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.

Surgical correction of moderate myopia: which method should you choose? I. Radial keratotomy will always have a place.

This set of "Viewpoints" articles examines the relative merits of radial keratotomy (RK), photorefractive keratectomy (PRK), and laser assisted in-situ keratomileusis (LASIK). Drs. Rowsey and Morley review advances in RK techniques, long-term results, and complications, and explain why RK will remain a viable method for correction of moderate myopia, notably its minimal cost. Drs. Steinert and Bafna review both PRK and LASIK, discussing techniques and results and comparing their advantages and disadvantages with each other and with RK. Dr. Dutton, as "Viewpoints" section editor, summarizes clinical, technologic, and economic aspects of all three techniques, concluding that all will find a place among refractive surgeons for some time to come.

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, TechnoMed 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 videokeratoscopy 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 TechnoMed 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.

The immunology of corneal graft rejection.

Corneal transplantation is the most successful of organ transplants due to the fact that the eye is an immunologically privileged site, and the cornea is an immunologically privileged tissue. The factors responsible for this include presence of the blood-aqueous barrier, the avascularity of the cornea, the absence of classic antigen-presenting cells (APCs) in the central cornea, inhibitory factors in the aqueous humor, the phenomenon known as anterior chamber-associated immune deviation (ACAID), and the intraocular expression of Fas ligand. Loss of ocular immune privilege can occur with breaching of the blood-ocular barrier, corneal neovascularization, migration of classic APCs to the center of the cornea, loss of inhibitory factors in aqueous humor, abrogation of ACAID, and loss of Fas ligand expression within the anterior chamber. The purpose of this review is to analyze these events and how they relate to corneal graft rejection. A discussion on future research and therapeutic modalities is provided.

Cystic epithelial downgrowth following clear-corneal cataract extraction.

Epithelial downgrowth is a serious complication of intraocular surgery. It is characterized by the diffuse or cystic proliferation of surface epithelium inside the eye. Advances in microsurgical technique that result in smaller surgical wounds and permit greater precision in wound closure should reduce the incidence of this complication. We report a case of epithelial downgrowth presenting 3 years after an uncomplicated clear-corneal cataract extraction with insertion of a posterior chamber silicone lens. The epithelial down-growth was amenable to surgical correction because the well-defined cyst could be excised en bloc.

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 Bowman's layer, 75 microns in thickness, which are inserted into the recipient stroma beneath Bowman's 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 Descemet's 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.

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.

Refractive corneal surgery with the Draeger rotary microkeratome in human cadaver eyes.

BACKGROUND: Instrumentation for performing a uniform lamellar keratoplasty has been undergoing various stages of refinement. Reliable reproduction and uniform thickness and diameter of lamellar resections is required before lamellar refractive keratoplasty can be considered safe and effective. METHODS: The authors used the Draeger rotary microkeratome with mechanical blade advance for lamellar dissections in 61 human cadaver eyes prepared by injecting Swinger-Kornmehl (SK) solution into the anterior chamber to a pressure of 35 to 40 mm Hg and by soaking for 30 minutes in SK solution. Spacer sizes of 0.25 to 0.40 units were utilized using an anterior lamellar disc diameter estimate between 8.0 and 8.5 mm and a stromal lamellar disc diameter estimate between 5.5 and 6.5 mm. Preoperative pachometry, anterior and stromal lamellar disc thicknesses, and anterior and stromal lamellar disc diameters were measured. RESULTS: The Draeger unit created anterior lamellar thickness between 100 and 268 microns. Stromal lamellar disc thicknesses were consistently between 90 and 161 microns. The continuous, unidirectional, rotary blade and the uniform mechanical advance of the instrument produced a generally uniform bed as evaluated by scanning electron microscopy, although undulations were still present. CONCLUSION: The Draeger microkeratome produced regular lamellar dissections; however, predictability of the thickness of the lenticules varied 10% to 20%, and of the diameter, 1.5% to 15%. Predictability improved with experience. This variability may reduce predictability of refractive outcome.

Photography of shock waves during excimer laser ablation of the cornea. Effect of helium gas on propagation velocity.

Shadow photography of shock waves excited by means of a xenon chloride excimer laser was performed to determine the shock wave propagation velocity in air, nitrogen and helium. Energy densities between 500 and 2,000 mJ/cm2 were used to ablate a rotating rubber cylindrical target and porcine corneas. In ablating the rubber cylinder, a shock wave velocity of 3.3 km/s was generated in air and nitrogen at 40 ns; this decreased to 1.4 km/s at 320 ns. When helium was blown on the target, the velocity increased by a factor of approximately two, to 5.9 km/s at 40 ns and 2.7 km/s at 320 ns. We suggest that blowing helium on the surface of the cornea during excimer laser ablation may speed the dissipation of high-energy acoustic waves and gaseous particles, and thus reduce the exposure and transfer of heat energy to the surrounding tissue.

Combined treatment of Acanthamoeba keratitis with propamidine, neomycin, and polyhexamethylene biguanide.

We developed an intensive treatment regimen of topical neomycin, propamidine, and polyhexamethylene biguanide that was tapered to a maintenance level over a 14- to 28-day period as toxicity developed. Since July 1991, we used this treatment on six eyes of five patients in whom Acanthamoeba keratitis was diagnosed clinically. All patients had positive cultures for microorganisms from their corneas or contact lens cases or had pathognomonic findings of pseudodendritic subepithelial infiltrates and radial keratone-uritis. After therapy, all patients improved within two to four weeks, with regression or resolution of neuritis and infiltrates, healing of epithelial defects, and lessening of pain. By three to four months, visual acuity had returned to 20/20 in all eyes. We believe the addition of polyhexamethylene biguanide to our treatment regimen in Acanthamoeba keratitis dramatically aided and hastened the clinical improvement in five consecutive patients and may, with early diagnosis, increase the number of medical cures.

Peters' anomaly: a review of 26 penetrating keratoplasties in infants.

We reviewed the specimen records log of the McGee Eye Institute Histopathology Service from January 1979 to December 1990 for penetrating keratoplasty specimens submitted with a clinical diagnosis of Peters' anomaly. The records of the 19 cases thereby identified were reviewed for clinical outcome and visual rehabilitation, and the histopathology of all specimens was reviewed and correlated with the clinical diagnosis. Two specimens from the same patient were eliminated as histopathologically inconsistent with Peters' anomaly; one patient's data were not used because the patient was an adult when first grafted. Six eyes were grafted two or more times, for a total of 26 grafts on 16 eyes in 10 patients. Mean age at the time of first transplant was 18 weeks (range, 3 weeks to 40 months). Mean follow up was 30 months (range, 7 months to 6 1/2 years). Five eyes had preoperative glaucoma which persisted postoperatively. Ten eyes developed glaucoma postoperatively. Of the 15 eyes with glaucoma, 14 were uncontrolled medically and 12 underwent cyclodestructive or Molteno filtering procedures, or both, to control pressure. Graft rejection developed in 9 of the 10 eyes that required a cyclodestructive procedure, with partial or complete graft failure occurring shortly after the procedure. Glaucoma did not develop in one eye; in one other eye, it was medically controlled. These 2 eyes maintained clear grafts. Of the 6 eyes that were regrafted, only 1 obtained ambulatory vision. Of the 26 eyes receiving grafts, the grafts failed completely in 17 and partially in 5; 4 have remained clear. Five patients maintain ambulatory vision.

Treatment of alkali-injured rabbit corneas with a synthetic inhibitor of matrix metalloproteinases.

Healing of corneal alkali injuries remains a severe clinical challenge. The authors evaluated the effect of a new synthetic inhibitor of matrix metalloproteinases (GM6001 or N-[2(R)-2-(hydroxamido carbonylmethyl)-4-methylpentanoyl]-L-tryptophane methylamide) on preventing ulceration of rabbit corneas after alkali injury. Topical treatment of corneas with severe alkali injuries with 400 micrograms/ml or 40 micrograms/ml GM6001 alone prevented ulceration for 28 days, although 8 of 10 corneas treated with vehicle perforated. Corneas treated with 4 micrograms/ml GM6001 had midstromal depth ulcers. Corneas treated with 400 micrograms/ml of GM6001 contained very few inflammatory cells and had significantly reduced vessel ingrowth compared with vehicle-treated corneas. Epithelial regeneration after moderate alkali injuries also was investigated. Persistent epithelial defects developed 4 days after moderate alkali injury in rabbit corneas treated with vehicle and progressively increased to an average of 20% of the original 6 mm diameter wound by 27 days after moderate alkali injury. By contrast, epithelial regeneration was complete and persisted for 21 days for corneas treated with a formulation containing GM6001 (400 micrograms/ml), epidermal growth factor (10 micrograms/ml), fibronectin (500 micrograms/ml), and aprotinin (400 micrograms/ml). Sporadic punctate staining developed in 20% of the corneas treated with the combination of agents between days 21-28 after moderate alkali injury. These results demonstrate that topical application of GM6001 prevented corneal ulceration after severe alkali injury and that a combination containing GM6001, epidermal growth factor, fibronectin, and aprotinin promoted stable regeneration of corneal epithelium after moderate alkali injury.

Suturing in lamellar surgery: the BRA-technique.

BACKGROUND: The principle of refractive corneal lamellar surgery rests on the modification of corneal shape after the removal of a superficial disk with a microkeratome. The 150-microns-thick disk is easily torn, rotated or decentered by the traditional eight-bite running suture, producing irregular astigmatism which is the major cause of visual deficit after these procedures. METHODS: We propose a new suture technique, designated the BRA suture, which we have used in more than 300 cases of various types of refractive corneal lamellar procedures. Based on the overlay concept, the suture is anchored in four points of the nonoperated corneal periphery. RESULTS: With this technique, the iatrogenic irregular astigmatism induced by the suture has been eliminated and corneal scars significantly reduced. This suture also decreases surgical time, accelerates visual recovery, and increases patient comfort due to its early removal. CONCLUSIONS: We consider this the ideal suture for refractive corneal lamellar surgery due to its effectiveness, simplicity, and safety.

Infectious endophthalmitis following sutureless cataract surgery.

Within the last 6 months, three cases of infectious endophthalmitis following sutureless cataract surgery have been referred to us. Two of these cases followed uncomplicated sutureless phacoemulsification with intraocular lens implantation. One case was complicated by a postoperative hyphema with additional surgery for clot removal 2 days following the initial procedure.

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.