A comparison of the efficacy and toxicity of and intraocular pressure response to viscous solutions in the anterior chamber

An intraocular-lens abrasion test, vital dye staining, and scanning electron microscopy were used for an in vitro comparison of endothelial protection offered by four viscous solutions of 1% sodium hyaluronate (Healon), 3% sodium hyaluronate (AmVisc), 4% chondroitin sulfate (Viscoat), and 2% methylcellulose. Wide-field specular microscopy with analysis of endothelial cell density and morphologic evaluation, pachymetry, and intraocular pressure measurements were also used to study the toxicity of the viscous solutions in an in vivo cat model with and without anterior chamber washout. All four solutions provided complete endothelial protection from mechanical trauma. Endothelial cell density and morphologic nature were unaffected during the in vivo toxicity study. A mild increase in intraocular inflammation occurred at one and two days after intraocular injection with all four viscous solutions. Intraocular pressure elevations peaked within four hours after instillation of the viscous solutions and were significantly reduced by anterior chamber washout.

Response of the corneal endothelium to cataract surgery

Regional changes in endothelial cell density, morphology, and corneal thickness were serially examined with a specular microscope after intracapsular cataract extraction (four eyes), extracapsular cataract extraction (five eyes), and extracapsular cataract extraction with posterior chamber lens implantation (13 eyes). Regardless of the type of cataract surgery, cell loss and morphologic changes (decreased percentage of hexagonal cells, increased cellular elongation, and increased coefficient of variation) were greatest and occurred within one week in the superior cornea. Similar changes occurred after one month centrally but were minimal inferiorly. Endothelial cell density stabilized, and the morphologic changes resolved within three months in all regions of the cornea. Corneal swelling resolved within one month. Differences between the procedures were noted only in the superior portion of endothelium, where cell loss and morphologic changes were greatest following intracapsular cataract extraction. Also, endothelial wound healing was complete and stable three months after cataract surgery, with or without posterior chamber lens implantation.

Corneal endothelial healing rate and the effect of topical retinoic acid

These studies were undertaken to evaluate wound healing rates of the corneal endothelium in vivo. After insertion of a 26-gauge needle into the anterior chamber of the rabbit eye through the limbus, a 5-0 nylon monofilament was introduced through the needle, and endothelial wounds were made by scratching the cells with the filament. The wounds were photographed with a wide-field specular microscope at various intervals. Montages of the wounds were made, and the areas of the wounds were determined by planimetry. Wound closure occurred rapidly in a linear manner during the first 6 hr after wounding, after which the rate of cell migration decreased. Healing rates (micron2/hr) during the first 6 hr were calculated by linear regression analysis. There was a direct linear correlation between the healing rate and initial wound area. The slope of this line for nine normal (untreated) corneas was 0.093 hr-1. Nine corneas were treated with 0.1% retinoic acid in petrolatum ointment, while eight control corneas received vehicle alone. The slope of healing rate versus initial wound area for treated corneas (0.11 hr-1) was significantly greater than control (0.097 hr-1). This was interpreted as a stimulation of corneal endothelial migration during healing by retinoic acid. As a result of this study, a method for analysis of corneal endothelial healing rate has been developed which can be used for comparison of healing rates among treatments when initial wound area cannot be standardized.

BSS Plus: a potential irrigating solution for neurosurgery

BSS Plus is a pH-stable balanced salt solution similar to glutathione bicarbonate Ringer's solution. Extensively used in ophthalmology, it is of potential value in neurosurgery. In comparative tests of its effectiveness, 28 cats underwent bilateral irrigation of the surface of the cerebral cortex with normal saline on one side and BSS Plus on the other. After 2 hours, a marked decrease was seen in the surface pH of the hemisphere irrigated with normal saline but not of the hemisphere treated with BSS Plus. Blood-brain barrier changes (measured with Evans blue dye techniques) were more evident following saline irrigation. Somatosensory evoked potentials and cerebral blood flow were not significantly altered. Conventional light microscopy using three standard stains did not reveal a significant difference. Transmission electron microscopy studies were performed in 14 animals and scanning electron microscopy in six. In five animals both transmission and scanning electron microscopy studies were conducted after irrigation with both agents without a cottonoid cover and with immediate harvest of superficial layers from the living brain and immersion-fixation in glutaraldehyde. Tissue preservation was superior on the BSS Plus side in all studies. This agent may represent an improved irrigation solution for neurosurgery, but further studies are required.

Specular microscopic evaluation of donor corneal endothelium

We performed wide-field specular microscopy and pachymetry on 92 donor corneas to evaluate the changes occurring in the endothelium during moist chamber storage of up to 48 hours. Endothelial changes were quantitated with computer-assisted morphometry. The donor corneas were divided into two groups: younger (mean age, 34 years) and older (mean age, 72 years). No significant differences in endothelial cell density, coefficient of variation in cell area (polymegethism), percentage of hexagonal cells (pleomorphism), or central corneal thickness were noted between younger and older donors when storage intervals were similar. Within each group, while endothelial cell density remained constant, a marked increase in polymegethism and pleomorphism developed when storage was prolonged beyond 12 hours. Corneal thickness also increased, but there was no correlation between thickness and the extent of the endothelial changes. These results suggest that specular microscopy is a more reliable method of screening donor tissue than donor age or corneal thickness.

Comparison of intraocular acetylcholine and carbachol

Commercially available 1% acetylcholine chloride and 0.01% carbachol chloride, which are commonly used as miotics in intraocular surgery, have recently been reformulated. Comparative studies of these agents show similar miotic activity. However, in vitro perfusion of human corneas demonstrated that 1% acetylcholine chloride causes marked changes in endothelial function and ultrastructure as compared to carbachol or BSS Plus. This study showed that 0.01% carbachol chloride was less toxic to the corneal endothelium than 1% acetylcholine chloride and suggests that 1% acetylcholine should not be used in corneas with compromised endothelium as in primary corneal endotheliopathies.

Long-term survival of cryopreserved corneal endothelium

Corneas of five patients who received cryopreserved penetrating grafts 15 years previously were evaluated by regional specular microscopy and computer-assisted morphometric analysis. This technique quantitates changes in cell size and shape as well as cell number. Comparisons were made with five eyes in four patients 15 years after penetrating keratoplasty utilizing fresh grafts. In three patients, fresh and frozen tissue were transplanted in the same host. These examinations showed no difference in structure or function comparing cryopreserved tissue with fresh donor tissue.

The efficacy of retinoic acid ointment for treatment of xerophthalmia and corneal epithelial wounds

In previous studies of topical application of retinoic acid to the eye, retinoic acid in an oil vehicle has been used. An all-trans-retinoic acid (Tretinoin, USP) formulation in a petrolatum-based ophthalmic ointment vehicle has now been developed which is chemically stable for at least one year. The ointment is effective at retinoic acid concentrations of 0.01-0.1% in reversing corneal keratinization in vitamin A-deficient, xerophthalmic rabbits. At 0.1% it also stimulates the healing rate of corneal epithelial wounds in rabbits and monkeys. Retinoic acid ointment may prove to be valuable clinically in the treatment of xerophthalmia, corneal epithelial erosions, and related ocular surface abnormalities.

Correlation of corneal endothelial pump site density, barrier function, and morphology in wound repair

After transcorneal freezing, physiologic function (pump and barrier) of the regenerating rabbit corneal endothelium was evaluated and compared with the morphologic differentiation that occurs during wound healing. Endothelial pump function was investigated utilizing the specific binding of tritiated ouabain to endothelial Na+/K+ ATPase (pump sites); the permeabilities of isolated de-epithelialized corneas to labeled inulin and dextran were measured to determine endothelial barrier function. Endothelial recovery after transcorneal freezing can be described as a three-stage process. Stage one is characterized by the establishment of an initial coverage of the wound by pleomorphic spindle-shaped cells which form a functional but incomplete barrier and minimal pump site density. In stage two, the cells assume a flattened configuration consisting of irregular polygons and establish nearly normal pump capacity. In stage three, a significant remodeling of the monolayer continues despite the layer's early physiologic recovery.

Corneal endothelial morphology after anterior chamber lens implantation

The morphologic features of the corneal endothelium were investigated by means of regional wide-field specular microscopy and computer-assisted morphometry in 13 eyes of nine patients who had undergone intracapsular cataract extraction with anterior chamber lens implantation more than one year previously. The endothelial cells in these patients demonstrated a significant increase in cellular elongation and the coefficient of variation in mean cell area and a significant decrease in the percentage of hexagonal endothelial cells when compared with age-matched controls (ten eyes of ten patients). The clinical implications of these long-term morphologic changes are unknown, but the changes may be indicative of an unstable endothelium or may be an early sign of continuing cell loss.

In vivo metabolism of topically applied retinol and all-trans retinoic acid by the rabbit cornea

Corneas of normal and vitamin A-deficient rabbits were treated topically with [11, 12-3H] retinol or [11, 12-3H] all-trans retinoic acid. Methanol extracts of these corneas were analyzed by high pressure liquid chromatography. Radiolabeled compounds were extracted from the corneas which co-migrated chromatographically with known retinoid standards. In agreement with studies on other tissues and organs, retinol was metabolized to retinoic acid and more polar compounds by corneas of normal and vitamin A-deficient rabbits. All-trans retinoic acid was isomerized to 13-cis retinoic acid in normal rabbit corneas; however, this trans-cis isomerization did not occur in vitamin A-deficient, xerophthalmic corneas.

Corneal endothelial changes in diabetic dogs

The corneal endothelium of alloxan diabetic dogs was examined by wide-field specular microscopy and compared to that of age-matched non-diabetic dogs. Computer-assisted morphometry of individual cells showed that the diabetic dog endothelium had marked polymegethism and pleomorphism similar to that previously described in diabetic patients. There also appeared to be a positive correlation between the degree of these endothelial changes and the diabetic control as demonstrated by HbA1 concentration.

Changes in the normal corneal endothelial cellular pattern as a function of age

Human endothelial morphologic changes were quantitated by specular microscopy and computer-assisted morphometry to establish normal baselines of various morphologic parameters. Cellular polymegethism and cellular pleomorphism increases with age, and normal baseline parameters are detailed. Furthermore, no significant difference in any morphologic parameters between the right and left eye and between central and peripheral endothelium was detected in the normal corneas examined. These normal morphologic baselines can possibly be utilized to detect early corneal endothelial pathology and/or cell loss nondetectable by cell density measurement.

Pump function of the human corneal endothelium. Effects of age and cornea guttata

The specific binding of tritiated ouabain to endothelial Na/K ATPase was used to quantitate the density of pump sites in the human corneal endothelium. Donor eyes, unsuitable for use in keratoplasty, were obtained from the Wisconsin Lions Eye Bank. The endothelium of each donor eye was examined using wide-field specular microscopy, and the specular micrographs were traced and digitized for the determination of cell density. Ouabain binding was measured in matched pairs of isolated endothelial sheets. A total of 26 pairs of donor eyes, ranging in age from 11 through 91 years, were studied. Twenty pairs, determined to have normal endothelia, were found to have a constant pump site density which was independent of donor age. Six donor pairs had moderate guttata; in this group pump site density was significantly increased. These results indicate that, although pump site density is normally constant in the human corneal endothelium, conditions which increase endothelial permeability, such as guttata, can cause a compensatory increase in pump site density and presumably pump function.

A larger corneal epithelial wound closes at a faster rate

In order to evaluate relationships between healing rates and initial wound area, epithelial wounds were made on rabbit corneas by scraping the epithelium within a 4-, 6.5-, or 8-mm trephine mark. The wounds were stained with fluorescein and photographed during healing. The wounded areas were measured by planimetry. Although larger wounds closed later than smaller wounds, all of the healing curves appeared to be linear. The mean healing rate of the 8-mm diameter wounds (0.91 mm2/hr) was significantly greater than that of the 6.5-mm diameter wounds (0.80 mm2/hr). The 4-mm diameter wounds healed at a significantly slower rate (0.37 mm2/hr) when compared to the 6.5-mm diameter wounds. The authors found a strong positive correlation between the healing rates and the initial wound areas. By comparison, regardless of the initial wound area, the wound diameter decreased at a rate of approximately 0.1 mm/hr, which may explain the dependency of the healing rate on the initial wound area. The healing rate varied considerably between animals with the same diameter wounds, but both eyes of each animal showed a similar healing rate.

Electroretinographic studies following vitrectomy and intraocular silicone oil injection

Vitrectomy was performed bilaterally in pigmented rabbits and followed by silicone oil injection in one eye only. Electroretinographic studies were performed preoperatively and at selected postoperative intervals. In the early postoperative period both eyes showed an initial reduction in a and b wave amplitudes, followed by a return to baseline values. The amplitudes were symmetrically and equally affected. Sequential studies over a 20-month period showed no deterioration in electroretinographic response in eyes with and without silicone oil injection.

Cellular migration and morphology in corneal endothelial wound repair

After a mechanical denudation of rabbit corneal endothelial cells, the healing process was followed with wide-field specular microscopy. Individual cell migration and morphologic changes were analyzed by computer-assisted morphometry. The cells surrounding the wound migrated to cover the defect without producing intercellular gaps. The greatest cellular migration and morphologic alterations occurred close to the wound edge. As the cells migrated toward the wound, they elongated and increased their surface area in the direction of the migration. As the healing proceeded, the cells lost their original hexagonal pattern, which returned after coverage was complete. The wound was covered completely by large, irregularly shaped cells showing mitotic figures between 24 and 48 hr. During this period, cellular migration decreased and normal cellular morphology began to recover. When mitosis decreased, the normal cellular pattern rearranged towards a more hexagonal shape. During the healing process, the degree and direction of cellular migration varied from cell to cell. Additionally, changes in cell-to-cell contact (positional changes of neighboring cells) occurred in one-third of migrating cells. Such cellular migration can account for monolayered cells sliding without producing gaps between individual cells.

Effects of intraocular irrigating solutions on the corneal endothelium after in vivo anterior chamber irrigation

We used wide-field specular microscopy and corneal pachymetry to evaluate the effect of anterior chamber irrigation with BSS and BSS Plus on the corneal endothelium of cats. Endothelial changes were quantitated by computerized morphometric analysis of individual cells. After short-term (15 and 30 minutes) and long-term (one and two hours) irrigation, endothelial cell density remained unchanged. Corneal thickness increased significantly in the BSS group after one hour of irrigation. BSS Plus caused minimal changes in endothelial morphologic characteristics regardless of the irrigation time. By comparison, BSS caused a significant increase in the coefficient of variation of cell area (polymegethism) and a decrease in the percentage of hexagonal cells (pleomorphism). These changes were more prominent after prolonged irrigation. The morphologic changes caused by BSS irrigation are indicative of a stressed endothelial monolayer that may be more susceptible to additional surgical trauma.

Comparison of the corneal endothelium in an American and a Japanese population

We compared the corneal endothelial morphology between an age-matched population of American and Japanese persons. Endothelial specular photographs were subjected to a computer-assisted morphometry of the area and shape of individual cells. The endothelium in the Japanese population showed a significantly higher cell density when compared with an age-matched American population. However, there was no difference in the degree of variations in cell area and cell shape between the two populations. The results suggest that higher endothelial cell density in the Japanese population could be related to the lower incidence of aphakic bullous keratopathy in the Japanese population.

Corneal endothelial changes in type I and type II diabetes mellitus

Forty-six corneas from 25 patients who had had type II (adult-onset) diabetes for more than ten years were examined by specular microscopy with quantitative morphometric analyses of individual endothelial cells. Thirty-four corneas from 21 age-matched nondiabetic subjects were examined for comparison. We also examined 31 corneas from 17 patients with type I (juvenile-onset) diabetes and compared them to 41 corneas from 23 age-matched normal volunteers. The corneal endothelium in type II diabetes showed no difference in cell density but demonstrated a significantly higher coefficient of variation, a decrease in the percentage of hexagonal cells, and a low figure coefficient compared to an age-matched nondiabetic population. Type I diabetes produced similar cell changes, but these changes occurred in the earlier decades. Moreover, we detected a significantly higher rate of cell loss in type I diabetes, resulting in a significant decrease in cell density in the fourth and fifth decades. These results clearly indicate that the diabetic endothelium is morphologically abnormal. The observed anatomic changes result in a less stable and more vulnerable cell layer, possibly explaining some of the persistent clinical changes in the diabetic cornea after surgical trauma.

Quantitation of Na/K ATPase pump sites in the rabbit corneal endothelium

In these experiments, the binding of 3H . ouabain, a specific inhibitor of Na/K ATPase, was used to quantitate the density of Na/K ATPase pump sites in the rabbit corneal endothelium. The uptake of ouabain by the corneal endothelium shows two components: one that saturates at a ouabain concentration near 2 X 10(-7) M (specific binding), and one component that increases linearly with increasing glycoside concentration (nonspecific uptake). The nonspecific uptake can be accounted for by that ouabain equilibrating with the extracellular space, which, estimated by inulin space, amounts to 13.0 nl/mm2 of endothelium. The saturable component of endothelial ouabain uptake is displaced by K+ ions, which is consistent with this fraction being bound to Na/K ATPase. Maximal endothelial ouabain binding was measured as 20.7 fmoles/mm2 of endothelium, which corresponds to 3.0 X 10(6) pump sites per cell. The density of Na/K ATPase pump sites in the rabbit corneal endothelium is comparable to densities reported for several transporting epithelia. These data are consistent with the known function of the endothelium in corneal deturgescense and corroborate the importance of Na/K ATPase in endothelial fluid transport.

Classification of corneal endothelial disorders based on neural crest origin

The corneal endothelium is derived from the neural crest. A general classification of disorders of development of the neural crest has been previously presented (Johnston). Disorders of the corneal endothelium may be considered according to a modification of this scheme to reflect its true embryologic origin. In this classification, corneal endothelial disorders are categorized as abnormalities of neural crest cell formation (cyclopia), migration (Peters' anomaly), proliferation (iridocorneal endothelial syndrome), final differentiation (Fuchs' dystrophy), and acquired abnormalities (metaplasia, abiatrophy, and proliferation).

Choroidal rete mirabile function and resistance to retinal oxygen toxicity in fish

Previous studies have suggested that resistance to O2 toxicity in teleost fish retina is directly related to choroidal rete mirabile function and to the chronically elevated PO2 at the retina. We tested this hypothesis in several species of fish with varying degrees of rete development. The effect of hyperbaric oxygen on O2 consumption, Na+-, K+-ATPase activity nd the ERG was recorded. Hyperbaric oxygen had no effect on the ERG of either the flounder, which has a large rete and elevated PO2, or the eel, which has no rete. Exposure to hyperbaric oxygen for 6 hr attenuated by 50% the ERG of the goosefish which has a small rete (retinal PO2 = 90 mmHg). Hyperbaric oxygen abolished the b-wave of the dogfish ERG and attenuated the skate b-wave by 80%. Elasmobranchs have no rete and low retinal PO2. Hyperbaric oxygen had no effect on O2 consumption and ATPase activity in any species studied. The ERG data supported the hypothesis that resistance to oxygen toxicity by the teleost retina is an adaptation to a chronically elevated PO2 generated by the choroidal rete.

The corneal toxicity of presurgical skin antiseptics

In a study of the corneal toxicity of some commonly used presurgical skin antiseptics, we used biomicroscopy, corneal pachymetry, healing studies, and electron microscopy to compare tincture of iodine (2% iodine, 2.35% sodium iodine, and 46% ethanol), Hibiclens (4% chlorhexidine and 4% isopropyl alcohol with detergent), pHisoHex (3% hexachlorophene and detergent), Lavacol (70% ethanol), 7.5% povidone iodine scrub (with a detergent), and 10% povidone iodine solution (without a detergent) in rabbits. Five minutes after application, moderate corneal epithelial edema was noted in all groups except the saline control group. After three hours there was marked corneal de-epithelialization, conjunctival chemosis, and anterior stromal edema in all groups except those treated with 10% povidone iodine solution and 0.9% sodium chloride. After one week all corneas had returned to normal. Accidental instillation of 7.5% povidone iodine scrub into the tear film of a 33-year-old man resulted in almost immediate chemical chemosis despite prompt irrigation, demonstrating the corneal toxicity of this substance. These results indicated that a 10% povidone iodine solution without detergent causes minimal corneal toxicity whereas the other presurgical skin antiseptics tested are toxic to the cornea.