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.

    2 p i r i e a nd p i z z i r a n i

    2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18

  • 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.

    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

    2011 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 18

  • 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 solitar