Epithelial response in penetrating keratoplasty

Central Corneal Subepithelial Haze Following Keratoplasty With Interrupted Sutures: A Novel Clinical Finding

Purpose

This study aims to describe a newly identified clinical finding of central corneal subepithelial haze following keratoplasty (both penetrating and lamellar) with interrupted sutures, and to explore its causes and management strategies.

Methods

Case series.

Results

The study included 7 males and 3 females, with an average age of 24.89 ± 6.57 years. Eight eyes underwent lamellar keratoplasty, and two underwent penetrating keratoplasty. Subepithelial haze appeared between 2 and 5 months postoperatively, associated with central corneal steepening. The mean BCVA improved from 0.88 ± 0.50 logMAR preoperatively to 0.51 ± 0.20 at haze documentation and 0.50 ± 0.16 after haze resolution. Selective suture removal resulted in haze resolution in 9 eyes, while delayed intervention in one case led to permanent scarring.

Conclusion

Central corneal subepithelial haze following keratoplasty with interrupted sutures is linked to suture tension and central corneal steepening. Early suture adjustment or removal is essential to prevent permanent scarring. Further studies are needed to better understand this complication's pathophysiology.

Managing Post-Keratoplasty Astigmatism: High-Tech vs. Low-Tech Imaging Techniques for Guiding Suture Manipulation

Astigmatism is a visually significant condition that can develop after keratoplasty. The management of post-keratoplasty astigmatism can be performed both when transplant sutures are in place and when they have been removed. Fundamental for astigmatism management is its identification and characterization in terms of type, amount, and direction. Commonly, post-keratoplasty astigmatism is evaluated through corneal tomography or topo-aberrometry; however, many other techniques can be used in case these instruments are not readily available. Here, we describe several low-tech and high-tech techniques used for post-keratoplasty astigmatism detection in order to quickly understand if it contributes to low vision quality and to determine its characteristics. The management of post-keratoplasty astigmatism through suture manipulation is also described.

Enhanced effect of double-stacked intrastromal corneal ring segments in keratoconus

We present a patient with poor visual acuity and contact lens intolerance due to advanced keratoconus who had femtosecond-assisted placement of two 0.35 mm intrastromal corneal ring segments (ICRS) in the right eye. Postoperatively, both rings migrated inferiorly and overlapped each other in a double-stacked formation. This resulted in a dramatic central shift of the cone and flattening of the inferior paracentral cornea with significant improvement in vision. To our knowledge, this is the first report of double-stacked ICRS in a human cornea and raises the possibility that significantly thicker segments may provide enhanced anatomic and visual effects in some keratoectatic patients.

The role of the limbus in ocular surface maintenance and repair

Since Claes Dohlman's original treatise on the corneal epithelium, a great deal has been learned about the biology of that layer. Its maintenance depends in part on centripetal movement of cells from the periphery toward the center. To some degree the supply of these peripheral cells appears to be dependent on the proliferation of cells at the limbus, from so-called 'stem cells'. Studies of stem cell replication and differentiation of their progeny will lead undoubtedly to new insights into the the mechanisms responsible for many of the chronic abnormalities of the central corneal surface.

Corneal epithelial stem cells: characterization, culture and transplantation

The epithelium covering the cornea at the front of the eye is maintained by stem cells located at its periphery, in a region known as the limbus. A lack or dysfunction of these so-called limbal stem cells (LSCs) results in the painful and blinding disease of LSC deficiency. In this review, current knowledge regarding the biology of these particular stem cells will be outlined, including recent advances that are enabling the gene expression analysis of these cells. The use of LSCs in therapeutic interventions for LSC deficiency will also be discussed, including the role for ex vivo expansion. In particular, the translation of basic science advances in LSC biology into therapeutic strategies will be highlighted.

Donor corneas for transplantation: a scanning electron microscopic study of the epithelium

PURPOSE

Donor corneas are processed in eye banks and used for transplantation as a standard routine. The maximum time limit post-mortem for harvesting donor tissue varies greatly between eye banks. This study aimed to examine the corneal epithelium for structural changes post-mortem.

METHODS

A total of 51 corneas harvested between 14 and 163 hours post-mortem were examined using scanning electron and light microscopy.

RESULTS

Cell loss occurred through desquamation of flat superficial cells during the first days. In corneas with a post-mortem time of more than 2-3 days, large superficial cell sheets and deeper cells detached, starting centrally. Deep peripheral cells remained. The loss of the superficial cells revealed the 3-dimensional structure of the epithelium and the membrane characteristics of deeper cells.

CONCLUSION

The longer the time post-mortem, the greater the epithelial cell loss. However, a rim of peripheral cells remained, even after 7 days. The superficial cell layer showed signs of strong lateral attachment and broke up in a sheet-like fashion. The intercellular adhesion between deeper cells and adhesion between the basal cells and the basement membrane appeared to be weak post-mortem. The cell membrane structures of the remaining cells were surprisingly well retained. The clinical implication of the study is discussed.

Stem cell differentiation and the effects of deficiency

Stem cells have several unique attributes, the key features being their potency and plasticity. They have the ability to give rise to multiple cell lineages and to transdifferentiate into totally different cell type(s) when relocated to a novel stem cell niche. Most self-renewing tissues are served by stem cells. At the ocular surface, the corneo-scleral limbus is believed to provide the niche for corneal epithelial stem cells. A large body of circumstantial evidence, both clinical and basic, supports this view. However, specific identification of limbal stem cells has proved elusive. Cytokeratin markers, vimentin, epidermal growth factor receptors, p63, and others have been used to identify epithelial cell populations at the limbus, which could harbour putative stem cells. In contrast, none of the known haematopoietic stem cell markers namely, CD34 and CD133, stain any specific subset of corneal or limbal epithelial cells. Singly or collectively, none of these markers point to any unique cell(s) that could be regarded as stem cells, supporting the notion that the corneal epithelium is served by 'committed progenitors' rather than by stem cells. Disease or destruction of the corneo-scleral limbus is associated with consequential events that eventually lead to visual impairment or blindness. Conjunctivalisation and vascularisation of the corneal surface and persistent or recurring epithelial defects are hallmarks of limbal deficiency.

Autologous limbal transplantation in unilateral chemical burns

PURPOSE

To describe the results of autologous limbal transplantation in the treatment of unilateral chemical burns.

PATIENTS AND METHODS

Two patients, a 40-year-old male (case 1) and a 35-year-old male (case 2), experienced grade III chemical trauma and were treated with autologous limbal grafting (case 1) after a postaccident period of 3 and 9 months, respectively. Change in visual acuity, epithelial healing time and postsurgical topography healing patterns were documented.

RESULTS

Snellen visual acuity improved from 0.1 to 1.0 in both cases. Epithelial healing time for cases 1 and 2 were 4 and 2 weeks, respectively. Corneal topography of case 1 showed an induced inferior steepness type of asymmetrical astigmatism in the graft area. Serial topography showed no induced astigmatism in the donor eyes.

CONCLUSION

Autologous limbal grafting is an adequate treatment for selected cases of unilateral chemical burns and facilitates rapid improvement in visual function. Early limbal grafting in case 1 resulted in rapid re-epithelialization and prevention of complications.

Chemical injuries of the eye: current concepts in pathophysiology and therapy

Chemical injuries of the eye may produce extensive damage to the ocular surface epithelium, cornea, and anterior segment, resulting in permanent unilateral or bilateral visual impairment. Pathophysiological events which may influence the final visual prognosis and which are amenable to therapeutic modulation include 1) ocular surface injury, repair, and differentiation, 2) corneal stromal matrix injury, repair and/or ulceration, and 3) corneal and stromal inflammation. Immediately following chemical injury, it is important to estimate and clinically grade the severity of limbal stem cell injury (by assessing the degree of limbal, conjunctival, and scleral ischemia and necrosis) and intraocular penetration of the noxious agent (by assessing clarity of the corneal stroma and anterior segment abnormalities). Immediate therapy is directed toward prompt irrigation and removal of any remaining reservoir of chemical contact with the eye. Initial medical therapy is directed promoting re-epithelialization and transdifferentiation of the ocular surface, augmenting corneal repair by supporting keratocyte collagen production and minimizing ulceration related to collagenase activity, and controlling inflammation. Early surgical therapy if indicated, is directed toward removal of necrotic corneal epithelium and conjunctiva, prompt re-establishment of an adequate limbal vascularity, and re-establishment of limbal stem cell population early in the clinical course, if sufficient evidence exists of complete limbal stem cell loss. Re-establishment of limbal stem cells by limbal autograft or allograft transplantation, or by transfer in conjunction with large diameter penetrating keratoplasty, may facilitate development of an intact, phenotypically correct corneal epithelium. Limbal stem cell transplantation may prevent the development of fibrovascular pannus or sterile corneal corneal ulceration, simplify visual rehabilitation, and improve the visual prognosis. Advances in ocular surface transplantation techniques which allow late attempts at visual rehabilitation of a scarred and vascularized cornea include limbal stem cell transplantation for incomplete transdifferentiation and persistent corneal epithelial dysfunction, and conjunctival and/or mucosal membrane transplantation for ocular surface mechanical dysfunction. Rehabilitation of the ocular surface may be followed, if necessary, by standard penetrating keratoplasty if all aspects of ocular surface rehabilitation are complete, or by large diameter penetrating keratoplasty if successful limbal stem cell transplantation cannot be achieved but other ocular surface rehabilitation is complete.

Conjunctival epithelial cells can resurface denuded cornea, but do not transdifferentiate to express cornea-specific keratin 12 following removal of limbal epithelium in mouse

Limbal stem cell deficiency contributes to recurrent corneal epithelial defects. We examined whether the conjunctival epithelium can transdifferentiate to corneal epithelium following surgically induced limbal stem cell deficiency. Mice were anesthetized by intraperitoneal injection of sodium pentobarbital. Partial or total epithelial removal was produced with a no. 69 Beaver blade under a dissecting microscope. The wounds were allowed to heal for 0-28 days, and the mice were examined every other day to evaluate re-epithelialization. Corneas were then subjected to histological, immunohistochemical studies and Western blot analysis with epitope-specific anti-keratin 12 antibodies. Partial epithelial defects re-epithelialized within 2 days and were normal in appearance and expressed cornea-specific keratin 12. In eyes with limbal deficiency, re-epithelialization progressed more slowly and was characterized by opacification; epithelial closure usually occurred by the 7th day. This epithelium differed from normal corneal epithelium in basic morphology, cell shape, and the presence of goblet cells at 2 weeks after injury. The epithelium at the center of injured corneas with total defect at 4 weeks had cornealike morphology and was devoid of goblet cells. These epithelial cells derived from conjunctiva did not express the cornea-specific keratin 12 as determined by immunohistochemistry, Western blot analysis and in situ hybridization. As evidenced by differences in morphology and the expression of cornea-specific keratin 12, conjunctival transdifferentiation does not occur in conjunctical overgrowth after the removal of limbal epithelium.

Comparative antioxidant protection of cultured rabbit corneal epithelium

Oxygen-free radicals may injure the epithelium of corneas in storage awaiting transplantation. This study compared the cytoprotective effects of several antioxidants against oxygen-free radical injury to rabbit corneal epithelial cells in vitro. Cultured rabbit corneal epithelial cells were exposed to oxygen-free radicals generated by xanthine oxidase and hypoxanthine. The cytoprotective activities of various antioxidants on this system were compared using established morphologic criteria. The results demonstrated that purpurogallin at 1.0 mM delayed cell necrosis to 9.98 +/- 1.16 min compared with 2.96 +/- 0.67 min without antioxidant protection. This degree of protection was significantly different from that provided by ascorbate (1.0 mM), trolox (1.0 mM), superoxide dismutase + catalase, catalase (92,000 IU/L), mannitol (1.0 mM), and superoxide dismutase (24,200 IU/L) (p < 0.01). We concluded that purpurogallin effectively protects corneal epithelium from oxygen-free radical injury and may help prevent such injury in corneal preservation solutions.

Corneal epithelial wound healing

Images

Stem cells and corneal epithelial regeneration

Self-renewing tissues such as the corneal epithelium contain stem cells which represent the proliferative reserve. Studies of cellular differentiation and proliferation suggest that corneal epithelial stem cells are localised exclusively in the basal limbal epithelium. Although regulatory factors for the amplification of corneal stem cells are unknown, serum factors such as retinoic acid might induce differentiation of stem cells to transient amplifying cells which are responsible for cell amplification. These cells are regulated by various polypeptide growth factors and extracellular calcium. Loss or malfunction of stem cells does not permit maintenance or regeneration of the corneal epithelial mass but leads to conjunctivalisation of the corneal surface. Clinically, several ocular surface disorders such as chemical burns can cause limbal damage and consecutive limbal insufficiency. Treatment for these disorders is available only by transplantation of healthy stem cells, which can be performed as both autograft and allograft.

Development of atypical amiodarone keratopathy in a corneal graft

The presence of fine epithelial deposits in a whorled pattern (cornea verticillata) as a consequence of treatment with amiodarone is well documented. We present a case of amiodarone keratopathy in a grafted cornea which is atypical in that the orientation of the pattern is rotated through nearly 90 degrees to that normally observed. This observation runs counter to the hypothesis that cornea verticillata is a manifestation of the line of lid closure. We speculate on the mechanism directing the migrational pathways of epithelial cells.

Squamous cell carcinoma of the cornea

We treated two patients with primary squamous cell carcinoma of the cornea without involvement of the corneoscleral limbus. Superficial keratectomy and cryotherapy in one patient and penetrating keratoplasty in the other patient resulted in no recurrence of the tumor after 46 and nine months, respectively. Actinic damage and late manifestation caused by poor vision in both eyes of both patients may have been the risk factors for development of this tumor.

Comparison of limbal and conjunctival autograft transplantation in corneal surface reconstruction in rabbits

Destruction of corneal surface was created in one eye of 24 rabbits by n-heptanol corneal epithelial debridement and surgical removal of limbal zone. One month later, the animals were equally subdivided into three groups of eight for limbal transplantation, conjunctival transplantation, and control without transplantation. During a 6-month postoperative follow-up, all corneas in the control group showed progressive vascularization and conjunctivalization. All corneas with limbal transplantation showed progressive decrease of vascularity, verified by fluorescein angiography. In contrast, all but one of the eight corneas of conjunctival transplantation showed progressive vascularization (P = 0.01). More important, the resultant epithelia showed corneal phenotype in limbal transplantation, but remained conjunctival in conjunctival transplantation, as verified by monoclonal antibodies AM-3, APSM-1, and AE-5. These results support the concept of the limbal location of corneal epithelial stem cells, and indicate that complete destruction of the limbal zone resulted in corneal vascularization and conjunctivalization, and that limbal transplantation has a better efficiency than conjunctival transplantation in restoring such destroyed corneal surface.

Corneal epithelial cell movement in humans

Evidence is presented which supports the centripetal movement of epithelial cells in the normal corneal epithelium. This movement is not, however, uniform and is influenced by various factors including corneal topography, surface disease states and lid shearing forces. We have studied epithelial morphology with corneal specular microscopy and have demonstrated altered morphology in keratoconjunctivitis sicca, neurotrophic keratitis, and contact lens wearing. Following penetrating keratoplasty, we found a vortex keratopathy in 70 per cent of patients up to two years after surgery. We also found pallisading of epithelial cells around sutures which indicated centripetal movement of epithelial cells around islands of stability created by obstructions. The eyelid also alters epithelial migration and turnover by increasing exfoliation from shearing forces. We advance a new hypothesis that the driving force in the central epithelial cell movement is the preferential loss of surface cells by exfoliation from the central apex secondary to the shearing forces of the upper lid.

Limbal autograft transplantation for ocular surface disorders

Limbal autograft transplantation is presented in 26 consecutive cases comprising both acute and chronic chemical injury (20 cases), thermal burns (2 cases), contact lens-induced keratopathy (3 cases), and ocular surface failure after multiple surgical procedures (1 case), with follow-up ranging from 2 to 45 months (mean, 18 months). The operative technique usually involved transfer of two free grafts of limbal tissue from the uninjured or less injured donor eye to the severely injured recipient eye, the latter having been prepared by limited conjunctival research and superficial dissection of fibrovascular pannus without keratectomy. Clinical results in 21 patients with follow-up of 6 months or more have consistently shown improved visual acuity (17 cases), rapid surface healing (19 cases), stable epithelial adhesion without recurrent erosion or persistent epithelial defect (20 cases), arrest or regression of corneal neovascularization (15 cases), and probable increased success for lamellar or penetrating keratoplasty (8 cases). No intraoperative complications were encountered, and no adverse reactions developed in donor eyes. Impression cytology in selected cases showed restoration of the corneal epithelial phenotype and regression of goblet cells from the recipient cornea. Therefore, limbal autograft transplantation is recommended for treatment of widespread ocular surface damage with loss of limbal epithelial stem cells and, specifically, for chemical or thermal burns, contact lens-induced keratopathy, and selected persistent corneal epithelial defects.

The multipotential cells of the limbus

Ample evidence exists that there is a centripetal movement of cells from the periphery of the cornea toward the centre. While conjunctival cells have the capacity to transdifferentiate into corneal epithelial cells, the limbal region appears to act as a barrier between the conjunctival and corneal epithelia, even after large epithelial defects are created. The existence of limbal stem cells is suggested by the apparent role of the limbus in acting as a source of peripheral corneal cells. While specific staining of limbal cells has been reported in the rabbit, there is no positive identification of such stem cells in the human. However, in the human there is negative staining for both a keratin cytoskeleton antigen and a cell surface antigen in the limbal epithelial zone. Efforts positively to identify human limbal stem cells continue, as do efforts to culture and transplant such cells.

Concept and application of limbal stem cells

Cumulative reported evidence indicates that some fraction of limbal basal epithelial cells are the stem cells for corneal epithelial cell proliferation and differentiation. Limbal epithelium is therefore crucial in maintaining the cell mass of corneal epithelium under normal conditions and plays an important role in corneal epithelial wound healing. Deficiency or absence of limbal stem cells explains well the pathogenesis of several ocular surface disorders characterised by defective conjunctival transdifferentiation or conjunctivalisation of cornea. This paper reviews and updates the basic concept of stem cells, the reported findings of limbal stem cells for corneal epithelium, and their therapeutic applications. Through this review, one hopes to gain a more complete understanding and increase proficiency in treating these diseases.

The Hudson-Stahli line. III: Observations on morphology, a critical review of aetiology and a unified theory for the formation of iron lines of the corneal epithelium

Observations as to the morphology, position and orientation of the Hudson-Stahli line are presented, based on the slit-lamp biomicroscopic examination of the eyes of six hundred and forty-four subjects. The origin of the pigments in the Hudson-Stahli zone and other corneal epithelial lines is reviewed, the evidence for either tear film dynamics or epithelial dynamics influencing the typical configuration is discussed and a unified theory for the formation of corneal iron lines is presented.

Treatment of corneal opacification in mucolipidosis IV with conjunctival transplantation

Mucolipidosis IV is a rare, inherited metabolic storage disease producing progressive psychomotor retardation and congenital corneal clouding. Histopathologic studies have shown that the corneal epithelium is strikingly involved with intracytoplasmic vacuolated storage material with relative noninvolvement of the corneal stroma and endothelium. Additionally, it has been noted that epithelial removal results in corneal clarity. We treated a 28-month-old patient with mucolipidosis IV with conjunctival transplantation with donor conjunctiva from an unaffected sibling. Improved corneal clarity resulted and has persisted with a follow-up of one year.

Clinical experience and grading of amiodarone keratopathy

Eighteen patients receiving the cardiac drug amiodarone were followed prospectively for the development of amiodarone keratopathy. Seventeen of 18 patients (94%) developed characteristic epithelial keratopathy in at least one eye within three months of the initiation of therapy. The pattern of the epithelial deposits was noted to undergo progressive changes in configuration as a function of the duration of amiodarone therapy. These evolving changes are well defined and allow development of a grading system for amiodarone keratopathy. A grading system as well as a proposed mechanism for evolving pattern of the keratopathy are presented.

Keratoepithelioplasty

Keratoepithelioplasty is a new surgical procedure for the treatment of persistent epithelial defects in patients without healthy donor tissue in their fellow eyes. After a total superficial keratectomy, lenticules of donor cornea covered by epithelium are placed at the corneoscleral limbus. The epithelium spreads from the lenticules and covers the center of the cornea. In three of four patients with persistent defects of long duration, healing was successful and vision improved. The three successful procedures were in patients who had had chemical injuries. They retained useful visual function without recurrence of epithelial healing problems. In the fourth case, it was impossible to determine whether the procedure was useful because the patient, who had atopic keratoconjunctivitis, required a penetrating keratoplasty two months after the keratoepithelioplasty.