J. Terry Ernest

Photodynamic Biologic Tissue Glue

We studied both heat- and light-activated tissue glues, and while a heat-activated mixture such as albumin and fluorescein isothiocyanate was effective, we believed that a light-activated substance would have less of an effect on adjacent tissue. Our glue uses a photosensitive singlet oxygen generator to cross-link a protein solder with corneal stromal collagen. The mixture consists of 18% fibrinogen and 2.6 mg/ml of riboflavin-5-phosphate activated with a blue-green (488-514 nm) Argon laser. We tested our glue by soldering 5-mm penetrating central corneal incisions made in human cadaver eyes. The strength of the closure was measured by cannulating the vitreous cavity with an 18-gauge needle connected to a saline reservoir. The pressure in the reservoir was elevated by connecting it to a sphygmomanometer. Immediately following tissue closure, the intraocular pressure was increased until the wound burst. We soldered and measured 10 eyes and found a mean bursting pressure of 154 mm Hg, with a range of 80-260 mm Hg. Our laser-activated tissue glue is an effective adhesive for corneal tissue, and we now plan to carry out toxicity studies in living animals.

Visual Function in Acute Posterior Multifocal Placoid Pigment Epitheliopathy

We examined a 19-year-old woman with acute posterior multifocal placoid pigment epitheliopathy one week after she noted blurring of central vision. Her corrected visual acuity was R.E.: 6/7.5 (20/25), and L.E.: 6/12 (20/40). The visual fields showed 10-degree pericentral scotomas. A color vision defect and an abnormal Stiles-Crawford effect were present. Dark adaptation showed a delayed time course, with normal final thresholds. The electro-oculogram was subnormal, suggesting widespread abnormality of the retinal pigment epithelium. Active lesions resolved within three weeks, but fluorescein angiography showed characteristic widespread residual changes. Within three weeks, she had normal visual acuity and a normal electro-oculogram. Other tests of visual function showed recovery with a slower time course. By one year, the visual fields, color matching, Stiles-Crawford effect, and dark adaptation were almost normal. Analysis of the color-matching data and Stiles-Crawford effect indicated that the abnormalities of macular function were caused by an underlying lesion of the pigment epithelium and photoreceptors. This caused a physical distortion of the photoreceptor layer and metabolic disfunction of the photoreceptors.

The Effect of Photocoagulation on the Choroidal Vasculature and Retinal Oxygen Tension

Light microscopy and latex-pigment injection of rhesus monkey eyes studied at varying times after retinal laser and xenon photocoagulation of varying intensity showed that the choriocapillaris was obliterated by a wide range of intensities but that the choroidal arteries and veins remained open. Retinal oxygen tensions acutely increased over the lesion but later subsided to normal. Multiple treatment sessions several days apart may reduce the risk of hemorrhage associated with hypermia secondary to photocoagulation.

Submacular Choroidal Circulation

A neoprene latex and pigment mixture was injected into the choroidal blood vessels of human cadaver eyes. When peripheral resistence was normal, a single arteriole filled a single lobule of the choriocapillaris drained by mulitple surrounding venules. The choridal veins interconnected and an increase in the peripheral resistance caused by elevation of the venous pressure resulted in filling of contiguous lobules in a retrograde manner through the venules that normally drain them.

Photodynamic biologic tissue glue to enhance corneal wound healing after radial keratotomy

Purpose: To evaluate the effect of photodynamic biologic tissue glue (PBTG) on corneal wound healing after radial keratotomy (RK). Setting: Cornea Research Laboratory, The University of Chicago, Chicago, Illinois, USA. Methods: Bidirectional, eight‐incision RK was done in one eye of eight Dutch pigmented rabbits. Then, PBTG was inserted into the RK incisions and activated with an argon blue‐green laser in four treatment eyes. The rabbits were divided into three groups: early, in which corneal wound healing was assessed at 1 and 3 weeks; late, in which corneal wound healing was assessed at 8 weeks; enhancement. Results: The PBTG‐treated keratotomy wounds had a more prominent epithelial healing response immediately after RK and a decreased propensity for wound dehiscence. Collagen fiber arrangement in the PBTG‐treated incisions was sagittal to the keratotomy wound 1 to 3 weeks after RK and then changed to a transverse orientation across the keratotomy wound by 8 weeks. The control keratotomy wounds had a less prominent epithelial healing response and developed late disorganization of the posterior keratotomy wound at 8 weeks. Keratometry measurements 2 months after RK showed corneal flattening of 1.0 diopter (D) in the PBTG‐treated eye and 6.5 D in the control eye, which is consistent with histologic studies showing more advanced wound healing in the PBTG‐treated eyes. After RK enhancement, the PBTG‐treated eye resisted further corneal flattening and had 4.5 D of corneal steepening; the control eye had 2.0 D of additional corneal flattening. Conclusion: The nontoxic, laser‐activated adhesive PBTG accelerated corneal wound healing after RK and simulated the placement of sutures into the RK wound. Thus, PBTG may be an alternative to sutures to correct hyperopia after RK in humans.

AIDS and the eyes

The eye is affected in 50-75% of adult AIDS patients. This rate of ocular involvement is much higher than that in symptom-free HIV-seropositive patients, and seems to increase in incidence with severity of disease. These observations indicate that regular screening of HIV-positive patients is warranted to allow early identification of potential vision and life threatening disease.

Optic disk oxygen tension

Abstract The optic disk oxygen tension has been measured polarographically in rhesus monkeys using a microelectrode. It was shown that the central retinal artery “leaks” oxygen and that there is a gradient in the surface oxygen tensions across the optic disk. Moreover, the optic disk oxygen was shown to compensate for changes in the perfusion pressure by the process of autoregulation.

The Effect of Systolic Hypertension on Rhesus Monkey Eyes After Ocular Sympathectomy

Systolic hypertension was induced in rhesus monkeys by obstructing the thoracic aorta and by ocular sympathectomy obtained with the retrobulbar injection of 6-hydroxydopamine. During the late phase of fluorescein angiography, fluorescein leaked from the choroidal circulation into the retina. The retinal vessels did not leak fluorescein. The effect was not permanent since fluorescein did not leak into the retina after the blood pressure returned to normal.

Isovolemic hemodilution increases retinal tissue oxygen tension

Abstract•Background: Therapeutic isovolemic hemodilution has been reported to improve blood flow and oxygen delivery. Few reliable measurements have been made, however, showing the effect of hemodilution on tissue oxygen tension.• Methods: We measured retinal oxygen tension during experimental isovolemic hemodilution in normal cats. Polarographic oxygen microelectrodes were placed in the vitreous humor within 100–200 μm of the retinal surface.•Results: Tissue oxygen tension increased initially during isovolemic hemodilution to a maximum approximately 50% above baseline at approximately two thirds of the original hematocrit level. Hemodilution beyond this point to lower hematocrits caused a steady decline in tissue oxygen tension. Cardiac output measured in one cat undergoing isovolemic hemodilution increased as hematocrit was lowered, but the cardiac erythrocyte flux actually decreased steadily.•Conclusion: The observed increase in tissue oxygen tension with hemodilution appears to be explained by a lesser reduction in capillary than in systemic hematocrit, coupled with an increased capillary blood flow. The increase in tissue oxygen tension we observed could in part explain the clinically beneficial effects of hemodilution.

Diffuse congenital hemangiomatosis with infantile glaucoma.

A white male infant was born with multiple hemangiomas of the skin and mucous membrane. At 7 months of age he exhibited the signs and symptoms of infantile glaucoma in each eye, but goniotomy was not possible because of vascularity in the angles. Cyclocryotherapy was used on multiple occasions to control intraocular pressure until a goniotomy could be done safely in one eye. The other eye has had good control of intraocular pressure without operation.