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S32 Oman Journal of Ophthalmology, Vol. 6, No. 3, Supplement
2013
Correspondence: Dr. Marcus Kernt, Department of Ophthalmology,
Ludwig-Maximilians-University of Munich, Mathildenstr. 8, 80336
Munich, Germany. E-mail: [email protected]
Copyright: 2013 Kernt and Kampik. This is an open-access article
distributed under the terms of the Creative Commons Attribution
License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original author and source
are credited.
The technical progress of the recent years has revolutionized
imaging in ophthalmology. Scanning laser ophthalmoscopy (SLO),
digital angiography, optical coherence tomography (OCT), and
detection of fundus autofluorescence (FAF) have fundamentally
changed our understanding of numerous retinal and choroidal
diseases. Besides the tremendous advances in macular diagnostics,
there is more and more evidence
that central pathologies are often directly linked to changes in
the peripheral retina. This review provides a brief overview on
current posterior segment imaging techniques with a special focus
on the peripheral retina.
Keywords: Angiography, AMD, diabetic retinopathy, fundus
autofluorescence, optical coherence tomography, RVO, SLO,
Wide-field imaging
Retinal vascular diseases such as diabetic retinopathy (DR),
retinal vein occlusion (RVO), and neovascular age-related macular
degeneration (AMD) are in Europe and the US, as well as in the
Middle East main cause of severe vision loss and blindness.[1-3]
Even if central pathologies, such as macular edema are often of
primary importance, there is more and more evidence that these
central changes are often directly linked to the peripheral
retina.[4,5] Considering the pathogenesis of diabetic macular edema
(DME) for example, there are a variety of biochemical changes
following diabetes mellitus leading to vascular endothelial damage
and a consecutive breakdown of the blood retina barrier in both,
the macular region and the peripheral retina. As a final pathway,
this results in both, DR and DME, to an increased secretion of
vascular endothelial growth factor (VEGF). As a consequence,
increased vascular permeability and stimulation of pathological
angiogenesis are not only the main causes of retinal
neovascularization, but also of macular edema.[6,7]
Thanks to new treatment options, such as intravitreal anti-VEGF
therapy, we do have the opportunity to help many of the patients
suffering from macular edema.[8,9] However, with particular
reference to the excessive secretion of growth factors in
patients with DR, DME, or RVO; we are often only able to treat more
or less in a symptomatic way: Macular edema is located in the
center of the posterior pole, but the ischemic retinal areas
providing a major stimulus for increased VEGF expression are often
located peripherally. In consequence, sole pharmacotherapy will not
allow us to treat causally anyhow. Moreover, recent data clearly
indicate that for long-term stabilization, the quantification of
(peripheral) ischemia is essential, as only this allows us to treat
these disease causally and in a comprehensive way (for example,
with an additive sectorial or pan-retinal laser therapy)[4,10,11]
[Figures 1a and b].
To give us a more comprehensive impression of retinal disease,
modern imaging devices are available that are specifically designed
to give us an image of the peripheral retina and therefore provide
additional valuable information for more comprehensive ophthalmic
treatment approaches.
In general, diagnostic fundus imaging has tremendously evolved
over the recent years and thereby significantly gained importance.
Initially consisting mainly from photographic fundus documentation
of central retinal pathologies, supplemented during the 1970s by
analog fluorescein angiography; both examination techniques were
usually based on analogous single 35-50 photographs of the central
of the retina, or, when the focus was set more on peripheral
lesions, based on composite images (e.g., Early Treatment Diabetic
Retinopathy Study (ETDRS) 7-field fundus photography), put together
out of a series of single shots being more or less difficult to
achieve and also being strongly operator and patient dependent.
Imaging of the peripheral retina
Marcus Kernt, Anselm Kampik
Department of Ophthalmology, Ludwig-Maximilians-University of
Munich, Munich, Germany
Review Article
Access this article onlineQuick Response Code:
Website: www.ojoonline.org
DOI: 10.4103/0974-620X.122292
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Kernt and Kampik: Imaging of the peripheral retina
Oman Journal of Ophthalmology, Vol. 6, No. 3, Supplement 2013
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Fortunately, technology has strongly advanced during the last
decades and especially during the last few years ophthalmic imaging
has made a large step forwards. The technical progress of the
recent years has revolutionized imaging in ophthalmology and
thereby changed our understanding of numerous retinal and choroidal
diseases. In addition, our knowledge about the vitreous and the
vitreoretinal interface has largely expanded and improved.
When we talk about imaging of the peripheral retina, particular
wide-field scanning laser ophthalmoscopy (SLO), but also digital
wide-field angiography have strongly evolved during recent years,
and still evolving.[12,13] As imaging quality has significantly
improved and handling has become easier, both, wide-field SLO and
angiography have found their way into broader clinical practice and
evidence about the benefits of these imaging techniques is
increasing almost from day to day.[12] But also wide-field fundus
autofluorescence (FAF) is now becoming more and more clinically
available providing completely new insights into peripheral,
retinal pathologies.[14-16]
A good example for new insight provided by wide-field imaging is
given by a recent study that showed clearly that even in the dry
AMD, which was primarily seen as a disease of the macula region and
the posterior pole, typical peripheral retinal changes commonly
occur, allowing the conclusion that AMD must now be better
understood as primarily panretinal disease.[15] As a consequence,
the peripheral retina may provide additional diagnostic information
allowing a better understanding of the disease [Figures 2a and
b].
So, what makes the difference between conventional ophthalmic
imaging and modern wide-field imaging devices? In principle, it may
be even possible to document peripheral retinal changes with a
conventional fundus camera. However, due to the relatively small
image angle (usually between 35 and 55) the implementation as a
documentation tool for peripheral retinal changes into daily
clinical practice is often technically difficult. Especially when
outer peripheral retinal pathologies should be pictured, image
quality is highly dependent on the operators technical skills as
well as the patients collaboration and optical aberrations are
often limiting image quality. In certain cases, for example in
premature infants for monitoring retinopathy of prematurity,
contact fundus cameras, such as the RetCam 120 are a pretty good
choice.[17,18] However, in systems like this the optical head has
to be placed on
the surface of the eye and it needs significant experience to
handle the device, impeding the spread of these machines into
everyday diagnostic routine [Figure 3].
An approach being more suitable for a widespread clinical use
represents noncontact wide-field fundus imaging. There are several
systems on the market right now and some of them are even
non-mydriatic. They are mostly easy to handle, technically highly
developed, and equipped with good image resolution; allowing to
accurately reproducing large areas of the central and peripheral
retina, being essential for a valid DR screening for
example.[3,19,20] In addition, most systems have specific software
solutions that provide additional diagnostic functions, such as
measuring tools or zooming features that allow to enlarge almost
any detail on the fundus in sometimes pretty good image quality.
Wide-field fundus imaging systems like this are either available as
stand-alone devices (such as the Optomap P200Tx system which
includes both a color fundus imaging, but also wide-field
fluorescein angiography (FA) and FAF allowing to map according to
the manufacturer (OPTOS Plc, Dunfermeline, UK) almost 180 of the
retina in one scan) or as add-on modules for existing imaging
devices (e.g., spectralis ultra wide-angle angiography module for
Heidelberg Retina Angiograph - 2 (HRA-2), Heidelberg Engineering,
Heidelberg, Germany; allowing wide-field FA, but also Indocyanine
Green Angiography (ICG) angiography [Figure 4].[12,21] These
imaging devices open up a host of new diagnostic applications and
are increasingly integrated into everyday clinical settings. In
(peripheral) retinal vascular disease, such as DR, and also in
patients suffering from uveitis and other inflammatory diseases of
the retina they have gained a particular area of
importance.[3,16,21] Several larger prospective studies for example
found that 200, non-mydriatic, ultra-widefield SLO imaging by
Optomap was as effective as ETDRS 7-field stereo color photographs
for assessing DR and correlates well with clinical
assessment.[3,19] The authors of one of these studies examined 141
consecutive patients with various levels of DR using Optomap
imaging and ETDRS 7-field photography.[3] The level of DR and the
presence of clinically significant macular edema (CSME) were graded
according to ETDRS classification. As a result, the techniques
agreed significantly, with both showing good intergrader
reproducibility and correlation with clinical assessment of DR. Of
note, Optomap imaging had a lower rate of nongradable images
compared with 7-field ETDRS, showing substantial correlation with
clinical assessment for detection of CSME.[3] As conclusion of
Figure 1: Optomap ultra-wide-fi eld scanning laser
ophthalmoscopy (SLO) color scan (a) and fl uorescein angiography
(b) of a patient with proliferative diabetic retinopathy (PDR).
Fluorescein angiography shows extensive ischemic retinal areas in
the periphery
ba
Figure 2: Optomap ultra-wide-fi eld scanning laser
ophthalmoscopy (SLO) color scan (a) and fundus autofl uorescence
(FAF) (b) of a patient with dry age-related macular degeneration
(AMD). FAF shows both centrally and peripherally signifi cant
changes that are almost invisible on the color image
ba
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Kernt and Kampik: Imaging of the peripheral retina
S34 Oman Journal of Ophthalmology, Vol. 6, No. 3, Supplement
2013
the study the author stated that the results clearly demonstrate
that Optomap imaging provides at least similar results for
assessment of DR levels and presence of CSME compared with ETDRS
7-field stereo color photographs. They added that Optomap
examination does not require much photographer experience and has a
fast learning curve; it also can be performed easily by trained
medical personnel. Therefore, Optomap provides promising properties
for peripheral screening programs and telemedicine in diabetes
patients.[3,19]
The key technology of the past decade in ophthalmology is surely
optical coherence tomography (OCT). Since its introduction in 1991,
OCT has revolutionized diagnostics in ophthalmology and has become
an indispensable tool in both, retina and glaucoma practice. It
provides noninvasive high-resolution in vivo imaging of retinal,
choroidal, and optic nerve head structures.[8,22-24] Therefore, OCT
is becoming more and more relevant for ophthalmic diagnostics and
has increasing impact on therapy. Beside substantial improvements
in resolution the increase of scanning speed has led to a wide
application in ophthalmology. Furthermore, the evolution of
software solutions for image analysis has contributed significantly
to make OCT technology an indispensable standard in macular
diagnostics. But we still have a different situation in the
assessment of peripheral retinal changes. So far, OCT was not
really applicable to detect or monitor peripheral retinal
pathologies, since there were no OCT systems that owned a
sufficiently high scanning speed allowing to asses wide-angle OCT
scans and thereby enabling a valid OCT imaging of the peripheral
retina. An important step towards this direction has recently been
done by a cooperation project of the Institute for Biomolecular
Optics of the Ludwig-Maximilians-University (LMU) in Munich and the
Department of Ophthalmology at LMU. The development of a novel
laser source allowed the development of an ultra-high-speed swept
source Fourier domain mode locking (FDML) OCT that was built to
improve existing technology.[25,26] FDML technology allows
ultra-fast, dense isotropic OCT sampling running at 1.68 MHz axial
line rate and also enables reconstruction of en-face fundus images
out of complete 3D datasets. Thus, using high-resolution OCT
technology, wide-field OCT scans can be produced which make it
possible to examine peripheral retinal changes in detail [Figures
5a and b]. The availability of this technology, but also by means
of commercially available wide-field OCT systems, such as the
recently introduced DRI Topcon OCT-1, the assessment of both,
central and the peripheral retina with OCT comes closer to every
day clinical practice.
In summary, besides all the progresses in macular diagnostics
and treatment, the technological advances of the last years have
brought the peripheral retina once again back in the focus and a
more comprehensive look at the ocular fundus steps into everyday
clinical practice. Even if not all interrelations between the
central and the peripheral retina are completely understood, new
imaging technologies allow now to display both, the macular and
peripheral retina, and thereby providing new insights that
have the potential to further improve our understanding of
retinal
disease.
Figure 3: Right eye fundus of a premature infant with retinal
hemorrhages, taken with the RetCam 120 (image courtesy of Prof.
Ehrt, LMU Munich)
Figure 4: Spectralis Ultra wide-fi eld fl uorescein (a) and
indocyanine (b) angiography of a patient with choroidal hemangioma.
Both retina and choroid show signifi cant abnormalities (courtesy
of Prof. Staurenghi, Milan)
ba
Figure 5: Ultra-high-speed Swept Source Fourier domain mode
locking (FDML) optical coherence tomography (OCT): En face imaging
of a left eye with proliferative diabetic retinopathy (PDR) and
status post panretinal and macular laser treatment (a), and a left
eye of a patient with central serous retinopathy (unprocessed data,
without image averaging) (b). Due to the large angle covered, FDML
OCT technology allows to image both, optic nerve and macular on one
scan
b
a
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Cite this article as: Kernt M, Kampik A. Imaging of the
peripheral retina. Oman J Ophthalmol 2013;6:S32-5.
Source of Support: Nil, Confl ict of Interest: None
declared.
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