6 Diagnostic Capability of Optical Coherence Tomography …
155
address this issue, central fixation was confirmed in each subject in our study by
ensuring the location of the foveal depression at the center of the macular scan.
Furthermore, interocular mean differences of macular thickness in non-amblyopic
patients have been investigated and were minimal, even if degrees of asymmetry
existed in considered individual patients. In addition, Szigeti et al. concluded that
patient age and AL should be taken into consideration in segmentation studies in
amblyopia [192]. Using their methodology they could observe subtle changes in
amblyopic eyes affecting the ONL of the fovea suggesting the possible involvement of
the photoreceptors. However, further studies are warranted to support this hypothesis.
6.4 Concluding Remarks
In conclusion, we consider that macular OCT image segmentation showing in vivo
structural changes of retinal tissue will yield a better insight into macular pathology
and therefore should play an important role in the future of the diagnosis and followup of neurological diseases affecting the optic nerve, such as MS which influences
a continuously increasing number of patients worldwide. Furthermore, it seems that
texture and optical properties of the retina derived from OCT images may provide a
useful additional tool in the hands of clinicians for the assessment of neurodegeneration and neuronal loss-related changes occurring in MS and other neurodegenerative
diseases. This may help the better differentiation of eyes with pathology and more
precise targeting of potential therapeutic interventions and could also be useful in the
follow-up of patients. In both types of diabetes there are early changes observable in
the retina of both the structure and its optical properties that may shed light on the
pathological processes preceding the occurrence of manifest retinopathy.
It is important to point out that retinal thickness measured by SD-OCT is different
from that measured by TD-OCT because the delineation of the outer boundary of the
retina differs in the two instruments as most SD-OCT instruments include the outer
segment–RPE–Bruch’s membrane–choriocapillaris complex in the measurements.
This needs to be kept in mind when making therapeutic decisions based on thickness
data, like, for example, in diabetes. It is well known that segmentation errors are
less frequent with SD-OCT that can be attributed to the greater acquisition speed and
better resolution of SD-OCT devices. Partly for this reason, the custom-built software
used in our studies facilitates the manual correction of segmentation errors by the
operators reducing the number of erroneous thickness calculations due to artifacts.
It is known that there is a high agreement and intraclass repeatability of macular
thickness in eyes with pathologies obtained by three OCT devices (Stratus TD-OCT
and two SD-OCTs, Spectralis and Cirrus OCT) even though each OCT device has a
unique method of defining algorithms and cannot be used interchangeably [199].
When performing OCT image segmentation studies involving adults it is suggested to take the effect of AL into consideration; additionally, it will be useful to
verify our observations in young subjects [56, 192].
155
address this issue, central fixation was confirmed in each subject in our study by
ensuring the location of the foveal depression at the center of the macular scan.
Furthermore, interocular mean differences of macular thickness in non-amblyopic
patients have been investigated and were minimal, even if degrees of asymmetry
existed in considered individual patients. In addition, Szigeti et al. concluded that
patient age and AL should be taken into consideration in segmentation studies in
amblyopia [192]. Using their methodology they could observe subtle changes in
amblyopic eyes affecting the ONL of the fovea suggesting the possible involvement of
the photoreceptors. However, further studies are warranted to support this hypothesis.
6.4 Concluding Remarks
In conclusion, we consider that macular OCT image segmentation showing in vivo
structural changes of retinal tissue will yield a better insight into macular pathology
and therefore should play an important role in the future of the diagnosis and followup of neurological diseases affecting the optic nerve, such as MS which influences
a continuously increasing number of patients worldwide. Furthermore, it seems that
texture and optical properties of the retina derived from OCT images may provide a
useful additional tool in the hands of clinicians for the assessment of neurodegeneration and neuronal loss-related changes occurring in MS and other neurodegenerative
diseases. This may help the better differentiation of eyes with pathology and more
precise targeting of potential therapeutic interventions and could also be useful in the
follow-up of patients. In both types of diabetes there are early changes observable in
the retina of both the structure and its optical properties that may shed light on the
pathological processes preceding the occurrence of manifest retinopathy.
It is important to point out that retinal thickness measured by SD-OCT is different
from that measured by TD-OCT because the delineation of the outer boundary of the
retina differs in the two instruments as most SD-OCT instruments include the outer
segment–RPE–Bruch’s membrane–choriocapillaris complex in the measurements.
This needs to be kept in mind when making therapeutic decisions based on thickness
data, like, for example, in diabetes. It is well known that segmentation errors are
less frequent with SD-OCT that can be attributed to the greater acquisition speed and
better resolution of SD-OCT devices. Partly for this reason, the custom-built software
used in our studies facilitates the manual correction of segmentation errors by the
operators reducing the number of erroneous thickness calculations due to artifacts.
It is known that there is a high agreement and intraclass repeatability of macular
thickness in eyes with pathologies obtained by three OCT devices (Stratus TD-OCT
and two SD-OCTs, Spectralis and Cirrus OCT) even though each OCT device has a
unique method of defining algorithms and cannot be used interchangeably [199].
When performing OCT image segmentation studies involving adults it is suggested to take the effect of AL into consideration; additionally, it will be useful to
verify our observations in young subjects [56, 192].