Ophthalmic imaging today: an ophthalmic …€¦ · · 2017-10-17Ophthalmic imaging has changed...

Review

Ophthalmic imaging today: an ophthalmicphotographer’s viewpoint – a reviewTimothy J Bennett FOPS1 and Chris J Barry MMedSci21Penn State Department of Ophthalmology, Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA; and 2Lions Eye Institute,Centre for Ophthalmology and Visual Science, Perth, Western Australia, Australia

ABSTRACT

Ophthalmic imaging has changed dramatically since the 1960swith increasingly complex technologies now available. Argu-ably, the greatest changes have been the development of thedigital camera and the speed, processing power and storage ofelectronic data. Already, ophthalmic practices in many majorinstitutions overseas have paperless medium storage and elec-tronically generated reporting from all equipment that use acomputer interface. It is hard to remember the widespreaduse of photographic film with its attendant costs, or even toremember the days before optical coherence tomography(OCT). These latest technical improvements in ophthalmicimaging are now standard in large Australian institutions andbecoming more widespread in smaller private practices. Thetechnicians that operate and maintain this ever-increasingplethora of gadgetry have seen their work practices changefrom the darkroom to the complexities of data-based imagingand storage. It is a fitting time to examine the contemporarystate of ophthalmic imaging and what lies on the horizon as wemove towards 2020.

Key words: fluorescein angiography, imaging system,indocyanine green angiography, retinal examination, scanninglaser ophthalmoscope.

INTRODUCTION

Ophthalmic imaging has long played an important role inthe documentation and diagnosis of ophthalmic diseases.Ocular photography is used to record medical conditions,track disease progression and create illustrations for publica-tion and education. The primary role of ophthalmic imaginghowever, goes well beyond documentation in its ability toaid in the diagnosis of a broad range of eye conditions.

The history of ophthalmic photography dates back to thelate 1800s when Jackman and Webster described a techniquefor photographing the retina of a living human subject.1 Thenext 50 years witnessed a slow advancement in instrumenta-tion and techniques. Photographic results were mostly inad-equate owing to slow film speeds, long exposures andinconsistent light sources. In the 1950s, electronic flash and35 mm cameras were adapted to ophthalmic instrumentsand modern ophthalmic photography was born.

Ophthalmic imaging can, at times, be either simple orincredibly complex. Ocular tissues can be opaque, translu-cent or transparent. Enhancement of anatomic features isoften achieved through lighting techniques, but sometimes,vital stains, fluorescent dyes, monochromatic light or special-ized optical devices or techniques are needed to adequatelydocument subtle pathology.

The following is a brief overview of the techniques beingused in ophthalmic imaging today.

EXTERNAL EYE PHOTOGRAPHY

Perhaps the most obvious, but least specialized, type of oph-thalmic imaging is termed ‘external photography’. Conven-tional macrophotography equipment and techniques areused to document the external appearance of the eyes andsurrounding lid and facial structures. It is commonly used todocument lesions of the eye or surrounding tissues, demon-strate facial nerve anomalies and record pre- and post-surgical alignment of the eyes or eyelids.

Digital single-lens-reflex cameras are used to avoid paral-lax between lens and viewfinder and they offer a variety ofcompatible lens and electronic flash choices. Magnificationfor routine external ocular photography ranges from full faceup to life size. Dedicated macro lenses are the best choice toprovide this range and facilitate repeatable magnificationsettings. Auxiliary electronic flash units with a variable posi-tioning system provide directional lighting that can be

� Correspondence: Mr Chris J Barry, Lions Eye Institute, Centre for Ophthalmology and Visual Science, 2 Verdun Street, Perth, WA 6009, Australia. Email:

[email protected]

Received 16 December 2007; accepted 23 June 2008.

Clinical and Experimental Ophthalmology 2008doi: 10.1111/j.1442-9071.2008.01812.x

© 2008 The AuthorsJournal compilation © 2008 Royal Australian and New Zealand College of Ophthalmologists

mailto:[email protected]

adjusted tangentially to demonstrate texture and elevation ormoved to an axial position to illuminate a cavity, or to accu-rately render skin colour with even lighting.

It is essential that a standardized series of images withknown magnification and lighting are used for the serialfollow up of facial and eye conditions so that images remaincomparable even when serial sets are taken over extendedperiods of time.2

Motility photographs are a series of external photographsshowing both eyes together in various positions of gaze(Fig. 1). They are used to demonstrate alignment or mis-alignment of the eyes owing to imbalanced extraocularmuscles or other disorders that can obstruct or limit normaleye movement. In addition to still images, these eye move-ment disorders are sometimes documented with video.

SLIT-LAMP PHOTOGRAPHY

Most high magnification photography of the anteriorsegment of the eye uses a photo slit-lamp. The photo slit-lamp is a variation of the slit-lamp biomicroscope routinelyused in ophthalmology to light and examine structures in theeye at magnifications up to 40¥.3

Slit-lamp photography offers the best opportunity forimagers to demonstrate their imaging skills and creativity. It isa technically and aesthetically challenging discipline thatrequires a good understanding of composition, magnification,lighting principles, precise exposure control and understand-ing of the pathology. Photo slit-lamps use beam splitters todirect image-forming light to a camera mounted on the instru-ment, or in some cases, two cameras to provide stereo capture.Electronic flash illumination is delivered through the samecondensing optics as the tungsten slit illuminator. Magnifica-tion at the film plane is adjustable from approximately 0.7¥ upto around 5¥, depending on the specific instrumentation. Theslit beam can be precisely controlled and adjusted from around or wide rectangular beam down to a very thin slit. A

secondary fill light is often available to add backgroundillumination and adjust lighting ratios.

Lighting techniques fall into two basic categories, directand indirect. Direct focal illumination can be deliveredaxially, or tangentially to produce highlights and shadow.Specular reflection can be used to detect surface irregularitiesin highly reflective structures. A very thin focal beam is oftenused to create a narrow cross-sectional view or ‘opticalsection’ of the normally transparent cornea and lens. Indirectillumination can take on many forms. Iris transillumination,sclerotic scatter and retroillumination of the cornea or lensare lighting techniques that are accomplished by bouncingor scattering light off other anatomical structures such as theiris, retina and sclera (Fig. 2).

Vital stains may be used as an adjunct to slit lightingtechniques to enhance visibility of certain ocular surfacedisorders.4–6 Topical applications of Rose Bengal, lissaminegreen or fluorescein can be applied to stain areas of missingor devitalized cells in the cornea and conjunctiva (Fig. 3).These dyes are best photographed using diffuse or broadbeam, focal illumination. Fluorescein staining can be illumi-nated with white light to demonstrate yellow staining orwith blue light to cause excitation and fluorescence of thedye-stained areas.

GONIO PHOTOGRAPHY

Auxiliary lenses are sometimes used with a photo slit-lamp tophotograph the inner structures of the eye that cannot bedirectly viewed with the slit-lamp.7 The most common lenstype is the gonio contact lens that utilizes internal mirrorsangled at approximately 60° to provide observation of thefiltering angle of the anterior chamber (Fig. 4).

SPECULAR MICROSCOPY

Specular microscopy is a variation of slit-lamp photographythat utilizes specialized single-purpose instruments to image

Figure 1. External photograph of the nine positions of gaze documenting thyroid-associated ophthalmopathy. The eye muscles are enlargedpushing the eye forward, preventing the eye moving properly and resulting in double vision.

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the endothelium of the cornea.8 High magnification andspecular reflection are necessary to delineate the cell bordersto detect cell density and morphology, which are indicatorsof corneal health (Fig. 5). Magnifications range from 20¥ to

200¥. Traditionally, specular microscopes required contactwith the patients’ cornea. The latest instruments utilize non-contact microscopy with semi-automated digital analysis ofcell counts and morphology.

a b

c d

Figure 2. Slit-lamp illumination.(a) Slit-lamp photograph withdirect, focal illumination of an eyewith keratoconus, a conical elonga-tion of the corneal curvature. (b)Specular illumination highlights the‘beaten metal’ appearance of thecorneal endothelium in a case ofFuchs’ corneal dystrophy. (c) Scle-rotic scatter, a form of indirectillumination, demonstrates the wide-spread appearance of granularcorneal dystrophy. (d) Thin-beamillumination helps to isolate struc-tures by creating an ‘optical section’of transparent tissues in the eye.Here it illustrates a pigmented cystthat has come in contact with theposterior surface of the cornea.

a b

c

Figure 3. Topical stains. (a) RoseBengal staining of devitalized areasof a squamous cell lesion. (b) Lissa-mine green staining of a similarsquamous cell neoplasm. (c) Topicalfluorescein staining shows thetear-film pattern in a patient withentropion and trichiasis. Diffuse illu-mination through a blue filter excitesfluorescence of the dye.

Ophthalmic imaging today 3


RETINAL PHOTOGRAPHY

The retina represents the single most important subject forophthalmic photographers (Fig. 6). Retinal imaging presentssome interesting challenges. Our goal is to photograph ana-tomic structures that can be measured in microns, withenough detail to make diagnostic decisions.

Successful retinal imaging relies on the interactionbetween the optics of the fundus camera with the optics ofthe eye itself. Fundus cameras utilize an aspheric objectivelens design that, when combined with the optics of thesubject eye, matches the plane of focus to the curvature ofthe fundus. Although it is essentially a low-power micro-scope placed just 2–3 cm from the subject, proper focus is setat or near infinity, because when aimed into the eye, the lightpath exiting the fundus camera then passes through therefracting optics of the cornea and the natural lens, which areusually focused at distance upon dilation. The focus controlof the fundus camera is used to compensate for refractiveerrors in the subject eye. The light needed to illuminate thefundus is delivered axially. The optical system of the funduscamera projects a ring of light from the internal strobethrough the dilated pupil. The ring shape allows a separationof the outgoing and incoming illumination (Gullstrandprinciple).9

Retinal cameras are often described by their optical angleof view. An angle of 30 degrees (30°) is considered thenormal angle of view and creates an imaging plane image2.5 times life size. Fixed-angle cameras usually offer thesharpest optics, but variable-angle cameras provide wide-angle capabilities between 45° and 60°. Wide-angle camerasneed to illuminate a broader area of retina, requiring a morewidely dilated pupil to accommodate a larger ring of light.Other angle of view options are available on some cameras,notably 20°, or accessory magnifiers can be used to increasethe range of magnification available and are particularly usedin the serial comparisons of optic discs in the evaluation ofglaucoma.

Peripheral fundus photography can be particularlychallenging. When the eye is rotated to the desired periph-eral field of view, the opening in the pupil appears elliptical,making it difficult to fit the entire illuminating beam withinits borders. The off-axis angle also causes the image-forminglight rays to pass through a flatter portion of the cornea,which will change focus and cause some distortion.

MONOCHROMATIC RETINAL PHOTOGRAPHY

Monochromatic retinal photography is the practice ofimaging the retina with the use of coloured or monochro-matic illumination (Fig. 7). In 1925, Vogt described the useof green light to enhance the visual contrast of anatomicaldetails of the fundus.10 The technique is still commonly usedin combination with fundus photography. Monochromaticretinal imaging is based on the use of contrast filters to altersubject tones in monochrome images and the increased scat-tering of light at shorter wavelengths. By limiting the spec-tral range of the illuminating source, the visibility of variousfundus structures can be enhanced.11

Blue light increases visibility of the anterior retinal layers,which are normally almost transparent in white light. Bluelight is absorbed by retinal pigmentation and blood vessels,providing a dark background against which the specularreflections and scattering in the anterior layers of the fundusis enhanced. Scattering in the ocular media can limit theeffectiveness of these wavelengths. The retinal nerve fibrelayer, the internal limiting membrane, retinal folds, cysts andepiretinal membranes are examples of semi-transparent scat-tering structures that are enhanced with short wavelengthillumination (Fig. 8). Because of excessive scattering at veryshort wavelengths, blue-green (cyan) filters of 490 nm areoften used.

Green light is also absorbed by blood, but is reflectedmore than blue light by retinal pigmentation and providesexcellent contrast and the best overall view of the retina. Itenhances the visibility of the retinal vasculature and commonfindings such as haemorrhages, drusen and exudates (Fig. 9).For this reason, green filter ‘red-free’ photographs are rou-tinely taken as baseline images in conjunction with fluores-cein angiography.

In red light, the retinal pigmentation appears more trans-parent revealing the choroidal pattern. Overall funduscontrast is greatly reduced with red illumination. Retinalvessels appear lighter and become less obvious at longerwavelengths. The optic nerve appears lighter and almostfeatureless. Red light is useful for imaging pigmentary distur-bances, choroidal ruptures, choroidal naevi and choroidalmelanomas (Fig. 10).

STEREO IMAGING

Stereo images enhance diagnostic information by providinga visual sense of depth and realism beyond ordinary two-dimensional photographs. The use of this technique in oph-thalmology dates back as far as 1909, but it was not until the

Figure 4. Gonio photograph of a pigmented cyst in the filteringangle of the same eye shown in Figure 2d.

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1960s that stereo fundus photography became widely usedafter Lee Allen described a practical technique for sequentialstereo fundus photography.12

This technique is a good example of how we can takeadvantage of the optical interaction between the subject eyeand camera. Laterally shifting the fundus camera a few mil-limetres between sequential photographs causes the illumi-nating beam of the fundus camera to fall on opposite slopesof the cornea. The resulting cornea-induced parallax createsa hyper-stereoscopic effect that is evident when the sequen-tial pair of photographs are viewed together. Stereo pairs areparticularly useful in identifying the anatomic location ofpathologic findings in retinal images. Stereo imaging is astandard protocol for many clinical trials investigating treat-ment of retinal diseases. Critical alignment of digital stereoimages can be accomplished through the use of dedicatedstereo display software. Controls typically include verticaland horizontal shift, and in some cases incremental rotation.They automatically crop overlapped borders and permitresizing. These programs offer a variety of output formats forstereo viewing including anaglyph, side-by-side, interlacedand ‘page-flip’ for LCD shutter glasses.

Stereo imaging techniques have also been used for slit-lamp biomicrography and, to a lesser extent, externalphotography. Unfortunately, the two commercial simulta-neous stereo cameras (both images of a stereo pair taken atthe same moment in time, Nidek 3Dx, Topcon TRC-SS) arenot available as of 2007. There are a variety of optical stereoviewers available for viewing digital images on a computermonitor. All stereo viewing devices are designed to deliverthe separate stereo images simultaneously but independentlyto each eye allowing the brain to fuse the pair and recreate athree-dimensional image.

FLUORESCEIN ANGIOGRAPHY

Ophthalmic photography has at times seemed almostsynonymous with fluorescein angiography. For over fourdecades, ophthalmologists have relied on fluorescein angiog-raphy as an important tool in the understanding, diagnosisand treatment of retinal disorders. This diagnostic imagingprocedure utilizes a retinal camera or a scanning laser oph-thalmoscope to capture rapid-sequence photographs of theretinal vasculature following an intravenous injection offluorescein sodium.13 Fundus cameras are equipped with amatched pair of exciter (465–490 nm) and barrier (520–530 nm) filters (narrow pass interference filters) along with afast recycling electronic flash tube that allows a capture rateof up to one frame per second. This technique facilitates thein vivo study of the retinal circulation (Fig. 11) and is particu-larly useful in the management of diabetic retinopathy andmacular degeneration, two leading causes of blindness. Onrare occasions, fluorescein angiography of the iris or otheranterior structures may be of value.

SCANNING LASER OPHTHALMOSCOPY

Fluorescein angiography can also be recorded using a con-focal scanning laser ophthalmoscope (cSLO) in place of theconventional fundus camera (Fig. 12). The cSLO uses a laserbeam of the appropriate excitation wavelength to scan acrossthe fundus in a raster pattern to illuminate successive ele-ments of the retina, point-by-point.14 The laser can deliver avery narrow wavelength band for more efficient excitation offluorescence than the flash illumination generated by an elec-

a bFigure 5. Specular microscopy.(a) High magnification specularmicrograph of a normal cor-neal endothelium. (b) Modern,non-contact specular micrographwith cell analysis that includes celldensity (cells/mm2, and morpho-logy. Photos: Thomas Link).

Figure 6. Wide-angle colour fundus photograph showing theoptic nerve, retina and choroid of a young patient with Stargardt’sdisease.



tronic flash tube. A confocal aperture is positioned in front ofthe image detector at a focal plane conjugate to the retina,effectively blocking non-image-forming light. The confocaloptical system and laser illumination combine to producehigh contrast, finely detailed images. The laser scan rate issynchronized at a frame rate compatible with digital videodisplay, providing a continuous high-speed representation ofthe flow dynamics of the retina and choroid. This can beespecially useful when documenting of the very early fillingstages in the identification of choiroidal neovascular feedervessels.

Both 30° and 50° (complete circle rather than clipped topand bottom with fundus cameras) auxiliary lenses are avail-able for the cSLO; the wide-angle lens is primarily used forperipheral imaging in either diabetic retinopathy or venousocclusive disease. In addition, real-time montaging softwareallows the operator to view a collation of peripheral imageson screen as a single ultra-wide angle image. However, thecSLO does not have the capacity to capture colour images ofthe retina.

An adapted cSLO (Heidelberg Retinal Tomogram,HRT3) can also be used for comparing optic nerve headparameters in glaucoma.15 Analysis of the optic disc headtopography relative to a confocal reference plane showssmall structural changes necessary to detect the progressionof glaucoma. Pictures are built up from scanned layers whichare represented as two-dimensional topographical or reflec-tivity pictures by the HRT software. Topographic changeanalysis compares serial visit data and a probability analysis iscompared with a normative database aiding in the identifi-cation of glaucomatous progression.

ICG ANGIOGRAPHY

Digital technology facilitates the use of another fluorescentdye, indocyanine green (ICG), for retinal and choroidalangiography (Fig. 13). The choroid is a highly vascular struc-ture found immediately behind the retinal pigment epithe-lium (RPE), which acts as a physical barrier between theretinal vascular system and the choroidal vascular system.

a bFigure 7. Monochromatic photo-graphy. (a) Colour fundus photo-graph of a suspected choroidalmelanoma. (b) Monochromaticphotograph of the same fundustaken through a red filter (peaktransmission at 615 nm) to enhanceand document the borders of thelesion.

Figure 8. Monochromatic fundus photograph taken with blue-green light (peak transmission at 490 nm). The lack of specularreflections in the dark, wedge-shaped areas identify a loss of retinalnerve fibres from glaucoma.

Figure 9. Green light is the most commonly used colour formonochromatic fundus photography. It enhances the contrastbetween retinal blood vessels and the optic nerve. In this case, agreen filter (peak transmission at 560 nm) nicely illustrates thepisciform yellow/white lesions characteristic of Stargardts’ disease.

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The view of the choroid is normally obscured by theRPE, both in clinical appearance and during fluoresceinangiography. With peak absorption and emission in the near-infrared range at 805 and 835 nm, respectively, ICG providesgreater transmission through the RPE and haemorrhage thanthe visible wavelengths used in fluorescein angiography(Fig. 13). ICG also binds more completely with blood albu-mins, so it normally remains within the fenestrated walls ofthe choriocapillaris, unlike fluorescein, which leaks freelyfrom these vessels.

Indocyanine green choroidal angiography was first per-formed in humans in 1972, but results were limited by insuf-ficient sensitivity of available infrared films.16 In the early1990s, two groups reported improved results with commer-

cially available digital angiography systems.17,18 The infraredsensitivity of available CCD cameras was combined withnew lens coatings that improved infrared transmission forICG angiography. In the early to mid 1990s, enthusiasm forthis procedure exceeded its practical applications.19 Use ofthis technique waned by the late 1990s as clinical researchhad defined a vital, but limited role for ICG angiography asan adjunct to fluorescein angiography.

Today, ICG is used in combination with fluoresceinangiography in a limited number of diagnoses where chor-oidal circulation is effected, such as macular degeneration.The goal in macular degeneration is to identify choroidalfeeder vessels that can be treated with a laser to preventdamage to the retina.20 ICG is used in a limited number ofdiagnoses where choroidal circulation is effected, particularyin polypoidal choroidopathy. ICG is increasingly hard toobtain in Australia with individual specific licensing toperform the procedure now required.

OPTICAL COHERENCE TOMOGRAPHY

Optical coherence tomography is a recent imaging proce-dure that is useful in the diagnosis of several retinal disordersthat have traditionally been imaged with fundus photogra-phy or fluorescein angiography.21,22 OCT imaging providesdirect cross-sectional images of the macula, retinal nervefibre layer and optic nerve for objective measurement andclinical evaluation in the detection of retinal diseases andglaucoma. It is particularly useful in the detection of macularholes, cystoid macular oedema, subretinal fluid and retinalpigment epithelial detachments (Fig. 14). Its greatest value,

Figure 10. Red light is particularly useful for documenting lesionsdeep within the retinal tissues or the choroid behind it. Longerwavelengths (peak transmission at 615 nm) partially penetrate theretina pigment epithelium and make it appear more transparent,revealing the scalloped edges of an unusual choroidal osteoma.

Figure 11. Fluorescein angiogram demonstrating haemorrhagesand vascular filling defects in a patient with Purtscher’s retinopathy.

Figure 12. A single frame from a fluorescein angiogram takenwith a cSLO showing a choroidal neovascular membrane. Thesquare format of the image is characteristic of cSLO images.



however, may lie in the ability to quantify and monitorchange in retinal thickness owing to macular oedema fromdiabetic retinopathy or other causes.

The OCT technology was originally developed at theMassachusetts Institute of Technology in 1991 and is basedon the principle of low coherence interferometry.23 The prin-ciple is analogous to ultrasound, except that near-infraredlight (820 nm) is used instead of sound. This differencepermits resolution of �10 mm. A superluminescent diodelight is directed at both the eye and a reference mirror at aknown spatial location. The time-of-flight delay of lightbackscattered from different layers of the retina is measuredand analysed. Retinal thickness is calculated by processingthe cross-sectional images using computer algorithms todetect tissue boundaries by searching for the highest rates ofchange in reflectivity. Although the technology has beenavailable for over a decade, OCT was mostly used in aca-demic settings or for research applications until the release ofthe Carl Zeiss Meditec OCT3 in 2002.

New instruments from six manufacturers have recentlyentered the marketplace using spectral or Fourier domainOCT techniques, and have made significant improvementsin both resolution and acquisition speeds, as well as three-dimensional representations of retinal and vitreal structures(Fig. 14c,d). The Heidelberg HRA2 has the ability for fluo-rescein and ICG angiographies, autofluorescence and spec-tral domain OCT with the Spectralis module. It remains tobe seen whether such a multifunctional device can maintaina high throughput rate for all its many functions available ina busy practice.

FUNDUS AUTOFLUORESCENCE

Fundus autofluorescence is a recently developed non-invasive imaging technique for documenting the presence oflipofuscin in the RPE. Lipofuscin is a fluorescent pigmentthat accumulates in the RPE as a metabolic by-product as theeye ages. When excited with short wavelength illumination,

a bFigure 13. Indocyanine greenangiography (ICG). (a) Monochro-matic green filter image of an eyewith a large subretinal haemorrhage.(b) Infrared imaging penetrates thehaemorrhage to reveal the circula-tion patterns of the retinal andchoroidal blood vessels after anintravenous injection of ICG. Photo:Gary Miller.

a b

c d

Figure 14. Optical coherencetomography (OCT). (a) A 3 mmline scan provides a cross-sectionalview of the normal retinal architec-ture and foveal depression. (b) A3 mm line scan of a patient with dia-betic retinopathy shows a loss of thenormal foveal depression, retinalelevation and fluid-filled cysts. (c)Spectral domain OCT line scancomprised of 4096 A-scans of anepiretinal membrane. Conventionaltime domain OCT has a maximumresolution of 512 A-scans. (d) Thehigh acquisition speed of SD-OCToffers 3D rendering from a cubescan pattern showing a pigmentepithelial detachment in age-relatedmacular degeneration.

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lipofuscin granules autofluoresce, exhibiting a broad emis-sion spectrum from 500 to 750 nm with peak emission atabout 630 nm.24

The original technique used a cSLO with the excitationwavelength set at 488 nm and a barrier filter at 500 nm or520 nm.25 Several frames are captured with the SLO, thenaligned and averaged to reduce noise. Because several framesare required, image quality may be affected by eye move-ment during capture. More recently, digital fundus camera-based systems have been developed which use high-sensitivity monochrome sensors with an excitation filter at580 nm and a barrier filter at 695 nm to avoid confoundingautofluorescence from the crystalline lens.26 Both systemsrequire significant amounts of light and increased gain set-tings to achieve adequate exposure and are subject to imagenoise. Despite the disparity in excitation wavelength andbarrier filters between the SLO and fundus camera systems,these two techniques obtain results that are quite similar inappearance.

Autofluorescence imaging has the potential to provideuseful information in conditions where the health of the RPEplays a key role. Hyperautofluorescence is a sign of increasedlipofuscin accumulation, which may indicate degenerativechanges or oxidative injury. Areas of hypoautofluorescenceindicate missing or dead RPE cells. Geographic atrophy thatappears as a window defect in fluorescein angiography willappear dark in autofluorescent imaging (Fig. 15). A numberof investigators are exploring potential applications of thisimaging technique in a variety of retinal diseases.27

NON-MYDRIATIC RETINAL CAMERASAND TELEMEDICINE

Non-mydriatic fundus cameras with digital capture capabili-ties are often used as screening devices for diabetic retinopa-thy and glaucoma. Fundus photography can be an effectivemethod of retinopathy screening that is capable of detectingmacular oedema and proliferative diabetic retinopathy, themost common causes of vision loss in diabetics. Non-mydriatic fundus cameras are designed with an infraredfocusing system that promotes physiologic dilation in a dark-ened room, making them simple to operate. They can be

placed at remote primary care sites and operated by availableclinical personnel such as nurses and medical assistants.Images can then be directed to a centralized reading centrefor image grading and treatment recommendations. Imagingwith non-mydriatic cameras has been shown to have a highsensitivity and specificity compared with an ophthalmic con-sultation28 and are becoming an integral tool in deliveringophthalmic care to rural and remote Australia as communi-cation technology becomes more pervasive, particularly inremote Aboriginal communities where the need is high.

Rural and remote diabetic screening programmes in Aus-tralia preceded many overseas programmes after recognitionof the high prevalence of diabetes in Indigenous com-munities.29 More streamlined screening programmes are nowunderway in the USA, UK and more recently, New Zealand.These innovative programmes allow ophthalmologists tomake more efficient use of their specialized training todeliver timely treatment to those patients who have beenpre-identified through telemedicine screenings. The role ofophthalmic photographers and other ophthalmic technicianshas also changed with involvement in training camera opera-tors and in key roles in reading centre workflows.

Conversely, the hand-held Nidek NM200 non-mydriaticcamera has been shown to image optic discs well in glaucomascreening but is unable to detect early-stage diabetic retin-opathy (intra-retinal microaneurysms) owing to the capturelight wavelength,30,31 although a hand-held device has beenused in prisons in Western Australia as part of an integratedapproach to telemedicine consultations with qualifiedsucess.32

OTHER IMAGING MODALITIES IN BRIEF

Various imaging instruments have found acceptance in nicheareas. For many years the Kowa RC-2 film camera wasadopted as a retinal camera for those difficult imaging taskssuch as recording examinations under anaesthesia (Fig. 16).The Kowa Genesis D, two megapixel hand-held digitalcamera has replaced the film version. The 120° Retcam isnow more widespread and frequently used for examinationsunder anaesthesia, particularly with neonatal imaging;however, there is an appreciable price differential.33 The

a bFigure 15. Fundus Autofluore-scence. (a) Monochromatic greenimage of a patient with age-relatedmacular degeneration. (b) Fundusautofluorescent imaging (excitationat 580 nm and barrier at 695 nm)non-invasively identifies pigmentarychanges and a choroidal neovascularcomplex.



Panoret 100 corneal contact camera is capable of a 130°angle of view of the retina using transcleral illumination.34

To date, there are geometric distortions that require mani-pulation and there is no capacity for fluorescein or ICGangiographies. Easy-to-use wide-angle imaging systemsremain a technically difficult and elusive instrument for main-stream usage.

Many other systems now produce computer recreationsof captured data. Corneal topography and corneal pachym-etry have been at the forefront of data representation, par-ticularly with the advent of laser corneal sculpting toimprove refractive errors. The Heidelberg Corneal SL-OCT,Zeiss Visante OCT and the Oculus Pentacam are now enter-ing the market and image the anterior chamber as a three-dimensional cross-sectional structure allowing iris angleanalysis, corneal topography, pachymetry and cataractanalysis. Perhaps these new modalities will replace high-resolution ultrasound B scans; only time will show which willbecome the dominant technologies.

SUMMARY

Ophthalmic photographers and ophthalmic technicians nowrequire continuing, high-level, ongoing education to remaincurrent with emerging technologies. Instrument integrationinto the practice workflow requires a collaboration withInformation Technology technicians; however, the ultimategoal of total electronic information remains tantalizinglyclose in Australia.

There are no dedicated ophthalmic photography trainingcourses in Australia, although the Royal Melbourne Instituteof Technology does offer a semester of ophthalmic photog-raphy training as part of a Bachelor of Science Degree ofApplied Scientific Imaging. Therefore, continuing educationis only available at overseas programmes associated withOphthalmic Conferences. These remain the only available

option to gain a contemporary overview of current andemerging technologies to be incorporated into future clinicalpractice. With the advent of digital imaging and storage andanti-VEGF treatments, workflows and practices have alreadychanged extensively even though Australian Medicare reim-bursement is only available for fluorescein angiography.

Large institutions are moving towards the sole use ofelectronic records, for example, the USA Veterans Affairsdepartment (VA). Since 1999, the VA’s 155 hospitals, 881clinics, 135 nursing homes and 45 rehabilitation centreshave been linked by a universal medical records networkthat allows any authorized person to look at 5.3 millionpatients’ records (personal communication: Associate Pro-fessor Len Goldsmith, Stamford School of Ophthalmology,2007). In tandem with this new wave of patient electronicinformation storage, retrieval, transmission and billing, theHealth Insurance Portability and Accountability Act in theUSA regulates and monitors the security and protection ofpatient’s information, and access is closely monitored. Theimplementation of a similar system in Australia has yet tobe initiated but must be the next logical goal in today’sdigital world.

Ophthalmic diagnostic imaging enhances the under-standing, diagnosis and treatment of a wide variety ofocular disorders. These images are used for decision-making purposes on a daily basis, and in some cases, phy-sicians rely on them as a ‘road map’ to guide laser therapy.The new technologies of wavefront imaging and microde-formable mirrors are already in the prototype stage imagingin vivo cone cells with high-resolution images. Theseupcoming technologies will require imaging staff to makethese purchases cost effective. Integrating this plethora ofdevices into the clinical workflow will maximize the ben-efits to patients in terms of clinical outcomes and is thelatest challenge in remaining in the forefront of tomorrows’high technology environment.

a bFigure 16. Retinopathy of prema-turity: vascular tortuosity involvingboth veins and arteries, imaged with(a) Kowa RC-2 and (b) Retcamcameras. Photos: Ditte Hess.

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INFORMATION RESOURCES

The Australian Institute of Medical and Biological Illustra-tion (http://www.aimbi.org.au) is the umbrella organizationin Australia for medical/ophthalmic photographers.

The Ophthalmic Photographers’ Society has produced ajournal since 1978. All Journals are available electronicallyvia the web and can be searched by key word, edition orauthor (http://www.opsweb.org/Publicat/Journal/JourSrch.html). The Ophthalmic Photographers’ Society can becontacted at: [email protected]

The Ophthalmic Imaging Association (http://www.oia.org.uk).

REFERENCES

1. Jackman WT, Webster JD. On photographing the retina of theliving eye. Philadelphia Photographer 1886; 23: 275.

2. Saine PJ. Tutorial: external ocular photography. J OphthalmicPhotogr 2006; 28: 8.

3. Martonyi CL, Bahn CF, Meyer RF. Slit Lamp: Examination andPhotography. Sedona, AZ: Time-One Ink Ltd, 2007.

4. Bennett TJ, Miller GE. Lissamine green dye – an alternative torose bengal in photo slit-lamp biomicrography. J OphthalmicPhotogr 2002; 24: 74–5.

5. Wiffen S, Barry C. Fundamentals 1: corneal epithelial fluores-cein staining. J Ophthalmic Photogr 2000; 22: 84–5.

6. Wiffen S, Barry CJ. Rose bengal staining of the ocular surface.J Ophthalmic Photogr 2001; 23: 73–5.

7. Curtis R. Goniophotography. J Ophthalmic Photogr 2004; 26:13–9.

8. Wong D. Textbook of Ophthalmic Photography. New York: Inter-Optics Publications, 1982.

9. Gullstrand A. Nobel Prize in Physiology or Medicine. Stockholm:Nobel Foundation, 1911.

10. Vogt A. Die Ophthalmoskopie im rotfreiem licht. GraefSaemisch Hand-buch der gesamten Augenheilkunde. Berlin: Springer Verlag, v3, 1925.

11. Behrendt T, Slipakoff E. Spectral reflectance photography. IntOphthalmol Clin 1976; 16: 95–100.

12. Allen L. Ocular fundus photography: suggestions for achievingconsistently good pictures and instructions for stereoscopicphotography. Am J Ophthalmol 1964; 57: 13–28.

13. Bennett TJ. Fundamentals of intravenous fluorescein angio-graphy. Curr Concepts Ophthalmol 2001; 9: 43–9.

14. Woon WH, Fitzke FW, Chester GH, Greenwood DG, Mar-shall J. The scanning laser ophthalmoscope: basic principlesand applications. J Ophthalmic Photogr 1990; 12: 17–23.

15. Zangwill LM, Weinreb RN, Beiser JA, Berry CC, Cioffi GA,Coleman AL. Baseline topographic optic disc measurements areassociated with the development of primary open angle glau-coma: the Confocal Scanning Laser Ophthalmoscopy AncillaryStudy to the Ocular Hypertension Treatment Study. Arch Oph-thalmol 2005; 123.

16. Flower RW, Hochheimer BF. Clinical infrared absorptionangiography of the choroids. Am J Ophthalmol 1972; 73: 458–9.

17. Yannuzzi LA, Slakter JS, Sorenson JA, Guyer DR, Orlock DA.Digital indocyanine green videoangiography and choroidalneovascularization. Retina 1992; 12: 191–223.

18. Guyer DR, Puliafito CP, Mones JM, Friedman E. Digitalindocyanine-green angiography in chorioretinal disorders.Ophthalmology 1992; 99: 287–90.

19. Flower RW. Choroidal angiography today and tomorrow[Guest editorial]. Retina 1992; 12: 189–90.

20. Stanga PE, Lim JI, Hamilton P. Indocyanine green angiographyin choroidal diseases: Indications and interpretation: anevidence-based update. Ophthalmology 2003; 110: 15–21.

21. Costa RA, Skaf M, Melo LA Jr et al. Retinal assessment usingoptical coherence tomography. Prog Retin Eye Res 2006; 25:325–53.

22. Puliafito CA, Hee MR, Lin CP. Imaging of macular diseaseswith optical coherence tomography. Ophthalmology 1995; 102:217–29.

23. Michelson AA, Lorentz HA, Miller DC, Kennedy RJ, Hein-drick ER, Epstein PS. Conference on the Michelson-MorleyExperiment. Astrophys J 1928; 68: 341.

24. Delori FC, Gragoudas ES. Monochromatic ophthalmoscopyand fundus photography. The normal fundus. Arch Ophthalmol1977; 95: 861–8.

25. von Ruckman A, Fitzke FW, Bird AC. Distribution of fundusautofluorescence with a scanning laser ophthalmoscope. Br JOphthalmol 1995; 79: 407–12.

26. Spaide RF. Fundus autofluorescence and age-related maculardegeneration. Ophthalmology 2003; 110: 392–9.

27. Schmitz-Valkenberg S, Holz F. Fundus autofluorescenceimaging in geographic atrophy. J Ophthalmic Photogr 2007; 29:74–80.

28. Diamond JP, McKinnon M, Barry C et al. Non-mydriatic fundusphotography: a viable alternative to fundoscopy for indentifi-cation of diabetic retinopathy in an aboriginal population inrural Western Australia? Aust N Z J Ophthalmol 1998; 26: 109–15.

29. Constable IJ, Knuiman MW, Welbourn TA et al. Assessing therisk of diabetic retinopathy. Am J Ophthalmol 1984; 97: 53–61.

30. Yogesan K, Constable IJ, Barry CJ, Eikelboom RH, McAllisterIL, Tay-Kearney ML. Telemedicine screening of diabetic retin-opathy using hand-held fundus camera. J Telemed Telecare 2000;6: 219–23.

31. Yogesan K, Constable IJ, Barry CJ, Eikelboom RH, MorganWH, Tay-Kearney ML. Evaluation of a portable fundus camerafor use in teleophthalmologic diagnosis of glaucoma. J Glaucoma1999; 8: 297–301.

32. Barry CJ, Henderson C, Kanagasingam Y, Constable IJ.Working towards a portable tele-ophthalmic system for use inmaximum security prisons: a pilot study. Telemed J E Health 2001;7: 1–5.

33. Flynn JT, Hess D. Telephoto-screening for retinopathy ofprematurity. J Ophthalmic Photogr 2000; 22: 54–7.

34. Shields CL, Materin M, Epstein J, Shields JA. Wide angleimaging of the ocular fundus. Rev Ophthalmol 2003; 10: 2.



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Ophthalmic imaging today: an ophthalmic …€¦ · · 2017-10-17Ophthalmic imaging has changed...

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