|Year : 2022 | Volume
| Issue : 3 | Page : 643-646
Beauty and the beam: Slit-lamp photography essentials
Santosh G Honavar1, Mrittika Sen2
1 Ophthalmic and Facial Plastic Surgery and Ocular Oncology Service, Centre for Sight, Hyderabad, Telangana, India
2 Ophthalmic and Facial Plastic Surgery and Ocular Oncology Service, Centre for Sight, Hyderabad, Telangana, India; Ocular Oncology Service, Wills Eye Hospital, Philadelphia, PA, USA
|Date of Web Publication||16-Jul-2022|
Dr. Santosh G Honavar
Ophthalmic and Facial Plastic Surgery and Ocular Oncology Service, Centre for Sight, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Honavar SG, Sen M. Beauty and the beam: Slit-lamp photography essentials. Indian J Ophthalmol Case Rep 2022;2:643-6
“When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence” - Ansel Adams
The slit lamp was developed by Alvar Gullstrand in collaboration with Zeiss in 1916. Slit-lamp biomicroscopy allows the examination of the anterior segment, including the eyelids, ocular surface, cornea, anterior chamber, lens, anterior vitreous and even the posterior segment, with the help of specific lenses. But how do we retain what we see? In the 1860s, when the first fundus camera was invented by Noyes in New York and Rosebrugh in Toronto, Helmhotz had voiced his skepticism: “I must confess I cannot yet believe that it will succeed in the human subject.” History has a funny way of emerging victorious. The first account of ophthalmic photography can be traced to Jackman and Webster who published the first image of the fundus in the summer of 1886. Since then, there has been leaps and bounds of evolution in ophthalmic imaging and photography. Ophthalmic photography is an essential means of documentation, tracking and follow-up of patients, patient education, training of residents and fellows, research and publication. Here we describe some essential requirements and principles to obtain high quality slit-lamp images.
| The Camera|| |
There is an array of cameras available in the market. The choice depends on the need, frequency of use, clinical setting, the cost, and the slit lamp being used. The better the camera, the better the resolution. The display resolution is higher with cameras using high-definition media interface. Smartphones have excellent display resolution and allow quick sharing of data. Image quality depends on spatial resolution measured as a function of image pixel density and field of view. The commercial slit lamp with single lens reflex camera yields images with highest image spatial resolution.
- Smartphone: We are in an age where telemedicine will be taking on a more active role in patient care. Smartphones are now available everywhere, including primary care centers and remote areas and in situations of emergency to obtain advice from tertiary centers. They are, therefore, very useful, and one can get good quality images for documentation, consultation and diagnosis.
- Digital compact camera (DCC): These are versatile, cost-effective and can be used for both clinical and intraoperative photography with appropriate adapters. Digital camera brings down the cost considerably, to nearly 1/40th of that of the slit-lamp based digital workstation. One can view the object of interest on the LCD screen. The size of the image is small and is easy to store and carry in the clinic and operating room, and is also easy to share. It has been found that DCCs produce images comparable to traditional slit-lamp cameras. These can also be handled by technicians in satellite centers and have a gentle learning curve.
- Commercially available slit-lamp mounted anterior segment cameras: These are a financial investment and do require upkeep and are most suitable for institutes with dedicated ophthalmic photography technicians.
| The Set-Up|| |
The camera can be hand-held against the eyepiece or fixed. Holding a smartphone camera to the eyepiece is an easy way to get decent pictures, but it is associated with instability and blurred images due to motions of the hand. It also makes it difficult to operate the slit lamp to focus, change magnification and control the illumination. Smartphones are easier to use even in the absence of adapters, with the illumination provided by the slit lamp.
Cameras can be attached to the slit lamp eyepiece that measures 35 mm with various commercially available adapters that meet the specifications of the slit lamp and the camera. One can get ascending or descending adaptable rings to fix the camera. The camera will need to be supported with one hand. It can also be attached to the side tube or observation eyepiece or the main eyepiece after removing the rubber cuff attached to the eyepiece.
Using a beam splitter with the adapter allows a separate channel without compromising on the binocular viewing system and allows for sharp focusing with binocular ocular resolution. But using an adapter for the camera with one of the eyepieces may be easier and more cost-effective.
| The Subject|| |
It is important to obtain informed consent from the patient to photograph, store and use the images for scientific purposes prior to taking pictures. One should also explain to the patient about how the images would be taken, ensuring better patient cooperation. The bright light from the slit lamp will be uncomfortable and the aim should be to obtain quality images quickly. Having a fixed camera also reduces patient time.
The area of interest must be cleaned of any discharge, crust, blood, or stain. The patient should be seated comfortably with their chin on the rest, forehead against the head band and the eye-marker on the slit lamp aligned to the lateral canthus. An external fixation target helps to reduce movements.
| The Photographer|| |
The photographer should have a clear idea about the area of focus. If the ophthalmologist is not the photographer himself, he should convey this information either by personally supervising the photography or by using large, labelled drawings. Studies have shown that slit lamp images obtained by trained ophthalmic technicians under remote supervision by ophthalmologists are comparable to those taken by ophthalmologists 90% of the times favoring their role in teleophthalmology. The photographer should take the image of the normal or unaffected eye first followed by the diseased eye. The images should be uniform, comparable and reproducible on follow-up visits. An assistant can help with holding the eyelids apart, everting the lids or instructing the patient to look in particular directions. It is always good to take multiple images and then later select the best one to store.
| The Illumination|| |
The ambient room illumination should be good. Flash should be turned off since illumination comes from the slit lamp. Two types of illumination are used in slit lamp photography: diffuse and slit. The angle between the eyepieces holder and light source should be set at 45° to minimize the glare from the light source.
Diffuse illumination with the diffuser in place and low magnification (5×) is useful for eyelid margins, everted eyelids for tarsal conjunctiva, bulbar conjunctiva, frontal view of the cornea, iris, and pupil. These images give orientation of the pathology in relation to identifiable structures of the eye; for instance, the laterality of the eye, the canthus and the limbus.
Direct slit illumination at a higher magnification (12×) centered on the pupil is useful for lens clarity, opacity and posterior capsule. Centered on the anterior chamber periphery, the peripheral cornea, iris, anterior chamber depth can be photographed better [Figure 1]a and [Figure 1]b.
|Figure 1: Direct slit-lamp photograph showing anterior lenticonus (a) and Kayser-Fleischer ring More Details (b). Scleral scatter highlighting granular corneal dystrophy (c) and retroillumination showing sutural cataract (d)|
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Specular reflection can be used in high magnification for corneal irregularities. The illumination and viewing arms are kept at 60° from each other and the beam is reduced to a 1-mm slit. Exposure needs to be reduced; the magnification on the slit lamp should be increased, keeping the endothelial layer in focus.
With indirect slit illumination, the light beam is reflected off other anatomical structures, namely, the iris, retina or sclera. These can be in the form of transillumination, sclerotic scatter [Figure 1]c and retroillumination [Figure 1]d, which are taken in techniques similar to slit-lamp examination.
There are specially designed retroillumination cameras available. Retroillumination is useful for evaluating and grading cortical and posterior subcapsular cataract, presence of lens vacuoles, Mittendorf dots, pseudoexfoliation of lens capsule and certain types of corneal opacities. [Figure 2]. The illumination arm is brought to the coaxial position and slit size is kept small. The images should be taken with the slit beam focused once on the iris at the pupillary margin and then on the subcapsular opacity.
|Figure 2: Slit-lamp photograph of the right eye showing (a) Ciliary body melanoma with angle invasion from 11:00 to 2:00 o'clock. (b) Retroillumination demonstrating the lens subluxation and cataract|
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Transillumination is important to delineate the margins of the tumor. A novel technique was described by Krohn et al. for transillumination photography of ciliary body and anterior choroidal melanoma and other intraocular tumors. The background illumination fiber cable of the slit lamp can be released from its distal end and tip gently pressed to the patient's globe. The examination room is darkened, the ISO is kept at 800 and the background illumination is maximized with the flash of the camera delivered through the background illumination cable synchronized with the camera shutter.
The AREDS System for classifying cataracts from photographs prescribes certain specifications that are meant for Topcon slit lamp (Topcon Corporation, Tokyo, Japan) and Neitz retroillumination cameras (Neitz Instruments Company LTD, Tokyo, Japan). However, these may be modified to obtain good quality images of the lens based on the available equipment (slit lamp and camera). The slit beam is fixed at 9.0 mm height and 0.3 mm width and focused at an angle of 45°, bisecting the central lens from 12:00 to 6:00 o'clock.
| The Focus and Magnification|| |
Begin with the lowest magnification and then gradually increase the magnification [Figure 3]. It is preferable to use the slit lamp magnification rather than zooming in with the camera. Higher magnification compromises on the depth of focus, and, therefore, deeper tissues may be out of focus while maintaining focus on the area of interest. This may be useful to focus on a corneal abrasion, foreign body or keratic precipitates when the iris need not be sharply focused. At lower magnification, the depth of focus is maintained. By combining compatible slit lamps and DSLR cameras, the magnification can be increased considerably to achieve information on thickness of corneal epithelium, tear film debris and corneal nerves.
|Figure 3: Slit-lamp photograph with direct diffuse illumination and (a) Low magnification showing iris melanoma of the right eye (see caruncle) from 7:00 to 9:00 o' clock with corectopia and iris seeding. The 360° limbal complexion–associated melanosis and sentinel episcleral vessels are also visible at low magnification. (b) Higher magnification photograph better delineating the endothelial touch and angle invasion|
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Some settings for the camera that have been described for slit-lamp photography are listed below:
Full view of eye: ISO 400, SS 1/60, 10×
Cornea view: ISO 400, SS 1/30, 16×
Iris view: ISO 400, SS 1/30, 30×
For smartphones, some prefer to keep the settings in continuous autofocus mode, whereas others prefer the “touch to focus” mode., Both modes work well and depend on the individual preference. Additionally, the slit lamp joystick needs to be moved to focus on the cornea, anterior chamber, lens, posterior capsule or anterior vitreous.
| The Accessories|| |
Photography with vital stains like Rose Bengal, lissamine green and fluorescein should be performed after obtaining images without the stains. It is important to clean or wipe away excessive stain prior to taking the pictures. Diffuse or broad beam, focal illumination should be used. For fluorescein, images should be obtained both with the white light to show the yellow colour and the cobalt blue filter to specifically cause excitation and fluorescence of the area in focus. It is best to reduce the exposure in the manual setting.
For photography of the angles, Goldman 2, 3 or 4 mirror goniolens or specialized goniophotography devices like EyeCam (Clarity Medical Systems, Pleasanton, CA) and Gonioscope GS-1 (Nidek Co., Gamagori, Japan) can be used. The optic nerve and surrounding retina can also be photographed using +60, +78 or +90 D lenses.
There are no fixed templates but only guidelines that one can follow for ophthalmic photography. One often achieves perfection by fiddling around with available tools and looking objectively through the eyepiece. It ultimately tests the creativity and ingenuity of the ophthalmologist—to click a standard photograph or to create a piece of art.
“You can't depend on your eyes when your imagination is out of focus”
- Mark Twain
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Bennett TJ, Barry CJ. Ophthalmic imaging today: An ophthalmic photographer's viewpoint - A review. Clin Exp Ophthalmol 2009;37:2-13.
Age-Related Eye Disease Study Research Group. The age-related eye disease study (AREDS) system for classifying cataracts from photographs: AREDS report no. 4. Am J Ophthalmol 2001;131:167-75.
Krohn J, Kjersem B. A modified digital slit lamp camera system for transillumination photography of intraocular tumours. Br J Ophthalmol 2012;96:475-7.
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[Figure 1], [Figure 2], [Figure 3]