Biomedical subjects

R Hariprasad

Publications and source records attributed to R Hariprasad.

3 recordsLinked to original sources

PubMed2006

A new quality assessment parameter for optical coherence tomography.

AIM: To create a new, automated method of evaluating the quality of optical coherence tomography (OCT) images and to compare its image quality discriminating ability with the quality assessment parameters signal to noise ratio (SNR) and signal strength (SS). METHODS: A new OCT image quality assessment parameter, quality index (QI), was created. OCT images (linear macular scan, peripapillary circular scan, and optic nerve head scan) were analysed using the latest StratusOCT system. SNR and SS were collected for each image. QI was calculated based on image histogram information using a software program of our own design. To evaluate the performance of these parameters, the results were compared with subjective three level grading (excellent, acceptable, and poor) performed by three OCT experts. RESULTS: 63 images of 21 subjects (seven each for normal, early/moderate, and advanced glaucoma) were enrolled in this study. Subjects were selected in a consecutive and retrospective fashion from our OCT imaging database. There were significant differences in SNR, SS, and QI between excellent and poor images (p = 0.04, p = 0.002, and p<0.001, respectively, Wilcoxon test) and between acceptable and poor images (p = 0.02, p<0.001, and p<0.001, respectively). Only QI showed significant difference between excellent and acceptable images (p = 0.001). Areas under the receiver operating characteristics (ROC) curve for discrimination of poor from excellent/acceptable images were 0.68 (SNR), 0.89 (IQP), and 0.99 (QI). CONCLUSION: A quality index such as QI may permit automated objective and quantitative assessment of OCT image quality that performs similarly to an expert human observer.

Aged↗

PubMed2000

Portable pupillography of the swinging flashlight test to detect afferent pupillary defects.

OBJECTIVE: To investigate the ability of a portable, personal computer-driven, pupillometer to record the pupillary response curve during the swinging flashlight test. Also, to determine whether these response curves can be used to identify and quantify relative asymmetry in the pupillary light reflex between eyes in healthy volunteers with simulated afferent pupil defects (APDs) and patients with optic neuropathies. DESIGN: Comparative, observational case series and instrument validation. PARTICIPANTS: Healthy volunteers with no known ocular disease and patients (n = 20) with various optic neuropathies noted to have relative APDs on examination. METHODS: Pupillary response curves of the right eye were recorded with a portable, electronic, infrared pupillometer from healthy volunteers (with and without simulated APDs) and patients with APDs while the light stimulus alternated between eyes, simulating the swinging flashlight test. Simulated APDs in healthy volunteers were created with increasingly dense neutral density filters in front of the left eye. MAIN OUTCOME MEASURES: Differences in constriction amplitude, latency, and constriction velocity of the pupillary response with right eye stimulation versus left eye stimulation in both groups of subjects. RESULTS: A significant correlation between neutral density filter strength and intereye differences was seen for all measurement parameters in volunteers with simulated APDs. Depending on the measurement parameter and stimulus intensity, simulated APDs of 0.6 log units or more could be distinguished from normal responses. Clinically graded true APDs had intereye differences similar to simulated APDs of the same density. Those with real and simulated APDs of 0.9 log units or more could be distinguished from healthy volunteers with 80% sensitivity and 92% specificity. Responses from those with real and simulated small APDs of 0.3 to 0.6 log units could not be distinguished reliably. CONCLUSIONS: Portable, personal-computer driven, electronic, infrared pupillography can record the swinging flashlight test accurately and identify large afferent pupillary defects. An affordable, portable, reliable device for identifying relative APDs would be useful in the identification and follow-up of patients with neurogenic vision loss.

Adult↗

PubMed1999

An intelligent, interactive platform for ophthalmic teaching, telemedicine, and telecollaboration: design considerations and prototype construction.

The development of technologies permitting processing, compression, and transmission of digital images and image sequences enables powerful methodologies for local and remote medical teleconsultation. We are developing a slit-lamp-based ophthalmic augmented reality (image overlay) environment incorporating features to permit real-time, interactive teaching, telemedicine, and telecollaboration. A binocular slit-lamp biomicroscope interfaced to a CCD camera, framegrabber board, and PC permits acquisition and rendering of anterior segment and retinal images. Computer-vision algorithms facilitate robust tracking, registration, and near-video-rate image overlay of previously stored retinal photographic and angiographic images onto the real-time fundus image. Our algorithms facilitate shared control of pointing, drawing, and measuring functions registered with the retinal image video stream and direct audio communication between an examiner (student, generalist) and remote observer (instructor, specialist). Bandwidth and video compression considerations limit the frame rate and latency for video stream transmission. Excellent and acceptable performance are demonstrated in model eyes over a local area network and through a modem connection, respectively. These studies represent the first investigations towards the design and implementation of an intelligent platform for ophthalmic telemedicine and telecollaboration.

Algorithms↗