Clinical presentation, risk factors and treatment outcomes of first allograft rejection after penetrating keratoplasty in early and late postoperative period.

PURPOSE: Corneal graft rejection is the most common reason for the failure of an allograft corneal transplant. We undertook this study to identify and compare risk factors and treatment outcomes for early and late corneal graft rejections after optical penetrating keratoplasty. METHODS: A retrospective case file analysis of 880 primary penetrating keratoplasties was performed at a tertiary ophthalmic care centre. Patients were divided into early rejectors (rejection episode within 6 months postoperatively) and late rejectors (rejection episode after 6 months postoperatively). Main parameters evaluated were demographics, preoperative diagnosis and clinical signs, donor tissue details, surgical technique, details of rejection episode, treatment, and outcome information. RESULTS: A total of 156 patients with rejection episodes were identified. Of these, 42 (26.9%) patients experienced early rejection episodes and 114 (73.1%) patients experienced late rejection episodes. Preoperative donor and recipient characteristics, surgical technique, and clinical presentation of graft rejection were found to be similar between both groups after a Bonferroni correction was applied (P>0.005). Treatment outcomes of graft rejections were not significantly different (P=0.46) between early and late rejectors, with 83% of patients responding to rejection treatment (80% early rejectors; 85% late rejectors). CONCLUSION: Patients with early and late graft rejection have similar characteristics and both groups respond to treatment equally.

Insulin receptor and insulin receptor substrate-I in rat retinae.

Insulin receptor substrate-I (IRS-I) is a major cytosolic substrate of the insulin receptor Expression of insulin receptor and IRS-I, and the distribution of these components of the insulin-signalling pathway, were investigated in rat retinae. Insulin receptor and IRS-I were located in retinal sections with anti-insulin receptor and anti-IRS-I antibodies. Reverse transcription-polymerase chain reaction (RT-PCR) of retinal mRNA was performed with primers specific for insulin receptor and IRS-I gene sequences. Immunohistochemistry demonstrated distinct but closely associated staining patterns for insulin receptor and IRS-I throughout rat retinae. The RT-PCR product from rat retinal insulin receptor mRNA corresponded to the high affinity insulin receptor isoform. The RT-PCR product for retinal IRS-I mRNA agreed with that predicted from the gene sequence. The expression of IRS- I and insulin receptors indicates a signalling mechanism by which insulin can influence retinal metabolism or function.

The effects of insulin on the electroretinogram of bovine retina in vitro.

PURPOSE: This study investigates the role of insulin in retinal function by examining the effects of insulin on the a- and b-waves of the electroretinogram (ERG) recorded from an in vitro bovine retina eye-cup preparation. METHODS: Bovine eyes were enucleated immediately after exsanguination, hemisected to form an eye cup, and transported to the laboratory in oxygenated medium. Eye cups were then transferred to a perfusion system that provided constant superfusion of oxygenated perfusate solution to the retina, enabling it to remain in a functional state in vitro. The ERG was recorded, as the retinal response to photic stimulation, from electrodes mounted within the perfusion system. The effects of insulin on the ERG were investigated by adding insulin to the perfusate solution. RESULTS: Application of insulin to the in vitro retina preparation decreased the amplitudes of the a- and b-waves of the ERG in a dose dependent manner with a maximal effect at doses of 0.1 U/ml and above. These effects were reversible. CONCLUSION: The reduction of ERG amplitudes may result from the hyperpolarising effect of insulin reported in other tissues. The findings suggest that insulin may have a regulatory role in retinal activity; however extrapolation of these results to the intact organism is dependent on the presence of insulin in retina.

Long chain polyunsaturated fatty acids and visual function in preterm infants.

Electroretinograms (ERG) were recorded at 40 weeks post-conceptual age (PCA) in 18 infants born prematurely (25-32 weeks gestation). Fatty acid composition of plasma and red cell phospholipids was measured within 4 days of birth and at time of ERG testing, and detailed record was kept of dietary intake. Correlations were seen between percentage intake of breast milk and docosahexaenoic acid (DHA) in both plasma (r = 0.818, P < 0.0001) and red cells (r = 0.534, P = 0.035) and significant differences in fatty acid profiles were seen between infants receiving > 50% and < 50% breast milk. No difference was seen in retinal sensitivity between infants receiving > 50% or < 50% breast milk. A positive correlation was seen between scotopic (rod) b-wave implicit time on ERG and DHA in both plasma (r = 0.733, P = 0.001) and red cells (r = 0.502, P = 0.04). A positive correlation was seen between arachidonic acid and rod ERG amplitude (r = 0.565, P = 0.022) which may reflect the higher AA/DHA ratio in the developing retina. These data did not support our hypothesis that increased dietary DHA results in enhanced retinal maturation. Visual acuity measured at 40 weeks PCA and again 3 months later was similar between groups. While subtle relationships were demonstrated between long chain polyunsaturated fatty acids and visual function, all infants were felt to be within age-appropriate normal range at expected date of delivery and at 3 months corrected age.

Photodynamic therapy: a 5-year study of its effectiveness in the treatment of posterior uveal melanoma, and evaluation of haematoporphyrin uptake and photocytotoxicity of melanoma cells in tissue culture.

A human melanoma cell line RVH-421 which selectively demonstrates melanin synthesis when cultured in L15 Leibowitz medium but not in RPMI medium was used as a model to examine haematoporphyrin derivative (HPD) uptake and the photocytotoxicity of photodynamic therapy (PDT). Confocal scanning microscopy and extraction fluorometry showed HPD uptake in both non-pigmented and pigmented melanoma cells. Phototoxicity was determined by incubating pigmented and non-pigmented monolayer cells with HPD, exposing them to variable periods of white fluorescent light and calculating the number of viable cells in the samples relative to the controls. Both the non-pigmented and pigmented melanoma cells were affected by light-dependent cytotoxicity which was greater in the non-pigmented cells. Melanin or other substances may reduce the photo-oxidative effects of PDT. Posterior uveal melanomas in 36 patients were treated with PDT with the longest duration of tumour control being 6.5 years. Kaplan-Meier survival analysis showed that 76% of melanomas were not growing at the end of the first year, declining to 62% at the end of the second year, with 38% showing no signs of growth at the end of the fifth year. No eyes were lost as a result of PDT. Cox's hazards analysis showed that the degree of tumour pigmentation and patient age at therapy significantly influence the tumour response to PDT.

Phototherapy of posterior uveal melanomas.

The results of phototherapy on a small series of 19 patients with uveal melanomas are presented. Laser radiation at a wavelength of 620 to 630 nm was used in conjunction with a 5 to 7.5 mg/kg dose of haematoporphyrin derivative administered 24 hours before treatment, with total doses/treatment averaging 960 J/cm2. Eleven patients received two treatments, and one received a third. The longest duration of tumour control to 30 September 1990 was 31 months. Of the 19 patients treated six had complete regression of the tumour, while another five had minor to significant regression. A strong correlation between degree of regression and degree of tumour pigmentation was found, the lighter tumours responding much better than darker tumours. There were also strong indications that if a tumour did not respond to the initial phototherapy it was very unlikely that subsequent phototherapy would provide any further benefit.

Volume measurement of intraocular tumours by cross-sectional ultrasonographic scans.

The volume of intraocular tumours can be calculated from tumour height and cross-sectional areas measured in maximal orthogonal B-mode ultrasonograms, on the assumption that the tumour morphology is hemi-ellipsoidal. Comparison of this method with an accurate but more complex computer-aided B-mode ultrasonic tomographic method demonstrated a highly linear relationship with a correlation coefficient of 0.93. Furthermore, the comparison of cross-sectional areas measured from B-scan images and histological cross-sections in a small series of enucleated eyes demonstrated that tumour cross-sectional area measured from ultrasound images provides an accurate representation of the true physical size of the tumour in the globe. This method can be easily implemented with readily available B-mode ultrasound equipment. Unlike previously reported volume measurement methods, customised hardware or software is not required. The method is rapid and easy to perform, and may offer a useful standard method of measuring and monitoring intraocular tumours.

Computer-assisted analysis of the electro-oculogram.

A method of acquiring and analysing electro-oculogram signals was developed using computer-aided techniques. The repetitive nature, characteristic shape and spectral properties of the electro-oculogram are used in the automated analysis, enabling the retinal resting potential to be investigated. Online computer-aided automatic analysis of the electro-oculogram is efficient, reliable and accurate. Automated analysis produced results that have a highly significant degree of correlation (P less than 0.001) with the results obtained manually from strip chart recording of the electro-oculogram signals. The increased accuracy of the automatic analysis system demonstrates a significantly reduced (McNemar's Test) false positive rate in classifying abnormal results on the basis of Arden ratio. The computer-aided analysis system offers a useful clinical means of measuring the electro-oculogram for diagnostic and research purposes.

Measurement of choroidal melanomas: a comparison of methods.

The prognosis for death from metastatic choroidal melanoma following enucleation has been shown to be strongly correlated with a number of risk factors of which the most important are age of onset, aggressive cell types and tumour volume. The advantages of enucleation for the treatment of choroidal melanomas are put into question by the singular lack of a parallel increase in life expectancy following this treatment, and evidence that it may promote the development of metastatic disease. Alternative forms of treatment have been introduced including observation of small and asymptomatic tumours. We are using a computer-aided system for serial measurement and statistical analysis of area and volume of choroidal melanomas. A comparison of results using our method and the conventional method of estimating volume by the product of basal area and height for 51 measurements on 15 eyes over a 6-month period showed an overestimation of volume by conventional methods which could be corrected by applying a "shape constant" determined by linear regression. Calculation of tumour growth rates is also shape-dependent, and a slowing in growth rate or even a reduction in melanoma size is possible.

Computer-aided area measurement of ocular images.

Using a combination of computer-aided measurement techniques and fundus camera images, the area of regions of interest on the fundus can be measured. If these area measurements are corrected for the magnification effects of the patient's visual system, and the fundus camera optics, an estimate of the true anatomical size of the measured object can be determined in physical units. While the results of measuring models indicate a maximum error of 6% for the system, the results of clinical trials demonstrate an average error of 10% for well-defined areas of interest, with increasing error of up to 30% for poorly defined areas of interest.

Computer-aided volume measurement of choroidal melanomas.

Using a combination of conventional B-scan ultrasonography, standard video techniques, computer image digitization and area analysis, it is possible to measure the volume of choroidal melanomas by area calculation of successive ultrasound image slices, allowing the monitoring of such tumors. The design of a combined water-bath and linear tracking B-scan transducer is presented, together with a description of the instrumentation and computer software required. The results of volume measurements performed upon eye models demonstrated that melanomas of volume greater than 100 mm3 could be measured with an average error of 6%. The problems associated with linear calibration of the system from scan-head to analysed image, resolution of the digitised image, reproducibility of the measurements, sources of error and assumptions made in formulating the measurement procedure are discussed.

Video and digital fluorescein angiography.

A video recording system, which provides real-time imaging and instant reporting of retinal fluorescein angiograms, with improved patient comfort, is described. Digital image-processing methods can be applied to video angiograms to improve image quality, quantitate retinal blood flow, measure areas, improve storage and access, and send images via phone lines or other electronic communication channels. Video image quality is somewhat inferior to conventional photographic techniques, but is more than adequate for diagnostic interpretation.

Abnormal fibrinolysis in retinal vein occlusion.

Some cases of central and branch retinal vein occlusion are associated with and may be caused by abnormal fibrinolytic mechanisms. The abnormality we described is that of plasminogen activator enzyme deficiency, which is a treatable condition. That seven cases were seen by one practitioner in a two year period may indicate that this particular condition is under-recognised.

Peripheral vascular disease as a mode of presentation of pseudoxanthoma elasticum.

Two men presenting with premature peripheral vascular disease and minimal risk for atherosclerosis were found to have pseudoxanthoma elasticum (PXE). Fluorescein angiography was found to be of potential value in the early recognition of angioid streaks and pseudoxanthoma elasticum. There was evidence of disruption of arterial elastic tissue which may contribute to atherogenesis in PXE. Management is presently limited largely to minimizing risk factors for atherosclerotic vascular disease.