Pinhole !

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.