Direct phoneoscopy:
Direct phoneoscopic image - IPhone 4s
The technique of direct visualization of the retina using close direct ophthalmoscopy with a conventional direct ophthalmoscope can be readily mimicked using certain smart phones with
the correct camera application. This technique I have named "direct phoneoscopy".
Using a phone camera with a wide angle lens allows us to directly image a wider retinal area than is achievable using a conventional direct ophthalmoscope. In many cases a direct view of the retina comparable to that previously only obtained using indirect ophthalmoscopy is possible.
The ideal camera phone for direct phoneoscopy will have:
1) a small Light to Lens (LL) distance
2) the lens positioned near the corner of the phone.
3) have a light whose illumination can be varied
4) has a lens with a wide angle.
In large animals, and small animals with dilated pupils, I prefer my iPhone XS max as it’s greater light sensitivity and image stabilisation means that I need less light to image the retina.
In small animals where I haven’t dilated the pupil the larger light to lens distance of all but the the iPhone4S starts to cause problems. The tiny 6mm Light to Lens distance of the iPhone 4s and it's small size means that this is still my favourite phone for imaging the small animal fundus. The iphone SE comes in at a close second with its small size and faster camera making up for the slightly larger light to to lens distance compared to the 4s although the new, dual lens, iPhone X phones look like they could take the top spot re retinal image quality despite being a little bigger than the 4S and the SE making them harder to use.
In my opinion the easiest phone to use for direct phoneoscopy in small animals to date is the iPhone 4s as it is least affected by pupil size however the increasing light sensitivity and lens quality seen with the newer generation iPhones means that as long as the pupil is big enough better images can be obtained with these newer phones. The newest generation dual lens iPhone Xs and derivatives have a lens to light distance only a little wider than the 4s which, coupled with their increased light sensitivity and processor speed make them the best iPhones currently available for small animal retinal photography.
the correct camera application. This technique I have named "direct phoneoscopy".
Using a phone camera with a wide angle lens allows us to directly image a wider retinal area than is achievable using a conventional direct ophthalmoscope. In many cases a direct view of the retina comparable to that previously only obtained using indirect ophthalmoscopy is possible.
The ideal camera phone for direct phoneoscopy will have:
1) a small Light to Lens (LL) distance
2) the lens positioned near the corner of the phone.
3) have a light whose illumination can be varied
4) has a lens with a wide angle.
In large animals, and small animals with dilated pupils, I prefer my iPhone XS max as it’s greater light sensitivity and image stabilisation means that I need less light to image the retina.
In small animals where I haven’t dilated the pupil the larger light to lens distance of all but the the iPhone4S starts to cause problems. The tiny 6mm Light to Lens distance of the iPhone 4s and it's small size means that this is still my favourite phone for imaging the small animal fundus. The iphone SE comes in at a close second with its small size and faster camera making up for the slightly larger light to to lens distance compared to the 4s although the new, dual lens, iPhone X phones look like they could take the top spot re retinal image quality despite being a little bigger than the 4S and the SE making them harder to use.
In my opinion the easiest phone to use for direct phoneoscopy in small animals to date is the iPhone 4s as it is least affected by pupil size however the increasing light sensitivity and lens quality seen with the newer generation iPhones means that as long as the pupil is big enough better images can be obtained with these newer phones. The newest generation dual lens iPhone Xs and derivatives have a lens to light distance only a little wider than the 4s which, coupled with their increased light sensitivity and processor speed make them the best iPhones currently available for small animal retinal photography.
Direct phoneoscopy – a step by step guide:
- Mydriasis is helpful but not always essential especially if using a phone with a short Light to lens distance.
- Open camera app – see the “Which App” section if you don’t already have a suitable app installed
- Turn the LED on continuously – if you do not have a suitable app installed use your embedded video app and turn the light on.
- Reduce the LED illumination – if this can not be done within the app then apply multiple (3) layers of micropore tape or similar to the LED.
- Image the tapetal reflection from arm’s length- the distant direct ophthalmoscopy technique can be mimicked in this fashion. Zoom in until the tapetal reflection fills the screen.
- Zoom out again prior to imaging the retina.
- Move the camera towards the eye – when the eye is closer than the camera’s minimum focal distance the retina will start to be imaged.
- Position the camera close to the cornea (2-5mm) in the same was you would position a direct ophthalmoscope when performing close direct ophthalmoscopy. Removing your camera case will make this easier.
- Tap the screen to focus on the optic nerve head.
- If your app allows separate focus and exposure (e.g. Camera +) then tap the tapetal fundus to avoid “white out” due to the highly reflective tapetum.
- Reposition the exposure on the non-tapetal fundus to image.
