Vision: Eye and Extraocular Structures (Nursing)

00:01 Let's continue our discussion of the special senses anatomy by focusing on vision.

00:08 Vision is a bit complicated.

00:10 So we'll start with the anatomy of the eye itself.

00:14 Externally, we can see a lot of structures pretty easily, including the eyebrow that sits superior to the eye, the upper eyelid, the other word for eyelid being palpebra.

00:26 We have the lower eyelid.

00:29 And the junction between the two called the commissure.

00:33 So we have one laterally, and we have one medially.

00:39 And then the surface of the eyeball itself is covered in a very special type of epithelium called the conjunctiva.

00:47 You may have heard that if you've heard of the term conjunctivitis, which is inflammation, usually due to infection of the conjunctiva.

00:56 Then the round portion that usually has some type of eye color to it is the iris.

01:04 And it's surrounds this circular black area, which is the pupil.

01:09 And it's actually not a structure you can touch.

01:12 It's actually the space in the center of the iris.

01:16 And it's just the space that sits right under the cornea here.

01:20 If we sort of look through the skin a little bit, we can also see components of what's called the lacrimal system.

01:26 Lacrimal refers to tears.

01:29 So when you hear that term, you think something about the tear ducts or the drainage of tears.

01:35 There's actually a lacrimal gland that sits in the upper outer or superior lateral aspect of the eye in the area surrounding the eye called the orbit.

01:47 And it transmits tear fluid through the lacrimal duct to reach the surface of the eye.

01:55 And it will sweep across the eye towards the medial surface, where it will coalesce add a little opening called the lacrimal punctum, and travel through tiny canals, either the superior inferior lacrimal canaliculus Canaliculus just means tiny canal.

02:14 And then there's also this lacrimal sac just to the medial and inferior aspect of the eye collecting tears, and will eventually drain through something called the nasolacrimal duct.

02:26 And that tells you where it's heading.

02:28 So naso tells you it's heading towards the nose.

02:32 And if you've ever noticed, when you've cried a lot, that sometimes you get a runny nose, this is why because the tears are going from lateral to medial and draining out through the nasal cavity.

02:45 Now we'll move on and talk about what moves the eyeball itself.

02:50 These are muscles sitting outside of the eye and therefore they're called extrinsic eye muscles.

02:58 We have one sitting superiorly called the superior rectus.

03:03 And wherever you see rectus, that means straight.

03:05 So that means there going to be some muscles that affect the eye that aren't running in a straight line.

03:12 We have a corresponding inferior rectus along the inferior surface of the eyeball, a lateral rectus, and a medial rectus.

03:22 But we also have a superior oblique muscle.

03:26 And that is just what it sounds like.

03:28 It's another muscle superiorly.

03:30 But it runs at an oblique angle as opposed to the superior rectus which is more straightforward.

03:36 Similarly, there's an inferior oblique, which again has more of a diagonal orientation.

03:44 So eye movement.

03:46 It's actually a little bit more complicated than you might think.

03:49 So we're just going to focus on one eye for the moment.

03:52 So when the eye looks laterally, that will be called abduction.

03:58 Abduction again means away from the midline, just like if you were to abduct at the shoulder, you're moving your upper limb away from the midline.

04:08 That would go under the control of the lateral rectus.

04:11 Because if you think a muscle running along the lateral surface of the eye were to contract, what would the effect be on the eyeball? Will be pulled laterally so that would be abduction.

04:24 Conversely, contraction of the medial rectus will pull the eye more medially and that would be towards the midline.

04:31 So that would be adduction.

04:35 Moving the eye upward in a more superior direction would be called elevation.

04:41 Moving it downward will be depression.

04:44 But because we have this superior rectus and inferior rectus, and the oblique muscles, it's not as straightforward as abduction and adduction.

04:55 The inferior oblique because of the way it's obliquely oriented when it contracts is going to move the eye, and sort of a combination of abduction and elevation.

05:08 Similarly, the superior oblique because of its oblique orientation is going to make the eye look down and out, or abduct and depress.

05:19 The inferior rectus on the other hand, because it's running in a straight direction, but actually the orbits at an angle, is actually going to depress the eye but in a more medial orientation.

05:31 Similarly, superior rectus will elevate it but in a more medial orientation than the inferior oblique.