Opaque Cornea Research Articles

Small mammal populations in maryland meadows during four years of herbicide (brominal®) applications

AbstractThe herbicide Brominal® was applied at the recommended rate to one plot in each of three paired 0.6‐ha plots; the other three plots were used as controls. Plots were sprayed once in the fall of 1988 and 1989 and twice in the spring of 1990 and 1991. Small mammals were trapped three times during each activity season (April‐October) to obtain population estimates before and after spraying and in the spring preceding fall spraying or the fall following spring spraying. Population estimates immediately after spraying gave no evidence of direct mortality. By 1991, dicot vegetation on treated plots was suppressed and mean numbers of meadow voles(Microtus pennsylvanicus)were less than on control plots. Because meadow voles favor dicots over monocots in their diet, reduced availability of dicots may have been related to the smaller vole population estimates. Species diversity of small mammals was negatively correlated with size of vole populations, but was not different between treated and control plots. Brominal apparently induced opaque corneas in nine voles. The condition was found in two voles too small to have been conceived at the time of the last previous spray nearly 8 months earlier, suggesting exposure to residue alone.

Therapeutic contact lenses

Therapeutic contact lenses are a rewarding area of optometric practice. Within Sunderland Eye Infirmary a diversity of ocular conditions present, creating a wide range of challenges. A variety of case histories will be discussed.A prosthetic scleral shell was made for a chemical burn injury which presented with symblepharon. A traumatic cataract (caused by a flying contact lens lid) was extracted and an aphakic hydrogel contact lens with an opaque iris print and clear pupil was required to maintain vision and decrease symptoms of glare. Two cases of perforating injury resulting in opaque corneas are shown. In one case the lens was ordered from a trial set, the other prosthetic contact lens was hand‐painted to match a photograph sent to the manufacturer. A hydrogel occlusive pupil contact lens was used to cover a dense white inoperable cataract caused by recurrent chronic uveitis in rheumatoid arthritis. This type of contact lens is also used for diplopia therapy.

Comparative Treatment of Experimental Staphylococcus aureus Endophthalmitis

To compare treatment strategies for Staphylococcus aureus endophthalmitis, we created an animal model in an aphakic rabbit eye and tested six different approaches to treatment. Rabbit eyes were rendered aphakic, and three weeks postoperatively, S. aureus organisms were injected into the vitreous cavity. One group was maintained as a control. Twenty-four hours after bacterial injection, six different treatment groups were created for comparison. Clinical inflammation scores, culture results 48 hours after treatment, histopathologic gradings, and development of total corneal opacity three weeks after treatment were assessed. Injection of vancomycin hydrochloride into the vitreous cavity was more effective than injection of cefazolin sodium (P = .01) in reducing the percentage of eyes that had positive culture results and also resulted in lower inflammation scores. Vitrectomy plus injection of either antibiotic was more effective than injection of the same antibiotic alone in reducing culture-positive results and reducing clinical inflammation scores. addition of systemic corticosteroids to intravitreal antibiotic injection did not improve any measure of outcome. Vitrectomy and injection of intravitreal vancomycin was the most effective strategy to sterilize the vitreous cavity, resulting in the lowest inflammation scores and the smallest percentage of eyes with opaque corneas. In an animal model of S. aureus endophthalmitis, the combination of vitrectomy and injection of intraocular vancomycin was the most effective strategy for rapidly controlling the infective process and improving the outcomes measured three weeks after treatment.

Fabrication of a keratoprosthesis.

For patients with opaque corneas that have a poor prognosis when using regular corneal transplants, a clear plastic "window" in the form of a keratoprosthesis may offer the only hope of usable vision. Various forms of such devices have been used for many years with varying degrees of success. The design, fabrication, and optical testing of two variations of a polymethylmethacrylate (PMMA) keratoprosthesis are described. Type 1 consists of a twin-plate collarbutton-style design that is used in eyes that have sufficient tear fluid production to maintain wetting of the anterior surface of the eye. Type 2 is of a similar design, with an added anterior cylinder that protrudes through a permanently closed eyelid, and is used in end-stage dry eyes.

Effect of Diclofenac on Corneal Haze after Photorefractive Keratectomy in Rabbits

To evaluate the ability of topical diclofenac to decrease corneal opacity after excimer laser photorefractive keratectomy (PRK). Twenty New Zealand white rabbits underwent a unilateral 193-nm excimer laser myopic photorefractive keratectomy to correct 5 diopters. There were four groups of five rabbits each. The first group of rabbits received postoperative topical treatment with placebo (Voltaren Ophthalmic vehicle), the second group received topical 0.1% diclofenac, the third group received topical corticosteroid (0.1% fluorometholone), and the fourth group received diclofenac and fluorometholone. In the first month, the topical drugs were applied four times daily, and in the second month twice daily. Corneal haze was graded from 0 (totally clear) to 4 (completely opaque cornea). Slit-lamp pictures were obtained at weeks 2, 4, and 8, and keratometry readings was performed at weeks 4 and 8. At week 8, the rabbits were killed, and the eyes were submitted for histologic examination. At week 8, there was less corneal haze in the diclofenac-treated animals and in the fluorometholone-treated animals than in the control group, but only in the diclofenac-treated group was the difference statistically significant. Combination treatment with diclofenac and fluorometholone did not result in a further decrease in haze. These data suggest that diclofenac and fluorometholone may influence corneal wound healing in rabbits after excimer laser PRK and support a potential role for using topical nonsteroidal anti-inflammatory drugs in preventing the development of excessive corneal haze after excimer laser surgery.

Congenital Hereditary Endothelial Dystrophy Associated with Glaucoma

Three children, ranging in age from 2 to 6 months, had diffuse and homogeneously opaque corneas, clinically consistent with congenital hereditary endothelial dystrophy. Bilateral elevated intraocular pressure (IOP) was a feature in all three children. Initially, all patients underwent glaucoma surgery to reduce IOP. Subsequently, a penetrating keratoplasty was performed in one eye of each patient to clear the visual axis. The excised corneal button was examined by light microscopy and by transmission and scanning electron microscopy. Postoperatively, all patients maintained clear corneal grafts. Results of histopathologic examination showed an absence of the endothelial cell layer in all patients. The presence of a variably thick collagenous layer posterior to the anterior banded zone of Descemet's membrane and the absence of endothelial cells were noted on transmission electron microscopy. Scanning electron microscopy confirmed absent, or scanty, and abnormal endothelial cells. The authors describe three patients with a clear association between congenital glaucoma and congenital hereditary endothelial dystrophy. This combination should be suspected where persistent and total corneal opacification fails to resolve after normalization of IOP.

Ciliary body haemangioma in a dog with secondary glaucoma

ABSTRACTA case of ciliary body haemangioma causing secondary glaucoma is described in an 11‐year‐ old English setter which presented with an acute history of ocular pain and an opaque cornea. Ultrasound was used to detect the tumour and a definitive diagnosis was made by histological examination after enucleation. Haemangioma in this location does not appear to have been previously reported in the dog.

Investigation of enzyme activities in severe burns of the anterior eye segment.

In severe burns of the anterior eye segment, including the cornea, limbus and adjacent conjunctiva, ischemia resulted from the necroses. While necrotic conjunctival and subconjunctival tissues may be removed to eliminate the toxic influence, the opaque cornea and ischemic sclera could not be removed. In the surrounding healthy tissues an inflammatory reaction developed, which brought about an infiltration of the damaged tissues by leukocytes and the release of lysosomal marker enzymes. N-Acetylglucosaminidase and cathepsin-D represent a number of other destructive enzymes involved with corneal and corneoscleral ulceration. Initially, their activities were low in the turbid, acellular cornea and increased 3 weeks after the burn. In the surrounding conjunctiva, these enzyme activities were normally higher than in the cornea and increased significantly after the burn. The elevated activities of N-acetylglucosaminidase and cathepsin-D in the conjunctiva and cornea were related clinically to corneal and corneoscleral ulceration.

C3 fixed in vivo to cornea from horses inoculated with Leptospira interrogans

C3 was detected bound in vivo to the opaque cornea of horses inoculated with killed Leptospira interrogans. Employing epithelial corneal cells isolated from a monolayer in tissue culture, we proved that C3 is fixed in vitro to the intact cell surface after incubation with a fresh equine anti- Leptospira serum. These findings, in addition to the infiltration of cornea with neutrophils and lymphocytes, may explain the mechanisms of tissue damage in recurrent uveitis of horses with leptospirosis.

The results of ischaemia in chemical injuries.

Severe burns of the anterior eye segment which include cornea, limbus and adjacent conjunctiva necrosis were accompanied by ischaemia. While necrotic conjunctival and subconjunctival tissue should be removed to eliminate its toxic influence, the opaque cornea and ischaemic sclera could not be removed. The ciliary body and the iris also suffer from ischaemic damage and under such conditions nutrient metabolites are deficient in the anterior segment of the eye. In the surrounding healthy tissues an inflammatory reaction begins after several days which induces an infiltration of the damaged tissues by leucocytes and an increase of N-acetylglucosaminidase and Cathepsin-D as demonstrated in model experiments and in patients. These destructive enzymes are apparently involved in the corneal and corneo-scleral ulceration and their activities may therefore be used to assess the severity of the ocular burn.

A quantitative evaluation of Fourier components in transparent and opaque calf cornea

Fourier transform methods were applied to STEM (scanning transmission electron microscopy) images to detect and quantify the subtle differences between the structure of normal transparent calf cornea and opaque calf cornea. In order for a tissue to be transparent, it can scatter or absorb only a small amount of light. Light scattering is minimized when the principal Fourier components of the spatial fluctuations in the index of refraction have wavelengths which are small relative to the wavelength of light (Benedek, 1971). Corneal opacity was produced as a result of high intraocular pressure (100-150 mmHg) when liquid was injected into calf eyes (0-2 weeks old). Pressurization created large structural defects and slight disruptions in the organization of the collagen fibers. Although the fiber organization appeared similar in the micrographs of both opaque and transparent corneas, Fourier analysis of STEM images collected at 50K magnification identified statistically significant differences. Far fewer Fourier components with wavelengths in the light scattering range (200-1100 nm) were observed in the transparent corneas than in the pressurized corneas as predicted by Benedek's theory. It was of interest that corneas treated with 100% glycerol prior to pressurization remained transparent at high intraocular pressures, possibly because glycerol stabilized the structure of the corneas and maintained a uniform index of refraction across the corneal stroma. The results demonstrate the effectiveness of Fourier analysis in detection and quantification of slight changes in structure at the electron microscopic level.

Magnetic Resonance Imaging in the Evaluation of Vitreoretinal Disease in Eyes with Intraocular Silicone Oil

Media opacification in eyes filled with silicone oil makes the evaluation of recurrent retinal detachment difficult. Ultrasonography through silicone oil is subject to significant imaging artifacts. We performed magnetic resonance imaging on six patients with unilateral intravitreal silicone oil to determine if the technique would detect detached retina and subretinal oil. All patients had undergone pars plana vitrectomy with silicone oil injection for proliferative vitreoretinopathy; five patients had encircling solid silicone scleral buckles. In five patients the media were clear, and ophthalmoscopic findings were correlated with magnetic resonance findings. Four patients had recurrence of inferior retinal detachment; magnetic resonance imaging demonstrated subretinal oil in three of these patients. One patient had a concentric, shallow, anterior retinal detachment; magnetic resonance scanning demonstrated a globular hyperintensity suggestive of subretinal oil. In the sixth patient, who had an opaque cornea, magnetic resonance imaging suggested that the retina was attached preoperatively; this was confirmed at subsequent surgery. A chemical shift artifact was helpful in defining the contour of retinal detachments and the presence of subretinal oil by outlining the silicone oil within the eye.

Transplantation of Congenitally Opaque Corneas from Eyes with Exaggerated Buphthalmos

We treated three eyes with marked buphthalmos and congenitally opaque corneas with cyclocryotherapy, one application in one eye and two applications in two eyes. The size of the eyes became rapidly smaller during the first two weeks postoperatively. Thereafter, corneal transplantation improved vision in each eye.

The use of a displaced, tinted zone, prosthetic hydrogel lens in the cosmetic improvement of a strabismic, scarred cornea

A customised prosthetic soft contact lens with a displaced tinted zone and reversed prism zonal thinning for orientation of the lens was used to improve the cosmetic appearance of a strabismic eye with a scarred, opaque cornea.

Walker-Warburg syndrome in a Japanese patient

We report the first Japanese female patient with Walker-Warburg syndrome. She had generalized muscle hypotonia with hydrocephalus due to Dandy-Walker malformation and bilateral microphthalmia with opaque corneas. She had severe motor and mental retardation. Muscle histology reflected advanced changes of muscular dystrophy. We discuss the relationship between Fukuyama congenital muscular dystrophy and Walker-Warburg syndrome, both of which fall within a spectrum of developmental abnormalities with a common cause. In Fukuyama congenital muscular dystrophy, ocular abnormalities are less severe.

Temporary Keratoprosthesis for Combined Penetrating Keratoplasty, Pars Plana Vitrectomy, and Repair of Retinal Detachment

The Landers-Foulks temporary keratoprosthesis was used to combine penetrating keratoplasty, pars plana vitrectomy, and scleral buckling in the management of 13 eyes with opaque cornea and posterior segment abnormalities. In seven cases, trauma precipitated the ocular disease. Complications of cataract surgery resulted in anterior and posterior segment pathology in six cases. The corneal graft was initially clear in all cases. However, corneal edema complicated phthisis bulbi in four cases and followed homograft reaction in two cases. Eight eyes with retinal detachment (RD) preoperatively were successfully reattached. In five eyes, the retina redetached as these eyes became phthisical. Visual function improved in six cases. In general, eyes with a history of trauma had a much poorer outcome than did eyes with anterior and posterior segment problems related to previous cataract surgery.

Participation of T lymphocyte in corneal edema in the early stage of herpetic stromal keratitis.

The participation of T lymphocytes in the immunopathogenesis of corneal opacity in herpetic stromal keratitis was investigated. In BALB/c mice infected intracorneally with herpes simplex virus type 1, corneal opacity was manifested 10 days after infection, while in athymic mice corneas remained almost clear. Histologically, all opaque corneas revealed stromal edema accompanied by the diffuse presence of polymorphonuclear cells and lymphocytes. When complement (C')-treated immune spleen cells were adoptively transferred into athymic mice 6 or 72 h after corneal infection, stromal keratitis with mild opacity was observed 10 days after transfer. The athymic mice given anti-Thy 1.2+C'-treated immune spleen cells failed to develop corneal opacity. The difference, as revealed by light and electron microscopy, was the presence or absence of lymphocytic infiltration and edema in the posterior third layers of the stroma and endothelial lesions. The endothelium was infiltrated by lymphocytes or macrophages and showed various stages of destruction. The main cause of corneal opacity in the early stage of herpetic stromal keratitis is thought to be stromal edema due to an adverse effect on the endothelium by immune T lymphocytes.

A NEW TEMPORARY KERATOPROSTHESIS FOR PARS PLANA VITRECTOMY

Using a new temporary keratoprosthesis in an eye with an opaque cornea and a proliferative vitreoretinopathy, a pars plana vitrectomy combined with a silicone oil injection was successfully performed. The new keratoprosthesis is made of silicone rubber and is fixed to the threphined corneal bed with four 10-0 nylon sutures. It permits an excellent view of the intraocular structures and allows vitreoretinal surgery even in the region of the pars plana and vitreous base. It is replaced by a corneal graft at the end of the vitrectomy.

Penetrating Keratoplasty After Placement of a Temporary Keratoprosthesis During Pars Plana Vitrectomy

Five eyes of five patients with opaque corneas underwent penetrating keratoplasty after pars plana vitrectomy. In each case, the Landers-Foulks temporary keratoprosthesis provided visualization of the vitreous cavity and retina, allowed successful removal of hemorrhagic vitreous, and permitted retinal reattachment. Corneal grafts remained clear in two eyes; three grafts developed stromal edema. Useful postoperative vision was achieved in two eyes. However, proliferative vitreoretinopathy, postoperative hypotony, atrophia bulbi, and corneal edema resulted in poor vision in three eyes.

Aplasia of the optic nerves

At birth, a full term baby showed marked cyanosis and respiratory distress, resulting from transposition of the great vessels. In spite of intensive care, and of balloon septostomies, the child died at the age of five days. The right eye was small and had an almost fully opaque cornea, together with other abnormalities of the anterior segment; the left eye was slightly larger, with a clear cornea. Both eyes showed varying degress of retinal dysplasia, and foci of microcystoid change. Macroscopically, and on histological examination of serial sections, the central retinal vessels were completely absent (a focus of neovascularisation in the vitreous of the right eye was apparently of choroidal origin). Furthermore, no optic discs, retinal ganglion cells and nerve fibres could be demonstrated. The optic nerves were missing. The findings are discussed.