3,485 research outputs found
Retinal imaging tool for assessment of the parapapillary atrophy and the optic disc
Ophthalmic diseases such as glaucoma are associated with progressive changes in the structure
of the optic disc (OD) and parapapillary atrophy (PPA). These structural changes may therefore
have relevance to other systemic diseases. The size and location of OD and PPA can be used
as registration landmarks for monitoring changes in features of the fundus of the eye. Retinal
vessel evaluation, for example, can be used as a biomarker for the effects of multiple systemic
diseases, or co-morbidities. This thesis presents the first computer-aided measuring tool that
detects and quantifies the progression of PPA automatically on a 2D retinal fundus image in
the presence of image noise. An automated segmentation system is described that can detect
features of the optic nerve. Three novel approaches are explored that extract the PPA and OD
region approximately from a 2D fundus image. The OD region is segmented using (i) a combination
of active contour and morphological operations, (ii) a modified Chan-Vese algorithm
and (iii) a combination of edge detection and ellipse fitting methods. The PPA region is identified
from the presence of bright pixels in the temporal zone of the OD, and segmented using
a sequence of techniques, including a modified Chan-Vese approach, thresholding, scanning
filter and multi-seed region growing methods. The work demonstrates for the first time how the
OD and PPA regions can be identified and quantified from 2D fundus images using a standard
fundus camera
Phase and Amplitude Responses of Narrow-Band Optical Filter Measured by Microwave Network Analyzer
The phase and amplitude responses of a narrow-band optical filter are
measured simultaneously using a microwave network analyzer. The measurement is
based on an interferometric arrangement to split light into two paths and then
combine them. In one of the two paths, a Mach-Zehnder modulator generates two
tones without carrier and the narrow-band optical filter just passes through
one of the tones. The temperature and environmental variations are removed by
separated phase and amplitude averaging. The amplitude and phase responses of
the optical filter are measured to the resolution and accuracy of the network
analyzer
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