Dr Simon Chen
MBBS BSc FRCOphth FRANZCO
Retinal & Cataract Surgeon, Vision Eye Institute, Sydney
Smartphone cameras are transforming photography as advances in sensor design, microprocessors and image processing software provide improved image capture quality. Eye-care professionals are increasingly using smartphones for slitlamp photography in preference to dedicated anterior segment cameras in diverse settings such private practice, public hospital clinics, emergency departments and low resource areas.
Slitlamp photos help document clinical signs to monitor disease, facilitate specialist referrals, assess contact lens fittings and educate patients, and can provide medico-legal documentation. When examining photophobic patients, images can be reviewed for pathology, minimising uncomfortable light exposure.
Any smartphone can take slitlamp photos but the Apple iPhone 6 is particularly well-suited for this and is the focus of this article.
Advantages of smartphones over anterior segment cameras
The first and probably most significant advantage to using a smartphone is cost. A new iPhone 6 costs less than $900 compared to over $20,000 for some anterior segment cameras.
Anterior segment cameras are mounted on slitlamps so patients may need to transfer between rooms to access the camera. This is particularly inconvenient for patients with limited mobility. Smartphones can be used with any slitlamp in any room, averting the need to transfer patients. This saves time, improves patient flow, reduces the risk of patient falls and makes it more likely that clinicians will go to the trouble of taking slitlamp images.
Compared to anterior segment camera software, smartphone software is usually more familiar, easier to use, and updated more regularly, and enables more efficient access to camera controls, image editing functions and image transfer via email or SMS.
In my experience, the iPhone 6 consistently takes better quality slitlamp photos than many anterior segment cameras, competitor smartphones and previous iPhones. This is due to a combination of factors, including the quality of the camera lens, sensor, processor and software.
Smartphones record images through the slitlamp eyepiece with no loss of light, unlike some anterior segment cameras that use beam splitters to divert portions of light to the camera sensor. The ability to see images captured live on screen image is an advantage of smartphones over some anterior segment cameras that lack this function, resulting in a captured image different from that seen through the slitlamp.
The iPhone 6 can record full HD video at 60 frames per second or HD video at 240 frames per second (higher quality and faster frame rates than anterior segment cameras), allowing slow-motion video capture. This enables the assessment of tear film and blinking dynamics in ocular surface disease as well as contact lens movement. Some anterior segment cameras cannot capture video.
Smartphone operating systems and apps are regularly updated at no cost to improve the efficiency and quality of image capture. Smartphones can be cost-effectively repaired when damaged or replaced when better smartphone cameras are released. In contrast, repairing, upgrading or replacing an anterior segment camera is more expensive and labour intensive.
|Slitlamp images taken with an iPhone 6
Apple iPhone 6 camera features
The iPhone 6 has an eight-megapixel camera and Apple 64-bit A8 processor, which speeds aspects of image acquisition including launching the Camera app, shot-to-shot time and HDR (High Dynamic Range) images.
The biggest advantage that the iPhone 6 has over previous models when taking slitlamp photos is its faster focusing speed. This is due to the iPhone 6 camera sensor employing advanced phase detection autofocus technology whereas older iPhones use a slower contrast detection autofocus method. The result is that the iPhone 6 focuses on anterior segment structures noticeably faster and more accurately than previous models.
This is important because there is a short window of opportunity to capture an image before patients blink or move their eyes. Poor quality smartphone images are often due to slow focusing speeds causing the camera to constantly refocus when patients blink or move their eyes, leading to a frustrating delay and reduction in quality. The iPhone 6 is able to focus almost instantly, enabling rapid image acquisition.
The native Camera app in iOS 8 allows independent control of focus and exposure as well as basic image editing and sharing. The HDR mode rapidly captures three shots at different exposures (long, normal and short) that are blended together to obtain a single well-exposed shot with increased dynamic range in high contrast situations.
Slitlamp photography using an iPhone without a slitlamp adaptor
With practice, the technique described below can be easily learned and used to take high-quality slitlamp images. The majority of patients can be photographed in less than 60 seconds, making this technique suitable for routine use in a busy clinical setting.
1. Focus on the area of interest as per a routine slitlamp exam. For most slitlamp photos, using the slitlamp’s neutral density filter to reduce illumination decreases the chance of an overexposed image and increases patient comfort.
Alternatively, a diffuser attachment can be used if available, or the mirror in the illumination column can be reversed so that its non-reflective surface is exposed.
2. Open the default Camera app on the iPhone by pressing the home button and swiping up from the camera icon on the bottom right of the lock screen. This averts the need to enter a passcode if the iPhone is locked, enabling you to start taking photos within seconds. Ensure that the camera flash is turned off.
3. Hold the iPhone in your dominant hand and align the camera lens behind a slitlamp eyepiece. Start away from the eyepiece then move closer until the image seen through the slitlamp eyepiece appears on the screen. Use the thumb and index finger of your non-dominant hand to stabilise the top of the iPhone and rest the little and ring fingers of that hand on top of the eyepieces (Figure right). Make small vertical or horizontal adjustments to the position of the iPhone until the image fills the screen. The correct plane is behind the eyepiece so the camera should not touch the eyepiece.
4. Tap the screen to focus on the area of interest. A yellow square and sun icon will appear around focus point. If the image looks too bright (over exposed), press the sun icon and drag down to make the photo darker (reducing the exposure).
5. Press the on-screen image capture button to take the photo. If blinking or eye movements interfere with image capture, lock the focus and exposure settings by tapping and holding the screen for two seconds over the area of interest until AE/AF LOCK appears on the screen. Next, activate Burst mode by pressing and holding the image capture button to rapidly take multiple photos (at 10 shots per second). Choose the best image from the series of photos taken.
Appropriate lighting techniques are important to optimise image quality but are beyond the scope of this article.
Adaptors such as EyePhotoDoc, Zarf iPhone adaptor, Magnifi iPhone adaptor and Tiger Lens are available to stabilise smartphones, removing the need to hand-hold them during slitlamp photography. Clinicians can also make slitlamp adaptors themselves using cheap and widely available materials.1
Smartphones can be used without slitlamps to capture images or video of eyelid lesions and ocular motility abnormalities. They can also be used to copy fundus images, optical coherence tomography scans, corneal topography scans and visual field tests from computer monitors or paper print-outs.
|Hand positioning used when taking slitlamp photos with an iPhone 6 Plus without a slitlamp adaptor
Informed consent should be obtained prior to taking images. Images can be automatically uploaded to the cloud for storage and transfer to a computer using services such as Evernote, Dropbox or iCloud. It is important to ensure patient confidentiality by using non-identifying labels such as patient file numbers instead of names, deleting images from the smart phone and protecting the device with a password.
Smartphone cameras can be used to efficiently capture high-quality slitlamp photos without a slitlamp adaptor or third-party software. The iPhone 6 has numerous advantages for slitlamp photography over previous iPhones, competitor smartphones and even dedicated anterior segment cameras.
- Papchenko TL. How to take slit lamp photos with any smartphone and without eyepiece adaptor. 2014, May 10, http://youtu.be/57cysrc2Irc