Iron-binding proteins in vitreous humour

The soluble protein composition of Macaque monkey vitreous humour was studied in order to understand its iron-binding properties. The protein content of vitreous humour was 217 micrograms/ml +/- 4.6%, 40% of which was serum albumin and 30% an iron-binding protein of hydrodynamic properties identical to that of transferrin or lactoferrin. Relative to serum, the vitreous humour contained a 13-fold excess of this protein(s). Isoelectric focusing, iron-binding and immunoelectrophoretic studies indicated that both vitreous humour and aqueous humour contained lactoferrin as well as serum transferrin. The iron-binding capacity of these proteins in vitreous humour was equivalent to the mass of haemoglobin iron contained in at least 570000 monkey erythrocytes. It was concluded that the intraocular lactoferrin originated from within the eye. These iron-binding proteins may play a protective role in ocular disturbances such as vitreous haemorrhage, iron foreign body toxicity and infection.

The retinal oxygen profile in cats

This study records for the first time the retinal tissue oxygen partial pressure as a function of location within the retina of the domestic cat. Tissue pO2 was recorded with oxygen sensitive microelectrodes that use the polarographic principle. The mean vitreal pO2 close to the internal limiting membrane was 20.2 +/- 2.3 mmHg. The internal limiting membrane does not act as a diffusion barrier for oxygen. As the electrode was advanced into the inner retina, the tissue pO2 rose gradually to a value of 24.6 +/- 2.3 mmHg and then fell to a minimum of 12.0 +/- 5.5 mmHg before rising again to a value of 29.2 +/- 2.5 mmHg. Further insertion resulted in a sudden steep rise of tissue pO2 values to 72.0 +/- 5.1 mmHg, after which there was no further alteration in measured values. Although the exact location within the retina of the recording electrode was not known, it is probable that the tissue pO2 minimum occurs at about the level of the inner nuclear layer. Therefore, it is probable that the retinal avascular layers receive their oxygen supply primarily from the choroidal circulation in the cat.

Cholesterol and lipoprotein-cholesterol levels in Western Australian rural diabetics

Total cholesterol, high-density lipoprotein-cholesterol (HDL-C) and non-HDL-cholesterol (non-HDL-C) were measured in the serum of diabetics from four country regions in Western Australia in order to document the levels and to examine the relationships between treatment mode, degree of diabetic control and lipid concentrations. In most age groups total cholesterol and non-HCL-C did not differ from levels in a large reference population, but HDL-C levels were generally lower. Male NIDDM patients on insulin had greater HDL-C levels than patients on oral hypoglycaemics, but their degree of control as determined by the level of glycosylated haemoglobin was poorer, and amongst female patients on insulin those with higher HDL-C levels had poorer control. These results confirm previous reports of higher HDL-C levels in patients on insulin, but are contrary to reports suggesting that better control is associated with higher HDL-C levels.

Effect of hypoxia on the maintained firing rate of retinal ganglion cells

The effect of systemic hypoxia on the maintained firing rate (MFR) of single retinal ganglion cells has been measured in the cat at a constant luminance level. Systemic hypoxia was produced by reducing the percentage of oxygen in the respiratory mixture under forced ventilation so that arterial PCO2 and pH were constant. Extracellular recordings were obtained from both X and Y retinal ganglion cells before, during, and after systemic hypoxia, with each cell acting as its own control. The MFR was unaltered by arterial PO2 levels of greater than 45 mm Hg. However, at and below this level of hypoxia the MFR was reversibly increased in 67% of the cells tested. Whether or not this increase occurred was independent of cell type or location. For arterial PO2 values of 24 to 34 mm Hg the initial increase in MFR was followed by a decrease for these cells; for PO2 values of less than 24 mm Hg the MFR showed a large initial increase followed by a complete cessation of firing. The remaining 33% of cells displayed only reduced MFR during hypoxia. The results indicate that ganglion cell function may be drastically affected by hypoxia. This may be relevant to the visual loss of a variety of retinal disorders.

The Arden grating acuity: effect of age and optical factors in the normal patient, with prediction of the false negative rate in screening for glaucoma

The Arden contrast sensitivity was investigated in normal persons, cataract eyes, and glaucoma patients with only plates 6 and 7 of the Arden grating set. The mean score of 90 normal eyes on plate 6 was 9.50 +/- 2.29 and on plate 7 it was 9.44 +/- 2.32. The mean scores of patients with early cataract were 14.51 +/- 2.99 on plate 6 and 13.74 +/- 3.26 on plate 7. Several patients with cataract missed the grating on plate 7. Mydriasis and miosis did not affect contrast sensitivity in normal eyes. Mydriasis significantly improved contrast sensitivity in patients with early cataract. In patients with glaucoma enlargement of the pupil from a miotic state to near normal size significantly improved contrast sensitivity. It is predicted that if plate 6 and 7 are used in mass screening for glaucoma in the elderly, there will be a false negative rate of 83% for plate 6 and 52% for plate 7. A false positive rate of 17% is predicted.

Glyoxalase phenotypes in patients with diabetes mellitus

Caucasian diabetic patients in Australian surveys showed a significant difference in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients with age of onset less than 40 years had a relative excess of glyoxalase homozygote 1-1 and a deficiency of types 2-1 and 2-2. Non-insulin dependent diabetic patients were not significantly different from non-diabetic subjects in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients without the complications of retinopathy or neuropathy also showed a significant excess of glyoxalase type 1-1 in relation to the control group. Genes controlling glyoxalase polymorphism appear to be associated with the variations of diabetes and its complications.

Chorioretinal biopsy in a patient with leukaemia

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Prevention of corneal burns during high-energy laser iridotomy

We used a plano hydrophilic bandage contact lens to protect the corneal epithelium and stroma from burns during laser iridotomy. The reduction of energy losses with this method, by the avoidance of corneal epithelial opacities, increases the chance of successful iridotomy when many applications of the laser are needed.

Image splitting--a technique for measuring retinal vascular reactivity

The observation of changes of pial vessel calibre has withstood the test of time in assessing cerebrovascular reactivity. A recent refinement has been the adoption of the image splitting television technique of Baez, which allows accurate and rapid measurements of vessel calibre to be made in situ. This method has been successfully applied to the eye, where the retinal vessels are readily visible through the pupil. Results are presented of preliminary experiments in normal persons, in whom an induced increased in intraocular pressure was associated with retinal vasodilatation.

Regeneration of retinal limiting membranes after chorioretinal biopsy in dogs

After chorioretinal biopsy in dogs, obtained without vitreous loss, accessory glial cells and fibroblasts filled the defect between cortical vitreous and bare sclera. The proliferating glial cells laid down a new basement membrane which was complete both on the internal and external aspects of the defect. After biopsy complicated by vitreous loss, however, cellular proliferation failed to re-establish complete internal and external limiting membranes, and new formed fibroblastic tissue extended into the vitreous. To our knowledge, this is the first report to describe effective regeneration of the internal limiting membrane of the retina in any species. These findings suggest that when vitreous loss can be avoided, healed chorioretinal biopsies are unlikely to lead to delayed pathological complications.

Association of retinopathy and glycosylated haemoglobin levels in diabetes mellitus

One hundred and forty patients with diabetes mellitus were examined in the small mining town of Kalgoorlie, Western Australia. The primary object was to determine the incidence of retinopathy in the diabetic community. One hundred and thirty-eight sets of data were obtained. There were 69 males and 69 females. The diabetes was controlled with orally administered hypoglycaemic agents in 62 patients, in 58 patients with insulin, and in 18 by diet alone. Forty-six of the 138 volunteers (33%), were found to have retinopathy and this included eight of the 14 Aboriginals taking part in the survey. Glycosylated haemoglobin levels ranged from 8.1% to 18.8% (mean 11.7%; SD; 2.28%) of total haemoglobin concentration, and plasma glucose levels from 1.2 mmol/L to 27.3 mmol/L (mean, 9.5 mmol/L, SD, 5.06 mmol/L); there was a positive correlation between levels of glycosylated haemoglobin and plasma glucose (r = 0.63; P less than 0.001). Diabetics with retinopathy had a mean glycosylated haemoglobin level of 12.5% compared with 11.3% in those without this complication. Examination by treatment groups showed that patients with retinopathy whose disease was controlled with insulin had significantly higher levels of glycosylated haemoglobin compared with those without this complication (0.01 greater than P greater than 0.001). Patients whose disease was controlled with orally administered hypoglycaemic agents did not show this difference.

Pseudomonas endophthalmitis associated with scleral necrosis

Three cases of pseudomonas endophthalmitis associated with scleral necrosis 3 to 10 years after pterygium excision and beta irradiation are described. The value of prophylactic repair of radiation-induced scleral necrosis and early aggressive management of pseudomonas endophthalmitis are emphasized.

Continual monitoring of fluorescein angiography

A system has been developed which enables continuous monitoring and recording of circulating fluorescein in the retinal blood vessels. This is achieved with minimal modification of a Zeiss fundus camera. A night vision television camera (lkegami) is used with illumination provided by the standard observation light of the fundus camera. This method offers advantages over standard fluorescein angiography in patient comfort, information obtained and the immediate evaluation of the fluorescein angiograms being available.

Macular oedema and retinal branch vein occlusion

The visual prognosis of patients suffering from retinal branch vein occlusion complicated by macular oedema is assessed in relation to the degress of capillary fallout. Extensive retinal capillary fallout associated with macular oedema was found to confer a poor visual prognosis in a series of 89 patients followed for an average time of 14 months. If the degree of capillary fallout associated with marular oedema was minimal, the visual prognosis was considerably improved.

Late complications of pterygium treatment

Long-term complications of pterygium excision and beta irradiation in 63 eyes of 57 patients are described. The age of the patients at treatment ranged from 27 to 69 years (mean 48 +/- 11), and complications were assessed 3 to 20 years later (mean 12 +/- 3). The pterygia were excised, leaving bare sclera, and beta irradiation of total dose 750 to 5200 rads (mean 3475 +/- 916) was given, except in 7 patients who had repeated courses or overlapping fields of beta irradiation. Scleral ulceration was present in 51 eyes and sectorial lens opacities with normal visual acuity (VA) in 19 eyes. Radiation induced cataract occurred in 3 eyes, with reduced vision. Ptosis, symblepharon, and iris atrophy were also seen. Pseudomonas endophthalmitis occurred in 4 patients with scleral ulceration. Beta irradiation to prevent recurrence of pterygia is a significant cause of iatrogenic ocular disease. There is a need to modify the beta irradiation dosimetry at present in use.

Chorioretinal biopsy in dogs

A simplified practical technique for biopsy of retina and choroid has been developed in dogs. A 270 degree circular scleral flap of 3 mm diameter is raised. The risks of chorioretinal bleeding and vitreous loss are greatly reduced by intravenous mannitol and controlled hyperventilation, with hyperoxygenation and transient, systemic hypotension under general anesthesia. Rreasonable ultrastructural detail was preserved in chorioretinal specimens of 1 mm diameter. Repeat biopsies in the same eye are feasible without significant complications.

Medical correlates and diabetic retinopathy screening

A systematic ophthalmological, medical, and biochemical screening of a rural population of diabetics in Western Australia is being carried out. A team of ophthalmologists, physicians, and paramedical personnel establish regional screening centres on a voluntary basis at weekends. Every attempt is made to locate and examine all known diabetics. All patients are given a thorough ophthalmic examination including standard multiple field colour fundus photography. Thorough physical examination includes assessment of cardiovascular and neurological status. Biochemical parameters include random blood sugar, urine analysis, serum creatinine, glycosylated haemoglobin, cholesterol, and high density lipoprotein. A detailed questionnaire and interview is carried out to assess the historical degree of control and the patient's knowledge of the control and management of diabetes. The sample now comprises an unselected population of 400 diabetics living in rural areas and allows comparison of areas which have scarce medical services with centres that are well supplied with medical practitioners. Incidence of retinopathy varies from 25 to 36 per cent of the diabetic population. Positive correlations of retinopathy have been found with duration, age, hypertension, level of control assessed biochemically at the time of examination, presence of ischaemic heart disease, peripheral neuropathy, and renal disease. Smoking also correlates positively. The data provide a baseline by which attempts to alter diabetic knowledge, management, and control may be measured in follow-up studies.

Retinal degeneration in Greyhounds

Retinal degeneration in 10 Greyhounds with clinical and ophthalmoscopic features is described, including results of electroretinography and fluorescein angiography for one affected dog. Clinical and histologic features differed from other kinds of retinal degeneration in dogs.

Continual monitoring of intraocular pressure: effect of central venous pressure, respiration, and eye movements on continual recordings of intraocular pressure in the rabbit, dog, and man

A new method has been devised for continual monitoring of intraocular pressure by radiotelemetry. The use of this instrument for monitoring intraocular pressure by a variety of ophthalmic conditions is described.

Long-term observations of proton-irradiated monkey eyes

Fifteen owl monkeys (30 eyes) that received proton irradiation of discrete areas of the retina and choroid have been observed for 3 1/2 years or more after irradiation. The dose delivered to the retina varied from a single dose of 1,600 to 4,750 proton rads and from 10,250 to 18,250 rads delivered in five fractions over a period of one month. Fundus examination, fluorescein angiography, and light and electron microscopy revealed chorioretinal changes at the area of irradiation. The part of the retina adjacent to the chorioretinal scar showed preservation of normal retinal vascular architecture on trypsin digest studies of the retina and on electron microscopic examination, even 1 mm from the edge of the scar. The results of this study suggest that proton beam irradiation may markedly reduce delayed ocular complications, especially radiation retinopathy, which is common to other forms of radiotherapy in the treatment of intraocular tumors.

Passive radiotelemetry of intraocular pressure in vivo: calibration and validation of continual scleral guard-ring applanation transensors in the dog and rabbit

Continual monitoring of intraocular pressure (IOP) by passive radiotelemetry, with a miniature scleral applanating device, mounted in a haptic contact lens (applanating transensor) is reported in the rabbit and dog. Several prototype transensors were calibrated in vivo in the rabbit and dog; a consistent linear output was obtained for each eye, although reproducibility of the slope between eyes over a period of time was less than ideal. Accuracy of determination of IOP was found to be better for the rabbit and will have to be improved before the instrument can be applied to the human. Multiple regression analysis of calibration studies in six rabbits established that the transensor output was not significantly affected by the small changes in body temperature and atmospheric pressure encountered during the study. Continual scleral tonometry with a standard Mackay-Marg tonometer showed that ocular rigidity has a significant effect on calibration curves, in contradistinction to standard Mackay-Marg corneal tonometry. A time-dependent decay in tonometer readings was more evident in canine eyes with low ocular rigidity. Since the transensor is also a guard-ring applanating device, calibration may be necessary for individual eyes and species.

Proton irradiation of choroidal melanomas. Preliminary results

Choroidal malignant melanomas in nine patients were treated with proton beam irradiation at the Harvard Cyclotron Laboratory, Cambridge, Mass. Each patient received five proton beam treatments in eight to ten days, totalling 4,730 to 8,570 rads at the tumor. No complications occurred during the treatment or follow-up period, which, at the time of this writing, ranges from one to 24 months, with an average of 12 months. No further growth of the tumor has been observed in any patient. Different signs of tumor regression have been noted. Resolution of the serous retinal detachments that accompanied some tumors is the earliest finding. Pigment changes over the surface of the tumor and adjacent pigment epithelium is a usual initial tumor response. Fluorescein angiography initially showed decreased leakage of dye; later, destruction of the tumor's vasculature and elimination of fluorescein leakage became evident. Only large choroidal vessels remained patient. Ultrasonography revealed decreased height of the tumors postirradiation, and the radioactive phosphorus (32P) uptake test, repeated in one patient, turned negative on postirradiation measurements.

Proton irradiation of small choroidal malignant melanomas

Five patients with choroidal malignant melanomas were treated with proton irradiation with a cyclotron. We developed an accurate method of aiming the proton beam within the eye. Four to five tantalum rings, 2 mm in diameter, were sutured to the sclera at the edges of the tumor, which is localized by indirect ophthalmoscopy and transillumination. The rings were used as markers for stereotactic radiography to align precisely the tumors with the proton beam. The patients were given a total tumor dose of 4,730 to 6,670 rads, delivered in five equal fractions, over a period of eight to nine days. All patients tolerated the treatments well without any adverse effects. The tumor response to therapy could not be evaluated at the completion of treatment since there was no immediate observable reaction of the tumor or of the surrounding retina. Although there has been no definite regression in any patient, we observed a change in the "color" of the tumor in the first two patients and resolution of two serous retinal detachments.

Infective keratitis in soft contact lens wearers

Eight cases of infective keratitis are reported in wearers of soft contact lenses. Four of them had normal eyes and were wearing lenses on a continual basis. One was wearing a lens continually for therapeutic reasons. Three others were wearing lenses daily or intermittently. The four latter cases were using contaminated lens solutions. Two of the continual lens wearers lost vision to the point of blindness. A significant factor in their bad outcome was the fact that both lived in areas remote from adequate ophthalmic services. Serratia liquefaciens was implicated in one case. This is thought to be the only reported case of corneal abscess due to this organism in the past 16 years. S. marcescens was grown in another case from the lens solutions and carrying case.

Vitreous structure, IV. Chemical composition of the insoluble residual protein fraction from the rabbit vitreous

Analysis of the structural proteins in the rabbit vitreous showed that the hydroxyproline content was 3.1 per cent w/w compared to a value of 10.9 per cent w/w for equivalent samples obtained from cattle. In contrast to the discreet fibers in bovine vitreous, the rabbit constituents occur as an aggregate of fibrils with a diameter of 15 to 20 å. The amino acid and carbohydrate composition was similar to vascular basement membrane and isolated fractions contained significant amounts of palmitic and stearic acids. The data indicate that the variability of vitreous structure in different species is not only quantitative, but also qualitative. It is suggested that in the rabbit the structural proteins may be derived primarily from the atrophied hyaloid system and that little, if any, secondary vitreous formation occurs in this animal.

Proton irradiation of simulated ocular tumors

Silicone sponges were sutured to the sclera of owl monkeys to create an indentation which would simulate a tumor of the posterior segment of the eye. A tantalum clip inserted in the silicone sponge served as a marker for radiographic localization of the simulated tumors. The acute lesions obtained on the retina and choroid after moderately high doses of proton irradiation suggest that this method of aiming the proton beam will be adquate for human clinical trials.

Vitreous substitution with gases

The effects of vitreous substitution with air, a sulfur hexafluoride-air mixture, an octafluorocyclobutane-air mixture, and physiological saline were compared in owl monkeys. Each gas caused an increase in ocular vascular permeability greater than that caused by saline, as measured by vitreous inflow of serum protein labeled with iodine I 131 and discgel electrophoresis. The duration of increased vascular permeability closely paralleled the time each gas remained in the vitreous cavity.

Physical properties of experimental vitreous membranes. I. Tensile strength

The tensile strength of vitreous membranes, induced by silk sutures imbedded in the vitreous body and removed one to two weeks later, was investigated in rabbits. Three types of membranes were distinguished by their appearance under an operating microscope; dense, opaque, cylindrical membranes, (Type 1), broken with 2 to 16 Gm. of force and elongated from 127 to 200 per cent before breaking; thin, cylindrical membranes, (Type 2), broken with 200 mg. to 2 Gm. of force and elongated from 51 to 152 per cent before breaking; and thin film-like membranes imbedded in formed vitreous gel, (Type 3), broken with 200 mg. to 5.5 Gm. of force and elongated from 53 to 186 per cent before breaking. Vitreous membranes formed two to eight weeks after surgery resisted forces greater than those required to detach rabbit retina. The results of the experiment are relevant in the design of vitrectomy instruments.