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

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  • Anterior and posterior segment photography. An alternativeapproach using a dSLR camera adaptor

    Chris G. Pirie and Stefano PizziraniDepartment of Clinical Sciences, Tufts Cummings School of Veterinary Medicine, 200 Westboro Rd, North Grafton, MA 01536, USA

    Address communications to:

    Dr. C. G. Pirie

    Tel.: 508-839-5395

    Fax: 508-839-7922

    e-mail: chris.pirie@tufts.edu

    AbstractPurpose To describe a novel digital single lens reflex (dSLR) camera adaptor foranterior and posterior segment photography.

    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

    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

    illumination during viewing was provided by a single white light-emitting diode(LED) within the adaptor, while illumination during exposure was provided by the

    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.

    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

    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.

    Key Words: anterior segment, camera adaptor, digital photography, digital singlelens reflex, posterior segment

    INTRODUCTION

    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

    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

    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

    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.

    MATERIALS AND METHODS

    Canine, feline, and equine patients presenting to the TuftsCummings School of Veterinary Medicine Ophthalmology

    2011 American College of Veterinary Ophthalmologists

    Veterinary Ophthalmology (2011) 18 DOI:10.1111/j.1463-5224.2011.00963.x

  • 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.

    Figure 1. Photograph of the dSLR camera adaptor alone with tube

    extension for the pop-up flash. Extension for an accessory flash is not

    shown.

    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

    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-

    dus. Reflected light from the fundus is transmitted through the indirect ophthalmic lens, camera lens, second plate beam splitter, and second linear

    polarizer onto the CMOS sensor of the camera body.

    Figure 3. Photograph of the dSLR camera adaptor mounted between

    the camera body and camera lens. This arrangement allows for imaging

    of the anterior segment.

    Figure 4. Photograph of the dSLR camera adaptor mounted between

    the camera body and camera lens with a 78D indirect ophthalmic lens

    secured to the camera lens. This arrangement allows for imaging of the

    posterior segment.

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  • 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

    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

    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,

    (a)

    (b)

    Figure 5. Stromal keratitis presumed secondary to FHV-1 in a cat.(a) Conventional image. (b) dSLR camera adaptor image (same eye as

    Fig. 5a). Note the absence of specular reflections, increased contrast,

    and visualization of corneal neovascularization and intrastromal

    infiltrates.

    (a)

    (b)

    Figure 6. Iris hypoplasia of a blue-eyed cat. (a) Conventional image.

    (b) dSLR camera adaptor image (same eye as Fig. 6a). Note transillumi-

    nation of the thinner iris tissue, both involving the pupillary and ciliary

    regions. The region of the collarette is thicker and does not

    transilluminate.

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  • 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

    RESULTS

    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

    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.

    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.

    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

    (a)

    (b)

    Figure 7. Thin-walled iridociliary cyst within the anterior chamber of

    a Golden Retriever associated with pigmentary uveitis. (a) Conventional

    image. Note the specular reflections. The cystic like structure is readily

    apparent; however, transillumination is minimal. (b) dSLR camera

    adaptor image (same eye as Fig. 7a). Transillumination of the thin-

    walled cyst is readily apparent, in addition to, folding (star shaped pat-

    tern) of the posterior aspect of the cyst.

    (a)

    (b)

    Figure 8. Nuclear sclerosis in a dog. (a) Conventional image. Note

    the bluish appearance of the central portion (nucleus) of the lens,

    because of the refraction of shorter wavelengths of visible light. These

    changes may be confused with cataract formation. (b) dSLR camera

    adaptor image (same eye as Fig. 8a). There is minimal refraction of light

    occurring at the nuclearcortical junction, typical of nuclear sclerosis.

    Light freely transmits through the nuclear region of the lens of this

    retro-illuminated image.

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  • 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.

    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).

    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,

    (a) (b)

    (c) (d)

    (e) (f)

    (g) (h)

    Figure 9. Various forms of cataracts in the dog. Multifocal punctate anterior cortical cataracts associated with hypocalcemia (a, b). Immature corti-

    cal cataract (c, d). Lamellar cataract (e, f). Immature posterior cortical cataracts (g, h). Conventional images (a,c,e,g,). dSLR camera adaptor images

    (b, d, f, h,). Note the absence of specular reflections, clear delineation of lenticular opacities, and increased image contrast. Regions of lenticular opaci-

    fications not identified in conventional images become clearly visible using the dSLR camera adaptor.

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  • 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).

    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. 13 illustrates the ability to document and monitordisease progression.

    DISCUSSION

    This preliminary report demonstrates that high-qualityreflex-free digital images of both the anterior and posteriorsegments are obtainable using this dSLR camera adaptor.This system is primarily designed to address a number ofcost prohibitive issues, utilizing a number of components

    (a)

    (b)

    Figure 11. Representative canine (a) and feline (b) posterior segment

    images obtained using the dSLR camera adaptor in conjunction with a

    40D indirect ophthalmic lens.

    (a)

    (b)

    Figure 10. Pseudophakia in a dog 1 year following cataract surgery.(a) Conventional image. The intraocular lens, anterior capsular pigment

    deposition, capsular fibrosis, and Elschnig pearl formations are identifi-

    able, however, lack detail, and contrast. Specular reflections obscure a

    portion of the image. (b) dSLR camera adaptor. Anterior pigment depo-

    sition and Elshcnig pearl formation are well delineated, and no specular

    reflections are present.

    Figure 12. Proliferative optic neuropathy in a horse.

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  • common to the examiner (i.e., dSLR camera and indirectophthalmic lens). As this system is an adaptor, its use is notlimited to one particular brand or model. Upgrading the sys-tem (i.e., increasing pixel count) is possible by altering thecamera body utilized. Furthermore, while not demonstratedin the current report, both still and videographic recordingsare possible using this adaptor and dependent on the capa-bilities of the camera body itself. As this is a digital-basedsystem, real time viewing, alterations and/or adjustments ingain, focus, and/or flash intensity are easily performed. Thisensures maximum image quality at the time when the imageis obtained. Additionally, immediate image evaluationallows for rapid diagnoses, improved patient/client educa-tion, and the initiation of appropriate treatment options. Nospecialized software or image editing programs are required.Unlike conventional imaging using a dSLR camera alone,

    this dSLR camera adaptor system offers direct viewing ofthe region of interest as provided by the solitary LED withinthe unit. As demonstrated in this report, it offers improvedimage contrast and eliminates specular reflections whenimaging the anterior segment, as compared to conventionalimaging. The latter feature may hold significant promise,specifically in regard to more objective automated

    evaluations of lenticular opacities (cataracts or posteriorcapsular opacifications). Some currently available imagingsystems designed with this purpose in mind are costly andmay be prohibitive.5,6 Additionally, several images taken atdifferent angles may be required for subsequent quantitativeanalysis.7 While a variety of software programs are availableand capable of eliminating specular reflections, the accuracyand reproducibility of these programs are dependent on theinitial image quality.In veterinary medicine, a practical photographic imaging

    system should meet several ideal parameters. It should berelatively inexpensive, portable, versatile, simple, and not beexcessively time consuming to use. We feel the dSLR adap-tor presented in this report meets these aforementioned cri-teria and provides a viable cost-effective alternative toexisting imaging systems while maintaining high qualityimages.Routine and repeatable acquisition of high quality images

    are dependent on a number of factors specific to the photog-rapher (alignment and focusing), the patient (head move-ment, pupillary dilation, media opacities), and the imagingsystem.8 Use of this dSLR adaptor does require a basicknowledge of photographic principles and a clear under-standing of the capabilities of the camera body employed.One limitation of the dSLR adaptor in its current design isthe use of cross-polarized filters that results in the need for agreater power of light emitting from the system.Much potential and promise exists with this novel system,

    and this preliminary report demonstrates an ongoing bodyof work. While not a feature of the current report, the dSLRcamera adaptor does allow for the insertion of various inter-ference filters. This provides the photographer the option toconduct more advanced imaging techniques (i.e., fluoresece-in angiography) and will be presented in a later publication.

    ACKNOWLEDGMENTS

    A special thanks to Drs S. Pumphrey and A. Welihozkiy,Mrs. BMazza andMrs. N. Manning for their assistance.

    FUNDING

    None.

    REFERENCES

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    2. Pirie CG, Pizzirani S. A new approach to digital posterior seg-

    ment photography using a camera adaptor (abstract). ARVO 2011,

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    3. Gullstrand A. Einfuhrung in die Methoden der Dioptrik des Auges des

    Menschen. S. Hinzel, Leipzig, 1911.4. Delori FC, Parker JS, Mainster MA. Light levels in fundus pho-

    tography and fluorescein angiography. Vision Research 1980; 20:10991104.

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    (b)

    Figure 13. Chorioretinitis with multifocal circumscribed lesions in acat, etiology unknown. (a) At initial presentation. (b) Two weeks follow-

    ing nonspecific therapy.

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  • 5. Chylack LT Jr, Wolfe JK, Friend J. Validation of methods

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    European-American Anticataract Trial (REACT). Ophthalmic Epi-demiology. 1995; 2: 5975.

    6. Grewal D, Jain R, Brar GS et al. Pentacam tomograms: anovel method for quantification of posterior capsule opacifica-

    tion. Investigative Ophthalmology and Visual Science 2008; 49:20042008.

    7. Findl O, Buehl W, Siegl H et al. Removal of reflections in thephotographic assessment of PCO by fusion of digital retroillumi-

    nation images. Investigative Ophthalmology and Visual Science 2003;44: 275278.

    8. Maberley D, Morris A, Hay D et al. A comparison of digital reti-nal image quality among photographers with different levels of

    training using a non-mydriatic fundus camera. Ophthalmic Epide-miology 2004; 11: 191197.

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