Biomedical subjects
Publications and source records attributed to K V Chalam.
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An Internet browser-based annotation system can be used to identify and describe features in digitalized retinal images, in multicentric clinical trials, in real time. In this web-based annotation system, the user employs a mouse to draw and create annotations on a transparent layer, that encapsulates the observations and interpretations of a specific image. Multiple annotation layers may be overlaid on a single image. These layers may correspond to annotations by different users on the same image or annotations of a temporal sequence of images of a disease process, over a period of time. In addition, geometrical properties of annotated figures may be computed and measured. The annotations are stored in a central repository database on a server, which can be retrieved by multiple users in real time. This system facilitates objective evaluation of digital images and comparison of double-blind readings of digital photographs, with an identifiable audit trail. Annotation of ophthalmic images allowed clinically feasible and useful interpretation to track properties of an area of fundus pathology. This provided an objective method to monitor properties of pathologies over time, an essential component of multicentric clinical trials. The annotation system also allowed users to view stereoscopic images that are stereo pairs. This web-based annotation system is useful and valuable in monitoring patient care, in multicentric clinical trials, telemedicine, teaching and routine clinical settings.
PURPOSE: To describe a dual-purpose lens that can be used both as a planoconcave direct-image lens and wide-angle lens. This lens provides good resolution, is autoclavable and self-stabilizing. DESIGN: New instrument design. METHOD: This lens has two components (lenses): the inferior element is a modification of the standard, self-stabilizing planoconcave, one-piece acrylic lens with 4 footplates and is used in a similar manner; the superior part is a biconvex glass lens in a high-temperature-resistant plastic casing. The superior plastic casing is screwed on the inferior lens to convert it into a wide-angle lens. The lens is used as a self-stabilizing, planoconcave or wide-angle lens and is sterilized by autoclaving. RESULT: The planoconcave direct-image inferior lens gives a high-resolution image with a field of view of 20 degrees. The wide-angle lens on assembly of the inferior and superior parts gives a static field of view of 80 degrees and a dynamic field of view of 98 degrees. CONCLUSION: The two-piece dual-purpose contact lens is an inexpensive substitute for both planoconcave and traditional wide-angle lens without compromising the stability and quality of the fundus image.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
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PURPOSE: To evaluate the utility scores in patients with varying degrees of visual morbidity due to diabetic retinopathy or ARMD. METHODS: Patients with vision < or =20/40 in one eye due to diabetic retinopathy or ARMD were enrolled. Utility scores were measured by the time trade-off (TTO) method after stratifying the patient population with visual impairment in the better eye (group 1, 20/20 to 20/40; group 2, 20/50 to 20/100; group 3, 20/200 to no light perception). RESULTS: Sub-group analysis revealed that subjects in group 1 were willing to give up a median of 1 year as compared to 3 years by the subjects in group 3 for perfect bilateral visual acuity (P<0.05). The median utility score was 0.94 for group 1, 0.96 for group 2 and 0.80 for group 3. While the utility scores for groups 1 and 2 were comparable (P>0.05), there was a significant difference in the utility scores between groups 1 and 3 and between groups 2 and 3 (P<0.05). There was no significant effect on the utility scores of age, educational level or prior ocular surgery. CONCLUSION: Substantial visual loss secondary to diabetic retinopathy or ARMD is associated with a significant decrease in utility scores. However, TTO scores were not sensitive enough to demonstrate a difference between subjects with mild (group 1) and moderate (group 2) visual loss in the better eye secondary to diabetic retinopathy or ARMD.
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This technique manages vitreous prolapse associated with posterior capsule rupture during phacoemulsification by performing small-gauge pars plana vitrectomy with a sutureless, self-sealing incision performed in a closed chamber, maintaining normal intraocular pressure. A high-speed cutter exerts minimal traction on the vitreous. Accessibility to the vitreous through the pars plana is better, ensuring more complete removal of the vitreous and restoration of normal anatomy.
OBJECTIVE: To evaluate and compare the relationships between the posterior surface of the crystalline lens and peripheral retina with the use of curved vitrectomy instruments. MATERIALS AND METHODS: Specially designed curved endolaser and vitrectomy probes were compared with conventional straight probes through sclerotomy sites at 3.0 mm and 4.0 mm, in 12 fresh cadaver phakic eyes. For the safety profile, the perpendicular distance between the probe oriented toward a reference point on the retina and the midpoint of the posterior surface of the lens was measured. For access to the retinal periphery, the distance between the ora serrata and the most peripheral accessible point on the retina without touching the crystalline lens with the probes was measured. RESULTS: The perpendicular distance between the probe and posterior surface of the lens increased, and the ability of the probe to reach the most peripheral accessible point on the retina improved with the curved probes as compared with straight probes. CONCLUSIONS: Curved probes can access the peripheral retina and ora serrata with lesser possibility to injure the crystalline lens during vitreous surgery than the standard straight probes.
PURPOSE: A new technique to manage posterior capsular rupture with vitreous prolapse into the anterior chamber during phacoemulsification under topical anesthesia using the sutureless self-sealing 25-gauge transconjuctival vitrectomy system. METHOD: In the event of vitreous prolapse into the anterior chamber, the corneal wound is sutured and cleared of vitreous. A trans conjunctival 25-gauge sclerotomy through the pars plana is made. The high speed 25-guage trans-conjunctival vitrectomy system (TVS-25) under topical anesthesia is introduced and vitrectomy is performed to clear the anterior chamber of vitreous. An anterior vitrectomy is also done. A foldable intraocular lens is subsequently inserted. RESULTS: The vitrectomy is performed in a closed chamber maintaining normal intraocular pressure. The high-speed cutter exerts minimal traction on the vitreous. The accessibility to vitreous improves through the pars plana route ensuring more complete removal of the vitreous and restoration of normal anatomy. Topical anesthesia avoids the risks of globe perforation, retrobulbar hemorrhage, and prolonged postoperative akinesia of the eye. CONCLUSIONS: The 25-gauge pars plana incision is small and self-sealing. This makes the procedure fast, effective, painless and safe.
Corticosteroids (glucocorticoids), used frequently as potent anti-inflammatory agents, increase the risk of glaucoma by raising the intraocular pressure (IOP) when administered exogenously (topically, periocularly or systemically) and in certain conditions of increased endogenous production (e.g. Cushing's syndrome). Approximately 18 to 36% of the general population are corticosteroid responders. This response is increased to 46 to 92% in patients with primary open-angle glaucoma (POAG). Patients over 40 years of age and with certain systemic diseases (e.g. diabetes mellitus, high myopia) as well as relatives of patients with POAG are more vulnerable to corticosteroid-induced glaucoma. The association of corticosteroid-induced ocular hypertension in other conditions which are considered as risk factors for glaucoma (racial origins, hypertension, migraine, vasospasm) is likely but not fully established. The proposed mechanism of corticosteroid-induced glaucoma includes morphological and functional changes in the trabecular meshwork system and is similar to the pathogenesis of POAG. Trabecular cells exposed to corticosteroids in vitro show endoreplication of nuclei, an increase in cell size and excessive production of an approximately 56kD glycoprotein, identified as myocilin and transcribed by the GLC1A gene. Induction of ocular hypertension after corticosteroid administration depends on the specific drug, the dose, the frequency of administration and the corticosteroid responsiveness of the patient. The risk of corticosteroid-induced glaucoma can be minimised with judicious use of corticosteroids, as well as education of patients and medical practitioners. New treatment modalities include modified steroids and nonsteroidal anti-inflammatory agents that will have less effect on the elevation of IOP.
PURPOSE: This study aimed to quantitate and compare the concentration of vascular endothelial growth factor (VEGF) in aqueous humor samples from patients with neovascular glaucoma (NVG), primary open-angle glaucoma (POAG), and cataract, as well as in serum samples of healthy human subjects. METHODS: The authors collected aqueous humor samples by using their previously published technique of limbal paracentesis. The authors determined the concentration of VEGF by using a competitive enzyme immunoassay system and four-parameter logistic curve fitting and performed statistical analysis by using the Mann-Whitney-Wilcoxon test. RESULTS: The authors detected VEGF in 12 of 12 samples from patients with NVG (mean +/- standard error of the mean, 29.267 +/- 7.350 ng/ml), 15 of 28 samples from patients with POAG (0.726 +/- 0.204 ng/ml), 4 of 20 aqueous humor samples from patients with cataract (0.257 +/- 0.043 ng/ml), and 16 of 16 human serum samples (20.246 +/- 1.568 ng/ml). The mean concentration of VEGF in aqueous humor of patients with NVG was 40- and 113-fold higher than that in patients with POAG and cataract, respectively, and the difference was statistically significant (P < 0.01). The VEGF level in patients with POAG was elevated compared with that in patients with cataract (P < 0.05). Although the mean concentration of VEGF in aqueous humor of patients with NVG was approximately 1.45-fold higher than that in serum, the difference was not significant (P > 0.05). CONCLUSION: The authors' findings show that patients with NVG had a significantly increased level of VEGF in the aqueous humor and implicate VEGF as an important factor in the pathogenesis of intraocular neovascularization in these patients. The authors discuss the possible role of the ciliary epithelium, in addition to retina, in the production of VEGF and the complementary function of basic fibroblast growth factor and other growth factors.
OBJECTIVE: To examine the relative levels of gamma-aminobutyric acid (GABA), glutamate, and vascular endothelial growth factor (VEGF) in the vitreous of nondiabetic and diabetic patients. METHODS: Undiluted vitreous samples were obtained from 22 patients with proliferative diabetic retinopathy (PDR) and 28 patients without diabetes who underwent pars plana vitrectomy. Simultaneous venous blood samples also were obtained. Amino acid concentrations were determined using sensitive high-performance liquid chromatography, and VEGF levels by quantitative enzyme-linked immunosorbent assay. Hemoglobin concentrations in the blood and vitreous were determined using spectrophotometry. RESULTS: The level of GABA in the vitreous of patients with PDR, 29.4 +/- 7.8 mumol/L, was significantly higher than in controls (18.4 +/- 5.5 mumol/L) (P = .004). The vitreous concentration of glutamate was higher in patients with PDR (24.7 +/- 14.0 mumol/L) compared with controls (9.1 +/- 5.1 mumol/L) (P < .001). Vitreous VEGF level was significantly higher in patients with PDR (1759 +/- 1721 pg/mL) compared with controls (27 +/- 65 pg/mL) (P < .001). There were moderately strong correlations between GABA and VEGF levels (r = 0.68) and glutamate and VEGF levels (r = 0.43). Elevated GABA, glutamate, and VEGF levels also correlated strongly with the presence of PDR. Correcting for possible introduction of these molecules by vitreous hemorrhage did not significantly alter these findings. CONCLUSIONS: Levels of glutamate potentially toxic to retinal ganglion cells are found in the vitreous of patients with PDR. Elevated vitreous GABA may reflect amacrine cell dysfunction and underlie electroretinographic oscillatory potential abnormalities seen in diabetic retinopathy. The correlations of glutamate and GABA levels with an elevated VEGF level provide biochemical support for ischemia-induced neovascularization in patients with PDR. These findings present opportunities for novel therapeutic modalities in the treatment of PDR.
By using the techniques of reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern hybridization, we demonstrated that human Tenon's capsule fibroblasts in primary cultures, express the messenger RNA (mRNA) transcripts encoding transforming growth factor-beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF), and platelet-derived growth factor (PDGF), but not those coding for aFGF and TGF-beta 2. Two PCR products were obtained for TGF-beta 1: a major fragment of 161 base pairs that corresponded to the expected size, and a minor sequence of 400 base pairs. An antisense oligonucleotide probe specific for TGF-beta 1 detected only the band of 161 base pair of PCR-amplified sequence. For bFGF, PDGF-A and PDGF-B, we obtained only a single PCR product with the anticipated length of 222, 225, and 217 base pairs, respectively. Southern blotting experiments revealed that these PCR-amplified fragments were specific for the respective growth factors. The negative control experiments without template did not reveal any amplification. No product for aFGF or TGF-beta 2 was detected. By radioimmunoassay, TGF-beta 1 protein was detected at the level of 24-30 pg ml-1 per 2 million Tenon's fibroblasts during a 24-hour period in acid-activated conditioned medium. These results indicate that human Tenon's capsule fibroblasts in primary cultures express TGF-beta 1 at the translational as well as at the transcriptional levels, and they also have the capacity to synthesize bFGF and PDGF. Considering the significant effects of bFGF, TGF-beta 1, and PDGF in wound healing response, these growth factors are implicated in tissue repair process after glaucoma filtration surgery that contributes to the failure of the procedure.
PURPOSE: To determine whether transforming growth factor (TGF)-beta 1 and -beta 2 and basic fibroblast growth factor (bFGF) induce the gene expression of TGF-beta 1 in the first-passage trabecular meshwork cells of the eye. METHODS: Trabecular meshwork cells were cultured from fresh porcine eyes and treated with 1 ng/ml of TGF-beta 1, TGF-beta 2, or bFGF for 1 hour. Cells maintained in serum-free medium were used as controls. Total cellular RNA was extracted, and the first-strand cDNA was synthesized. Multiplex polymerase chain reaction (PCR) and competitive PCR were performed on aliquots of the cDNAs by using either endogenous (glyceraldehyde-3-phosphate dehydrogenase [G3PDH]) or exogenous sequence (PCR mimic for TGF-beta 1) as internal standards, respectively. The obtained products were quantitated by laser densitometry, and statistical analysis was performed. RESULTS: The findings show that trabecular cells in vitro express the TGF-beta 1 messenger RNA constitutively. Both the techniques of multiplex PCR and competitive PCR demonstrated that the addition of either TGF-beta 1 or TGF-beta 2 at a concentration present in normal aqueous humor increased the mRNA levels of TGF-beta 1 by 2.82-to 3.07-fold over the controls, and these results were statistically significant (P < 0.01). Basic fibroblast growth factor did not have an effect on TGF-beta 1 expression (P < 0.05). CONCLUSIONS: Transforming growth factor-beta 1 activates its own gene expression in trabecular cells. Considering the multifunctional property of this cytokine, which includes increased deposition of extracellular matrix material and growth inhibition of trabecular cells, a change in its concentration within the eye would have a profound effect because of this autoinductive activity. Transforming growth factor-beta 2 treatment of trabecular cells also increased their expression of the TGF-beta 1 gene. The authors previously showed that the level of TGF-beta 2 in the aqueous humor of glaucomatous eyes is significantly higher than that of age-matched nonglaucomatous controls. The current finding suggests that this growth modulator may exert its effects directly on the trabecular cells or that it may act indirectly through upregulating the production of TGF-beta 1.