Explain Like I'm Five | Don't Panic!
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ELI5: How do contacts sit perfectly on the middle of the eyeball? (self.explainlikeimfive)
submitted 5h ago by blueberrybleachmango
I wear coloured contacts everyday and I’ve always wondered this. If they were to shift too much the colour would obscure my vision, but they rarely do. How do they stay perfectly in place?
rubseb 1 points 4h ago
Your eye has a bump at the front where your pupil and iris are. This bump is your *cornea*. It's actually a little lens as well and is responsible for much of your eye's focusing power. Your contact lens fits over this bump and the bump (mostly) keeps it in place.
YellsAtGoats 1 points 4h ago
This.
In fact, when you are prescribed contact lenses, the dimensions of your cornea are part of the prescription. Buying contact lenses with the wrong dimensions can result in lenses that slide all over the place, or are uncomfortable, or even injure your eye.
Source: Been using contact lenses for about 15 years, both prescription and costume lenses.
In fact, when you are prescribed contact lenses, the dimensions of your cornea are part of the prescription. Buying contact lenses with the wrong dimensions can result in lenses that slide all over the place, or are uncomfortable, or even injure your eye.
Source: Been using contact lenses for about 15 years, both prescription and costume lenses.
Remarkable_Air_172 1 points 4h ago
Oh so is their any possibility for some humans not to have this bump, but still have good sight !!!
North-Pea-4926 1 points 4h ago
The bump bends light properly so you can see. A poorly shaped bump produces badly focused vision (either farsighted or nearsighted depending on the shape).
https://www.mayoclinic.org/diseases-conditions/farsightedness/symptoms-causes/syc-20372495#:~:text=If%20your%20cornea%20or%20lens,is%20the%20opposite%20of%20nearsightedness.
https://www.mayoclinic.org/diseases-conditions/farsightedness/symptoms-causes/syc-20372495#:~:text=If%20your%20cornea%20or%20lens,is%20the%20opposite%20of%20nearsightedness.
Remarkable_Air_172 1 points 4h ago
Ooh ya i totally forgot about convex and concave lenses !! So a person without h any blend will basically be sightless
North-Pea-4926 1 points 4h ago
Farsighted to the point of effective blindness, if I am interpreting the source correctly. Their vision won’t be darker like we traditionally think of blindness, but you certainly can have poor enough vision to be “legally blind”.
rubseb 1 points 4h ago
No.
BringMyMagnets 1 points 4h ago
Your eye has a slight bulge at the front, that covers your iris and pupil. Since your eye is also wet, the contact lens sits snugly on a thin layer of water on top of this bulge, which keeps it in place. It can still slip, but mostly it rides on there like hat (a front hat)
garbagetoss1010 1 points 1h ago
As a couple people already said, the cornea (clear central surface of the eye) is more forward and more curved than the rest of the eye.
When we prescribe contact lenses, two important parts of the prescription are Base Curve (the curvature of the lens should match the eye) and Diameter (the contact lens shouldn't be too big or too small). These two factors influence how the contact lens sits on the eye. It should move about half a millimeter or so when you blink, and quickly slide back on a little cushion of tears.
This explanation ignores the actual power of the lenses which is mostly responsible for your clear vision; and the material they're made out of, which is important for breathability and lubrication.
When we prescribe contact lenses, two important parts of the prescription are Base Curve (the curvature of the lens should match the eye) and Diameter (the contact lens shouldn't be too big or too small). These two factors influence how the contact lens sits on the eye. It should move about half a millimeter or so when you blink, and quickly slide back on a little cushion of tears.
This explanation ignores the actual power of the lenses which is mostly responsible for your clear vision; and the material they're made out of, which is important for breathability and lubrication.
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