Purpose: Quantification of outer retinal layers in humans. Method: 11 eyes in healthy subjects and 3 eyes in patients
after resolution of central serous chorioretinopathy (CSCR). Multiple line scans were obtained using OCT Stratus and
scans were registered and averaged to enhance contrast. The distance from the inner-outer segment junction to the
posterior part of the retinal pigment epithelium (RPE-OScomplex) was calculated. In addition, the reflectance of the outer
photoreceptor layer in the foveal center was compared to that peripheral to the fovea. Results: Mean thickness of the
RPE-OScomplex in healthy subjects was 77.3 μm, in CSCR 52.9 μm. The thickness of the RPE-OScomplex was significantly
correlated to visual acuity (r=0.95, p<0.01). The ratio of reflectance (fovea/parafovea) was 1.06 in healthy subjects,
1.18 in CSCR eyes. Conclusion: The RPE-OScomplex thickness was markedly reduced in eyes after resolution of CSCR
and highly correlated to the visual acuity, the correlation to total foveal thickness was less. An increased backscatter
was seen in CSCR, probably due to photoreceptor disorganization and atrophy.
Optical coherence tomography (OCT) has already proven an important clinical tool for imaging and diagnosing retinal diseases. Concerning the standard commercial ophthalmic OCT systems, speckle noise is a limiting factor with respect to resolving relevant retinal features. We demonstrate successful suppression of speckle noise from mutually aligning a series of in vivo OCT recordings obtained from the same retinal target using the Stratus system from Humphrey-Zeiss. Our registration technique is able to account for the axial movements experienced during recording as well as small transverse movements of the scan line from one scan to the next. The algorithm is based on a regularized shortest path formulation for a directed graph on a map formed by interimage (B-scan) correlations. The resulting image enhancement typically increases the contrast-to-noise ratio (CNR) with a factor of three or more and facilitates segmentation and quantitative characterization of pathologies. The method is currently successfully being applied by medical doctors in a number of specific retinal case studies.
For daily practice, in particular clinical studies using optical coherence tomography, the commercial OCT3/Stratus
scanner has until now been the prevalent instrument of choice. Whereas the ongoing development of OCT-systems will
permit evaluation of pathology on a cellular scale, this is a goal which is not within the limit of the present generation of
clinical OCT. On the other hand it is possible to get improved retinal information from clinical equipment like the OCT3
system by registering and combining a series of scans. Due to the widespread clinical use of OCT3 this paper explores
the potential improvement for a number of clinical cases using such a technique. The basic idea of composite image
enhancement might also be useful for image-enhancement with the new generations of OCT equipment.
The application of Optical Coherence Tomography (OCT) within ophthalmology is today relative widespread, the reason being that it is a major help in revealing details of structural damage and retinal patho-physiology that otherwise can be difficult to detect. Yet, there is still space for improvement and the OCT systems continuously improve both their speed and resolution. Besides the possibility of upgrading the hardware there is however also a possibility for "bootstrapping" the present generation of commercial devices by adequate post-processing of the acquired signals. We present evidence that with an existing commercial system it is possible to improve the signal-to-noise ratio of the recorded images by fusing multiple scans of the same retinal region. In order to achieve this improvement it is necessary to align a number of noisy signals. We have explored a number of different techniques for achieving this goal. The improvement is sufficient to reveal details that are impossible or difficult to observe from the individual OCT recordings.
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