Mark A. Terry

THE EVOLUTION OF LAMELLAR GRAFTING TECHNIQUES OVER TWENTY-FIVE YEARS

Summary. The history of lamellar keratoplasty (LK) surgery spans over 100 years, and the advantages of lamellar surgery have long been known. The surgery is usually used for tectonic purposes; however, new techniques and technology over the past 25 years have expanded the applications of LK in optical rehabilitation. Instrumentation such as viscoelastics, diamond knives, ultrasonic pachymetry, artificial anterior chambers, advanced microkeratomes, and the excimer laser have enhanced our ability to work more safely in the tedious microsurgical environment of the lamellar procedure. Advances in surgical techniques such as deep lamellar anterior keratoplasty and deep lamellar endothelial keratoplasty have expanded the application of lamellar surgery to endothelial replacement and have achieved visual results approaching those of penetrating keratoplasty while reducing the rate of rejection and improving the long-term graft stability. As research continues, LK promises to be an increasingly important option for the corneal surgeon.

Endothelial replacement without surface corneal incisions or sutures: topography of the deep lamellar endothelial keratoplasty procedure.

Purpose. To evaluate the immediate postoperative corneal topography after the deep lamellar endothelial keratoplasty procedure. Methods. Eight eye bank eyes underwent deep lamellar endothelial keratoplasty through a 9.0-mm limbal incision replacing the central 7.0 mm of posterior stroma and endothelium through the lamellar pocket wound. Orbscan topography was performed before and after surgery, and simulated keratometry readings and central corneal diopter power were recorded. The change in astigmatism and corneal power from preoperative to postoperative readings was then determined. Results. The net change in corneal astigmatism averaged 0.4 ± 0.5 diopters (range, −0.1 to 1.1 diopters). The net change in corneal power averaged −0.2 ± 0.4 diopters of flattening (range, −0.9 to +0.2 diopters). Neither the astigmatism nor the corneal power levels after this surgery were significantly different from the preoperative topography (p = 0.22 and 0.27, respectively). Conclusions. The deep lamellar endothelial keratoplasty procedure, with its absence of corneal surface incisions or sutures, has no significant effect on immediate postoperative corneal topography. The potential advantages of this procedure over penetrating keratoplasty in the treatment of endothelial dysfunction are considerable.

In pursuit of emmetropia: Spherical equivalent refraction results with deep lamellar endothelial keratoplasty (DLEK)

Purpose To determine if the new technique for endothelial transplantation of DLEK (deep lamellar endothelial keratoplasty) can offer predictable corneal curvature and improved refractive spherical equivalent results compared with reports for traditional penetrating keratoplasty. Methods Twenty-seven consecutive Fuchs corneal dystrophy patients received DLEK surgery to replace their endothelium. Topographic corneal curvature and refractive spherical equivalents were evaluated at preop and at 6 and 12 months postop. Results At 6 months (n = 27) the average corneal curvature was 43.8 ± 1.4 D, representing a mean change from preop corneal curvature of only −0.1 ± 1.7 D. At 12 months (n = 18) the average corneal power was 43.5 ± 1.7 D. The average corneal curvature at 6 and 12 months was not significantly different from pre-op (P = 0.119). The average refractive spherical equivalent result at 6 months was −0.44 ± 1.7 D, and at 12 months was −0.44 ± 1.6 D. The 6- and 12-month refractive spherical equivalent results were not statistically different from the preop spherical equivalent refractions (P = 0.922). All patients could be easily refracted, and several patients were fit with stable glasses as early as 3 months after DLEK surgery. Conclusion DLEK surgery preserves the preoperative corneal curvature and therefore allows better matching of postop corneal curvature to the IOL power. This increase in predictability of the postoperative corneal curvature makes the choice of IOL power for the new “triple procedure” more accurate, eliminates the need for contact lens wear after PK, and provides earlier visual rehabilitation after endothelial replacement.

Standardized DMEK Technique: Reducing Complications Using Prestripped Tissue, Novel Glass Injector, and Sulfur Hexafluoride (SF6) Gas.

Purpose: To report low complication rates in Descemet membrane endothelial keratoplasty (DMEK) using sulfur hexafluoride (SF6) gas, a novel glass injector, and donor tissue prestripped by an eye bank technician. Methods: A standardized technique of DMEK was performed in 80 consecutive Fuchs corneal dystrophy cases using technician-prestripped tissue, a novel glass injector, a modified Yoeruek tap technique, and an SF6 gas (20% concentration) bubble for prolonged tissue support. Twenty-five donors were premarked with an “S” stamp for intraoperative orientation. Surgery was performed by 2 experienced DMEK surgeons and 2 inexperienced cornea fellows. Complications were recorded, and the percent endothelial cell loss was calculated at 6 months postoperatively. Results: There were 5 cases that received an air bubble injection postoperatively (6% rebubble rate). There were 6 grafts that immediately failed, 2 because of excessive surgical trauma, and 4 because of upside-down graft placement documented by optical coherence tomography. None of the 25 cases with an S stamp failed. Recipient corneas cleared quickly with no clinical evidence of toxicity from the SF6 gas bubble, and the grafts experienced a mean endothelial cell loss of 27% at 6 months. Conclusions: Tissue prestripped by an eye bank technician can be safely used for DMEK surgery. SF6 gas for prolonged tissue support may reduce the rebubble rate in DMEK, with no apparent acute toxic effect. An unrecognized upside-down graft was the primary cause of graft failure in this series. Upside-down grafts may be eliminated by the use of donor tissue premarked by the eye bank with an S orientation stamp.

New screening methods for donor eye-bank eyes.

PURPOSE Current methods of screening donor eyes for corneal transplantation are not always effective in excluding corneas with abnormal topography. We used the Orbscan to determine whether corneal-thickness maps could be used as a technique for donor tissue screening. METHODS Forty eye-bank eyes were measured with the Orbscan, and a corneal-thickness map was generated. Average central pachymetry measurements from each map were compared with the thinnest midperipheral thickness reading. Two eyes from a donor who had photorefractive keratectomy (PRK) and two eyes from a donor with keratoconus were then compared with the normal donor eye results. RESULTS The average difference between the thinnest midperipheral pachymetry and the central pachymetry in the control group was 0.040 +/- 0.026 mm. The eyes from the donor with PRK showed larger disparities between the central and midperipheral thicknesses because of the thinned central cornea, with differences of 0.154 mm in the right eye and 0.106 mm in the left eye. The eyes from the donor with keratoconus had midperipheral corneas that were thinner than the center, indicating eccentric, ectatic cones. The differences in thickness between the center and midperiphery in the eyes from the donor with PRK and the donor with keratoconus differed from the control group by >2 SD. CONCLUSIONS Diseases or surgery that affect the relationship between the central and midperipheral corneal thickness may be screened through Orbscan pachymetry mapping with comparison with a normal range.

Objective screening methods for prior refractive surgery in donor tissue.

Purpose. Laser refractive surgery presents a growing contamination of the available corneal donor pool. There currently is no objective method for screening donor tissue for previous refractive surgery. We evaluated the usefulness of pachymetry and curvature maps in the screening of donor corneas. Methods. Pachymetry and curvature maps were generated from the Orbscan for 40 normal donor eyes. The average central pachymetry measurement was subtracted from the thinnest average midperipheral pachymetry measurement for each map to generate a normal range of pachymetry measurements. For curvature, the average curvature at the 3-mm zone was subtracted from the average curvature at the 7-mm zone to generate a normal range of corneal curvature. The pachymetry and curvature results from 10 donor eyes that had undergone refractive surgery were then compared with the normal range for each technique. Results. The average difference in pachymetry measurements between the midperipheral and central cornea for normal eyes was 0.040 ± 0.026 mm. Four of 10 corneas that had undergone refractive surgery were outside two standard deviations of this normal range. The average difference in corneal curvature between the 7-mm zone and the 3-mm zone for the healthy eyes was −0.2 ± 1.0 diopters. Four (40%) of 10 corneas that had undergone refractive surgery were identified with this method. When combined, the pachymetry and curvature methods detected seven (70%) of 10 corneas that had undergone refractive surgery. Conclusion. Regional differences in thickness and curvature in donor eyes may provide methods for screening for refractive surgery for myopia. Refinement in mathematical manipulations may further improve the sensitivity of these techniques.

A multicenter study to map genes for Fuchs endothelial corneal dystrophy: Baseline characteristics and heritability

Purpose: To describe the methods for family and case–control recruitment for a multicenter genetic and associated heritability analyses of Fuchs endothelial corneal dystrophy (FECD). Methods: Twenty-nine enrolling sites with 62 trained investigators and coordinators gathered individual and family information, graded the phenotype, and collected blood and/or saliva for genetic analysis on all individuals with and without FECD. The degree of FECD was assessed in a 0 to 6 semiquantitative scale using standardized clinical methods with pathological verification of FECD on at least 1 member of each family. Central corneal thickness was measured by ultrasonic pachymetry. Results: Three hundred twenty-two families with 330 affected sibling pairs with FECD were enrolled and included a total of 650 sibling pairs of all disease grades. Using the entire 7-step FECD grading scale or a dichotomous definition of severe disease, heritability was assessed in families via sib–sib correlations. Both binary indicators of severe disease and semiquantitative measures of disease severity were significantly heritable, with heritability estimates of 30% for severe disease, 37% to 39% for FECD score, and 47% for central corneal thickness. Conclusions: Genetic risk factors have a strong role in the severity of the FECD phenotype and corneal thickness. Genotyping this cohort with high-density genetic markers followed by appropriate statistical analyses should lead to novel loci for disease susceptibility.

Stamping an S on DMEK Donor Tissue to Prevent Upside-Down Grafts: Laboratory Validation and Detailed Preparation Technique Description.

Purpose: To report endothelial cell loss (ECL) caused by a novel S-stamp preparation technique for Descemet membrane endothelial keratoplasty (DMEK). Methods: Six cadaveric human corneas were prepared for DMEK transplantation using a single standardized technique, including the application of a dry ink gentian violet S-stamp to the stromal side of Descemet membrane. Endothelial cell death was evaluated and quantified using computerized analysis of vital dye staining. Results: ECL caused by the S-stamp was 0.6% (range 0.1%–1.0%), which comprised less than one-tenth of the total ECL caused by our preparation of the DMEK graft from the start to finish, including recovery, prestripping, S-stamping, and trephination (13.7% total ECL, range 9.9%–17.6%). Conclusions: Our novel S-stamp donor tissue preparation technique is intuitive to learn and holds the promise of preventing iatrogenic primary graft failure due to upside-down grafts without causing unacceptable increases in ECL.

Evaluation of prior photorefractive keratectomy in donor tissue.

PURPOSE To describe a case in which an eye donor had prior bilateral photorefractive keratectomies and to elucidate possible methods of evaluation and screening of donor tissue. METHODS Case report. A 62-year-old eye donor was reported to have received radial keratotomy before his death. Further investigation by the eye bank showed a history of photorefractive keratectomy (PRK), not radial keratotomy. The corneas were therefore not used for transplantation, and the eyes were evaluated by slit-lamp examination, photography, corneal topography, and histology. RESULTS Slit-lamp and photographic examination did not indicate the presence of PRK ablations. Corneal topography mapping with the TMS-1 was relatively ambiguous for identifying PRK flattening, while multiple data formatting of the cornea with the Orbscan resulted in the strongest suggestion of prior PRK. Histologic analysis showed central corneal thinning and loss of Bowmans membrane consistent with PRK. CONCLUSIONS In the absence of a positive donor history for PRK, current methods of screening donor tissue for prior PRK often are insufficient to exclude these corneas from use in transplantation. More refined placido imagery corneal topography or newer technologies such as the Orbscan may allow more sensitive and specific methods of donor tissue screening.

Histologic evidence of retained fetal layer of the descemet membrane after presumed total removal for endothelial keratoplasty: a possible cause for graft failure.

Purpose: This is, to our knowledge, the first report of histology after failed Descemet-stripping endothelial keratoplasty (DSEK) surgery in a patient. We describe the interface histology found in a case of donor nonadherence and subsequent graft failure in a patient after DSEK. Methods: An 83-year-old woman with a history of Fuchs dystrophy underwent DSEK surgery and subsequently underwent full-thickness penetrating keratoplasty (PKP) because of nonadherence of the donor disc and presumed graft failure. Specimens from the initial stripping of the Descemet membrane, the failed donor disc, and the full thickness of the patients remaining cornea containing the recipient bed after her DSEK and PKP procedures were histologically evaluated by light microscopy. Results: Microscopic examination of the initial stripped recipient Descemet membrane revealed a “delamination” of the Descemet membrane involving the fetal layer. After PKP, histopathologic study of the recipient button revealed residual fetal Descemet membrane retained on the recipient DSEK interface. Examination of the failed donor disc showed healthy tissue. Conclusions: In DSEK surgery, there are multiple reasons that the donor graft button may fail to adhere to the recipient posterior corneal surface. In this instance, histologic study revealed that the Descemet membrane was split by the stripping, and the fetal layer of the Descemet membrane was retained on the central part of the patients posterior cornea. Despite histologically normal donor endothelial cells, the inability of the donor tissue to adhere may have been caused by the coating of the central recipient bed with retained fetal Descemet membrane.