Mobile applications: Eye test using mobile phone (NETRA)

Some things are simple just by using current technology and combining them in interesting ways.

Problem statement: It is difficult to get an eye test in remote parts of the world where the doctors do not visit or cannot visit. Alternatively, an eye test requires complex instrumentation and is expensive that the Doctor even if he visits the remote area.

Solution: A device that fits on the phone that enables the Dr to conduct an eye test. The cheap device fits on standard mobile phone screen and enables the doctor or patient to perform an eye exam quickly. This system is called NETRA: Near-Eye Tool for Refractive assessment.

How does NETRA work?

Process: A plastic eye piece costing about $2 fits on the phone. The user looks through the eyepiece and aligns two lines. This is repeated at a few angles for 8 times. Once done, the software calculates the refractive index and delivers the prescription. The process takes 2 minutes.

Principle: The device seeks to replace expensive laser based devices that uses a Shack-Hartmann sensor with a laser. This sensor measures displacement of the spot inside the eye to estimate the wavefront (that is distorted by the eye lens). However, with NETRA technology, the user is asked to move the spots till all the spots are aligned on the retina. This spot movement compensates for small aberrations in the eye.

Accuracy: About 0.4 diopter dependent on the resolution of the phone screen.

What it cannot do: It cannot measure astigmatism since it is difficult to back-calculate all the light paths that are possible if the eye is distorted.


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