statistically significant. With respect to UVA, 63% improved by an average of 4.25 lines per patient (range, +2 to +9). Twenty-six percent (26%) lost an average of 5.6 lines (range, −2 to −8), and 10% had no change. The average follow-up time was 8 months for both BSCVA and UVA. When patients were stratified by their treatment indications and ranked in order of BSCVA outcome, patients with Salzmanns nodular degeneration did the best, followed by those with prior refractive surgery, corneal dystrophies, and corneal scars. Even though BSCVA did not improve as much in the corneal scar group, 50% of the patients reported an improvement in the symptoms they experienced before surgery based on questionnaires. Conclusion. BioMask appears to have potential as an ablatable mask material when used in conjunction with PTK for the treatment of corneal surface irregularities.

COMPARISON OF THREE COMPUTERIZED VIDEOKERATOSCOPY SYSTEMS WITH KERATOMETRY

Purpose: To compare the reproducibility of computerized videokeratoscopy systems by using normal eyes and calibrated objects. Methods We evaluated the reproducibility of three commercially available videokeratoscopes [EyeSys, Tech-noMed C-Scan, and PAR Corneal Topography System (CTS)] with the manual keratometer (Bausch & Lomb) by using calibration spheres and 10 normal subjects (20 eyes). All video-keratoscopy and keratometer results were obtained by one investigator (R.M.). Each eye and calibration sphere were submitted to 10 serial examinations by using each system. The average K of all points within the central 3.0 mm of the topography systems (central 3.0 mm) was compared with the average K of the manual keratometer. Results All videokeratoscopy systems correlated well with each other and manual keratometry when accessing aspheric and spherocylinder calibration balls. EyeSys central keratometry clinical results had the strongest correlation with the average keratometry results at 35%, followed by PAR-CTS at 25% and C-Scan at 5%. Among the videokeratoscopy units, EyeSys and PAR-CTS had the strongest correlation at 65%. The correlation between the Tech-noMed C-Scan and both the EyeSys and PAR-CTS systems was 25%. There was a statistically significant difference (p < 0.05) between the systems when analyzing the results obtained from clinical subjects. The average keratometry (K) difference of human eyes between videokeratoscopy systems is <0.35 diopters (D) (p < 0.05), which may be clinically significant. The average manual K reading (42.97 D) is statistically significantly flatter (p < 0.05) than each of the videokeratoscopy units (EyeSys = 43.49 D; PAR = 43.48 D; C-Scan = 43.83 D). Comparing the 10 measurements of each eye or calibration object in the same videokeratoscopy system verified that the devices give reproducible results. The average standard deviation (ASD) of the keratometer was 0.10 D. The ASD of the videokeratoscopy units was 0.05 D for the EyeSys, 0.29 D for the PAR-CTS, and 0.31 D for the C-Scan systems. Conclusion Based on this study, we should not assume that the results of different topography systems can be interchanged in clinical studies.

Corneal topography as a predictor of refractive change in the prospective evaluation of radial keratotomy (PERK) study.

The first operated eyes of 435 patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were evaluated by photokeratography to document the preoperative and postoperative corneal shape. We determined by regression analysis and analysis of variance that the corneal shape preoperatively improved the prediction of the corneal shape 6 months postoperatively in the 3-mm-clear-zone population. The reduction of myopia in all 435 eyes ranged from 1.25 to 9.75 diopters. We studied the effect of the preoperative corneal shape on this variability in the outcome of the surgery using rings 2 and 7 on photokeratography and corneal diameter. In the 3-mm-clear-zone group, eyes with flat prolate corneas had a greater reduction in myopia (4.65 D); those with steeper, more spherical corneas had less reduction in myopia (3.48 D). In addition, eyes with a 3-mm clear zone and flat central corneas alone (8.0 mm = 42.19 D) flattened approximately 0.75 D more than those with steep central corneas (7.0 mm = 48.21 D). In the 3.5-mm and 4.0-mm clear zone groups, the change in corneal curvature was not related to the preoperative curvature. A stepwise regression analysis of the 151 eyes in the 3.0-mm-clear-zone population demonstrated the following predictive equation for radial keratotomy; change in cycloplegic refraction = -14.55 + [-2.097 x average ring-2 radius] + [3.605 x average ring-7 radius] + [0.69 x horizontal corneal diameter] + [0.079 x age] + [-0.379 x spherical equivalent cycloplegic refraction]. There was a 1.17-D observed difference in the effect of radial keratotomy between those eyes with a steep/steep corneal topography (7.2% of the 3.0-mm-clear-zone population) and the flat/flat topography (29% of the 3.0-mm-clear-zone PERK population). A knowledge of corneal topography provides an additional tool for understanding the operative variability of radial keratotomy.

Use of a Mirror Needle Holder With Transsclerally Sutured Posterior Chamber Intraocular Lenses

A mirror needle holder has been designed to facilitate the passage of a needle through the ciliary sulcus during transscleral fixation of posterior chamber (PC) intraocular lens (IOLs). Two human postmortem eyes were used to demonstrate the efficacy of this mirror used as the needle holder. This method was compared with the current method of passing sutures without view of the ciliary sulcus. The mirror needle holder demonstrated precise passage of the needle into the ciliary sulcus by direct visualization of the ciliary processes and sulcus. This method may avoid the complications associated with transsclerally sutured PC IOLs during penetrating keratoplasty and secondary IOL placement.

The Tampa Trephine technique with cat corneal endothelium.

The Tampa Trephine (Martin Marietta Speciality Components, Largo, FL, U.S.A.) penetrating keratoplasty technique uses a 7.0-mm corneal donor button with six rectangular 1 x 2-mm tabs of Bowmans layer, 75 microns in thickness, which are inserted into the recipient stroma beneath Bowmans layer. We evaluated the safety of the Tampa Trephine tissue-trephination method on the cat corneal endothelium combining vital staining and scanning electron microscopy, comparing it with the standard Weck trephination technique. The Tampa Trephine tissue trephination produces a donor button with a 6.7-mm diameter central area of normal endothelium. Localized peripheral areas of cellular loss, endothelial and Descemets tears, endothelial detachment, and folding along the border of the trephination were observed with the Tampa Trephine method, all located in an area of < or = 150 microns, adjacent to the edge of the button. Standard trephination induced a localized peripheral area of endothelial damage < 50 microns in extension from the donor edge. A theoretic maximal 8.4% peripheral endothelial cell loss is induced with the Tampa Trephine trephination method, compared with a 2.8% loss with the standard procedure. The peripheral location of the alterations after the Tampa Trephine does not hinder the viability of the corneal endothelium, as it has been clinically observed.

THE EFFECTS OF THE TAMPA TREPHINE TECHNIQUE ON THE CAT CORNEAL ENDOTHELIAL MORPHOMETRY

eyebank (p=0.13). Positive cultures were more frequent for corneas excised in-situ (39/125, 31.2%) than for those enucleated (152/851, 17.9%), p<0.001. Three cases of endophthalmitis (0.28%) and one suture abscess occurred. Rim cultures were negative in all of these cases. Action was documented in response to positive cultures in 17 cases (8.1%). This included starting (4), restarting (4), increasing frequency of (2), or changing (2) topical antibiotic therapy, subconjunctival and intravenous antibiotic therapy (1), phone calls to patients (3) and extra clinic visits (5). The average estimated cost of routine rim cultures in 1994 was

Corneal modulators and their use in excimer laser phototherapeutic keratectomy.

137 per donor cornea. Conclusions: Routine donor corneal rim cultures are of no clinical value in penetrating keratoplasty and are an unnecessary expense. Supported by NIH Grant EY02037, Research to Prevent Blindness Inc., and the Mayo Foundation.