Digital Photography For Ophthalmologists
– An economical alternative
note: digital photography and cameras have made some major strides since this article was written in 2006, but there are still some valuable tips.
As residents at the University of Iowa, we are frequently presenting cases during our morning rounds. Many of these cases are seen "after hours" when it is difficult to document ocular problems because photography services are not available. Over the last three years, we developed an economical method for photographing ocular findings using a $300 digital camera. Ophthalmologists in training and clinical practice can utilize this technique to provide high quality external and anterior segment photography services for their patients without the expense of both a digital camera and slit lamp mounted photography system costing over $15,000. Below we discuss our experience using consumer-grade digital cameras in an academic setting.
Digital Photography Basics
There are a large variety of digital cameras on the market. With rapid expansion in technology, we now have numerous options at affordable prices. As first year ophthalmology residents, we started using the Canon PowerShot S230 Digital Elph which is a 3.2 megapixel (MP) camera that stores images on a Compact Flash (CF) memory card. The Canon S230 has been replaced with an equivalent model, the Canon PowerShot SD110, which maintains the 3.2 MP resolution but uses a Secure Digital (SD) memory card. Both cameras are less than 3.5 inches long and weigh less than 6 ounces! These cameras fit nicely into a pocket or in a cell phone case attached to the belt. After demonstrating the utility of these cameras to the department, they have now become standard equipment for all Iowa residents.
The high resolution and portability of these cameras make them ideal for use in a diverse clinical setting where one would like to obtain external and slit lamp photographs. We have found that a 3 MP resolution exceeds our needs for documenting clinical findings, making digital copies of imaging studies, and presenting cases. However, for those who demand higher resolutions (or who survive on more than a resident salary), Canon also offers the PowerShot S410 and S500 that provide 4 and 5 MP resolution, respectively, for less than $400.
Storing and organizing digital images after acquisition is one of the problems with this approach. For the time being, images can be stored on a secured personal computer using a filing system of your choosing. A simple system would be to store images by patient or by disease process. A more sophisticated system would allow both. As practices move to electronic medical records, however, this problem will disappear. At the AAO meeting in 2004, for example, a wide variety of companies offered systems that allow the uploading of digital files to individual electronic charts. As residents, we have organized images from "classic" and unusual cases into folders such that they can be found later. Using this approach, some of the Iowa residents will have over 4000 images after finishing their training.
External Photographs of the Eye
Because our resident budgets do not allow us to try out a variety of cameras, we will describe the specifics of how we have used the Canon PowerShot S230 and SD110. The principles described below will apply to other cameras, however.
A) The black arrowhead indicates that the camera is in center focus mode. There is a white rectangle where the camera will auto focus on the subject. The blue arrowhead indicates that the camera is in no flash photography mode.
B) The black arrowhead indicates that the camera is set to macro mode. In macro mode, the photographer will be able to capture images as close as 4 inches from the subject.
All digital cameras have an auto-focus system. The Canon PowerShot uses the proprietary AiAF system that automatically attempts to select the best focus. For clinical photography, we have found that the AiAF should be turned off and the camera set to "center focus" (Figure 1). As the name implies, "center focus" forces the camera to focus only on the center object. This is important, for instance, when a lid lesion is the subject of interest, and the AiAF system may focus on the eyelashes instead of the lesion. The ISO setting should be set to AUTO until the physician is more experienced with the different ISO speeds of the camera. Flash may or may not be needed depending on ambient lighting. We recommend trying to capture images with both the flash and no flash settings to see which provides a better image. The most important setting is the macro function (denoted by a flower symbol, Figure 1) which allows the camera to focus on close objects. Depending on the model, object distance to the lens may vary from 2 inches to 4 inches in macro mode. Because it allows images to be taken from a short distance, the macro setting provides detailed images of the eye (Figure 2). To assure proper focus with the PowerShot cameras, press the shutter button half-way. A green box will appear on the LCD viewfinder when the area of interest is in focus (Figure 3). If a yellow box appears, then the camera should be repositioned until depression of the shutter button half-way down results in a green box. Depressing the shutter all the way down then captures the image.
This photograph was taken with the Canon PowerShot S230 in macro mode without flash photography. In macro mode, we are able to document the corneal defect.
3A) Pressing the shutter button half-way down will allow the photographer to determine if the subject is in focus. A green rectangle appears when the camera is in focus. A yellow rectangle appears when the camera position requires adjustment to place the subject in focus. Pressing the shutter button completely down will capture the image.
3B) Positioning of the digital camera for slit lamp photography may be facilitated with an adaptor or fingers. This requires practice, but camera positioning is easy to learn, particularly for surgeons with steady hands. One of the first year residents (Jordan Graff, MD) has used this technique to capture images of the posterior pole using a 90D lens.
Most digital cameras also offer video capturing. We have used this feature on the PowerShot cameras to document abnormalities of ocular movement including nystagmus and strabismus.
Slit Lamp Photography
Using the settings outlined above with a slit lamp biomicroscope, we have captured high resolution images of the anterior segment.
For slit lamp photography, the camera needs to be set to:
- Center focus
- AUTO ISO
- Macro mode
- Flash off
To take a photograph, focus on the desired anterior segment finding with the slit lamp using either the left or right biomicroscope ocular. Through the same eye piece and using the LCD viewfinder on the camera, center and focus on the subject by moving the camera away or towards the eyepiece. Ideally, a spacer between the eyepiece and camera lens can be made, but using a finger works well too (Figure 3). Remember to depress the shutter half-way down until the green box appears indicating that the subject is in focus. If a yellow box appears, then reposition the camera slightly and depress the shutter half-way down again. For certain ocular findings, such as keratic precipitates, iris transillumination defects, or lens opacities, an external light source is not necessary (Figure 4). Because digital cameras lack the dynamic range of the eye, however, most anterior segment photographs require an external light source. We balance a Finhoff transilluminator on the arm of the slit lamp or have an assistant hold the transilluminator. Without an external light source, the camera will usually make a poor choice regarding exposure, and the result is an image that is either too dark or too bright. The external light source provides enough background illumination so that the camera can capture the scene correctly (Figure 5).
As with external photography, video can be acquired through the slit lamp. We demonstrated this by documenting a Seidel positive traumatic wound that resulted in extrusion of vitreous through a scleral defect (video in Windows Media Format).
4A) Transillumination defects of the iris in pigment dispersion syndrome.
4B) Slit lamp photography denoting crystalline deposits in the cornea of a patient with cystinosis. Without an external light source to provide diffuse illumination, the camera highlights only the slit beam.
5A) Diffuse illumination with a Finhoff transilluminator permits photography of a suppurative corneal ulcer. The slit beam is narrowed to demonstrate marked ulceration and corneal thinning, and the diffuse illumination allows photography of adjacent pathology.
5B) A conjunctival melanoma was photographed through the slit lamp ocular in macro mode without a flash. The slit beam is used to emphasize the elevated melanoma, and diffuse illumination permits the photography of the whole lesion.
Inexpensive digital photography is altering the educational environment at the University of Iowa. It has proven to be a great method to document ophthalmic diseases and to obtain opinions from faculty. Images have also been used to educate patients and family members about diseases by displaying them on computer monitors or on the camera’s LCD display. With an unrestricted grant for resident education arranged by Allergan, residents at the University of Iowa are photographing ophthalmic cases with their compact digital cameras and presenting them at departmental morning rounds and on the internet (www.EyeRounds.org).
There is also promise for this approach in clinical practice. Armed with a computer, optional photoprinter, and digital camera, ophthalmologists can offer high resolution photography services for their patients at an affordable price.