the contact lens exam
Slit Lamp Photography by Cell Phone
BY JOHN MARK JACKSON, OD, MS, FAAO
A dedicated slit lamp digital camera photography set up is an invaluable tool for any clinical setting. Being able to photodocument an ulcer, corneal staining, or a GP contact lens fit can be a great aid for baseline exam findings, monitoring change of a condition, or for patient education.
But what if you don't have one of these expensive systems or you're working at a satellite office that doesn't have one? Never fear; you can still take photos through the slit lamp. I've previously written about using a handheld digital camera for this, but you can also use a piece of equipment that you probably take with you everywhere: your cell phone.
Most cell phones these days have a camera. Some of the "smartphones," such as the iPhone and Blackberry models, have cameras with very good resolution. Taking a slit lamp photo with a cell phone is as easy as holding the phone up to the slit lamp ocular and snapping away. Below are some tips to help you get the most out of taking photos this way.
A How-to for Successful Photos
First, get the structure you want to photograph focused and stationary through the slit lamp oculars. Second, realize that the cell phone camera has a very tiny lens. If you will recall your first-year optics courses, only a small area of the slit lamp ocular is actually "filled" with light coming out. This is the "exit pupil" for the system. You will have to line up the cell phone lens with the exit pupil of the ocular. This can be a little tricky.
You need to start with the cell phone about a foot away from the ocular and center the exit pupil in the phone's screen, as shown in Figure 1 (taken with an iPhone). The exit pupil is the small white circle in the ocular. Slowly move the phone closer to the slit lamp until the screen fills up with the slit lamp view. This will take some practice! Once you are aligned, snap your photo.
Figure 1. Slit lamp ocular and exit pupil viewed through the phone.
Figure 2 shows a photo of a Paragon CRT lens (Paragon Vision Sciences) taken with an iPhone through the slit lamp. The quality is pretty good; you can even read the engraving on the lens and see bubbles under it.
Figure 2. Paragon CRT lens captured with an iPhone.
Wide beam fluorescein shots work well through the slit lamp, but with white light the photos can be overexposed. You can put a piece of transparent tape over the slit lamp mirror to act as a diffuser.
Optic section shots don't work well because there is not enough background light for the entire eye to show up in the photo. I've experimented with having an assistant highlight the background with a penlight. This can work but it is a little cumbersome.
Once you have a good photo, you have to get it off the phone. Depending on your phone, you could either e-mail it to yourself or transfer it to your computer via Bluetooth or a cable.
Taking photos like this isn't an optimal solution, but it sure can help in a pinch or augment your existing system. CLS
Dr. Jackson is an associate professor at Southern College of Optometry where he works in the Advanced Contact Lens Service, teaches courses in contact lenses and performs clinical research.