Long-sightedness and presbyopia: What is the difference between them?
What’s the difference between long-sightedness and presbyopia? Long-sightedness is where the optics of the eye are not powerful enough. Think of the eyes as a camera with film in the back and a lens in the front. The optics aren’t strong enough, which means that light coming from the distance where the light rays are parallel are brought into focus behind the back of the eye, so they are blurry. Things that are close are even worse.
Presbyopia is the loss of ability to shift focus from distance to near and back out. This affects all of us. As the natural lens inside the eye goes on its journey to becoming a cataract, it gradually hardens up and whether you’re short-sighted have perfect distance vision or long-sighted you’re typically going to experience this frustration with shifting focus from distance to near back out again mid-to-late forties.
Long-sightedness and presbyopia are quite distinct things: What you find is that people who are long-sighted may not be aware that they’re a bit long-sighted, because of their accommodation. So accommodation is the name given to the ability to shift focus. Someone who’s a little bit long-sighted, typically in their twenties, will have great vision because they will accommodate a little bit and use that flexibility of the lens to bring distant objects into focus. Then they’ll contract that ring of muscle to make the lens even more powerful to see near. In their early twenties, they can do that very effectively.
You find the patients who are long-sighted, tend to get hit earlier harder by presbyopia. It unmasks their long-sightedness, so they are typically the kind of person who, in their thirties, might start to notice “I do not see so well for near”. Their friends are okay, but they start noticing they hold things a bit further away. And it’s only much later when they’re presbyopia has taken hold and that lens has stiffened up. That blurry distance vision becomes unmasked, and actually, they’ll start wearing the specs for distance.
Interestingly, a lot of long-sighted patients even though they may attend an optometrist or an optician who said “you should wear those for driving” often not wear them because they find that they feel ok and that their distance vision isn’t too bad. What they almost always can’t do after the age of 40 or 30 is see up close or near.
So there are two different things presbyopia, ageing of the inside of the eye and long-sightedness, blurring distance vision even worse of the near.