Recognizing and Eliminating Photographic Artifacts

Artifacts can be defined as a physical interruption or interference of a latent image to its photographic media, be it film plane or computer capture board. These can cause poor results, both artistically and diagnostically, and can be broken down into categories.

Patient induced artifacts are typically the most common. Patients tend to blink rapidly during photography, and the chance of photographing a patient’s lids or lashes are good. Poor media, due to corneal changes, cataracts, or vitreous opacities will hinder photographs as well. Make sure the patient is positioned properly and comfortably, with their chin firmly down in the chin rest and their forehead against the bar. To reduce corneal changes, remind the patient to blink often, and capture the pictures between blinks. Telling the patient not to blink will lead to tearing and discomfort for the patient. Cataracts and vitreous opacities are problems that the patient cannot help change, so try changing the angle of your viewing to see if you can look around a cataract, or have the patient rapidly move their eye around to shift any vitreous opacities to outside the optical center.

Also common are artifacts caused by the camera. Dust or smudges on the objective lens will show up in pictures as white spots or blurry areas. Take care of the lens and blow dust off with a manual blower, and cover the lens when not in use. Patients that tear during photography can blink and splash the front surface of the objective lens, causing spots that, when dried, are difficult to remove. Cleaning smudges off of an objective lens can also be a difficult and tedious task (see previous article).

Photographer induced artifacts are more easily remedied. A desaturated, almost bluish photograph may indicate that your working distance is too far, and a washed out, whitish picture may mean you are too close to the subject. These artifacts should be seen through the eyepiece as well, so adjust your working distance if you are seeing these. Remember, “garbage in, garbage out”. In order to find your proper working distance, move the camera into position until the retina has evenly distributed color saturation. Then move the whole camera slightly to one side then the other, producing white or yellow arcs of light. These indicate that you are in the proper plane. To eliminate these arcs of light, simply move the camera in the opposite direction of the arcs.

Film processing artifacts, obviously, occur after the picture has been captured and the film goes through its developing process. These may present themselves as spots, especially water spots on black and white angiography film. If this is a recurring problem, consider switching labs or speaking with them directly. Most commercial labs are not used to processing fluorescein angiograms, and may not understand the significance of an artifact. In the case of color film, the type of film you are using, as well as the processing lab’s chemicals can affect color saturation. Make notes of any problems and check for trends.

When dealing with electronic images, computers can create a whole new batch of artifacts, including static interference, partial images due to low memory, and images affected by viruses. The most common digital artifacts are black spots, resulting from dust or smudges on the glass surfaces within a relay lens. As with the objective lens, these are best removed using a manual blower, and without any liquid. If you are unable to eliminate these artifacts, the camera manufacturer may need to be called to further investigate. Lighter colored anatomy, such as optic nerve heads or retinal scars, can be “blown out”, or so white that the edges become indistinct. This artifact is called blooming, and usually can be fixed by lowering the flash setting, or not enhancing the image.

Differentiating between digital artifacts and camera artifacts will save a lot of time. Black artifacts are typically associated with digital imaging, resulting from shadows of a foreign object such as dust, and occur in the camera optical system after the fundus camera has captured the image. Camera artifacts are usually white in color, and occurs in the camera optical system before the fundus camera captures the image, such as dust on the objective lens.

 Author:

Darrin Landry is the owner of Bryson Taylor Inc., an ophthalmic consulting company
specializing in ophthalmic photography and technical skills instruction.