Pinhole! Squint & peep through a tiny pinhole. It focuses image right on the retina. Identifies immediately the cause of poor vision.
- If acuity improves with “pinholing,” that’s refractive error. The patient needs glasses. Nothing to do with eye disease.
- If vision remains blurry, that’s organic eye disease of whatever etiology.
It’s not uncommon for visual acuity to differ in each eye. Personally, I’ve always had 20/20 vision in my right eye, 20/400 in the left [I can’t read the big “E”, though I know it’s there & cheat]. So I drive with my right eye, read with my left, & [hopefully] may never need glasses.
There are various devices you can use. Or simply punch a few pinholes in a cardboard card & have the patient squint through them. It works by obviating the light rays which land out of focus, so the retina only catches the one direct set [see pix]. So if you personally need glasses, and ever get stuck on top of a mountain with them broken, make pinholes to navigate home.
