A smartphone lens attachment, D-EYE gives a better visual of the pupil and eye. Once you see the red reflex from the eye, the D-EYE is correctly focused.

It gives a better visual of the pupil and eye. Once you see the red reflex from the eye, the D-EYE is correctly focused. You can increase the field of view by moving the phone/D-EYE closer to the eye, without changing the focus.
“D-EYE uses the principle of direct ophthalmology. It’s like looking through a keyhole – the closer you are to the keyhole, the wider the field of view you have beyond it, said Dr. Russo.
Using the smartphone’s auto focusing capabilities, refractive errors can be corrected to compensate between -10D myopia to +10D hyperopia. Even with undilated pupils, it’s possible to scan the retina with a field of view of 5-8 degrees.
Optic disc with pupils as small as 2mm, can be viewed so the D-EYE can offer a rapid screening for glaucoma or hypertensive retinopathy for undilated pupils.
Source-Medindia