Improved excimer laser photorefractive keratectomy system

An improved 193 nm excimer laser photorefractive keratectomy system is described here. The delivery system was optimised to produce a smooth keratectomy bed, to minimise the healing response, and to reduce the regression of the refractive result. A spatial filtering system was used to smooth the energy distribution within each pulse, and the iris was adjusted for every pulse, to eliminate steps and other irregularities from the keratectomy profile. An image rotator was used to average out any remaining non-uniformities in the energy distribution. The results from the first 39 eyes treated with this laser system with a maximum follow-up of 18 months, are summarised. No epithelial healing problems were noticed, and little or no loss of corneal clarity was noted at any stage during healing. Twenty of the keratectomy procedures were normally sighted myopic corrections, with a maximum follow-up of 5 months. Minimal regression of the refractive correction was seen during the first 8 weeks.

Poly(2-hydroxyethyl methacrylate) sponges as implant materials: in vivo and in vitro evaluation of cellular invasion

The pore size and the in vivo behaviour of four poly(2-hydroxyethyl methacrylate) sponges were investigated. The sponges were synthesized by polymerization of monomer in 70, 80 and 90 wt% water, respectively. In one of the formulations, a high amount of initiator was added. The average pore diameter was calculated with Ferry's equation and the results compared to those obtained by examination of samples using environmental scanning electron microscopy. The use of the equation greatly underestimated the size of pores. We also showed that the pores in polymers obtained in 70 wt% water were not interconnected, whilst the pores in polymers obtained in 80 and 90 wt% water, respectively, were larger and interconnected throughout the polymer. When implanted subcutaneously in rabbits, only the latter polymers allowed invasion and proliferation of cells. Penetration and proliferation of cells in these sponges were also assessed by an in vitro method using cultured human fibroblasts. The procedure included the overlaying of a glass plate covered by confluent cultured cells on to the surface of polymer impregnated with collagen. The depth of migration and number of sections needed to be cut to count a fixed number of invading cells were measured after incubation for 2 wk and used as indicators in comparing the ability of various sponges to allow cellular invasion. The assay showed that more cells invaded a hydrogel sponge produced in 80 wt% water than one produced in 90 wt% water. It also showed that the cut polymer surfaces allowed a greater cellular invasion than the moulded ones.

Excimer laser sclerostomy: the in vitro development of a modified open mask delivery system

The argon fluoride (ArF) excimer laser at 193 nm ablates the ocular tissues with a new order of precision and virtually no adjacent damage. A glaucoma filtration operation has been designed in which small-bore sclerostomies are created using the ArF excimer laser delivered through an open mask. The mask plicates the conjunctiva at the limbus prior to ablation. Removing the mask at the end of the procedure allows the conjunctiva to relax back to its original position, separating the conjunctival and scleral wounds. Formal conjunctival dissection is thus avoided. Feasibility studies in cadaver pig eyes, using a fluence per pulse of 400 mJ/cm2 and a pulse repetition rate of 20 Hz, indicate that sclerostomies of 300 microns diameter can be reliably formed if an en-face air jet is built into the mask to raise the pressure in the target area, preventing aqueous flooding.

Segmentation of fluorescence in the retinal microcirculation--is it a valid indicator of blood cell flow?

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Developmental study of chondroitin-6-sulphate in normal and dystrophic rat retina

The RCS rat is a widely studied model of human retinal dystrophies including retinitis pigmentosa. Chondroitin-6-sulphate (C6S) in the interphotoreceptor matrix was localised immunocytochemically in both the normal congenic and dystrophic strains of the RCS rat up to 65 days postnatally. From postnatal days 5 to 15 the distribution of C6S in both strains was similar, being localised in the interstices of developing inner and outer segments and adjacent to the RPE surface. In the normal rats, the distribution of C6S did not change with age. In the RCS rats, however, at postnatal days 20 to 35 staining was observed as a dense band at the junction of inner and outer segments and no staining was observed adjacent to the surface of the RPE. At postnatal day 45 onwards there was a decrease and a complete absence of C6S staining in these rats. This change in the pattern of staining correlated with the morphological observation of the progressive degeneration of photoreceptor cells suggesting that C6S may be important in photoreceptor degeneration in the RCS rat.

Laser microsclerostomy for primary open angle glaucoma: a review of laser mechanisms and delivery systems

A number of different lasers and delivery systems are currently used in experimental sclerostomy procedures. These are discussed with reference to their performance in terms of cutting accuracy and trauma to the adjacent tissues. Lasers emitting wavelengths close to the absorption peaks of water in the mid-infrared region and organic polymers in the far ultraviolet region have a short absorption pathlength in the sclera and produce the least adjacent thermal tissue trauma. These ablating lasers cannot be delivered gonioscopically, and contact endoscopic techniques trap hot expanding gases within the forming sclerostomy channel causing secondary thermal and mechanical damage. Optimal results should be obtained using an ablating laser delivered either through an open mask or a modified endoscopic system incorporating an adequate exhaust mechanism.

Flow patterns of blood cells in the retinal capillaries. Retinal capillary flow patterns

We present a new technique for retinal blood cell angiography which was used to investigate flow patterns of blood cells in the retinal capillary net of normal cats. Capillary paths were defined to be the path taken by the labelled blood cells from the terminal arteriole to the entry point into a collecting venule. We were able to define two types of capillary paths. The 'simple' paths were minimally coiled and had a high blood cell flux. The 'complex' paths were coiled, structurally complex and had a low blood cell flux in comparison to the simple paths of the same eye. A simultaneous fluorescein angiogram was performed to reveal the complete anatomy of the capillary net in which the functional paths exist. The possibility that such flow patterns exist in the human retina should be considered.

In vitro cytotoxicity of melanized poly(2-hydroxyethyl methacrylate) hydrogels, a novel class of ocular biomaterials

Due to their ability to absorb ultraviolet and visible radiation, we have proposed the melanized poly(2-hydroxyethyl methacrylate) hydrogels as biomaterials suitable for the manufacture of soft artificial intraocular lenses. Their biocompatibility has not been evaluated so far. In this study, poly(2-hydroxyethyl methacrylate) containing various amounts of adrenochrome-melanin were synthesized and the cytotoxicity of their aqueous extracts was assessed by using four in vitro testing techniques (trypan blue dye exclusion, inhibition of DNA synthesis, lactate dehydrogenase release, and inhibition of cell growth). Assays were based on incubation with human choroidal fibroblasts. By the first three techniques, no cytotoxicity was found in the extracts. The inhibition of cell growth test showed a slight cellular protein loss, however only in the extracts of polymers with high melanin content. The results suggest that the release of potentially toxic agents from melanized hydrogels into an aqueous medium is not significant. However, when an assay in collagen gel was carried out in the presence of specimens of melanized hydrogels, a toxic reaction was clearly revealed. This can be caused by a delayed release of toxic molecules from melanin, or by some other mechanism. The use of melanin-containing polymers as implant materials becomes questionable and further research is necessary.

A new magnifying indirect stereo ophthalmoscope

A new magnifying indirect stereo ophthalmoscope had been designed, built, and tested. Magnification is achieved by means of Keplerian telescopic systems mounted in each eyepiece. Schmidt or Pechan prisms are incorporated to shorten the length of the telescopic systems. Using a +20 diopter condensing lens, the total retinal magnification achieved with this system varies from 5.6x at a 40-cm observation distance to the aerial image to 9.4x at a 25-cm observation distance. When the fundus is viewed through a dilated pupil extraordinary stereopsis is obtained. When combined with the magnification, this stereopsis greatly enhances the view of the posterior segment of the eye.

Improved method for calculation of corneal topography for any photokeratoscope geometry

Accurate and efficient calculation of the anterior corneal surface topography by photokeratoscopy has become important for the management or surgical treatment of refractive errors. Methods have been published that describe such calculations. The algorithms described here eliminate an assumption made in some of the earlier computational methods without an excessive increase in the computation time or increased sensitivity to measurement errors. This results in an enhanced accuracy for reconstructing corneal topographies. Computer simulation results indicate an improved accuracy in measuring the topography for nonspherical corneas. The equations given here apply to any general photokeratoscope geometry and can easily be used in computer programs. In a notable previous publication concerning the more common flat faceplate keratoscope geometry, several of the equations were presented with errors. These errors are identified as an aid to anyone who had already attempted to use those equations in a computer program.

"Black prosthesis" revisited: a study of epinephrine-induced pigment deposits on poly(methyl methacrylate)

To investigate in detail the "black prosthesis" syndrome, experimental production of melanin from epinephrine was performed both in bulk and onto the surface of a common prosthetic material, poly(methyl methacrylate) (PMMA). The study by ultraviolet/visible spectrometry showed that the radiation-absorptive properties of PMMA were significantly enhanced; a sample treated for 20 days in epinephrine absorbed all ultraviolet radiation up to a 344-nm wavelength and transmitted only 4.9% from the ultraviolet spectrum at 400 nm and 16.2% from the visible spectrum at 500 nm. Transmission electron microscopy studies suggest that melanogenesis occurs on the surface of PMMA, and the pigment does not penetrate the polymer. Using infrared spectrometry, it was confirmed that the pigmentation is caused by a melanin formed through the oxidative polymerization of epinephrine.

Further studies on ultraviolet-absorbing hydrogels for intraocular lenses: relationship between concentration of a polymerizable benzophenone, absorption, and extractability

A tendency to reduce the use of benzophenone absorbers is currently evident in the manufacture of the UV-absorbing IOLs, mainly because the cutoff wavelengths are inferior to those provided by benzotriazoles. In principle, by incorporating large amounts of benzophenones it may be possible to achieve high cutoff wavelengths. A covalently bondable benzophenone UV absorber, Cyasorb UV-2098, was incorporated in poly(2-hydroxyethyl methacrylate) (PHEMA) in increasing concentrations, and certain associated phenomena were investigated. At 4% w/w absorber content, the nonhydrated polymers turned partially opaque. In water-swollen hydrogels, opacification occurred at a lower absorber content (2% w/w). By using extraction techniques and gas chromatography, we also found that up to 8% w/w of the absorber remained unpolymerized and could leach out from any material containing less than 5% w/w absorber. In samples with higher initial content of absorber, the amount of unreacted, leachable absorber was significantly higher (25% to 30%). Based on this study model (hydrogel/Cyasorb UV-2098), we concluded that benzophenone absorbers cannot provide cutoff wavelengths higher than those provided by benzotriazoles.

Cytotoxic effects of residual chemicals from polymeric biomaterials for artificial soft intraocular lenses

Development of improved hydrogels for soft intraocular lenses, based on 2-hydroxyethyl methacrylate monomer, requires the use of various other monomers and polymerization additives which have potential ocular toxicity. Three monomers, 2-hydroxyethyl methacrylate, methyl methacrylate, and 2-ethoxyethyl methacrylate, as well as two common inhibitors, hydroquinone and 4-methoxyphenol, were subjected to in vitro cytotoxicity assays as aqueous solutions at different concentrations. A new polymerization initiator, 2,2'-azo-bis-(2,4-dimethyl valeronitrile), was thermally decomposed in water at different concentrations and the products were also assayed for cytotoxicity. Assays were based on incubation with human choroidal fibroblasts. Cell death was evaluated by trypan blue dye exclusion, DNA synthesis inhibition, and lactate dehydrogenase tests. While methyl methacrylate and 2-ethoxyethyl methacrylate were found nontoxic, the other chemicals displayed high cytotoxicity. However, when extracts of synthesized poly(2-hydroxyethyl methacrylate) specimens, differentially treated after polymerization, were subjected to the same assays it was found that toxicity from residual 2-hydroxyethyl methacrylate monomer was lost during steam sterilization and storage in water because of the removal of the monomer through aqueous washing. The lack of toxicity in these specimens suggests that residual contents of inhibitor and initiator are too low to cause toxic effects on choroidal fibroblasts. It is concluded that hydrogels have low cytotoxic effects in vitro.

Bovine corneal stroma ablation rate with 193-nm excimer laser radiation: quantitative measurement

Excimer lasers operating at 193 nm may become important surgical instruments in ophthalmology because of their ability to ablate tissue with excellent precision and minimal damage to adjacent tissue. However, the precision is limited by the accuracy of the measurement of the amount of tissue ablated per pulse at the fluence used. A measurement of the ablation rate of bovine corneal stroma over the range of fluences most likely to be useful for corneal surgery (50-400 mJ/cm2) is presented. The technique used produced reproducible results, the data from 47 animal eyes being averaged to further increase the precision. For this range of fluences, these results show a more precise measurement than previously published tissue ablation rate data. These results should be useful in accurately predicting the result of corneal surgery using the excimer laser if species differences are not major.

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. I. A review

The use of short-pulsed lasers in ophthalmic surgery inspired and called for research on the damage inflicted by the laser radiation upon the acrylic polymers from which artificial intraocular lenses are made. The possible release of toxic monomers by laser-induced depolymerization is of great concern but past investigations of this phenomenon have been very limited. The present knowledge of various types of laser-induced damage to transparent polymers is reviewed with particular emphasis on the acrylic materials and intraocular lenses.

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. II. Study of monomer release from artificial intraocular lenses

Commercial intraocular lenses and polymer specimens, both poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) p(HEMA), were subjected to various levels of irradiation from a Q-switched Nd:YAG laser, and then to extraction and sample-enrichment techniques. The extracts were analysed by capillary gas chromatography. In PMMA samples, residual contents of 0.05-0.89% (wt) MMA were found and it appeared that the laser radiation did not cause a detectable increase of the monomer content. No residual HEMA could be found in p(HEMA) samples before or after laser bombardment. It is concluded that the accidental exposure of lenses to Nd:YAG laser cannot produce a significant release of monomers. Depolymerization induced by laser is a process unlikely to occur at the energy levels used in ophthalmic surgery.

The patency of the retinal vasculature to erythrocytes in retinal vascular disease

This paper presents the first evidence that in retinas with experimentally induced vascular disease some vessels contain only plasma. This was demonstrated by a histologic technique developed specifically to test the hypothesis that at some stage in retinal vascular disease, vessel patency to erythrocytes is lost before vessels close to plasma. Using this technique, we visualized three major components of the circulation at all retinal locations: the erythrocytes; the plasma as marked by the presence of 0.2-micron fluorescent microspheres; and all functioning endothelial cell nuclei, which were marked by the fluorochrome bis-Benzimide. It was assumed that the distributions of the erythrocytes and small particles in retinal whole mounts reflected accurately the true in vivo distributions at the moment of circulation arrest. Postenucleation the retina can be viewed and photographed within 45 min of circulation arrest. The technique was used on normal rats and on rats induced with a fast-developing model of retinal vasculopathy. With this model, we demonstrated retinal vascular segments perfused by plasma but containing no erythrocytes with functioning endothelial cells in the vessel walls. This may mean that an early factor in some retinal vascular pathologies is tissue hypoxia caused by reduced erythrocyte perfusion.

Fluorescein angiographic findings in three patients with long-term intravitreal liquid silicone

The long-term retinal effects of intravitreal liquid silicone (ILS) remain controversial. In this study fundus fluorescein angiographic findings in three patients with long-term ILS are presented. Sluggish or absent blood flow was observed in retinal arterioles that lay in close proximity to the ILS, and the arterioles themselves appeared narrowed. It is suggested that ILS may have a long-term effect on the retinal vasculature, owing either to direct vascular damage, secondary to damage to the neuroretina, or to the ILS preventing diffusion of oxygen into the vitreous cavity.

Retinal detachment and its relation to cataract surgery

In Western Australia during the period 1 January 1976 to 31 December 1987 1089 eyes of 1044 patients in hospital were operated upon for primary rhegmatogenous retinal detachment due to causes other than penetrating trauma. Of these eyes 295 (27%) were aphakic or pseudophakic. During this period the annual number of cataract operations in the State increased by a factor of 245%, while aphakic and pseudophakic retinal detachment operations rose by only 55%. The declining risk of retinal detachment following cataract surgery is attributed to improvements in microsurgical techniques. In 1983 and 1984 the incidence of aphakic and pseudophakic retinal detachments dropped significantly (p less than 0.05). At about this time extracapsular cataract surgery became widespread in the State, and this may explain the observed fall in retinal detachment operations. Since 1984 the incidence has risen owing to the rapidly increasing prevalence of pseudophakia in the resident population.

Chemical investigations of ultraviolet-absorbing hydrogel material for soft intraocular lenses

A poly(2-hydroxyethyl methacrylate) hydrogel material exhibiting ultraviolet-absorbing properties was synthesized by simultaneous polymerization, crosslinking, and covalent bonding of an available polymerizable absorber. The two-stage leaching experiments carried out by aqueous extraction and the analysis of the concentrated extracts by high resolution capillary gas chromatography showed very low levels of additive released through leaching action. This proves that the ultraviolet absorbers can be successfully incorporated by covalent bonding in soft hydrogel intraocular lenses.

Subretinal new vessel recurrence in age-related macular degeneration

Laser photocoagulation with argon or krypton is currently used to treat selected patients with age-related macular degeneration and sudden visual loss from subretinal new vessel formation. In 102 consecutive cases, treated over two years, closure of the vessels was achieved without additional major visual loss in 79% when assessed at two months. Early failure occurred in 21% and was due either to selection of cases with central location or failure to close the new vessel. Later failures due to recurrent subretinal new vessel formation or progression of other macular degenerative changes has occurred in a further 28% so far. Although controlled clinical trials show a significant benefit of treatment, the overall impact of these few successes on the population with macular degeneration is small. Further understanding of the mechanism of subretinal new vessel formation is urgently required. Areas under investigation include the response of injured retinal pigment epithelium, choroid and retina and cellular production of facilitatory factors including proteases and fibronectin.

Pharmacokinetics of intravitreal injection. Assessment of a gentamicin model by ocular dialysis

Intravitreal drug administration is the treatment of choice for bacterial endophtalmitis, but improved knowledge of vitreal pharmacokinetics is essential for the development of optimal antibiotic regimes. We used our recently developed sampling device to estimate vitreal gentamicin concentrations for up to 30 hr after an intravitreal bolus injection of gentamicin. The device is based on the principle of dialysis, whereby a constant flow rate of dialysate through a loop of dialysis fiber in the vitreous attains a gentamicin concentration proportional to the intravitreal gentamicin level around the fiber. The dialysate is continuously recovered and the collected samples then assayed for gentamicin. Normal cat eyes and those with induced bacterial endophthalmitis formed the two groups tested. Concentration-time data fitted well to an open single compartment pharmacokinetic model that incorporated the processes of transfer of drug from the injection site to the sampling site (a function of diffusion within the vitreous), and the elimination from the sampling site (a function of elimination from the vitreous). The initial phase of transfer between the injection and sampling site was rapid and rates were comparable in the two groups. Elimination rate constants were uniformly greater in infected eyes than in controls (0.107 hr-1 compared to 0.055 hr-1). Aqueous humor gentamicin concentrations in control eyes varied between 3 and 6 times those found in fellow infected eyes at the end of each experiment. Accelerated elimination of gentamicin from the vitreous body of eyes with endophthalmitis may be explained by increased permeability of the blood-retinal barrier.

A new method for continuous intraocular drug delivery

A novel device for the continuous intraocular delivery of drugs is described. The active intraocular component of the device is made from hollow haemodialysis fibres. During operation, the drug to be administered diffuses from a small extraocular reservoir to the intraocular fibres, where it passes through the semipermeable walls and into the vitreous body. The delivery of gentamicin by the device into the vitreous body of the cat is compared with direct intraocular injection techniques. Characteristics of the process of drug delivery were influenced by the geometry and design of the device. A reservoir concentration of 10 g/L gentamicin sulphate in a device with four fibres, each 5 mm long, resulted in stable vitreal gentamicin levels of 104 to 128 mg/L at 10 hours. Intravitreal injection of 0.1 ml of a 10 g/L solution of gentamicin caused localised peaks of intravitreal gentamicin concentration in the range 1180 to 3296 mg/L, before falling to 356 to 665 mg/L at 10 hours. The device provides the opportunity of a more controlled and continuous drug delivery, thus avoiding the high localised concentrations that may occur with direct injection techniques in which the required dose is delivered as a bolus. Refinement of a device of this type may result in a clinically useful method of intraocular drug delivery for drugs which present a risk of localised retinal toxicity or require repetitive administration with conventional intraocular injection techniques.

Ridley intraocular lens revisited: chemical analysis of residuals in the original lens material

Two original Ridley intraocular lenses, made of poly(methyl methacrylate) (PMMA) at least 35 years ago, were extracted in two different media, diethyl ether and water. The extracts were suitably processed and analyzed by high resolution capillary gas chromatography. Residual monomer (MMA) was detected in both extracts. The amount of MMA in the aqueous extract was significantly lower than that in the ether extract. It is postulated that the residual monomer in lenses originated from an incomplete polymerization at the time of the polymer production. However, the MMA content found in one lens (0.147%) is comparable to that currently detected in modern IOLs, and probably does not cause toxic reaction in the eye because it is leached out by aqueous fluid action to a very low extent.

Retinal detachment following Nd:YAG capsulotomy

In a retrospective study of 862 patients undergoing Nd:YAG capsulotomy for secondary posterior capsule opacification after extracapsular cataract surgery, the prevalence of retinal detachment was found to be 1.4% with minimum follow-up of six months. Thirty-eight per cent of these detachments occurred within the first two months and 69% occurred within the first six months following capsulotomy. The increase in the prevalence of retinal detachment following Nd:YAG capsulotomy is most likely due to changes in the vitreous which occur when the posterior capsule is no longer intact.

Ocular dialysis. A new technique for in vivo intraocular pharmacokinetic measurements

A new technique, using the principle of dialysis, enables continuous determination of the concentration of compounds within the vitreous humor of the eye. A semipermeable catheter inserted into the cat vitreous cavity was continuously perfused with a normal saline solution. Gentamicin concentration in the dialysate, after subconjunctival or intravitreal injection, was used to calculate gentamicin concentration in the vitreous from the catheter's recovery ratio, as calibrated in vitro. After subconjunctival injection, no gentamicin was detected in the vitreous for up to eight hours. From four to eight hours after intravitreal injection of approximately 100 micrograms of gentamicin sulfate, its vitreal concentration ranged from 30 to 80 mg/L and from nine to 16 hours it fell from 26 to 22 mg/L. This method may prove useful for the study of the pharmacokinetics of many drugs and metabolites in the eye.

A new method for oxygen supply to acute ischemic retina

This paper introduces a new method for supplying oxygen directly to ischemic inner retina, using an oxygen source in the vitreous. Acute retinal vascular occlusion was created in cat eyes by direct pressure on the optic disk and its margins with a glass probe. The satisfactory occlusion of the retinal vessels was documented by direct observation, and functionally by recording the ERG. The vascular occlusion caused a large decrease in the size of the ERG b wave, with no change in the a wave amplitude. The oxygen source was a catheter made of strands of an oxygen-permeable membrane which was inserted into the vitreal cavity. After successful vascular occlusion was documented, 100% gaseous oxygen was perfused through the catheter while recording the ERG. In response to the perfused oxygen the b wave partially recovered. Ventilating the animal with 100% oxygen when the retinal vessels were occluded also caused recovery of the b wave amplitude. Termination of the vitreal oxygen source caused a decrease in b wave amplitude to the level previously observed after the occlusion of the retinal vessels. When the retinal circulation was restored by removal of the glass probe the b wave recovered. The results show that it is possible to supply adequate oxygen to the inner retina via the vitreous to replace the oxygen normally supplied by the retinal circulation. Modification of this method may be useful for the treatment of recent and incomplete retinal vascular occlusion.

The effect of vitreous humour on prostaglandin production by cultured rabbit chorioretinal fibroblasts

Factors in vitreous humour which regulate prostaglandin production were investigated using cultured rabbit chorioretinal fibroblasts. These cells produced predominantly prostaglandin E2, 6-ketoprostaglandin F1 alpha, a compound likely to be a metabolite of prostaglandin E2 and 5-hydroxyeicosatetraenoic acid. The synthesis of 6-ketoprostaglandin F1 alpha was nearly completely inhibited by the cyclooxygenase inhibitor aspirin and partially inhibited by 10(-6) M dexamethasone (49%) and 10(-5) M forskolin (68%). Addition of 10% rabbit vitreous humour to subconfluent cells maintained in Dulbecco's modified Eagle's medium plus 1% fetal bovine serum resulted in stimulation of 6-ketoprostaglandin F1 alpha production by as much as 246% as measured by radioimmunoassay. Chorioretinal fibroblasts labelled by [3H]arachidonic acid incorporation into cellular phospholipids synthesised greater amounts of all labelled arachidonic acid metabolites in response to vitreous humour. It was concluded, therefore, that there are factors present in vitreous humour of molecular weight above 10 kDa which are capable of stimulating cellular cyclooxygenase activity. Confluent cells also responded to a factor(s) present in vitreous humour. The fraction of less than 10 kDa inhibited 6-ketoprostaglandin F1 alpha production by 50% when used at a concentration of 10%. Furthermore, 6-ketoprostaglandin F1 alpha production in confluent cells (but not subconfluent cells) was inhibited to 40% of control levels by vitamin C at a concentration of 1 mg/100 ml. The latter result points to an inhibitory role for vitamin C in vitreous humour. We conclude, therefore, that vitreous humour contains factors important for the regulation of prostaglandin metabolism in the eye.

Prevalence of diabetic complications in relation to risk factors

The prevalence of diabetic complications is reported from a cross-sectional study of rural diabetic subjects in Western Australia. Logistic-regression analysis has been used to discover potential risk factors associated with each complication. A distinction has been made between time-related variables (age, age at diagnosis, duration of diabetes) and other risk variables. We have attempted to identify the major time-related risk variables for each complication and then examined the effect of other risk variables after accounting for the major time-related variables. The important time-related variables were found to be duration of diabetes for retinopathy, age for macrovascular disease, duration and age at diagnosis of diabetes for sensory neuropathy, and age for renal impairment. When matched on these important time-related variables, the overall prevalences of complications for insulin-dependent (IDDM) compared with non-insulin-dependent (NIDDM) diabetic patients were essentially the same. An exception is renal impairment, for which IDDM patients had a higher prevalence than did NIDDM patients of the same age. After allowing for time-related variables, the analysis also demonstrates positive independent associations between diabetic control (glycosylated hemoglobin) and retinopathy and between diabetic control and macrovascular disease. Plasma cholesterol (positively) and high-density lipoprotein cholesterol (negatively) were related independently to both macrovascular disease and renal impairment. Very few differences in the risk-factor profiles for complications were found for IDDM compared with NIDDM patients after allowing for time-related variables.

Clinical results of hydrogel lens implantation

Polymethylmethacrylate has proven to be a useful intraocular lens (IOL) implant material and remains the most widely used material for the fabrication of IOLs. Complications, however, from IOL implantation still occur. A hydrogel lens has been designed for posterior chamber placement. A clinical study from August 1983 to June 1985 was undertaken to determine the safety and efficacy of this new lens manufactured from 38% poly HEMA. The noninflammatory postoperative complications were limited to lens decentration and opacification of the lens capsule. Three cases of posterior capsule opacification required YAG laser capsulotomy. Laser capsulotomy is feasible and the lens appeared to be more resistant to damage from the YAG laser than polymethylmethacrylate lenses. In general, the material appeared to be well tolerated and there have been no cases of persistent iritis or clinically detectable cystoid macular edema. If the visual acuity outcome by age decade for all patients irrespective of follow-up time is considered, 92% of patients achieved 20/40 or better corrected visual acuity.

Trachoma: 1985 update in Western Australia

Aboriginal preschool and school children were surveyed in the Eastern Goldfields Region and the Eastern Kimberley Region of Western Australia between 1979 and 1985. Statistics from these surveys show that there has been an apparent change in pattern of follicular trachoma since the National Trachoma and Eye Health Programme in some of the communities. The prevalence of follicular trachoma in the 0 to 9 year old age groups had declined from 26.4% in 1977 to 8.8% in 1984/1985 in the Eastern Goldfields and Red Centre combined (0.10 greater than p greater than 0.05). The prevalence reduction occurred in areas where there have been improvements in school hygiene and housing. The prevalence of cicatricial trachoma has also apparently declined from 65% in 1977 to 39% in 1985 in the Red Centre, from 39% in 1977 in the Eastern Goldfields to 21.7% in 1985, and from 58% in 1977 to 24.9% in 1985 in the Eastern Kimberley, Communities at risk were identified and recommendations made for frequency of continued screening, depending on age, distribution and location.

Mass screening of the optic disc for glaucoma: a follow-up study

Because of the high false positive and negative rates for detection of suspects when screening for glaucoma by tonometry, we screened 12 156 subjects over the age of 40 years or with a stated family history of glaucoma by examining the optic discs. This was followed by Schiotz tonometry. Eight hundred and twelve (6.7%) suspects were referred to their primary physician for investigation by an ophthalmologists. A database program was used to send out follow-up letters to both suspects and ophthalmologists. Three hundred and seventy-nine replies were received from ophthalmologists: 100 (26.4%) of these suspects had ocular hypertension and 68 (17.9%) had glaucoma. Of these 68, 60 (15.8%) had chronic simple glaucoma, five (1.3%) had secondary open-angle glaucoma, and three (0.79%) had primary closed-angle glaucoma. The prevalence of all types of glaucoma in this group for which follow-up was obtained was at least 0.56% of the total number screened. Assuming that the prevalence was similar for the group for whom no replies were obtained, the prevalence of glaucoma in this population is approximately 1.19%. Screening by optic disc examination is therefore likely to detect most cases of glaucoma.

Vitreous haemorrhage after cataract extraction

One hundred eyes undergoing intracapsular cataract extraction and 100 undergoing extracapsular extraction were examined prospectively within one week postoperatively and again at 6-10 weeks postoperatively. Indirect ophthalmoscopy showed vitreous haemorrhage in 36% of the intracapsular group and 13% of the extracapsular group. Vitreous haemorrhage was significantly related to the occurrence of operative hyphaema (p less than 0.01) but not to iridectomy (p greater than 0.05). In the intracapsular group the use of chymotrypsin significantly reduced the incidence of vitreous haemorrhage (p less than 0.01). Three different types of vitreous haemorrhage were identified--streaks, diffuse haze, and beads in the vitreous base. Wound haemorrhage and operative hyphaema account for most cases, but it is suggested that zonular traction may be responsible for the bead haemorrhages and also for the retinal haemorrhages reported by other authors. Although no difference in visual result or incidence of cystoid macular oedema was observed in this study, a relationship to the vitreoretinal pathology of aphakia is suggested.

Taxol for the treatment of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) results in retinal detachment and visual impairment due to fibroblastic proliferation in the vitreous and subsequent cellular contraction. The authors have used an in vitro model for PVR to evaluate the action of the antineoplastic drug, taxol, on chorioretinal fibroblast proliferation and contractility. Dose response curves obtained show taxol to be a potent inhibitor of both cellular events. Fifty percent inhibition of contraction and proliferation occurred at 2 X 10(-8)M and 3 X 10(-9)M, respectively. On the basis of this pharmacodynamic data, three dosage regimes were chosen to evaluate possible prevention of PVR in an animal model based on the intravitreal injection of cultured fibroblasts. These animals trials show that a single intravitreal dose of either 35 micrograms or 0.5 microgram taxol significantly reduces incidence and extent of PVR. The average grade of vitreoretinal traction at 28 days for 35 micrograms taxol and 250,000 cells was 0.4 (control 1.8); for 35 micrograms taxol and 700,000 cells, 1.0 (control 2.2); and for 0.5 microgram taxol and 250,000 cells, 1.0 (control 2.3). Delayed optic nerve damage was noted with the highest dose used, but a good therapeutic margin may exist. Long-term clinical histopathologic and electrophysiologic studies will be required. The authors conclude from these preliminary studies that taxol holds definite promise for the relief of traction retinal detachment and PVR.

Models for assessing scar tissue inhibitors

The main purpose of animal models for proliferative vitreoretinopathy (PVR) is to develop pharmacologic therapies for this common cause of blindness. A very large number of pharmacologic agents appear to have potential use in this application by preventing cell proliferation and/or contraction. In practice, however, it has been found that prohibitively extensive numbers of animals and laboratory services are required to establish drug efficacy, safety, and dosage regimes. To lessen this work load and to accelerate drug screening programs, the authors have developed an in vitro model for PVR based on chorioretinal fibroblast growth in three-dimensional collagen lattices. This model yields precise data on the effect of drugs on cell proliferation and contractility. Trifluoperazine, colchicine, 5-fluorouracil, dexamethasone, and penicillamine were screened in this model. The first three agents were found to be inhibitory; on the basis of the pharmaco kinetic data, obtained dosage regimes for animal testing were developed. The results obtained are discussed in terms of the in vitro model and the biochemical action of these drugs on the cellular events in PVR. In vitro screening of drugs prior to animal testing offers a significant advance in the quest for a pharmacologic prevention of blindness due to PVR.

Diabetes in part-aborigines of Western Australia

One thousand, two hundred and eighteen diabetic subjects living in and around country towns of Western Australia were screened for complications of diabetes. This population included 134 subjects of Aboriginal descent, who were compared with the Caucasoids taking part. In the Aboriginal group there was a greater proportion of Type 2 (non-insulin-dependent) diabetic patients, a relative female preponderance (69% compared with 51%) and a tendency to present at an earlier age of onset than their Caucasoid counterparts. Diabetic complications were at least as common in the Aboriginal group as in the Caucasoid patients. Indeed, retinopathy within 10 years of onset of diabetes was more common in the Aborigines. Peripheral neuropathy was more prevalent in Aborigines treated by diet alone or oral hypoglycaemic agents than in Caucasoids. A much greater prevalence of proteinuria was an additional feature of the Aboriginal subgroup (29% versus 4%).

Models for assessing scar tissue inhibitors

The main purpose of animal models for proliferative vitreoretinopathy (PVR) is to develop pharmacologic therapies for this common cause of blindness. A very large number of pharmacologic agents appear to have potential use in this application by preventing cell proliferation and/or contraction. In practice, however, it has been found that prohibitively extensive numbers of animals and laboratory services are required to establish drug efficacy, safety, and dosage regimes. To lessen this work load and to accelerate drug screening programs, the authors have developed an in vitro model for PVR based on chorioretinal fibroblast growth in three-dimensional collagen lattices. This model yields precise data on the effect of drugs on cell proliferation and contractility. Trifluoperazine, colchicine, 5-fluorouracil, dexamethasone, and penicillamine were screened in this model. The first three agents were found to be inhibitory; on the basis of the pharmacokinetic data, obtained dosage regimes for animal testing were developed. The results obtained are discussed in terms of the in vitro model and the biochemical action of these drugs on the cellular events in PVR. In vitro screening of drugs prior to animal testing offers a significant advance in the quest for a pharmacologic prevention of blindness due to PVR.

Effect of cyclic AMP on cellular contractility and DNA synthesis in chorioretinal fibroblasts maintained in collagen matrices

Dibutyryl cyclic AMP (db-cAMP), theophylline and forskolin were found to be potent inhibitors of DNA synthesis and cell contractility in chorioretinal fibroblasts maintained in 3-dimensional collagen matrices. Dose-response curves were constructed for the inhibitory action of these agents on both cellular parameters and their interrelationship examined by regression analysis. The results obtained indicate that these parameters were equally inhibited by cAMP with the exception of high concentrations of db-cAMP (greater than 10(-3) M) where a greater effect on DNA synthesis than cell contractility was observed which was attributed to additional inhibition of DNA synthesis by db-cAMP degradation products. It is proposed from the present results and those of other investigators that cAMP regulates non-transformed fibroblast proliferation and contraction through a common regulatory mechanism possibly involving cAMP-dependent protein kinases and calcium ions.

Clinical macrovascular disease in Caucasoid diabetic subjects: logistic regression analysis of risk variables

A cross-sectional study of 1084 Caucasoid diabetic subjects in rural Western Australia revealed a high rate of clinical macrovascular disease (46%), including coronary heart disease (13%), stroke (8%), and peripheral vascular disease (38%). Age was the major time-related variable for total macrovascular disease and for peripheral vascular disease, with identical prevalence rates in Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes when age was taken into account. In 179 Type 1 diabetic subjects, logistic regression analysis showed no associated risk factors other than age. In 905 Type 2 diabetic subjects the independent risk factors for total macrovascular disease, identified by a forward step-wise selection procedure, were age as the major contributor, with plasma creatinine levels and plasma glucose levels (all p less than 0.001), high-density lipoprotein cholesterol levels, serum total cholesterol levels, and the (supine-erect) systolic blood pressure difference (all p less than 0.05). There were no direct associations with percentage desirable weight, cigarette smoking or male sex. Type 2 diabetic subjects demonstrated a very strong negative association between high-density lipoprotein cholesterol levels and coronary heart disease, and significant associations were found also between plasma glucose levels and coronary heart disease (p less than 0.01), and glycosylated haemoglobin levels and peripheral vascular disease (p less than 0.001).

Catecholamines in aqueous humour of glaucoma patients

Aqueous humour catecholamine concentrations were assayed in open angle glaucoma, and cataract patients during surgery, under general anaesthesia. Plasma catecholamines were measured at the same time. Aqueous humour noradrenaline is apparently reduced by pretreatment with adrenaline, timolol and pilocarpine. (Noradrenaline concentrations were 0.599 +/- 0.239 ng/ml in glaucoma, and 0.970 +/- 0.445 ng/ml in cataract patients.) Dopamine was found in two of six cataract patients (0.123 and 0.318 ng/ml), and in all the glaucoma group (0.221 +/- 0.170 ng/ml). Plasma noradrenaline concentration was probably increased in glaucoma, when compared to the cataract patients. These results confirm our findings in the non-human primate, and suggest that adrenaline may act, at least in part, by causing denervation or inhibition of noradrenaline release in the anterior segment of the eye, and probably by release of dopamine into the aqueous humour. The unexplained and new finding of dopamine in the aqueous humour may have some bearing on the action of dopaminergic drugs for the treatment of glaucoma. Future treatment of ocular hypertension may rely more on sympathetic denervation than on conventional adrenergic therapy.

Corneal endothelial loss with new intraocular lenses

When we compared the effect of a hydrogel intraocular lens on the corneal endothelium of rabbits to the damage produced by uncoated methylmethacrylate intraocular lenses and methylmethacrylate lenses coated with sodium hyaluronate or methylcellulose, we found that the endothelial damage produced by the hydrogel lenses in a standard 0.25 mm2 of contact was 3.6%. This value was not significantly different from that for the control corneas (0.4%). Uncoated methylmethacrylate lenses caused 62% endothelial loss but coating them with sodium hyaluronate or methylcellulose reduced the loss to 27% and 57% respectively. The results suggested that a hydrogel intraocular lens produces minimal endothelial damage and that coating a methylmethacrylate lens with sodium hyaluronate or methylcellulose does not provide reliable endothelial protection.

Aqueous humor catecholamines

The catecholamines norepinephrine, (NE) epinephrine (E) and dopamine (DA) were detected for the first time in the aqueous humor of humans under general anesthesia and monkeys under ketamine. The catecholamine levels in aqueous humor of 9 humans were assayed. NE was 0.796 +/- 0.457 ng./ml., E ranged between 0 and 0.132 ng./ml. in 4 out of 9 subjects, and DA was found in 2 of the 9 eyes. (0. 123ng ./ml. and 0. 318ng ./ml..) Plasma levels were measured in 8 of the human subjects at the time of aqueous sampling -NE was 0.311 +/- 0.171, E ranged between 0 and 0.097 (4 out of 8 subjects) and DA was detected in one subject- 0.037 ng./ml.. Monkey aqueous levels were NE:2.843 +/- 0.668 and DA:0.462 +/- 0.177 ng./ml., with an intact iris. (N = 8 eyes.) NE was 0.497 +/- 0.049, and DA 0.426 +/- 0.218 ng./ml. after total iridectomy. (N = 4 eyes) E was not detected in the monkey under these conditions. Whilst NE may be produced in part by the iris, DA levels were not affected by iridectomy. This implies that DA may be produced by structures unrelated to sympathetic nerve endings of the iris in the anterior segment of the non-human primate eye, perhaps by diffusion from the ciliary body or retina. Ketamine is known to inhibit catecholamine uptake, which may explain the high levels measured in the monkey. Human aqueous catecholamine levels measured under anesthesia may be affected by a variety of the drugs used. It is postulated that dopaminergic neurones and associated receptors may be present in the anterior segment of the eye. This may explain the presence of aqueous humor dopamine and the effects of dopaminergic drugs on intraocular pressure.

Assessing the risk of diabetic retinopathy

We used multiple logistic regression to analyze cross-sectional data on 1,006 patients with diabetes mellitus who were examined in a rural diabetic screening program. The factors found to have independent and significant associations with the presence of retinopathy were duration of diabetes, albuminuria, serum creatinine, glycosylated hemoglobin, and plasma glucose levels, blood pressure, and percentage of desirable weight. By comparing the contribution of each significant factor to the deviance from the regression models, we estimated the relative importance of each. Duration of diabetes was by far the most important predictive factor. The logistic model provided a good fit to the observed prevalence rates in various risk groups but was less satisfactory for predicting the presence or absence of retinopathy in individual patients. The discovery of presently unknown risk factors may improve this situation.

Draining pus from the cornea

Thirteen patients with varying grades of suppurative keratitis were studied with regard to their response to keratoplasty. In all patients there was a rapid improvement in symptoms and signs. In eight of the 13 there was restoration at least of previous function: one patient lost all vision due to secondary closed-angle glaucoma, because he refused further surgery. Corneal graft opacification occurred in three eyes; one other became partially opaque; whilst in a fourth, the lamellar graft remained clear while the original autograft failed. At last follow-up, all eyes were normotensive and free of symptoms. Keratoplasty should assume an important part of the management of suppurative keratitis, from both theoretical and practical considerations.

Progress in continual eye pressure monitoring

Observations of intraocular pressure (IOP) variations in response to CO2, adrenaline, speech and compression of the neck veins were documented by continual monitoring of IOP by radiotelemetry. Carbon dioxide increased IOP in the supine, but not in the erect, conscious subject. Adrenaline 2% caused a rapid short-lived painful increase in IOP, followed by a profound decrease. This was due to an increase in facility of outflow and was associated with paralysis of the sympathetic supply to the iris. Speech caused a small rise in IOP which was reversed by rest in silence. Compression of the neck veins caused a variable increase in IOP. These physiological variations in IOP may contribute to the errors of tonometry.