Anterior and posterior segment photography. An alternative approach using a dSLR camera adaptor

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<ul><li><p>Anterior and posterior segment photography. An alternativeapproach using a dSLR camera adaptor</p><p>Chris G. Pirie and Stefano PizziraniDepartment of Clinical Sciences, Tufts Cummings School of Veterinary Medicine, 200 Westboro Rd, North Grafton, MA 01536, USA</p><p>Address communications to:</p><p>Dr. C. G. Pirie</p><p>Tel.: 508-839-5395</p><p>Fax: 508-839-7922</p><p>e-mail: chris.pirie@tufts.edu</p><p>AbstractPurpose To describe a novel digital single lens reflex (dSLR) camera adaptor foranterior and posterior segment photography.</p><p>Methods The adaptor was used to evaluate canine, feline, and equine patientspresenting to Tufts Ophthalmology service. Anterior segment imaging was conductedwith the adaptor mounted between a dSLR camera body (Canon 7D) and a macro</p><p>lens (Canon EF-S 60mm/f2.8). Posterior segment imaging was performed with theaid of an indirect ophthalmic lens mounted in front of the macro lens. Coaxial</p><p>illumination during viewing was provided by a single white light-emitting diode(LED) within the adaptor, while illumination during exposure was provided by the</p><p>pop-up flash or an accessory flash. Corneal and/or lens reflections were eliminatedusing a pair of linear polarizers, having their azimuths at right angles to one another.</p><p>Results This dSLR camera adaptor provides quality high-resolution, reflection-free,images of both the anterior and posterior segments. It was easy to transport,assemble, and handle. The necessary adjustments, positioning, and focusing required</p><p>for quality images were easily performed.Conclusion The described dSLR camera adaptor provides an alternative to existingimaging systems. High-resolution image acquisition occurred at a fraction of the costof established imaging system, particularly those devoted to the posterior segment.</p><p>Key Words: anterior segment, camera adaptor, digital photography, digital singlelens reflex, posterior segment</p><p>INTRODUCTION</p><p>The eye is the only organ that offers direct examination insitu because of its accessibility and transparency. This allowsfor accurate documentation of both normal physiology andclinically observable disease(s).1 Photography is the mostefficient and reliable method to document normal and path-ological findings, monitor disease progression, assessresponse to treatment, and protect against litigation. Fur-thermore, ocular imaging serves a fundamental basis forteaching, research, and client educational purposes.Photography holds many uses in ophthalmology and</p><p>there is a high demand for the acquisition of quality images.Imaging of the anterior segment is generally conducted withthe aid of a standard dSLR camera with or without the use ofa slit lamp biomicroscope. Imaging of the posterior segment,however, relies on a dedicated imaging system (i.e., funduscamera). One of the most important attributes of any imag-ing system is its ability to take publication-quality (highquality) images. However, there is often a strong positive</p><p>correlation with high quality imaging systems and cost. Thisis particularly true with systems dedicated to the posteriorsegment and may be a significant limiting factor. Further-more, the moderate bulk of these systems may reduce theirversatility and portability. Finally, as technological advance-ments continue, some digital-based imaging systemsbecome obsolete in a relatively short period of time. In vet-erinary medicine, equipment costs, weight, versatility, andportability are significant considerations, with cost likelybeing the most important and potentially limiting factor.Based on the aforementioned considerations, we sought</p><p>to devise a new instrument capable of acquiring high-resolutionimages of both the anterior and posterior segments of theeye. In this report, we describe a new dSLR camera adaptorsystem which is versatile, portable, and of low cost.</p><p>MATERIALS AND METHODS</p><p>Canine, feline, and equine patients presenting to the TuftsCummings School of Veterinary Medicine Ophthalmology</p><p> 2011 American College of Veterinary Ophthalmologists</p><p>Veterinary Ophthalmology (2011) 18 DOI:10.1111/j.1463-5224.2011.00963.x</p></li><li><p>department were imaged for the purpose of this report.Patients undergoing posterior segment imaging were dilatedwith 1% tropicamide ophthalmic solution. A minimum of20 min between tropicamide instillation and imaging wasallotted to ensure maximum pupillary dilation. Gentle man-ual restraint was performed by an assistant during imageacquisition to minimize patient movement; however, ocularmovement was unrestricted. All imaging was conducted in adarkened room.</p><p>Figure 1. Photograph of the dSLR camera adaptor alone with tube</p><p>extension for the pop-up flash. Extension for an accessory flash is not</p><p>shown.</p><p>Figure 2. Schematic diagram of the adaptor system. Note, for anterior segment viewing, removal of the indirect ophthalmic lens is required. Lightemanating from the flash and LED is reflected by either a mirror and/or beam splitter, focused by a series of condensers, and transmitted through one</p><p>of two linear polarizers. A second plate beam splitter within the adaptor reflects light into the camera lens, indirect ophthalmic lens, and onto the fun-</p><p>dus. Reflected light from the fundus is transmitted through the indirect ophthalmic lens, camera lens, second plate beam splitter, and second linear</p><p>polarizer onto the CMOS sensor of the camera body.</p><p>Figure 3. Photograph of the dSLR camera adaptor mounted between</p><p>the camera body and camera lens. This arrangement allows for imaging</p><p>of the anterior segment.</p><p>Figure 4. Photograph of the dSLR camera adaptor mounted between</p><p>the camera body and camera lens with a 78D indirect ophthalmic lens</p><p>secured to the camera lens. This arrangement allows for imaging of the</p><p>posterior segment.</p><p>2 p i r i e a nd p i z z i r a n i</p><p> 2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18</p></li><li><p>Design of the systemThe adaptor as shown in Fig. 1 is 60 mm in length andweighs a total of 280 g. It mounts between a camera body(Canon 7D; Canon, Tokyo, Japan [22.2 14.9 mm CMOS;17.9 million effective pixel count]) and a camera lens (CanonEF-S 60mm/f2.8; Canon). It provides true coaxial illumina-tion for viewing via a single dimmable LEDmounted withinthe adaptor. Illumination during exposure is provided by thepop-up flash or an accessory flash. As illustrated in a sche-matic diagram (Fig. 2), light emanating from the flash andLED is reflected by either a mirror and/or beam splitter,focused by a series of condensers, and transmitted throughone of the two linear polarizers. A second plate beam splitterwithin the adaptor reflects light into the camera lens alone(anterior segment imaging) or the camera lens and indirectophthalmic lens (posterior segment imaging) and onto theobject of interest. Reflected light is transmitted backthrough the indirect ophthalmic lens and camera lens (pos-terior segment imaging) or camera lens alone (anterior seg-ment imaging), second plate beam splitter and second linearpolarizer onto the CMOS sensor of the camera body. In thecurrent design, reduction and elimination of specular</p><p>reflections were obtained using a pair of linear polarizerswith their azimuths perpendicular to one another. A morecomplete technical description of the adaptor is reported ina recent publication.2</p><p>TechniqueVisualization of the region of interest occurs with the aidof a solitary LED through the viewfinder of the camera(monocular) or on the liquid crystal display screen duringthe live view feature (binocular). Focusing may beachieved either automatically or manually by moving thesystem closer to or further from the globe. Settings com-mon to the amateur photographer (i.e., shutter speed, aper-ture, ISO) can easily be varied to maximize image qualityor to adjust for patient variables (i.e., tapetal variations,ocular movements). Imaging of the anterior segment of theglobe is performed with the dSLR camera adaptormounted between the camera body and camera lens(Fig. 3). Imaging of the posterior segment is based on theprinciple of indirect ophthalmoscopy and performed withan indirect ophthalmic lens secured in front of the cameralens (Fig. 4).3 The indirect ophthalmic lens forms a real,</p><p>(a)</p><p>(b)</p><p>Figure 5. Stromal keratitis presumed secondary to FHV-1 in a cat.(a) Conventional image. (b) dSLR camera adaptor image (same eye as</p><p>Fig. 5a). Note the absence of specular reflections, increased contrast,</p><p>and visualization of corneal neovascularization and intrastromal</p><p>infiltrates.</p><p>(a)</p><p>(b)</p><p>Figure 6. Iris hypoplasia of a blue-eyed cat. (a) Conventional image.</p><p>(b) dSLR camera adaptor image (same eye as Fig. 6a). Note transillumi-</p><p>nation of the thinner iris tissue, both involving the pupillary and ciliary</p><p>regions. The region of the collarette is thicker and does not</p><p>transilluminate.</p><p>o phth a lm i c p hotog r a p h y u s i n g a d s l r c am e r a ad a p t o r 3</p><p> 2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18</p></li><li><p>inverted aerial image at the object plane of the camera lenswhich then forms a final image for the camera sensor. Assuch, the indirect ophthalmic lens is positioned such thatits object plane and that of the camera lens are identical.Alteration of the indirect lens is possible as it is indepen-dent of the adaptor. This allows for alterations in magnifi-cation(s) and field of view(s) obtained. In a recent study, weevaluated 28D, 40D, 60D, 78D, and 90D indirect ophthal-mic lenses. Use of these lenses provided an approximatemagnification range between 1 and 4 and an approximatefield of view range between 30 and 95 degrees within thehorizontal axis.2</p><p>RESULTS</p><p>The average power densities provided by the solitary LED,pop-up flash, and an accessory flash (Canon 580 EXII) were0.1, 0.2, and 2 mW/cm2.2 These values do not exceednational standards for safe retinal exposure to light as calcu-lated by Delori et al.4 The dSLR camera adaptor system was</p><p>easy to transport, assemble, and handle. Necessary adjust-ments, positioning, and focusing required to obtain qualityimages were easy to perform and required little training.Assistance in holding patients was fundamental.</p><p>Anterior segment photographyThe following series of anterior segment images illustratesthe capabilities of the dSLR camera adaptor system. Forcomparative purposes, images of the same globe wereobtained using the same camera body (Canon 7D) and cam-era lens (60 mm macro lens). These images will be referredto as conventional images.</p><p>CorneaSpecular reflections from the corneal surface can oftenreduce image quality and obscure regions of particular inter-est. Figure 5 demonstrates improved visualization and con-trast, in addition to, elimination of specular reflections usingthe dSLR camera adaptor. Intrastromal infiltrates within the</p><p>(a)</p><p>(b)</p><p>Figure 7. Thin-walled iridociliary cyst within the anterior chamber of</p><p>a Golden Retriever associated with pigmentary uveitis. (a) Conventional</p><p>image. Note the specular reflections. The cystic like structure is readily</p><p>apparent; however, transillumination is minimal. (b) dSLR camera</p><p>adaptor image (same eye as Fig. 7a). Transillumination of the thin-</p><p>walled cyst is readily apparent, in addition to, folding (star shaped pat-</p><p>tern) of the posterior aspect of the cyst.</p><p>(a)</p><p>(b)</p><p>Figure 8. Nuclear sclerosis in a dog. (a) Conventional image. Note</p><p>the bluish appearance of the central portion (nucleus) of the lens,</p><p>because of the refraction of shorter wavelengths of visible light. These</p><p>changes may be confused with cataract formation. (b) dSLR camera</p><p>adaptor image (same eye as Fig. 8a). There is minimal refraction of light</p><p>occurring at the nuclearcortical junction, typical of nuclear sclerosis.</p><p>Light freely transmits through the nuclear region of the lens of this</p><p>retro-illuminated image.</p><p>4 p i r i e a nd p i z z i r a n i</p><p> 2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18</p></li><li><p>inferior half of the cornea are difficult to visualize in the con-ventional image; however, they are readily apparent in theimage obtained using the dSLR camera adaptor.</p><p>IrisUsing conventional imaging and standard illuminationtechniques, demonstration of specific and unique featuresof the iris tissue may be problematic. As the dSLR cameraadaptor provides coaxial illumination, transillumination ofthe iridal tissue is possible and aided by the tapetal reflec-tion. This allows for clear illustration of both normal andpathological changes of the iris tissue (Fig. 6) and/or cleardemonstration of structures such as thin-walled iridociliarycysts (Fig. 7).</p><p>LensImaging of the lens and demonstration of potential patho-logical changes often relies on either scattering of lightvia direct-illumination and/or obstruction of light viaretro-illumination. The latter is a preferred means to dem-onstrate nuclear sclerosis, as direct-illumination may be mis-leading to some examiners because of the refraction of theshorter wavelengths of light (Fig. 8). Retro-illumination alsoprovides improved visualization of more subtle changes inlens transparency, a characteristic which is improved uponby the tapetum. Figure 9 is a compilation of various cataractformations which illustrates improved visualization and con-trast of lenticular opacities using the dSLR camera adaptor.Similar improvements may be noted in pseudophakic eyes,</p><p>(a) (b)</p><p>(c) (d)</p><p>(e) (f)</p><p>(g) (h)</p><p>Figure 9. Various forms of cataracts in the dog. Multifocal punctate anterior cortical cataracts associated with hypocalcemia (a, b). Immature corti-</p><p>cal cataract (c, d). Lamellar cataract (e, f). Immature posterior cortical cataracts (g, h). Conventional images (a,c,e,g,). dSLR camera adaptor images</p><p>(b, d, f, h,). Note the absence of specular reflections, clear delineation of lenticular opacities, and increased image contrast. Regions of lenticular opaci-</p><p>fications not identified in conventional images become clearly visible using the dSLR camera adaptor.</p><p>o phth a lm i c p hotog r a p h y u s i n g a d s l r c am e r a ad a p t o r 5</p><p> 2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18</p></li><li><p>demonstrating capsular opacities and lens regrowth follow-ing phacoemulsification (Fig. 10). As this system providescoaxial illumination, the resultant images obtained are trueretro-illumination. Conventional imaging, because of theoff axis displacement of the flash, does not provide true coax-ial illumination. Visualization of lenticular opacities isimproved upon further by the elimination of specular reflec-tions (i.e., Purkinje reflexes) from the cornea and the lensitself. These artifacts have the potential to obscure regionsof particular interest (Fig. 9c).</p><p>Posterior segment imagingExamples of images obtained using a 40D indirect ophthal-mic lens in conjunction with the adaptor system of both thenormal canine and feline fundus are presented in Fig. 11.A more extensive demonstration of the variable magnifica-tion(s) and/or field of view(s) obtainable is presented in arecent report.2 Figure 12 demonstrates the capabilities ofthis system to document fundoscopic disease in the horse,and Fig...</p></li></ul>