Anterior Stromal Lamellae Research Articles

Intraoperative Optical Coherence Tomography-Guided Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty.

To describe the feasibility and outcomes of intraoperative optical coherence tomography (OCT)-guided, femtosecond laser-assisted deep anterior lamellar keratoplasty in which the lamellar and tunnel cuts were completed by laser. The Ziemer Z8 system was used to scan the corneas intraoperatively and guide the stromal lamellar and tunnel cuts created by the laser. Thirty porcine eyes and 3 human cadaver globes were used to evaluate the accuracy of laser-created intrastromal tunnels and the feasibility of achieving big-bubble pneumatic dissection. The tunnel distance above the Descemet membrane (Dt-dm) was set at 100 and 130 μm, and the accuracy of laser cut was assessed by anterior segment OCT and histological sections. Fourteen patients with keratoconus or corneal scars were then included to evaluate the clinical outcomes. The deviation from the targeted Dt-dm was 5.5% to 8.6% and 0.7% to 9.8% for the 100 and 130 μm groups, respectively. The achieved thickness had a significantly and positively strong correlation with the targeted thickness (r = 0.86; P < 0.001). In all cases, the anterior stromal lamella was removed without difficulty, except in the patients with corneal scars in whom some remaining stromal fiber attachments were observed. A type 1 big bubble was successfully achieved in all patients. We present the accuracy and clinical outcomes of femtosecond laser-assisted, intraoperative OCT-guided deep anterior lamellar keratoplasty, in which controlled lamellar and tunnel cuts at desired depths were performed by laser in one step, and a successful big bubble was achieved.

Survival of Mushroom Keratoplasty Performed in Corneas With Postinfectious Vascularized Scars

To report the visual outcomes and graft survival rates of mushroom keratoplasty for the treatment of postinfectious corneal scars. Prospective, noncomparative, interventional case series. A microkeratome-assisted mushroom-shaped keratoplasty was performed in 31 eyes of 31 patients with a central vascularized full-thickness leukoma, resulting from infectious keratitis of various origin (herpes simplex virus, n = 16; bacteria, n = 10; Acanthamoeba, n = 5), with healthy endothelium. The donor graft consisted of a large anterior stromal lamella (9.0 mm in diameter and ± 250 μm in thickness) and a small posterior button (5 to 6 mm in diameter). Visual acuity, refraction, and endothelial cell density were evaluated before surgery, as well as at 12, 24, and 36 months after surgery, and the postoperative graft survival rate was evaluated. Three years after surgery, in 26 (83.8%) of 31 patients, best spectacle-corrected visual acuity was 20/40 or better with a refractive astigmatism of 4.5 diopters or less. The endothelial cell count at the last follow-up examination averaged 1584 ± 381 cells/mm(2), with an average cell loss of 40.7% from the preoperative value. The survival rate at 3 years was 90.3%, improving to 96.7% when excluding nonimmunologic causes for graft failure. Similarly to penetrating keratoplasty, microkeratome-assisted mushroom keratoplasty restores vision in eyes with postinfectious, full-thickness, central corneal scars. For these vascularized corneas at high risk for immunologic rejection, mushroom keratoplasty combines the visual and refractive advantages of large penetrating keratoplasty grafts with the high survival rate of small penetrating keratoplasty grafts.

Quantified Histopathology of the Keratoconic Cornea

This study systematically investigated and quantified histopathological changes in a series of keratoconic (Kc) corneas using a physiologically formulated fixative to not further distort the already distorted diseased corneas. Twelve surgically removed Kc corneal buttons were immediately preserved and processed for light and transmission electron microscopy using an established corneal protocol. Measurements were taken from the central cone and peripheral regions of the host button. The sample size examined ranged in length from 390 to 2608 μm centrally and 439 to 2242 μm peripherally. The average corneal thickness was 437 μm centrally and 559 μm peripherally. Epithelial thickness varied centrally from 14 to 92 μm and peripherally from 30 to 91 μm. A marked thickening of the epithelial basement membrane was noted in 58% of corneas. Centrally, anterior limiting lamina (ALL) was thinned or lost over 60% of the area examined, whereas peripheral cornea was also affected but to a lesser extent. Histopathologically, posterior cornea remained undisturbed by the disease. Anteriorly in the stroma, an increased number of cells and tissue debris were encountered, and some of these cells were clearly not keratocytes. It is concluded that Kc pathology, at least initially, has a distinct anterior focus involving the epithelium, ALL, and anterior stroma. The epithelium had lost its cellular uniformity and was compromised by the loss or damage to the ALL. The activity of the hitherto unreported recruited stromal cells may be to break down and remove ALL and anterior stromal lamellae, leading to the overall thinning that accompanies this disease.

Mushroom keratoplasty in pediatric patients

Objective To report the outcome of mushroom keratoplasty for the treatment of full thickness corneal disease in pediatric patients with healthy endothelium. Methods A retrospective analysis of pediatric patients who underwent mushroom keratoplasty. The medical records of pediatric patients suffering from full thickness corneal stromal disease with normal endothelium who underwent mushroom keratoplasty at our Institution were included. A two-piece donor graft consisting of a large anterior stromal lamella (9.0 mm in diameter and ±250 μm in thickness) and a small posterior lamella (5–6.5 mm in diameter) including deep stroma and endothelium, prepared with the aid of a microkeratome had been transplanted in all cases. Ophthalmic examination including slit lamp examination, best corrected visual acuity, and corneal topography was performed preoperatively and at each postoperative visit on all patients. The endothelial cells were assessed by specular microscopy in these patients. Results Six eyes of six patients (five males and one female) were included. The mean age was 9.3 years (range 5–15 years). Average follow-up was 17.8 months (range 9–48 months). There were no early or late complications recorded. All corneas were clear at the last follow up visit. Preoperative best corrected visual acuity (BCVA) was worse than 20/70 in all six eyes. Postoperatively, four eyes achieved BCVA of 20/40 or better. Endothelial cell loss ( n eyes = 3 averaged 24% (range 19–31%). The mean endothelial cell loss was 24% (range 19–31%) among these patients. Conclusions Microkeratome assisted mushroom keratoplasty is a viable surgical option for pediatric eyes with full thickness corneal stromal disease and healthy endothelium. Mushroom keratoplasty combines the refractive advantage of a large penetrating keratoplasty with the survival advantage of a small penetrating keratoplasty. Furthermore, mushroom keratoplasty exhibits the mechanical advantage of a shaped keratoplasty.

Fine Structure of the Interface between the Anterior Limiting Lamina and the Anterior Stromal Fibrils of the Human Cornea

To use transmission electron microscopy (TEM) to investigate further the ultrastructural details of the collagen fibrils linking the anterior limiting lamina (ALL; Bowman's membrane) of the human cornea to the anterior stromal lamellae. Six disease-free corneas from donors aged 42 to 82 years were fixed (2% glutaraldehyde in 80 mM sodium cacodylate) and processed for TEM within 72 hours postmortem. A series of overlapping images, at 10,204x magnification, of the central corneal ALL-stroma interface were assembled. The features of the terminal ends of fibril bundles at the interface with the anterior stroma were quantitatively assessed. TEM revealed apparently terminating anterior stromal fibril bundles adjacent to the ALL. These terminating lamellae (7.8 per 100 mum) were embedded in an electron-dense material within the surrounding stromal matrix and were termed electron-dense formations (EDFs). The mean width of these stromal features was 1.6 mum. At intervals, anterior stromal lamellae approached the ALL and, in a shallow manner, inserted into the ALL. Such projections (5.4 per 100 mum) into the ALL were, on average, less than 1 mum. Numerous fibrils (29.8 per 100 mum) extended from the ALL into the stroma with a mean length of 0.8 mum. The interface the ALL forms with the anterior stroma is complex, and TEM revealed at least three different types of fibrillar arrangements, which may serve optical requirements rather than provide a structural function.

Microkeratome-assisted Mushroom Keratoplasty With Minimal Endothelial Replacement

To report the outcome of a new keratoplasty technique aimed at treating full-thickness opacities with minimal removal of recipient endothelium. Interventional case report. A deep central scar was removed using microkeratome-assisted mushroom-shaped keratoplasty, consisting of a large anterior stromal lamella (9.0-mm in diameter) and a small posterior button (5.0-mm in diameter) including deep stroma and endothelium. Complete suture removal was performed 3 months after surgery. Visual acuity, refraction, and computerized corneal topography were evaluated pre- and postoperatively. Best spectacle-corrected visual acuity improved from 20/60 to 20/20 at 6 months postoperatively. Postoperative refraction was -2.50-1.00 x 20 degrees. Microkeratome-assisted mushroom keratoplasty may offer visual and refractive advantages over conventional keratoplasty surgery. Because most of the recipient endothelium is preserved and may spread onto the posterior surface of the small donor button, graft decompensation secondary to immunologic rejection may be avoided with this technique.

The Non-Uniform Distribution of Albumin in Human and Bovine Cornea

In our previous studies, we noted a non-uniform distribution of protein tracer preferentially entering the anterior stromal lamellae of the cornea from the limbus. Given other differences reported previously between the anterior and posterior lamellae of the cornea, and the number of corneal disorders in which abnormalities are preferentially confined to either the anterior or posterior lamellae, we were prompted to examine the distribution of albumin in normal human and bovine cornea.The distribution of albumin in bovine and human cornea was studied immunohistochemically. Total soluble protein and albumin in the anterior 1/3 and posterior 2/3 of the central, middle and peripheral cornea of bovine eyes was measured biochemically. To aid in interpreting the findings, a theoretical model was developed based upon the combined effects of diffusive and convective transport.Using immunohistochemical methods, in both bovine and human eyes, intense staining of albumin was found in the anterior 1/3 of the corneal stroma. There was a gradual reduction in staining intensity from the limbus to the central cornea in the anterior corneal stroma. Less staining was found in the posterior 2/3 of corneal stroma. Additionally, a greater concentration of soluble protein and albumin was found in the anterior stroma than in the posterior stroma of the bovine eyes by biochemical analyses. The theoretical model demonstrated that this distribution of protein required a difference in excluded volume fraction between the anterior and posterior stroma and was consistent with a convective flux originating at the limbus and passing through the corneal stroma.The soluble proteins of the bovine and human cornea are preferentially concentrated in the anterior cornea and near the limbus. This distribution is likely due to differences in excluded volume fraction between the anterior and posterior stroma and a small convective flux passing through the cornea.

Nd:YAG Laser Photo-induced Adhesion of the Corneal Epithelium

We retrospectively studied eight patients with recurrent corneal erosions treated with the Nd:YAG laser using 0.4- to 0.5-mJ pulses applied to the region of Bowman's layer through an intact epithelium. All eight patients had resolution of their symptoms after treatment. Mean follow-up time was 21.2 months (range, 12.6 to 36.6 months). A patient who was scheduled for diagnostic enucleation for a posterior choroidal mass consented to undergo this laser treatment with varied energy settings six days before his enucleation. His cornea was studied with specular microscopy, light microscopy, and transmission electron microscopy. Light microscopy of the cornea disclosed rare 100-microns defects in Bowman's layer with subjacent compaction of the anterior stromal lamellae. Electron microscopy showed minute foci of disruption in Bowman's layer with new collagen formation. Fine fibrils connected the basal epithelial cells to the new collagen. Nd:YAG laser photo-induced adhesion of the corneal epithelium may represent an effective treatment alternative for patients with recurrent corneal erosions.

HSV-induced reactivation: contribution of epinephrine after corneal iontophoresis.

A modified, bilateral iontophoresis technique was used to evaluate herpes simplex virus (HSV) reactivation and epinephrine distribution and concentration in full-thickness corneas and in trigeminal ganglia of rabbits. Infectious virus was recovered from 58% of epinephrine-induced eyes 24-96 hours after iontophoresis. A histochemical adrenochrome oxidation method localized epinephrine exclusively in the corneal epithelium and anterior stromal lamellae after iontophoresis. Epinephrine introduced iontophoretically into the corneal epithelium and stroma did not reach the ganglion level as detected by the assay. Radiometric-enzymatic assay of corneal and ganglionic tissues demonstrated a transient increase in total corneal catecholamine levels from an average of 417 micrograms to an average of 778 micrograms ; concentrations returned to approximate control values 24 hours after iontophoresis. Ganglion total catecholamine levels increased from an average of 606 micrograms to an average of 1211 micrograms for a 12-hour period and remained elevated at 24 hours after iontophoresis. Epinephrine acting directly on the corneal epithelium and epinephrine metabolites at the ganglion level could act synergistically to induce ocular and ganglionic HSV reactivation.

Correlative Microscopy and Tissue Culture of Congenital Hereditary Endothelial Dystrophy

A 4 1/2-year-old boy with congenital hereditary endothelial dystrophy underwent successful bilateral penetrating keratoplasties. Visual acuity in both eyes was restored to 6/18 (20/60). Correlative microscopic analysis of the corneal button obtained from the first transplant showed an irregular epithelium, a continuously thickened Bowman's layer, fragmentation and homogenization of the anterior stromal lamellae, a mildly enlarged stromal fibril diameter, abnormal collagen layers posterior to Descemet's membrane, atrophic paracentral corneal endothelium, and absent central endothelium. The endothelial cells from the second corneal button were placed in tissue culture and failed to demonstrate any growth characteristics of differentiation into normal appearing cells after 14 days. We concluded that the endothelial cells in congenital hereditary endothelial dystrophy are functionally and morphologically abnormal. Early penetrating keratoplasty can be successful in such cases.

Reis-B�ckler's dystrophy

A case of Reis-Bückler's dystrophy in a 36-year-old man is reported. Its clinical aspect is compared with its histological and ultrastructural features. The slight reticular opacities situated superficially in the central part of the cornea, immediately beneath the epithelium, correspond to dark, irregular deposits. These replaced the basal membrane and Bowman's membrane and are composed of granular material, glycogen granules, and short fibers. These short, curved, osmiophilic fibers whose diameter is approximately 130 A are also located inside the anterior stromal lamellae. These deposits seem to be the characteristic feature of this particular and rare dystrophy, stated as by Hogan. Their nature and origin are discussed.