Actions of the Eye Video

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  • 0:01 Normal Actions of the Eyes
  • 0:25 Accommodation & Convergence
  • 1:22 Refraction,…
  • 2:48 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson goes over some of the normal actions of the eyes with respect to vision: visual acuity, convergence, accommodation, emmetropia, and refraction.

Normal Actions of the Eyes

Can you see this screen right now? I'm assuming you can, which means that I'm going to use this to show you some of the normal actions of the eyes, ones you don't even really think about. I don't mean things like the eyes moving up and down as you look around a room. Instead, this lesson is going to define accommodation, convergence, refraction, emmetropia, and visual acuity.

Accommodation & Convergence

As we go through the first two terms, those of you who are viewing the video lesson format will need to look at the little eyeballs at the bottom of your screen for a representation of what your eyes are doing. Look at the screen where this video is playing. Can you see how there is a pencil that's far away from you, then moves towards you, then moves far away again?

Your eyes are able to interpret this movement through the process of accommodation, adjustments of various parts of the eye, including the lens, in order to allow the eyes to focus on objects at varying distances. Primarily, if the eyes are focused on something far away from them, their lens is flattened. If the object is close, the lens becomes rounder in shape.

As an object, like the pencil on-screen now, comes towards you, your eyes also converge. Convergence is the coordinated inward turning of the eyes. Yep, it looks kind of silly on screen and I'm sure a friend of yours can probably do this on cue as well as they cross their eyes.

Refraction, Emmetropia, & Visual Acuity

The reason you can even see any of these objects near or far is owed in part to refraction. Refraction is the ability of the cornea and lens to bend incoming light rays and focus them on the retina.

The cornea is the transparent part of the eye that cover the colorful iris and the dark hole in the middle of the iris, called the pupil. The retina is the light-sensitive layer in the back of the eye that helps transmit light information to the brain so the brain can process this into an image we can understand.

The relationship between refraction of the eye and the shape of the eye at rest such that light focuses exactly on the retina, resulting in perfect vision is called emmetropia, where 'emmetr-' means 'the correct measure' and '-opia' means 'visual condition.' Emmetropia doesn't require any corrective lenses as you can understand.

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