Three Common Photographic Misconceptions
Even the most seasoned photographer can harbor misconceptions about the art of ophthalmic photography. Whether passed down from mentors, or self conjectured, misconceptions and bad habits can lead to poor results. In this first segment, we look at photographer related misconceptions.
1.The camera focus needs to be adjusted throughout a picture series.
Once a focus has been set, with both the crosshairs of the eyepiece and the fundus in sharp focus, you shouldn’t have to adjust the focus of the camera. In standard 35mm photography, the subject of the photograph is only in focus at a certain distance. If this subject moves away or closer to the camera, the focus would need to be adjusted. With a fundus camera, the focus is on infinity, so if the patient sits back in the chair and you move the fundus camera back, the fundus is still in focus, regardless of the working distance. In order to get a full picture of the fundus, the patient and the camera would have to be positioned properly of course, but the focus does not have to be adjusted. This fact will save you a lot of wasted time refocusing during an angiogram. Once your pre injection green photos are in sharp focus, do not touch the focusing knob again, unless you move to the other eye. In that case, a minor adjustment of the focus may be necessary.
If you find that the view through the eyepiece is out of focus, check other factors, such as:
- eyepiece setting may have moved
- patient is not blinking, causing the cornea to dry out, producing hazy media
- the camera or patient is not positioned properly
2. If the photographer has a refractive error of –1.00 diopters, the camera reticle
(eyepiece) can automatically be set for –1.00
This is misleading. The marks on the eyepiece are not actually “measured” to be in diopters. Frequently some emmotropic photographers find their eyepiece setting at -2.00 or higher.
Factors throughout the day may affect your eyepiece setting, such as low or high blood sugar. If you have multiple cameras in a practice setting, your eyepiece setting may vary from camera to camera.
Checking your eyepiece setting throughout the day will prevent your pictures from being
blurry.
To check your eyepiece setting:
- turn the setting to the highest plus (+) setting.
- Place a white sheet of paper in front of the camera.
- Relax your eyes by looking at a distant point.
- Look through the eyepiece with both eyes open, and notice the blurry crosshairs in the center of your view.
- In one quick motion, dial the eyepiece down towards the zero (0) mark, making sure you do this quickly, stop when the crosshairs are in sharp focus. Turning the eyepiece slowly will allow for accommodation and give false measurements.
- Repeat this process three (3) times to ensure a proper reading.
- Check this throughout the day.
3. I can clean the front lens of my fundus camera with any optical cleaner.
The front lens of the fundus camera, called the objective lens, is made of a soft, coated glass. This is easily scratched by even the mildest abrasive. Throughout the day, the objective lens of the camera is touched, sneezed on, coated with tears, and coughed on. In order to view the front surface of this lens, drop the minus (-) diopter lens into the camera and focus on the lens. If there are smudges on the front of the lens, breathe on the lens, forming a fog of condensation. Take a cotton ball (or the inside of an eye patch), and starting from the center, wipe gently in a circular fashion out to the edge of the lens. Repeat this if necessary. Wearing unpowdered exam gloves will reduce the danger of oil from the skin coming in contact with the lens.
If this doesn’t do the trick, you may need to apply a liquid to the lens to move more stubborn material. Using a cotton tipped applicator is not recommended, as solvents may break down plastic applicators or the glue used in wooden applicators, which also offer the possibility of scratching the lens. Solvents recommended need to evaporate fast and non-streaking, such as denatured alcohol, acetone, and ether. If chemicals pool around the edges of the lens, this may break down the cement that holds the lens in place. The same circular wiping technique described before is preferable. Do not saturate the cotton ball, and squeeze out any excess fluid, taking care not to allow the oil on your fingers to contact the cleaning surface of the cotton ball.
Preventative maintenance is key to keeping the objective lens clean. Always cap the lens when not using, and use a manual blower to blow dust off of the lens. Canned or compressed air contains condensation, which can damage the coating on the lens when applied at high pressure.
Author:
Darrin Landry is the owner of Bryson Taylor Inc., an ophthalmic consulting company
specializing in ophthalmic photography and technical skills instruction.