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.

Effects of ocular injury and administration of brain-derived neurotrophic factor on survival and regrowth of axotomized retinal ganglion cells

Optic nerve transection in adult rats results in the death of approximately 50% of the axotomized retinal ganglion cells (RGCs) by 1 week and nearly 90% by 2 weeks after injury. The capacity of brain-derived neurotrophic factor (BDNF) to prevent this early, severe loss of RGCs was investigated in vivo by intravitreal injections of BDNF [5 micrograms in 5 microliters of bovine serum albumin/phosphate-buffered saline (BSA/PBS)] or vehicle (5 microliters of BSA/PBS). Using quantitative anatomical techniques, we show that (i) all RGCs survived 1 week after a single injection of BDNF at the time of axotomy. (ii) RGC densities decreased in the BDNF-treated retinas by 2 weeks but remained significantly greater than in the untreated controls. (iii) An enhanced RGC survival was obtained with single injections of BDNF from 6 days before to 5 days after axotomy. (iv) Repeated injections resulted in greater numbers of surviving RGCs, an effect that declined to undetectable levels by 6 weeks. (v) There were indications for an endogenous local source of trophic support whose expression was triggered by ocular injury, particularly to the anterior part of the eye. (vi) With multiple BDNF injections, there was profuse axonal sprouting around the optic disc. This remarkable intraretinal growth was not, however, reflected in increased RGC innervation of the peripheral nerve grafts, which are known to facilitate regeneration when used as optic nerve substitutes.

The cellular basis of corneal transparency: evidence for ‘corneal crystallins’

In vivo corneal light scattering measurements using a novel confocal microscope demonstrated greatly increased backscatter from corneal stromal fibrocytes (keratocytes) in opaque compared to transparent corneal tissue in both humans and rabbits. Additionally, two water-soluble proteins, transketolase (TKT) and aldehyde dehydrogenase class 1 (ALDH1), isolated from rabbit keratocytes showed unexpectedly abundant expression (approximately 30% of the soluble protein) in transparent corneas and markedly reduced levels in opaque scleral fibroblasts or keratocytes from hazy, freeze injured regions of the cornea. Together these data suggest that the relatively high expressions of TKT and ALDH1 contribute to corneal transparency in the rabbit at the cellular level, reminiscent of enzyme-crystallins in the lens. We also note that ALDH1 accumulates in the rabbit corneal epithelial cells, rather than ALDH3 as seen in other mammals, consistent with the taxon-specificity observed among lens enzyme-crystallins. Our results suggest that corneal cells, like lens cells, may preferentially express water-soluble proteins, often enzymes, for controlling their optical properties.

Indocyanine green-assisted peeling of the internal limiting membrane may cause retinal damage

PURPOSE

To demonstrate possible retinal damage caused by indocyanine green dye for staining of the internal limiting membrane in surgery for idiopathic macular hole.

METHODS

Consecutive interventional case series. We report on the ultrastructural findings of the internal limiting membrane in 10 eyes of 10 patients.

RESULTS

All specimens revealed not only the internal limiting membrane, but also some small amounts of retinal elements, such as the plasma membrane of Müller cells and other undetermined structures. This indicates a cleavage plane not exactly at the inner undulating aspect of the internal limiting membrane but within the innermost retinal layers.

CONCLUSION

Dilutions of indocyanine green as recommended in the literature may alter the structure of the retina to some degree. Possible factors responsible for this inadvertent action may include (1) concentration, (2) osmolarity pH, (3) time of tissue contact, and (4) mechanical factors from more forceful traction during peeling. Although functional consequences of these findings remain unclear as yet, factors that may induce damage to the innermost retina should be elucidated.

The pathology of primary blast overpressure injury

Primary blast injury occurs in civilian and military detonations and from the firing of weapon systems. The pathology of primary blast injury has been reported for the last 70 years and has primarily been limited to descriptions of gross pathology and histology. Commonly accepted tenets have not been confirmed as blast overpressure experiments in enclosures and with multiple detonations have been conducted. Organ systems other than the ear and the lung are playing a greater role in injury definition and research importance. This paper is an overview and update of the current understanding of the pathology of primary blast injury.

Grading scales for contact lens complications

Grading scales have been developed to assist practitioners in recording the level of severity of ocular complications of contact lens wear. Eight common complications are depicted in five levels of severity--from grade 0 (normal) to grade 4 (severe). The intersubject variance in grading was determined to be 1.0 scale units, which by coincidence concurs exactly with the key design strategy of the grading scales that each grading step of 1.0 corresponds to a clinically significant difference in severity.

Eye injuries: a prospective survey of 5671 cases

5671 patients with injuries presenting to a busy eye casualty department were examined prospectively to determine the incidence, aetiology, and severity of the injury. Of these cases 69.9% occurred at work, 18.3% during leisure and domestic activities (excluding recognised sport), 2.3% during sport, and 1.9% were due to assaults; contact lens injury occurred in a further 2.3%, and the cause was unknown in 5.3%. One hundred and two (1.8%) patients required admission to hospital, and of their injuries 13.7% occurred at work, 22.6% during leisure and domestic activities, 42.2% at sport, 18.6% during assault, and 2.9% from an unknown cause. Children under 10 years of age accounted for 4% of the total patients presenting, but for more than 18% of those admitted and 26% of ocular penetrations. 98.3% of all injuries involved periorbital or superficial ocular structures only. The remainder involved intraocular structures. The majority of serious injuries were contusional. There was only one case of intraocular foreign body. This indicates that, while most injuries still occur in the workplace, sport and leisure activities account for the majority of serious injuries. While most injuries do not threaten sight, they do so disproportionately in children.

Traumatic retinopathy in primates. The explanation of commotio retinae

We have produced experimental commotio retinae in 12 owl monkeys by blunt trauma. The ophthalmoscopic and fluorescein angiographic appearance of this contrecoup lesion is identical to the acute traumatic retinal opacity in humans. We examined these eyes by light and electron microscopy from 4 hours to 12 weeks after injury. Immediately after injury, the only abnormality is disruption of the receptor outer segments. From one to six days after trauma, many receptor cells undergo degeneration. The retinal pigment epithelium phagocytoses the degenerating outer segments, occasionally migrating into the retina. There is no extracellular retinal edema. The opacity of commotio retinae seems to represent disrupted receptor cells. Visual loss may result from permanent loss of receptors. The pigment epithelial response to traumatic receptor damage is similar to that observed in experimental retinal detachment and light-induced retinal damage.

Method of production and natural history of experimental posterior penetrating eye injury in the rhesus monkey

We developed an experimental model for a posterior penetrating eye injury that resulted in traction retinal detachment in 21 rhesus monkey eyes. The standard injury was an incision through the pars plana with vitreous prolapse and incarceration; the wound was then carefully closed with microsurgical techniques. At one to two weeks after injury, detachment of the posterior vitreous occurred and detachment of the retina occurred between seven and 11 weeks. The development of retinal detachment was related to traction on the peripheral retina over the vitreous base; and to the contraction of epiretinal membranes on the peripheral and equatorial retina. Our study supports clinical observations on the importance of blood in the vitreous in the development of vitreous traction and traction retinal detachment after a posterior penetrating injury.

Multivariate analysis of prognostic factors in penetrating ocular injuries

We used a multivariate statistical analysis to identify factors predicting visual outcome in 281 eyes that underwent primary repair of a penetrating ocular injury. Visual acuity of 20/800 or better on initial examination was the most important factor, with these eyes 28 times more likely to have a final visual acuity of 20/800 or better than eyes with initial visual acuities worse than 20/800. The effect of other factors differed depending on the initial visual acuity. In patients with initial visual acuities of 20/800 or better, youth (less than or equal to 18 years) was a significant predictor of final visual acuities of 20/50 or better. In patients with initial visual acuities worse than 20/800, a laceration limited to the cornea was the best predictor of good visual outcome. Absence of an expelled or subluxed lens and lacerations limited to a location anterior to the rectus muscle insertions were also important predictors of good visual outcome. When an intraocular foreign body was present these factors were no longer significant and older age (greater than 18 years) was the most important predictor of good visual outcome.

Histology of wound, vitreous, and retina in experimental posterior penetrating eye injury in the rhesus monkey

We performed a histologic study to support our clinical observations on the mechanisms responsible for traction retinal detachment after a penetrating injury in the rhesus monkey eye. The monkey eyes (40 eyes; 40 monkeys) were characterized by intraocular fibrosis with the formation of a cyclitic membrane and epiretinal and subretinal membranes. The progression to a fibrous ingrowth from the wound occurred only in eyes with blood in the vitreous. The intravitreal fibroblastic proliferation had its origin mainly from the stroma of the ciliary body and choroid at the wound but probably also from the nonpigmented ciliary epithelium. A fibroblastic response was present within the vitreous as early as four days after injury, and had progressed to form a cyclitic membrane by six weeks. Epiretinal membranes were identified as early as four weeks after injury. They were most prominent over the peripheral retina anterior to the equator. It is likely that they are derived from multiple cellular sources including the fibrous ingrowth from the wound but they were also connected to the surface of the retina by bridges of tissue indicating a glial origin. The subretinal membranes appeared to be derived from both retinal pigment epithelium cells and glial cells.

Experimental double-perforating injury of the posterior segment in rabbit eyes: the natural history of intraocular proliferation

A reproducible model of double perforating injury of the posterior segment of the rabbit eye was developed. Immediately after injury, a viterous condensation was visible between wounds. The scleral exit wound was sealed by fibroblastic proliferation of probable episcleral origin by the fourth day and the entrance similarly by the seventh day. Cellular proliferations originating in the wounds crossed the vitreous cavity following the vitreous injury tract or condensed vitreous to the disc or to the vitreous base. The earliest intraocular proliferations, composed of spindle-shaped, fibroblast-like cells, were seen at day 4. Occasional pigment epithelia were present in and on these proliferations. Other proliferations occurred directly on the retinal surface adjacent to the wounds. The transvitreous proliferations employed the vitreous as a scaffold, while the surface proliferations used the retinal surface for contact guidance.

Histopathology of commotio retinae

The pathogenesis of commotio retinae in animal models has included extracellular edema, intracellular edema, and photoreceptor outer segment disruption. Histopathologic findings obtained within 24 hours of blunt trauma in a human eye with clinically-observed commotio retinae revealed photoreceptor outer segment disruption and damage to the retinal pigment epithelium. The major site of injury in commotio retinae seems to be at the level of the photoreceptor outer segment-retinal pigment epithelium junction.

Tissue damage by pulsed electrical stimulation

Repeated pulsed electrical stimulation is used in a multitude of neural interfaces; damage resulting from such stimulation was studied as a function of pulse duration, electrode size, and number of pulses using a fluorescent assay on chick chorioallontoic membrane (CAM) in vivo and chick retina in vitro. Data from the chick model were verified by repeating some measurements on porcine retina in-vitro. The electrode size varied from 100 microm to 1 mm, pulse duration from 6 micros to 6 ms, and the number of pulses from 1 to 7500. The threshold current density for damage was independent of electrode size for diameters greater than 300 microm, and scaled as 1/r2 for electrodes smaller than 200 microm. Damage threshold decreased with the number of pulses, dropping by a factor of 14 on the CAM and 7 on the retina as the number of pulses increased from 1 to 50, and remained constant for a higher numbers of pulses. The damage threshold current density on large electrodes scaled with pulse duration as approximately 1/t0.5, characteristic of electroporation. The threshold current density for repeated exposure on the retina varied between 0.061 A/cm2 at 6 ms to 1.3 A/cm2 at 6 micros. The highest ratio of the damage threshold to the stimulation threshold in retinal ganglion cells occurred at pulse durations near chronaxie-around 1.3 ms.

RPE Damage Thresholds and Mechanisms for Laser Exposure in the Microsecond-to-Millisecond Time Regimen

PURPOSE

The retinal pigment epithelium (RPE) cells with their strongly absorbant melanosomes form the highest light-absorbing layer of the retina. It is well known that laser-induced retinal damage is caused by thermal denaturation at pulse durations longer than milliseconds and by microbubble formation around the melanosomes at pulses shorter than microseconds. The purpose of this work was to determine the pulse width when both effects merge. Therefore, the RPE damage threshold and mechanism of the damage at single laser pulses of 5-micros to 3-ms duration were investigated.

METHODS

An argon laser beam (lambda 514 nm) was externally switched by an acousto-optic modulator to achieve pulses with constant power in the time range of 5 micros up to 3 ms. The pulses were applied to freshly prepared porcine RPE samples serving as a model system. After laser exposure RPE cell damage was proved by the cell-viability stain calceinAM. Microbubble formation was detected by acoustic techniques and by reflectometry.

RESULTS

At a pulse duration of 5 micros, RPE cell damage was always associated with microbubble formation. At pulses of 50 micros, mostly thermal denaturation, but also microbubble formation, was detected. At the longer laser pulses (500 micros, 3 ms), RPE cell damage occurred without any microbubble appearance.

CONCLUSIONS

At threshold irradiance, the transition time from thermal denaturation to thermomechanical damage of RPE cells is slightly below the laser pulse duration of 50 micros.

Late traumatic dislocation of laser in situ keratomileusis corneal flaps

PURPOSE

To report the management and outcome of late-onset traumatic dislocation of laser in situ keratomileusis (LASIK) flaps.

DESIGN

Retrospective, observational case series.

PARTICIPANTS

Four patients with late-onset LASIK flap dislocation occurring after mechanical trauma at various intervals (10 days-2 months) after the procedure.

INTERVENTION

In all cases of postoperative traumatic LASIK flap dislocation, the flap was refloated with scraping and irrigation of the underlying stromal bed within 12 hours of the injury. A bandage contact lens was placed, and a regimen including topical antibiotics and corticosteroids was instituted in all cases.

MAIN OUTCOME MEASURES

Best spectacle-corrected visual acuity and complications associated with the surgery were monitored.

RESULTS

Postoperative follow-up ranged from 4 to 21 months. Nonprogressive epithelial ingrowth was noted in one patient and diffuse lamellar keratitis developed in another patient. All patients recovered pretrauma spectacle-corrected visual acuity.

CONCLUSIONS

Corneal LASIK flaps are prone to mechanical dislocation as late as 2 months after the procedure. Appropriate management results in recovery of optimal visual outcomes.

Retinal damage secondary to chronic light exposure, thresholds and mechanisms

The effect upon the retina of exposure to large fields of bright visible light has been evaluated. The thresholds for permanent retinal damage for four hour exposures in rhesus monkeys have been established for white light, and laser lines of 514.5 nm, 488 nm, 457.9 nm, and 590 nm. The damage has been evaluated by ophthalmoscopy, electroretinography and light and electron microscopy. The shortest wavelength light (457.9 nm) is more effective in causing damage, particularly histological damage, which is spread throughout the fundus and throughout the retinal layers. Functional damage shown by the electroretinogram follows a different action spectrum without the increased effect in the blue. There appears to be more than one mechanism for retinal damage in chronic light exposure, and at least one mechanism is not dependent solely upon the visual pigment and the pigment epithelium. Thresholds of permanent damage appear to be within one or two log units of light levels encountered in the normal visual environment. Newer data suggest that this damage is additive. Daily one hour exposures for four days produce damage equivalent to a single four hour exposure at the same retinal irradiance.

Dehydration injury as a possible cause of visual field defect after pars plana vitrectomy for macular hole

PURPOSE

To present the hypothesis that a visual field defect after pars plana vitrectomy for macular hole may be caused by dehydration injury to the nerve fiber layer during the fluid-air exchange.

METHODS

In a consecutive nonrandomized series of 45 operations on 35 eyes of 34 patients with full-thickness macular hole, the surgical method was changed with postoperative visual field testing performed.

RESULT

The incidence and location of the post-operative visual field defect was affected only by changing the location of the infusion cannula.

CONCLUSION

Dehydration injury of the nerve fiber layer during the fluid-air exchange should be considered as a possible cause of visual field defect after pars plana vitrectomy for macular hole.

Interleukin (IL)-6, interleukin (IL)-8 levels and cellular composition of the vitreous humor in proliferative diabetic retinopathy, proliferative vitreoretinopathy, and traumatic proliferative vitreoretinopathy

PURPOSE

To investigate the interleukin (IL)-6 levels, IL-8 levels, and cellular composition of the vitreous humor in patients with proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and traumatic PVR.

METHODS

Vitreous samples from 14 patients with PDR, 10 patients with PVR, and 10 patients with traumatic PVR were analyzed. Fifteen cadaver eyes were used as controls. Cytokine levels were measured by ELISA.

RESULTS

Elevated IL-6 levels were detected in the vitreous of 12 (85.7%) of the PDR patients, eight (80%) of the PVR patients, and all (100%) of the traumatic PVR patients. None of the control IL-6 results were elevated. Vitreous IL-8 levels were elevated in 12 (85.7%) of the PDR patients, six (60%) of the PVR patients, all (100%) of the traumatic PVR patients, and one (6.7%) of the control eyes. Cytological examination of the vitreous specimens revealed a predominance of macrophages (50%) in the PDR samples and a predominance of retinal pigment epithelial (RPE) cells (60%) in the PVR samples. In contrast, neutrophils predominated (88%) in the traumatic PVR samples.

CONCLUSION

The findings suggest that IL-6 and IL-8 may be involved in the pathogenesis of PDR, PVR, and traumatic PVR. High proportions of RPE cells and macrophages are associated with elevated IL-6 and IL-8 levels in the vitreous of PDR and PVR patients; however, the fact that these cells are not predominant in traumatic PVR suggests that different immune response mechanisms may be active in the pathogenesis of these disorders.

Endothelial damage with cataract surgery techniques

PURPOSE

To evaluate intraoperative endothelial damage after planned extracapsular cataract extraction (ECCE) with difference capsulotomy techniques and phacoemulsification.

SETTING

San Carlos University Hospital, Castroviejo Institute, Madrid, Spain.

METHODS

In this prospective, randomized study, 60 patients with senile cataract scheduled for cataract surgery were divided into three groups of 20 each: Group 1 had phacoemulsification; Group 2, planned ECCE with continuous curvilinear capsulorhexis; and Group 3, ECCE with letter-box capsulotomy. Preoperatively and 3 months postoperatively, endothelial cell density, percentage of hexagonality, and the cell size variation coefficient were determined by contact specular microscopy; endothelial permeability was examined by anterior segment fluorophotometry and central corneal thickness, by ultrasonic pachymetry. Results were analyzed using the two-tailed Student's t-test and analysis of variance.

RESULTS

In all three groups, endothelial permeability and cell loss increased significantly from the preoperative values, but there were not significant differences among the postoperative values. Mean cell loss was 11.8% in Group 1, 12.8% in Group 2, and 10.1% in Group 3. There were no differences between the preoperative and postoperative morphometric indexes. Postoperative pachymetric measurements were not significant.

CONCLUSIONS

Endothelial response was not statistically significantly different among the surgical techniques, although endothelial damage was lower in Group 3, which could indicate a protective effect of the anterior capsule during cataract extraction. Endothelial barrier function remained disturbed despite the apparent morphological stabilization.

Use of autologous cultured limbal and conjunctival epithelium in a patient with severe bilateral ocular surface disease induced by acid injury: a case report of unique application

PURPOSE

Reconstruction of the ocular surface in a case of severe bilateral partial limbal stem cell deficiency (LSCD) with extensive symblephara using autologous cultured conjunctival and limbal epithelium.

CASE REPORT

A 31-year-old woman presented with severe bilateral ocular surface disease with partial limbal stem cell deficiency, symblephara, lid and facial scarring, with a vision of 20/400 and counting fingers at 1 m in both eyes. Limbal and conjunctival tissue was harvested from the healthy-appearing left eye and used to generate two sheets of composite epithelium consisting of central limbal and peripheral conjunctival cells. The limbal tissues were explanted in the central region while the conjunctival tissues were explanted on the periphery of the deepithelialized human amniotic membrane (HAM) and nurtured using human corneal epithelial cell medium. After successful generation of a monolayer from both tissues had been confirmed, the composite of cultivated limbal and conjunctival epithelium with HAM was transplanted in each eye after excision of fibrous tissue and release of symblephara. One year postoperatively, the patient had a best spectacle-corrected visual acuity of 20/40 in the right eye (preoperative acuity 20/400) and counting fingers at 1 m in the left eye (same as preoperative) with a stable ocular surface.

CONCLUSIONS

Autologous cultured epithelial transplantation is as an excellent option in selected patients with bilateral partial LSCD with small area(s) of healthy limbus in either eye and avoids the attendant risk of rejection and cost and potential toxicity of immunosuppression in allogeneic tissue transplantation. This case also highlights the feasibility of generating a composite culture of limbal and conjunctival epithelium using a single amniotic membrane.

Ultrasound biomicroscopy. High-frequency ultrasound imaging of the eye at microscopic resolution

UBM presents us with a new method of imaging the anterior segment of the eye at high resolution. Its strengths lie in its ability to produce cross-sections of the living eye at microscopic resolution without violating the integrity of the globe. UBM, although lacking the resolution of optical microscopy, gives us images in living eyes without affecting the internal relationships of the structures imaged. There are many other applications of this new imaging method. Examples of other uses include imaging adnexal pathology, assessing corneal changes with refractive surgery, the assessment of trauma, and determination of intraocular lens position.

Blink-related microtrauma: when the ocular surface harms itself

Superior limbic keratoconjunctivitis results mechanically from blinking under prolonged unphysiological conditions. The pathogenic process is known as blink-related microtrauma. This review aimed to explore the validity of a general theory that besides superior limbic keratoconjunctivitis, there may be other diseases of the ocular surface arising from mechanical microtrauma. A review of relevant clinical and microscopic lesions in a range of ocular surface disorders with possible mechanical aetiology was conducted. New terms were selected to facilitate understanding of such new aetiology. Besides superior limbic keratoconjunctivitis, other ocular surface disorders regarded as primarily derived from blink microtrauma are: other filamentary keratitides; blepharospasm and severe ptosis; canthal/palpebral froth; affections from disordered eyelid lining; and contact lens related damage. A group of secondarily microtraumatic disorders was identified, including the example of microtrauma impacting upon interpalpebral bulbar prominences. Superior limbic keratoconjunctivitis is the archetype of diseases affecting a unique combination; namely, the ocular surface conjoined with its lacrimal fluid. It is only one among many diseases actively generated within the confines of 'a self-harming surface'.

Extent of initial corneal injury as the mechanistic basis for ocular irritation: key findings and recommendations for the development of alternative assays

Currently, there are no recognized alternative tests to eliminate the use of animals in ocular irritation testing. A major reason no replacement alternatives have been developed is that the current in vivo data set provides no perspective regarding the critical cellular and molecular changes involved in initial ocular injury, subsequent responses, and repair processes in standard in vivo tests. Without this perspective, mechanistically based replacement tests cannot be developed and validated. We have proposed that the level of ocular irritation is related to the extent of initial injury, and that regardless of the processes leading to tissue damage, the extent of initial injury is the principal factor determining the outcome of ocular irritation. This article summarizes the results from our studies of various surfactants and nonsurfactants of differing irritancy that support our hypothesis. Our findings indicate that a mechanistically based alternative to in vivo ocular irritation tests would be the microscopic or biochemical measurement of initial injury using either ex vivo or in vitro corneal equivalent systems composed of corneal epithelial, stromal keratocyte, and corneal endothelial cell layers. This work also provides a well-characterized panel of materials of varying types and irritation for use in developing and validating alternative tests.