Sheldon M. Buzney

Receptors and growth-promoting effects of insulin and insulinlike growth factors on cells from bovine retinal capillaries and aorta.

It has been suggested that elevated levels of insulin or insulin-like growth factors (IGFs) play a role in the development of diabetic vascular complications. Previously, we have shown a differential response to insulin between vascular cells from retinal capillaries and large arteries with the former being much more insulin responsive. In the present study, we have characterized the receptors and the growth-promoting effect of insulinlike growth factor I (IGF-I) and multiplication-stimulating activity (MSA, an IGF-II) on endothelial cells and pericytes from calf retinal capillaries and on endothelial and smooth muscle cells from calf aorta. We found single and separate populations of high affinity receptors for IGF-I and MSA with respective affinity constants of 1 X 10(-9) M-1 and 10(-8) M-1 in all four cell types studied. Specific binding of IGF-I was between 7.2 and 7.9% per milligram of protein in endothelial cells and 9.1 and 10.4% in the vascular supporting cells. For 125I-MSA, retinal endothelial cells bound only 1.7-2.5%, whereas the aortic endothelial cells and the vascular supporting cells bound between 5.6 and 8.5% per milligram of protein. The specificity of the receptors for IGF-I and MSA differed, as insulin and MSA was able to compete with 125I-IGF-I for binding to the IGF-I receptors with 0.01-0.1, the potency of unlabeled IGF-I, whereas even 1 X 10(-6) M, insulin did not significantly compete with 125I-MSA for binding to the receptors for MSA. For growth-promoting effects, as measured by the incorporation of [3H]thymidine into DNA, confluent retinal endothelial cells responded to IGF-I and MSA by up to threefold increase in the rate of DNA synthesis, whereas confluent aortic endothelial cells did not respond at all. A similar differential of response to insulin between micro- and macrovascular endothelial cells was reported by us previously. In the retinal endothelium, insulin was more potent than IGF-I and IGF-I was more potent that MSA. In the retinal and aortic supporting cells, no differential response to insulin or the IGFs was observed. In the retinal pericytes, IGF-I, which stimulated significant DNA synthesis beginning at 1 X 10(-9) M, and had a maximal effect at 5 X 10(-8) M, was 10-fold more potent than MSA and equally potent to insulin. In the aortic smooth muscle cells, IGF-I was 10-100 times more potent than insulin or MSA. In the retinal and aortic supporting cells, no differential response to insulin or the IGFs was observed. In the retinal pericytes, IGF-I, which stimulated significant DNA synthesis beginning at 1 X 10(-9) M, and had a maximal effect at 5 X 10(-8) M, was 10-fold more potent than MSA and equally potent to insulin. In the aortic smooth muscle cells, IGF-I was 10-100 times more potent than insulin or MSA. In addition, insulin and IGF-I at 1 X 10(-6) and 1 X 10(-8) M, respectively, stimulated these cells to grow by doubling the number of cells as well. In all responsive tissues, the combination of insulin and IGFs were added together, no further increase in effect was seen. These data showed that vascular cells have insulin and IGF receptors, but have a differential response to these hormones. These differences in biological response between cells from retinal capillaries and large arteries could provide clues to understanding the pathogenesis of diabetic micro- and macroangiopathy.

Differential responsiveness to insulin of endothelial and support cells from micro- and macrovessels.

The pathologies of diabetic micro- and macroangiopathy are different, suggesting that diabetes affects these two types of vascular tissue in a dissimilar manner. We have compared insulin receptors and the effects of insulin on cultured endothelium from calf retinal capillaries and aorta, and the vascular supporting cells, retinal pericytes, and aortic smooth muscle cells. 125I-insulin binds to high affinity insulin receptors on all four cell types. Receptor concentrations were similar except for aortic smooth muscle cells, which have 10-fold fewer receptors than the other cell types. Insulin at a concentration of 10 ng/ml stimulated [14C]glucose incorporation into glycogen in retinal endothelial cells and pericytes and aortic smooth muscle cells, but had no effect on aortic endothelium. Insulin over a concentration range of 10 ng/ml-10 microgram/ml, stimulated [3H]thymidine incorporation into the DNA of retinal pericytes, and endothelial cells and aortic smooth muscle cells but had no effect on aortic endothelial cells. These data suggested that a differential response to insulin may exist between endothelium of micro- and macrovasculature, and suggest that retinal capillary endothelium and retinal pericytes are both very insulin-sensitive tissues.

Laser Photodisruptors: Damage Mechanisms, Instrument Design and Safety

Short-pulse neodymium: YAG clinical laser systems permit noninvasive incision of transparent intraocular structures. Selection and safe use of these photodisruptors, however, require a limited understanding of certain basic physical principles. These principles are reviewed and applied in a series of optical experiments designed to study the performance and safety of clinical, short-pulse laser systems. The results of these experiments are presented, in addition to an analysis of current and proposed photodisruptors.

Image enhancement for the visually impaired: the effects of enhancement on face recognition

Image enhancement has been shown to improve face recognition by visually impaired observers. We conducted three experiments in an effort to refine our understanding of the parameters leading to this effect. In experiment 1 we found that the band of spatial frequencies between 4 and 8 cycles/face is critical for face recognition. In experiment 2 we found that enhancement of these frequencies and the resulting image distortion actually reduced recognition performance for normal observers. Since the degradation of performance by low vision is larger than the effect of distortion, the enhancement that reduces performance for normal observers may still be beneficial for the visually impaired observer. Experiment 3 found that patients tend to prefer images enhanced at frequencies higher than the critical frequencies found in experiment 1. Such individually selected enhancement did not improve recognition in comparison with uniformly applied enhancement. The lack of an enhancement effect may be due to the small variability in enhancement frequencies selected by our subject population.

Retinal Circulatory Changes Related to Retinopathy Progression in Insulin-dependent Diabetes Mellitus

To quantify the vascular deterioration of the diabetic retina, retinal circulatory changes in 45 insulin-dependent diabetic patients, and in 17 normal controls, were measured and divided into four groups according to severity of retinopathy. The noninvasive laser Doppler technique was used to measure the systolic/diastolic variation of red blood cell velocity (V) at sites along temporal retinal arteries. Flow pulsatility [V (systole)/V (diastole)] was 18% lower (P less than 0.00001) in the mild-retinopathy group than in normal controls, but 35% higher (P less than 0.001) in the severe-retinopathy group than in the mild-retinopathy group. Repeated measurements in three eyes during the progression from mild or moderate to severe retinopathy showed progressive increases in both flow pulsatility and mean retinal blood flow. Altered flow pulsatility appears to be a sensitive indicator of vascular alterations during the progression of diabetic retinopathy.

Endophthahiiitis Caused by the Coagulase-negative Staphylococci: I. Disease Spectrum and Outcome

PURPOSE The coagulase-negative staphylococci are the most common causes of postoperative endophthalmitis. This study investigates the variability in the disease spectrum and visual outcome of coagulase-negative staphylococcal endophthalmitis in a large, single-center series. METHODS Ninety consecutive cases of coagulase-negative staphylococcal endophthalmitis were investigated retrospectively from two time periods, 1978 to 1982 and 1985 to 1987, separated by a transitional period in cataract surgery technique. Using a detailed protocol, inpatient, outpatient, and microbiologic records were analyzed. Six-month visual acuity results were obtained. RESULTS Diagnosis frequently was delayed, often suspected only after hypopyon development. Thirty-seven percent of patients presented more than 1 week after the inoculating event, and 13% presented after more than 1 month. Variable asymptomatic intervals and gradually worsening inflammatory prodromes are noted. Painless endophthalmitis occurred in 16%. Non-epidermidis infections comprised 28%. With vitrectomy/intraocular antibiotic management, 38% and 68% achieved visual acuities of 20/50 and 20/400, respectively. Overall, 10% of patients developed late retinal detachments. This occurred in only 4% of patients, with endophthalmitis occurring after cataract surgery. CONCLUSION Ophthalmologists should become familiar with the emerging concepts of delayed-onset, chronic, and often painless endophthalmitis in which the coagulase-negative staphylococci play a prominent role.

Retinal capillaries: proliferation of mural cells in vitro

Capillaries from bovine, monkey, and human retinas maintained in tissue culture produced a monolayer of cells. Autoradiographic and electron microscopic evidence indicated that the mural cells (intramural pericytes) were the cells that proliferated. Since intramural pericytes are damaged selectively in diabetes mellitus, their availability in culture will be useful in seeking means to control diabetic retinopathy.

Endophthalmitis Caused by the Coagulase-negative Staphylococci: 2. Factors Influencing Presentation after Cataract Surgery

PURPOSE This study, comprising 60 patients with coagulase-negative staphylococcal endophthalmitis which occurred after cataract surgery, was designed to define the variation in disease presentation and visual outcome and to evaluate statistically the role of the primary surgery and its management. METHODS An intensive evaluation of microbiological, inpatient, outpatient, and cataract surgery charts was made retrospectively using a standardized protocol. The predictive value of surgical, iatrogenic, and clinical factors was analyzed for their influence on defined aspects of the disease pattern and of the visual results using multiple regression models, via a stepwise technique. RESULTS There was commonly a significant asymptomatic latent period after cataract surgery. The median diagnostic delay was 7 days; 22% of patients presented after 2 weeks and 12% after 1 month. Symptoms progressed longer than 3 days in 25% of patients. Ten percent had no pain. Clinical variation proved largely unrelated to cataract surgery events and postoperative management; bacterial factors were implicated. Good visual outcome was associated statistically with intensive topical corticosteroid in the symptomatic period, but was negatively associated with operative subconjunctival corticosteroid. CONCLUSIONS The clinical variation in cases of postoperative coagulase-negative staphylococcal endophthalmitis poses particular problems for diagnosis in the outpatient setting. Surgical and perioperative events (except corticosteroid use) probably can be disregarded in studies of endophthalmitis management.

Factors modulating the effect of retinoids on cultured retinal pigment epithelial cell proliferation.

The effect of several naturally-occurring retinoids and 13-cis-retinoic acid on the proliferation of cultured bovine retinal pigment epithelial (RPE) cells was investigated. None of the retinoids tested were toxic to the cultures and all, except retinylpalmitate, inhibited cell proliferation when given for more than 3 days. The relative potencies of the retinoids were; all-trans-retinoic acid greater than 13-cis-retinoic acid greater than all-trans-retinol approximately equal to all-trans-retinaldehyde. Uptake of retinoic acid by cultured RPE cells was 10-fold less than the uptake of retinol. Although retinoic acid-treated cultures showed strong density-dependent growth inhibition, cellular proliferation was inhibited more in sparse cultures than in dense ones. Retinoic acid did not significantly inhibit the proliferation of first passage bovine or rabbit RPE cells, but partially inhibited the proliferation of first passage human RPE cells. The sensitivity of all these cultures to growth inhibition by retinoic acid increased in subsequent subcultures, yet there was no effect of passage number on retinoic acid uptake. This study demonstrates that RPE cell proliferation can be inhibited by retinoic acid but the sensitivity of these cells to the retinoids effects are modulated by incubation time, in vitro aging, and cell density.

Posterior vitreous detachment following panretinal laser photocoagulation

A total of 30 eyes of 19 patients with type I diabetes, varying severity of retinopathy, and no posterior vitreous detachment (PVD) were studied clinically, and vitreous examination was performed by preset lens biomicroscopy. Follow-up was 4.0–7.5 years. A total of 15 eyes underwent panretinal laser photocoagulation (PRP) and 15 eyes were left untreated. The incidence of PVD was 8 of 15 (53%) after PRP and 1 of 15 (7%) in untreated eyes (P<0.02). Minimal vitreous hemorrhage occurred in 4 of 7 treated eyes (57%) that did not develop PVD and in only 2 of 8 (25%) that did. In treated eyes with no history of vitreous hemorrhage, the incidence of PVD was 6/9 (67%); in treated eyes with minimal vitreous hemorrhage at any time, it was 2/6 (33%). In treated eyes, the presence of Diabetic Retinopathy Study (DRS) high-risk characteristics was equally frequent in eyes that developed PVD as in those that did not. These data suggest that PVD occurs following PRP, independent of the severity of diabetic retinopathy or prior vitreous hemorrhage.