Demystifying Smartphone Blindness

9:15 PM

We've all heard those eyecare "urban legends"

  • If you hold your eyes in that position you'll go cross-eyed!
  • If you watch TV laying down you'll get a lazy eye!
  • If you spend all day on your cellphone you'll go blind!
For two women at Gordon Plant of Moorfield's Eye Hospital in London, there were a scary few moments where that last one didn't seem so crazy after all.  Both women presented with vision loss in one eye that lasted around twenty minutes.  They had been laying in bed on their side, one eye closed or against the pillow, the other looking at their cell phone screen.  When they got up to do something else, they noticed a disturbing issue -- the eye that had been closed was seeing perfectly well, but the eye that had just been reading the screen was now significantly blurry, just seeing vague shapes and outlines.  For one women this was nearly a nightly occurrence, lasting for 15 to 20 minutes at a time. For the other she woke up even after sleeping with a vision difference in the "cell phone" eye for a few minutes.  

So are cell phones really making the eyes go bad?  The phenomenon behind "Transient Smartphone Blindness" is a very common one, and easy for you to experiment with at home if you are curious.  
  1. Go into a dark room.
  2. Cover one eye with your hand
  3. Look at a small bright light (a light bulb, a flashlight, -- please, not a laser pen though!) for 20-30 seconds.  Blink normally.  If your eye hurts or gets uncomfortable, stop the experiment of course; no need to make yourself miserable.
  4. Uncover your other eye and turn the room lights on
What do you see?  The eye that was covered is fine, but the other eye that was just looking at that bright light is probably very blurry/seeing spots or smudges.  In a minute or two you'll be completely back to normal, but you just demonstrated what's happening in smartphone blindness.  The eye that was covered was completely shielded from the bright light of the cellphone.  All of its photoreceptors (light detecting cells lining the back of the eye or retina) were inactive, ready to respond to any visual stimulus.  The eye that was looking at the light (or cell phone) had all of it's photoreceptors dedicated to that central area of vision being used, and used a lot depending on how bright the light was.  When photoreceptor cells respond to light, the process requires that they continually reactivate and send the message of what they are "seeing" to the brain.  Exposed to light for an extended time, and the photoreceptors will "bleach." They've been so busy responding to light and sending their signal to the brain for processing that they reach a capacity where they can't respond anymore; they've entered recovery mode until they have enough energy to respond again.  That's why you see black spots or an after image after looking at a bright light.  Once the cells have a chance to recover, vision will return to normal.  

Check out how differently eyes that are "dark adapted" (or were covered when exposed to bright light) can behave versus an eye that has been "bleached" by prolonged light exposure. Electroretinography is a measurement of how the actual photoreceptor retinal cells react.  After just 20 minutes of cell phone use, the eye that had been viewing the cell phone had significantly lower sensitivity to light than the eye that had been covered, which behaved with normal photoreceptor amplitude of response and was able to see even dim light sources. The difference in what the eyes were "seeing" is what sent these two women to the doctor.  By comparison, the eye that had been bleached by the cell phone seemed "blind" when compared to the eye had completely normal function. 

Take Home
Cell phones won't permanently blind you, but understanding the effects that looking at a harsh light source can have your eyes will definitely make you question your habits.  Our eyes can't adjust to changes in light levels as quickly as our world is often encouraging these days, leaving our eyes sensitive and red, and our vision blurry.  The average American spends 6 hours a day on their cellphone alone, not taking into account computer, TV, and other digital devices.  That's not the worst of it: the average teenager spends a whopping 9 hours a day on their cell phone, so with each generation we would only expect our eyes to give us more and more issues from the demands they face.  If we want our eyes to react quickly and clearly, we have to give them an environment that promotes their success:
  • Take breaks every 20 minutes; blink and look away from the screen. 
  • Decrease the brightness settings on your phone and look into blue blocker apps or lens coatings for your glasses.  
  • Don't use your cellphone or tablet in a dark room -- having ambient room light can help prevent your photoreceptors from bleaching out by spreading the light processing load over a larger area of cells.  
  • Yes, keep both eyes open if you want your two eyes to see the same after your done with screen time.  Most people's eyes work best together, and when placed into different lighting conditions, you'll definitely notice that they can't see the world equally when they've had completely different work loads. 

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