what is a perimeter?
A 'perimeter' is a device used to quantify one's visual field. It generates a graph called an 'isopter' which looks like this:
What use this this data for a clinician? Ophthalmologists use this to determine the presence and progression of a lot of diseases that are vision-threatening, such as glaucoma, macular degeneration and even neurological conditions.
Unfortunately, due to the interactive nature of this examination, perimetry cannot be done on infants. This is a huge problem because certain vision-threatening diseases like Glaucoma or hemianopia can be present since birth, and it might rob the child of their vision even before the child reaches an age where they begin communicating, if not treated in time. A lot of these diseases start eroding one's vision from the side (the peripheral vision) before reaching the center and rendering one completely blind.
As of now, the clinical method used to check a child's peripheral vision is by observing their response to bright toys brought in from the periphery of their visual field.
We tip the perimeter to it's side, resulting in the dome-shaped structure shown above, and have the child lie in an a supine position (which is a very comfortable and natural position for them). We have programmable LED strips light up the periphery of the visual field of the child in a pre-defined pattern depending on the test we want to do (static testing of quadrants and hemispheres of the visual field - which is always a sphere OR kinetic testing of response to a moving target coming from the periphery to the center of the field). We call our device the "pediatric perimeter". The dome is completely dark from the inside and the light source target is the only thing visible in the child's visual field. We use an infrared camera to watch the infant's responses.
On the bottom right is a sped-up video showing a child actually being tested.
This is a video made from the GUI for the pediatric perimeter built by our team. On the left you see a live feed of the infant, by which the clinician can note their responses. The right has a live isopter - the red dots show the position of the moving light source. The person performing the test presses a button (acting as a surrogate for the infant) when they make an unambiguous response. The locus of these red dots then forms the isopter for the infant.
This is the FIRST TIME such data could be taken from infants. The device has been covered as a "hot topic" at the 2016 Annual meeting of the Association for Research in Vision and Ophthalmology (ARVO). Dr Premnandhini Satgunam, associate research optometrist at the LV Prasad Eye Institute, is the principal investigator for this project and I was working with her as the project manager and engineering team lead. I wrote a lot of the code myself, it's available on github. For the hardware, I would like to acknowledge the amazing work of the following student interns:
- Karthik Reddy
- Dhruvil Soni
- Abhishek Baronia
- Sandeep Vempati (now joined our team full-time)