Ultrastructural analyses of enzyme-treated microfibrils in rabbit corneal stroma.

Microfibrils have been identified within and between corneal collagen lamellae in a number of vertebrate species in a variety of developmental and pathological conditions, but they are relatively rare in normal adult animals. The present study was undertaken to analyze corneal microfibrils in adult rabbits using enzymatic digestion techniques. Transmission electron microscopy (TEM) showed clusters of 10-15 nm microfibrils arranged in quasi-parallel bundles within or between orthogonally arranged stromal collagen lamellae. When corneas were fixed with tannic acid/glutaraldehyde, the entire stroma showed increased electron density and microfibrillar bundles were heterogeneously stained. Peripheral fibrils were more electron-dense than those located more centrally. Following sequential detergent solubilization of unfixed corneas, all cellular elements were removed and collagen lamellae were distorted. Microfibrillar bundles remained intact, however, and resembled untreated controls. Subsequent treatment with pepsin, trypsin or elastase resulted in swollen corneal tissues in which collagen lamellae were no longer distinguishable but individual collagen fibrils maintained their morphological integrity. In these tissues microfibrillar bundles were rarely identifiable and were reduced to randomly oriented fragments or clusters of filamentous material. Testicular hyaluronidase or chondroitinase ABC did not affect the fibrils. These data indicate that rabbit corneal microfibrils are proteinaceous and that the tannic acid-staining component of the bundles is not glycosaminoglycan. The fibrils are indistinguishable from those identified as oxytalan in cornea and other ocular tissues. Moreover, their sensitivity to elastase and preferential staining with tannic acid/glutaraldehyde strongly suggest they may be related to the elastic system of fibrils.

Isolation and characterization of fibronectin from bovine aqueous humor.

Aqueous humor collected from freshly enucleated bovine eyes was passed over a gelatin affinity column, and bound material was eluted with 4M urea. When fractionated by sodium dodecyl sulfate electrophoresis, the eluted material co-migrated with human plasma fibronectin and protein standards of approximately 220,000 daltons. Amino acid analyses demonstrated a composition similar to that of human plasma fibronectin and fibronectin synthesized by cultured cells. The concentration of fibronectin in aqueous humor is approximately 100 times less than in human plasma.

Cytokeratin expression in corneal endothelium in the iridocorneal endothelial syndrome.

The immunocytologic characteristics of two formalin-fixed, paraffin-embedded corneas from patients with the iridocorneal endothelial (ICE) syndrome and unaffected control corneas were studied. Binding of polyclonal antisera to Factor VIII, S-100 protein, involucrin, neuron specific enolase (NSE), and the lectins peanut agglutinin and Ulex europaeus agglutinin-1 was performed using the standard peroxidase-anti-peroxidase method. We detected reactive patterns of monoclonal antibodies to cytokeratins (34BE12 is a 56-58 kD mouse IgG reactive to stratified epithelia; Pkk1 is a 44-54 kD mouse IgG reactive to simple epithelia; and KL1 is a 55-57 kD mouse IgG reactive to epidermis and simple epithelia) using the standard avidin-biotin complex method. Staining properties were similar for the polyclonal antisera, lectins, NSE, and chromogranin in corneas with ICE syndrome and in the controls. However, the cytokeratins 34BE12, Pkk1, and KL1 were detected in the endothelium of the corneas with the ICE syndrome but not in the controls. These findings suggest that various cytokeratins are expressed in the corneal endothelium in the ICE syndrome that are not expressed in unaffected corneal endothelium.

Oval corneal opacities in beagles. III. Histochemical demonstration of stromal lipids without hyperlipidemia.

We found oral stromal avascular corneal opacities in 128 eyes of 75 beagles from 497 studied. There were three morphologic types that progressed in severity with time; nebular, racetrack, and white arc. Histochemical study of the earliest morphologic type (nebular) revealed neutral fats, cholesterol, phospholipids, and sometimes fatty acids both intracellularly and extracellularly. We found no elevation of serum cholesterol or triglycerides except in dogs with the most advanced morphologic type (white arc) and no alteration in thyrometabolic function. We think that oval stromal opacities in beagle corneas are a primary disorder of corneal lipid metabolism closely resembling the central crystalline dystrophy of Schnyder and may be an animal model for this human disease.

Posterior collagenous layer of the cornea. Ultrastructural classification of abnormal collagenous tissue posterior to Descemet's membrane in 30 cases.

We studied the transmission electron microscopy of the abnormal collagenous tissue posterior to Descemet's membrane in 30 human corneas that represented 19 different diseases. We named this abnormal tissue the "posterior collagenous layer" of the cornea and classified it into three morphologic types: (1) banded posterior collagenous layer, characterized by 110-nm wide-spacing material, (2) fibrillar posterior collagenous layer, characterized by loose meshwork of collagenous fibrils 20 to 30 nm in diameter, and (3) fibrocellular posterior collagenous layer, characterized by fibroblasts in connective tissue. The published ultrastructural studies of 88 corneas that represented 13 different clinical disorders fit this classification well. The posterior collagenous layers often formed multiple lamellae, but no pattern was invariably associated with a specific clinical disorder. We think these multiple layers represent successive periods of deposition of collagen by a stressed corneal endothelium and provide a lifelong record of senescent and pathologic events.

Management of pseudophakic corneal edema with reconstruction of the anterior ocular segment.

The following surgical techniques were used to treat pseudophakic corneal edema in 13 consecutive eyes: penetrating keratoplasty (13 eyes), mechanical anterior vitrectomy (ten eyes), removal of intraocular lens (13 eyes), gonioplasty with opening of peripheral anterior synechiae using a dental mirror (seven eyes), iridoplasty using a round needle (six eyes), and insertion of a replacement intraocular lens (12 eyes). The most common intraoperative complication was hemorrhage in the angle. Although the angle was open 360 degrees to the ciliary body in 12 of the 13 eyes at the end of surgery, a few peripheral anterior synechiae recurred in six eyes at six weeks. Short-term results suggest that this technique can restore the structure of the anterior ocular segment, decrease progressive peripheral anterior synechiae and glaucoma, and possibly decrease cystoid macular edema.

A systematic method of drawing corneal pathologic conditions.

We describe a method of indicating corneal pathologic conditions in the patient record by color-coded frontal and slit sketches. The practice improves biomicroscopic skill, provides an easily reviewed record of the disease's course, helps monitor observations of ophthalmologists in training, and creates a standardized method of notation.

The Hanna suction punch block and trephine system for penetrating keratoplasty.

We describe a new system for corneal trephination. The system for cutting donor buttons consists of a concave Teflon well in which the donor corneoscleral shell is secured by gentle suction. A cylindrical guide ensures that the disposable razor blade trephine is centered and is perpendicular during punching from the endothelium. The suction mechanical trephine used for the host has the following features: (1) a gun-sight alignment system for reliable centering, (2) a 360 degrees limbal suction ring that secures the trephine to the eye and ensures perpendicularity of the cut, (3) support surfaces on either side of the disposable razor blade that support the cornea during cutting to create near-vertical uniform wound margins, (4) rotation of the trephine with a manually operated gear system for smooth cutting, and (5) a calibration device that governs the extension of the blade and also allows cutting without descent of the blade.

Pneumocephalus. A sign of intracranial involvement in orbital fracture.

Fractures of the orbit resulting from blunt or penetrating injury that involve the paranasal sinuses may tear the dura and allow air to enter the cranial cavity (pneumocephalus). Pneumocephalus is sometimes the only sign of intracranial involvement. It is characteristically delayed in onset and clinically unsuspected, so that routine follow-up roentgenograms of patients with orbitosinus fractures may be the only means of assuring early detection. Roentgenographically, the air may be seen in spidural, subdural subarachnoid, intracerebral, or intraventricular locations. Prophylactic parenterally administered antibiotics may prevent intracranial infection. However, since about 25% of patients still develop meningitis, surgical repair of the dural fistula is often necessary.

Configuration of corneal trephine opening using five different trephines in human donor eyes.

In this laboratory study, we used five different corneal trephines on 60 fresh human donor eyes with controlled intraocular pressure to study the variation in the size and shape of the trephine openings. With all trephines, the average diameter of the button was larger than the diameter of the trephine at the epithelial side (mean difference, 0.21 mm; range, 0.06 to 0.35 mm) and the endothelial side (mean difference, 0.42 mm; range, 0.13 to 0.79 mm), presumably because the corneal tissue protruded into the trephine during cutting. The trephines that produced the most uniform opening were a nondisposable suction trephine and a freestanding disposable blade, but they caused some undercutting.

Penetrating keratoplasty for pseudophakic corneal edema with exchange of intraocular lenses.

We studied one eye in each of 25 consecutive patients with pseudophakic corneal edema. Each patient underwent a penetrating keratoplasty with exchange of intraocular lenses and was followed up for 12 to 38 months (mean, 18.7 months). The corneal graft remained clear in 22 (88%) eyes, but only eight eyes (32%) had acuity of 20/40 or better; nine eyes (36%) manifested cystoid macular edema, and six eyes (24%) had degenerative maculopathy. Elevated intraocular pressure was present in 12 eyes after surgery, with three eyes manifesting visual field loss; in all eyes the condition was controlled medically. Peripheral anterior synechiae appeared postoperatively in two eyes. We now treat severe cases of pseudophakic corneal edema with a penetrating keratoplasty, meticulous anterior vitrectomy, gonioplasty, iridoplasty, and exchange of intraocular lenses, employing a flexible-loop anterior chamber lens or a posterior chamber lens sutured to the iris.

Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery.

OBJECTIVE: To determine the long-term effects and stability of refraction following a standardized technique of radial keratotomy for myopia in the nine-center Prospective Evaluation of Radial Keratotomy (PERK) Study 10 years after surgery. METHODS: Radial keratotomy using eight centripetal incisions was performed to reduce myopia of -2.00 to -8.75 diopters in 1982 and 1983. A mean of 10 years later, patients underwent a standardized ophthalmic examination similar to previous study examinations. RESULTS: Of 427 patients (793 eyes that underwent radial keratotomy), 374 patients (88%) (693 eyes) returned for the 10-year examination. Of 675 eyes with refractive data, 38% had a refractive error within 0.50 D and 60% within 1.00 D. For 310 first-operated eyes, the mean refractive error was -0.36 D at 6 months and changed in a hyperopic direction to + 0.51 D at 10 years. The average rate of change was +0.21 D/y between 6 months and 2 years and +0.06 D/y between 2 and 10 years. Between 6 months and 10 years, the refractive error of 43% of eyes changed in the hyperopic direction by 1.00 D or more. The hyperopic shift was statistically associated with the diameter of the clear zone. Uncorrected visual acuity was 20/20 or better in 53% of 681 eyes and 20/40 or better in 85%. Loss of spectacle-corrected visual acuity of 2 lines or more on a Snellen chart occurred in 3% of all 793 eyes that underwent surgery. Among 310 patients with bilateral radial keratotomy, 70% reported not wearing spectacles or contact lenses for distance vision at 10 years. CONCLUSION: The PERK technique of radial keratotomy eliminated distance optical correction in 70% of patients, with a reasonable level of safety. A shift of the refractive error in the hyperopic direction continued during the entire 10 years after surgery.

Refractive keratoplasty in monkeys using intracorneal lenses of various refractive indexes.

The refractive power of the cornea can be altered with an intracorneal lens when it is inserted within a freehand lamellar-pocket incision. The effectiveness of the implant in altering the refractive power of the cornea depends on the refractive index of the intracorneal lens, since little change in the anterior corneal curvature occurs. Thirteen nonhuman primate eyes received intracorneal lenses made of synthetic polymers with refractive indexes ranging from 1.3686 to 1.633. The lidofilcon-B hydrogel (refractive index, 1.3686) lenses created no significant alteration in the refractive power of the cornea. The polymethylmethacrylate (refractive index, 1.4900D) and polysulfone (refractive index, 1.633) lenses created a predictable and significant alteration of corneal power that increased with each implant with a successively higher refractive index. The polymethylmethacrylate lens created a refractive alteration that was approximately 31% of the lens power in air. The polysulfone lens created a corneal power alteration that was approximately 40% of the lens power in air.

Preliminary computer simulation of the effects of radial keratotomy.

We created a computerized mathematical model of the eye for the simulation of refractive surgery. This model used a slightly prolate shape for a moderately myopic eye and an idealized aspheric profile for the cornea. The finite element method and the nonlinear Mooney-Rivelin law were used to analyze stress-strain relationships. Radial keratotomy changes stress distribution in the cornea and the anterior sclera, with major changes at the paracentral and peripheral ends of the incisions. The model predicted that there would be a flattening of the central cornea with a posterior displacement, which increased with an increase in intraocular pressure. A change in the length of the incision of 0.5 mm produced a significant change in correction. For small clear zones (3 to 4 mm), incisions of equal length produced comparable changes in refraction. We found that the effect of the corneal radius of curvature on the amount of refractive change was negligible. We studied the effect of elasticity coefficients and corneal anisotropia.

Factors affecting outcome and predictability of radial keratotomy in the PERK Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study used a standardized surgical technique that included a central clear zone with a diameter of 4.0, 3.5, or 3.0 mm. Multiple regression analysis of the outcome in one eye from each of 411 patients disclosed that the diameter of the central clear zone, patient age, and depth of the incision scar were the major factors affecting the change in refraction one year after surgery. Preoperative factors examined that did not have a significant influence on the outcome were sex, average central keratometric power, corneal thickness, corneal diameter, intraocular pressure, and ocular rigidity. The predictability of radial keratotomy, ie, the precision with which the outcome can be estimated, was measured by the 90% confidence interval for the change in refraction based on the regression equation. The width of this interval within each clear zone group was as follows: 4.0 mm, 2.49 diopters; 3.5 mm, 3.38 D; 3.0 mm, 4.12 D. For all 411 eyes, the 90% confidence interval was approximately 3.50 D wide. Thus, the surgeon could be 90% certain that an individual patient's refraction would be within 1.75 D of the predicted value one year after surgery.

Histopathology of traumatic corneal rupture after radial keratotomy.

Two patients (three eyes) had previously undergone technically successful radial keratotomy procedures and subsequently sustained blunt injury to the eyes in motor vehicle accidents one and two years after surgery, respectively, with rupture of the cornea along the keratotomy scars. One case subsequently required penetrating keratoplasty to recover 20/50 visual acuity. The second patient died, but had he survived, the extensive ocular injuries would have required significant surgical and medical care to restore vision. Histologic and ultrastructural studies demonstrated incomplete wound healing in the three corneas. Individuals who have had radial keratotomy, like those who have had penetrating keratoplasty, are at increased risk of corneal rupture after direct ocular trauma.

Effect of diameter and depth on the response to solid polysulfone intracorneal lenses in cats.

Impermeable, solid polysulfone intracorneal lenses (ICLs) can change corneal refractive power but will not allow diffusion of nutrients from the aqueous to the anterior stroma. Lenses of 4, 5, 6, and 7 mm in diameter were implanted in 50 cat eyes at depths ranging from 45% to 95% of corneal thickness to determine the effect of depth and diameter. Two types of stromal opacities occurred during follow-up: peripheral amorphous opacity (100%) and crystalline-granular lipid central opacity (79%). No eyes implanted with a 4-mm ICL ulcerated, but ulceration occurred in 28% of the eyes overall. Because opacification occurred with all lens diameters and implantation depths, metabolic demands of the cornea are not met. No safe limit exists at which these ICLs can be predictably used in cat eyes.

Subepithelial fibrosis after myopic epikeratoplasty. Report of a case.

A 29-year-old man with a -22.00-diopter myopia in the right eye underwent a planar, nonfreeze myopic epikeratoplasty and postoperatively developed a central subepithelial opacity. The opacity recurred after two superficial keratectomies; finally, another epikeratoplasty was performed. Light microscopic examination of the original button showed that the epithelium was thickened, collagenous subepithelial fibrocellular tissue was present, and Bowman's layer was focally disrupted. The stroma was edematous and peripherally scarred with scattered keratocytes. Examination by transmission electron microscopy revealed keratocytes lying anterior and posterior to Bowman's layer. The subepithelial fibrocellular tissue corresponded to an area of a break in Bowman's layer and probably originated from the donor stroma. The break in Bowman's layer may have been caused by the microkeratome cuts, but its origin is not certain.

The relationship of visual acuity, refractive error, and pupil size after radial keratotomy.

To better define the relationship between residual refractive error, uncorrected visual acuity, and pupil diameter, we compared 42 eyes that had an eight-incision radial keratotomy according to the Prospective Evaluation of Radial Keratotomy Study protocol with 42 matched control eyes. The parameters measured were best corrected visual acuity, uncorrected visual acuity, and the change in cycloplegic refraction with enlarging pupil diameter. The best corrected visual acuity was 20/16 in both the radial keratotomy and control groups, but the variability (SD) was higher in the radial keratotomy group. The average uncorrected visual acuity was 0.35 (35%) better in the radial keratotomy group, but the variability was 1.77 times higher. Change in refraction with dilation occurred in 9% of the controls and 36% of the radial keratotomy patients, indicating a significant difference (P = .002). The change in refraction with dilation in the eyes with radial keratotomy was almost equally split between a hyperopic change (17%) and a myopic change (18%), which was much different than in the control eyes, only 2% of which changed in a hyperopic direction and 7% in a myopic direction. The radial keratotomy patients with a myopic change had the best uncorrected visual acuity, indicating that positive spherical aberration yielded the best aspherical surface for uncorrected visual acuity.

Computer-assisted videokeratography of corneal topography after radial keratotomy.

We used computer-assisted videokeratography to compare the topographies of 32 corneas from 23 subjects after radial keratotomy with those of 47 normal corneas from 47 subjects controlled for age and preoperative keratometric and refractive power. Three ophthalmologists independently classified color-coded videokeratographs based on the color-coded pattern of dioptric power distribution and the cross-sectional shape. Corneas that had radial keratotomy exhibited a polygonal pattern not seen in normal eyes; this occurred in 59% of corneas. All normal corneas demonstrated a cross-sectional shape configuration that was steeper centrally than peripherally; 79% of corneas after radial keratotomy had a shape that was flatter centrally than peripherally. After radial keratotomy, the dioptric power increased from the center to the periphery (radius of approximately 4.6 mm) by 2.8 +/- 2.2 diopters (mean +/- SD), with a sharp inflection zone ("paracentral knee") 2.7 mm from the center; normal corneas showed a smooth decrease in power from the center to the periphery of 1.9 +/- 0.5 diopters.