Major Disorders of the Eye: Definitions & Terminology

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  • 0:01 The Odd Things You See
  • 0:36 Anisocoria & Cataracts
  • 2:08 Retina, Optic Nerve, &…
  • 4:50 Nystagmus
  • 5:25 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Have you ever seen those weird-looking spots or specks in your field of vision randomly floating about? This lesson tells you what they are and defines many other weird and wonderful conditions of the eye.

The Odd Things You See

Have you ever seen those strange little black specks or stringy looking things in your vision? They weren't dust floating around, but it seemed as if it they were. And then when you moved your eyes, they seemed to move away when you tried to look at them more closely and directly. Do you know what those spots are called?

Here we're going to define a wide swath of the weird and wonderful disorders that affect the eye, be they odd movements, odd shapes, or the odd things you see.

Anisocoria & Cataracts

Let's take a look at a couple of terms that you can see in a person's eyes when looking directly at their center, where the iris and pupil sit. The iris is the colorful part of your eye, and the pupil is the dark black hole in the middle of the iris.

Behind the iris is the lens, the thing that switches shape to help you look near or far. The lens is normally a pretty transparent color, like glass in your window. But then again, there are different types of glass. Some glass can be rather opaque and fuzzy, making it hard to see through. If the lens becomes opaque, and thus loses transparency, we call this a cataract. A cataract, in other words, is a complete or partial opacity of the lens that leads to vision loss.

Why does it cause vision loss? It's because light passes through the lens to reach the photoreceptors in the back of the eye. If the lens is like a foggy window, then you won't be able to see well through it, now would you?

Another thing you might be able to see in some people when looking directly at the center of their eyes is anisocoria, the term for an abnormal condition where the pupils are of unequal sizes, meaning one pupil is larger than another. 'Aniso-' means 'unequal,' 'core(o)-' means 'pupil,' and '-ia' means 'an abnormal condition or state.' This can occur as a result of something like damage to the nervous system.

The Retina, Optic Nerve, & Vitreous Fluid

Speaking of the nervous system, there's something called papilledema, the swelling of the optic nerve, the one responsible for vision. This occurs as a result of increased fluid pressure within the skull, called intracranial pressure.

The optic nerve is closely associated with the retina, which is basically made of tiny photoreceptors that help us pick up the light coming in through the pupil and lens of the eye before transmitting this information to the optic nerve. The retina can be susceptible to many problems. This includes a retinal tear or a retinal detachment, where the retina is actually pulled away from the back of the eye.

More interestingly, there's a condition called retinitis pigmentosa that involves the retina. This is the degeneration of the retina, one that produces night blindness, as well as a reduced visual field. Basically, people with this condition get a kind of tunnel vision because they lose their peripheral vision, in addition to night blindness, and eventual complete blindness.

The retinal detachment or tear I noted before can be caused by something called vitreous detachment, a process where the vitreous gel of the eye shrinks with age, pulling on the retinal surface. The gel inside the eye, called vitreous humour, or just vitreous, has a lot of little fibers within it that attach to the retina. If the gel shrinks, these fibers can pull on the retina and tear or detach it. This can result in permanent loss of vision if not taken care of right away.

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