Ingo Schmack

Cohesive tensile strength of human LASIK wounds with histologic, ultrastructural, and clinical correlations.

PURPOSE To measure the cohesive tensile strength of human LASIK corneal wounds. METHODS Twenty-five human eye bank corneas from 13 donors that had LASIK were cut into 4-mm corneoscleral strips and dissected to expose the interface wound. Using a motorized pulling device, the force required to separate the wound was recorded. Intact and separated specimens were processed for light and electron microscopy. Five normal human eye bank corneas from 5 donors served as controls. A retrospective clinical study was done on 144 eyes that had LASIK flap-lift retreatments, providing clinical correlation. RESULTS The mean tensile strength of the central and paracentral LASIK wounds showed minimal change in strength over time after surgery, averaging 2.4% (0.72 +/- 0.33 g/mm) of controls (30.06 +/- 2.93 g/mm). In contrast, the mean peak tensile strength of the flap wound margin gradually increased over time after surgery, reaching maximum values by 3.5 years when the average was 28.1% (8.46 +/- 4.56 g/mm) of controls. Histologic and ultrastructural correlative studies found that the plane of separation always occurred in the lamellar wound, which consisted of a hypocellular primitive stromal scar centrally and paracentrally and a hypercellular fibrotic stromal scar at the flap wound margin. The pathologic correlations demonstrated that the strongest wound margin scars had no epithelial cell ingrowth-the strongest typically being wider or more peripherally located. In contrast, the weakest wound margin scars had epithelial cell ingrowth. The clinical series demonstrated the ability to lift LASIK flaps without complications during retreatments up to 8.4 years after initial surgery, correlating well with the laboratory results. CONCLUSIONS The human comeal stroma typically heals after LASIK in a limited and incomplete fashion; this results in a weak, central and paracentral hypocellular primitive stromal scar that averages 2.4% as strong as normal comeal stroma. Conversely, the LASIK flap wound margin heals by producing a 10-fold stronger, peripheral hypercellular fibrotic stromal scar that averages 28.1% as strong as normal comeal stromal, but displays marked variability.

Corneal Ectasia After Excimer Laser Keratorefractive Surgery : Histopathology, Ultrastructure, and Pathophysiology

PURPOSE To evaluate the histopathology and ultrastructure of corneas developing ectasia after LASIK or photorefractive keratectomy (PRK). DESIGN Retrospective case series. PARTICIPANTS Thirteen specimens from 12 patients undergoing corneal transplantation for progressive ectasia after LASIK (12 specimens) or PRK (1 specimen) were obtained for histopathologic and ultrastructural evaluation. METHODS All 13 ectatic corneas were submitted in formalin for light microscopy. Nine specimens were bisected, and the second half was placed in 2.5% glutaraldehyde for transmission electron microscopy (TEM). MAIN OUTCOME MEASURES Corneal histopathology, ultrastructure, and pathophysiology. RESULTS Light microscopy of the post-LASIK specimens showed corneal epithelial hypoplasia and occasional foci of epithelial hyperplasia, Bowmans layer breaks, a normal stromal thickness of the LASIK flap, a normal thickness of the hypocellular primitive stromal scar, a thinned residual stromal bed (RSB), and larger than normal artifacteous interlamellar clefts in the RSB of the ectatic region. The post-PRK specimen showed similar findings with the addition of a thinned hypercellular fibrotic stromal scar. TEM showed thinning of the collagen lamellae and loss of lamellar number in the RSB of post-LASIK ectasia corneas or throughout the entire corneal stromal bed in the post-PRK ectasia cornea, with the posterior aspect of the corneal stroma being most affected. CONCLUSIONS Histopathologic and ultrastructural studies suggest that interlamellar and interfibrillar biomechanical slippage occurs when the cornea becomes ectatic after LASIK or PRK in the postoperative stress-bearing regions of the corneal stroma. This 2-phase chronic biomechanical failure process is similar to that seen in keratoconus. Composite sciences classify this chronic biomechanical failure process as interfiber fracture. FINANCIAL DISCLOSURE(S) The authors have no proprietary or commercial interest in any materials discussed in this article.

Refractive Surgery Trends and Practice Style Changes in Germany over a 3-Year Period

PURPOSE To study the current practice styles and preferences of refractive surgeons in Germany. METHODS In February 2008, a seven-item questionnaire regarding the practice of refractive surgery was mailed to 282 members of the German Society of Intra-ocular Lens Implantation, Interventional, and Refractive Surgery (DGII) and the Commission of Refractive Surgery (KRC). Most questions were identical to our 2005 German refractive surgery survey. All data were analyzed in a masked fashion. RESULTS The response rate was 42.2%. The majority (68%) of respondents reported that they perform refractive surgery in laser centers (exclusively or partially) followed by general hospitals (19.4%) and universities (12.6%). Although LASIK was the predominant type of refractive surgery performed (80.6%), other refractive procedures included refractive lens exchange (60.2%), photorefractive keratectomy (47.6%), phakic intraocular lens implants (45.6%), laser-assisted subepithelial keratectomy (36.9%), epithelial laser in situ keratomileusis (15.5%), intracorneal rings (5.8%), and limbal relaxing incisions (2.9%). The volume of refractive surgery procedures and the preferred type of excimer laser systems, microkeratomes, and diagnostic devices varied at different institutions. Most respondents performed either wavefront-guided custom ablation or wavefront-optimized ablation (63.1%) compared with conventional excimer laser correction (36.9%). CONCLUSIONS Refractive surgery practice styles and preferences in Germany are comparable to trends in other European countries. Although LASIK is the most commonly performed refractive procedure, the numbers of various surface ablation techniques and refractive intraocular lens procedures are increasing.

Subconjunctival herniated orbital fat : A benign adipocytic lesion that may mimic pleomorphic lipoma and atypical lipomatous tumor

Prolapse of subconjunctival intraconal orbital fat is a rare cause of an intraorbital mass lesion. Over the past several years, we have seen a number of cases in which this prolapsed fat was confused pathologically with a neoplasm of adipocytic lineage, specifically pleomorphic lipoma and atypical lipomatous neoplasm (well-differentiated liposarcoma). We report the clinical, histopathologic, and immunohistochemical findings in 21 specimens from 17 patients, all of whom presented with prolapsed intraconal orbital fat. All specimens were routinely examined and processed for light microscopy. Immunohistochemistry for CD34, CD68, S100 protein, vimentin, α-smooth muscle actin, and Ki-67, and Giemsa, Masson trichrome, and alcian blue histochemical stains were performed. Clinical and follow-up information was extracted from a chart review. The mean age (±SD) of the patients was 65.6±11.9 years (range: 41 to 85 y); 2 were women and 15 were men. Subconjunctival prolapsed orbital fat was localized in the superotemporal quadrant or lateral canthus around the rectus muscle below the lacrimal gland. The lesions were unilateral in 10 and bilateral in 7 patients. No recurrence was clinically evident over a mean (±SD) follow-up time of 2.5±3.2 years (range: 1 mo to 13.5 y). Histopathologically, all specimens showed an admixture of mature fat, fibrous septae lacking hyperchromatic cells, adipocytes with intranuclear vacuoles (Lochkern cells), multinucleated giant cells with a wreathlike configuration of normochromatic nuclei (floret cells), and varying numbers of histiocytes, lymphocytes, plasma cells, and mast cells. “Control” sections of normal orbital fat showed occasional Lochkern cells but lacked floret cells. By immunohistochemistry, the floret cells expressed only CD34 and vimentin, whereas the Lochkern cells expressed CD34, S100 protein, and vimentin. We conclude that subconjunctival herniated orbital fat commonly contains multinucleated floretlike giant cells, fibrous septae, and Lochkern cells, features that may result in diagnostic confusion with pleomorphic lipoma and atypical lipomatous neoplasms. Importantly, specific diagnostic features, such as aggregates of bland spindled cells associated with wiry collagen, as seen in pleomorphic lipoma, and enlarged hyperchromatic cells within fibrous septae, as in atypical lipomatous neoplasms, are entirely absent in herniated orbital fat. Multinucleated floret cells present in prolapsed orbital fat likely represent a reactive phenomenon, as they are not present in normal orbital fat.

Donor corneas misidentified with prior laser in situ keratomileusis.

Purpose: To evaluate the rate of donor corneas misidentified as recipients of previous laser in situ keratomileusis (LASIK) surgery in the eye banks. Methods: One hundred sixty-one donor corneas identified as having had previous LASIK surgery from 15 eye banks were sent to the Emory Eye Center between January 2002 and August 2005. Determination of the previous LASIK surgery was made from the medical history and/or slit-lamp examination in the contributing eye bank. Histologic examination of the corneas was performed to confirm the diagnosis. Results: Information regarding the decision making was available in 155 corneas out of 161. Among 155 corneas, 16 donor corneas (10.3%) revealed no evidence of previous LASIK surgery in the histology. The rate of misidentified corneas as having previous LASIK was 13.5% in history only group (10 of 74) and 18.2% in those determined by the slit-lamp examination only (4 of 22). In corneas determined by both history and slit-lamp examination, the misidentified rate decreased to 3.4% (2 of 59). Conclusions: There is approximately a 10% rate of misidentified post-LASIK corneas in eye banks. A decision made by both history and slit-lamp examination decreases the misidentification rate compared with using only either method alone.

Histopathological findings in postmortem eyes after photodynamic therapy for choroidal neovascularisation in age-related macular degeneration: report of two cases

Background: To report the histopathological findings after photodynamic therapy (PDT) in eyes obtained postmortem with choroidal neovascularisation (CNV) secondary to age-related macular degeneration (AMD). Methods: Two eyes were obtained postmortem from two patients with CNV secondary to AMD. Both of the patients had been treated with PDT. Serial sections through the posterior poles were obtained and stained with haematoxylin-eosin, periodic acid-Schiff, Masson trichrome or phosphotungstic acid haematoxylin (PTAH). Two-dimensional reconstructions were prepared and compared with fluorescein angiograms. Results: The interval between PDT and death was 3 months and 17 months in each patient, respectively. Light-microscopic examination showed that CNV enveloped with retinal pigment epithelium (RPE) in both eyes. The average size of the CNV was 550×280 µm. One eye had combined (subRPE/subretinal) growth pattern CNV, and the other eye had both type I (subRPE) and combined growth pattern CNV. All specimens contained fibrous proliferation and patent vascular channels within the CNV, and there was no thrombus formation within the vascular channels. No apparent abnormalities in the choroid were observed by light microscopy. Conclusions: Although involution with fibrous tissue proliferation occurred, PDT did not result in permanent occlusion of the vascular channels in the CNV. Our findings indicate that PDT may accelerate involution of CNV, thus limiting its size and preserving photoreceptors.

Meta-analysis of Postoperative Outcome Parameters Comparing Descemet Membrane Endothelial Keratoplasty Versus Descemet Stripping Automated Endothelial Keratoplasty

Purpose: This meta-analysis compares Descemet membrane endothelial keratoplasty (DMEK) with Descemet stripping automated endothelial keratoplasty (DSAEK) to evaluate their strength and weakness profiles. Design: Meta-analysis. Methods: We performed a meta-analysis and searched the peer-reviewed literature in PubMed, Cochrane Library, Web of Science, and Embase following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Prospective and retrospective trials performing and comparing DMEK and DSAEK were included. Effects were calculated as odds ratios or standardized mean differences. Results: A total of 11 studies with a total of 723 eyes (350 DMEK and 373 DSAEK) were included. No significant difference was found regarding the total detachment rate, graft failure, and rejection. One of 340 eyes undergoing DMEK showed total detachment and 5 of 363 eyes undergoing DSAEK showed total detachment (P = 0.28). Six of 280 eyes undergoing DMEK showed graft failure; 1 of 313 eyes undergoing DSAEK developed this complication (P = 0.18). No rejection was observed in 158 eyes undergoing DMEK; 4 cases of rejection occurred in 196 eyes undergoing DSAEK (P = 0.37). No significant difference was found regarding endothelial cell loss (P = 0.48). There was a significantly higher partial detachment rate with DMEK: 88 of 340 eyes undergoing DMEK showed partial detachment; 16 of 363 eyes undergoing DSAEK showed this complication (P < 0.00001). DMEK was superior in best-corrected visual acuity after 6 months (P < 0.001), subjective evaluation of visual acuity (P = 0.001), patient satisfaction (P < 0.001), and was the method preferred by patients (P = 0.001). Conclusions: DMEK and DSAEK have a similar complication profile. However, the superiority in the visual outcome and patient satisfaction makes DMEK the preferred option for most patients.

Characteristics of Corneal Astigmatism of Anterior and Posterior Surface in a Normal Control Group and Patients With Keratoconus.

Purpose: To evaluate and compare power and axis orientation of anterior and posterior astigmatism in eyes with keratoconus with healthy eyes. Methods: In this retrospective cohort study, we examined 861 eyes of 494 patients diagnosed with keratoconus at the Department of Ophthalmology, University Hospital Frankfurt, and 256 eyes of 256 healthy individuals. Using a Scheimpflug device (Pentacam HR), we measured the magnitude and axis orientation of anterior and posterior corneal astigmatism, corneal thickness, and conus location. The results were compared between different stages of the disease according to the Amsler–Krumeich classification and the control group. Results: Magnitude of corneal astigmatism was 3.47 ± 2.10 diopters (D) on the anterior surface and 0.69  ± 0.40 D on the posterior surface in eyes across all keratoconus stages. We found a significant increase of anterior and posterior corneal astigmatism with progression of disease (P < 0.01, 1-way analysis of variance) and a significant correlation between anterior and posterior corneal astigmatism (r = 0.77, P < 0.01). In contrast to eyes of healthy individuals, in which posterior corneal axis alignment is vertical in most cases independent of anterior alignment, we found in eyes with keratoconus a match between anterior and posterior alignment when alignment was vertical in 97% of eyes, 46% when oblique and 61% when horizontal (Cohen kappa coefficient &kgr; = 0.55, P < 0.01). With progression of disease, alignment of anterior and posterior corneal astigmatism became increasingly vertical. Conclusions: In eyes with keratoconus, posterior axis alignment of corneal astigmatism is in line with alignment of the anterior surface in the majority of cases. Posterior astigmatism axis alignment could potentially be used in algorithms to support diagnosis and staging of keratoconus.