Chapter 12: Eyes

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Welcome back to the Deep Dive.

We are doing something a little special today, aren't we?

We are.

This is part of our Last Minute Lecture series, and it's specifically designed for, those of you who might have a clinical exam in the morning, or perhaps you just realized your anatomy knowledge has gotten a little rusty.

That's right.

We are stripping away all the fluff and really just getting right down to the rigorous details.

Today, we are tackling a massive topic for anyone in the health professions.

A huge one.

We are diving into chapter 12 of Bates' Guide to Physical Examination and History -Taking, the 13th edition.

The focus is entirely on the eyes.

They say they're the windows to the soul, but if you look at the source material, they're also, well, they're windows to the central nervous system, the vascular system, and a whole lot more.

It's funny because I think most people, even students, tend to think of the eye exam as just read the chart on the wall.

It's so much more.

It is arguably one of the most information -dense areas of the entire body.

You can diagnose hypertension, diabetes, increased intracranial pressure, often just by looking into someone's eyes.

It is the only place in the body where you can look directly at a nerve and a blood vessel without making a single incision.

It's incredible.

So here's our mission for this deep dive.

We are going to provide a comprehensive audio summary of chapter 12, and to be clear, we are going to stick strictly to the text provided.

We'll walk you through the anatomy, the physiology, the history -taking, and then that daunting physical exam step by step.

And we will finish with the pathologies, the red flags you absolutely cannot miss.

Exactly.

So if you're driving to clinicals or cramming for an exam, keep listening.

Let's start where Bates says we always should, anatomy and physiology.

And the book starts with the structure that holds it all together.

The orbit.

The orbit, yeah.

It's that quadrilateral -shaped bony socket in the skull.

And it's not just a cup.

It's really a protective housing.

Right.

It ensures the eye is shielded and optimized for function.

And sitting right inside that orbit, you have the eyeball itself.

Bates describes the eyeball as spherical.

And checking the text, it really highlights the tough white outer covering known as the sclera.

The white of the eye.

The white of the eye.

Correct.

But here is a connection that is absolutely vital to understand, and Bates makes a very specific point of this.

The sclera is continuous with the dura of the central nervous system.

So it's literally connected to the covering of the brain.

Exactly.

The eye is, in a very real sense, an extension of the brain.

That explains so much.

It explains why eye findings can tell us so much about what's happening inside the skull.

If the brain swells, that pressure travels right down the line.

Precisely.

Now, moving to the front of the eye, we've got the colored part, the iris, and then the pupil, the black dot, right in the center.

And the iris is actually a circular muscle.

Yeah.

It's not just decorative, you know.

Right.

It's functional.

Very functional.

It controls the aperture, the pupil dilating and constricting to control how much light gets in.

And covering all of that, the pupil and the iris, is the cornea.

It's transparent, continuous with the sclera we just talked about, but it's crystal clear.

And then we have the eyelids.

It seems simple, they open and close, but there's some specific terminology here that I think students really need to nail down.

The opening between the eyelids, for example, is called the palpebral fissure.

Right.

The palpebral fissure.

And normally, when the eye is open and just kind of resting, the upper eyelid covers just a little bit of the iris.

Okay.

However, and this is a really key landmark, it should not cover the pupil,

ever.

If the eyelid troops low enough to cover the pupil, you're blocking vision.

And that's a significant clinical finding.

Bates also talks about the conjunctiva.

This trips students up sometimes because it sounds like two different things, but it's really one continuous sheet, isn't it?

It is one sheet.

It's just named for what it's covering.

So you have the bulbar conjunctiva, which covers the anterior eyeball, the white part, the sclera.

It adheres pretty loosely to the underlying tissue, but then it meets the cornea at a very specific border, a landmark called the limbus.

The limbus.

Okay.

That's the transition zone.

And the second part of the conjunctiva.

That would be the palpebral conjunctiva.

That's the part that lines the eyelids themselves, the inside of the eyelid.

Got it.

And the two parts, the part on the eye and the part on the lid, they meet in a folded area, a pocket called the fornix.

This little fold is what allows the eyeball to move around freely without tearing the membrane.

Which is brilliant.

And when someone has a bloodshot eye, that's just the conjunctiva getting

injected is the term, right?

With blood due to inflammation or dilation of those vessels.

That's exactly it.

Now, if we look at the eyelid itself, it's not just a flap of skin.

There's some hardware inside, you know, holding it up and giving it structure.

Okay.

What's in there?

There are these firm strips of connective tissue called tarsal plates.

These give the lid its shape and consistency.

And embedded within those plates are the mybomian glands, also known as tarsal glands.

And they run vertically.

They do.

And they open right onto the lid and margin those little tiny dots you can sometimes see.

And they produce oil, right?

I remember that from a lecture.

Exactly.

They provide the oily lubrication for the ocular surface, which is the top layer of the tear film.

If those get blocked, you get issues like shalations, which, you know, we'll definitely discuss later.

So how do we open our eyes?

It's not magic.

It's muscle.

The primary muscle is the levator palpebrae superioris.

Big name.

It's a mouthful.

And that one is powered by?

That's cranial nerves three, the oculomotor nerve.

Yes.

But there's a backup or maybe more like an assistant.

And that's Miller's muscle.

Miller's muscle, yes.

And this is where it gets really interesting for diagnosis.

Miller's muscle isn't controlled by a cranial nerve directly in the same way.

No, it's the autonomic nervous system.

Exactly.

It is innervated by the sympathetic nervous system.

It contributes just a little bit to lid elevation.

This is why if you have a sympathetic nerve lesion -like in Horner syndrome, you get a droopy eyelid or atosis.

So it's not a paralyzed CN30?

No, it's a parallel sympathetic supply to that little helper muscle.

It's a subtle but important difference.

So you need both the cranial nerve and the sympathetic system working together for full proper eye opening.

Fascinating.

Let's talk about tears.

The lacrimal apparatus, I usually just think of tears as salty water, but Bates implies it's a bit more of a cocktail.

Oh, the tear film is surprisingly complex.

It protects the conjunctioid and cornea from drying out.

It inhibits microbial growth.

It's a very active layer.

And it actually has three layers.

Three layers just in a tear.

Three layers, yes.

It's an oily layer from those meibomian glands we just mentioned, and that prevents evaporation.

Then there is an aqueous layer.

That's the water part from the lacrimal glands.

And finally, a mucinous layer from the conjunctival glands that, well, it helps the tears stick to the eye surface.

And the flow of traffic here is really important for understanding drainage issues, isn't it?

It is.

So the lacrimal gland is in the super lateral orbit that's up into the outside, just above the eyeball.

The tears wash across the eye diagonally from top out to bottom in, and they drain medially.

They go into two tiny holes on the inner eyelid called the lacrimal puncta.

Then they travel through these tiny tubes called canaliculae to the lacrimal sac, then down the nasolacrimal duct, and finally into the nose.

Which is exactly why your nose runs when you cry.

It's not a myth.

It's literally tears draining into your nasal cavity.

That's the plumbing.

Okay, let's go deeper.

Internal anatomy.

Behind the iris, we have the lens.

The lens, yes.

It's transparent and it's suspended by ligaments called zonial fibers.

And this is how we focus.

How does that work?

The ciliary body muscles, which are attached to those fibers, they contract or relax.

This changes the tension on the zonial fibers, which in turn changes the thickness of the lens.

And that process is called accommodation.

So it's an active process.

Very active.

It allows us to focus on near objects or distant objects.

And the eye isn't empty.

It's filled with fluid.

Bates breaks us down into three chambers, which is a distinction I think a lot of people, even me, sometimes miss.

It's an important one.

You have the anterior chamber, which is the space between the cornea and the iris.

Then you have the posterior chamber between the iris and the lens.

Okay, anterior and posterior.

Both of those are filled with aqueous humor.

This is a clear liquid that's constantly being produced by the ciliary body.

And it circulates.

It's not just stagnant in there.

It has to circulate.

It flows from the posterior chamber through the pupil into the anterior chamber.

And then it drains out through a structure called the canal of shlem.

This whole circulation system is what controls your intraocular pressure.

And if that drain, the canal of shlem gets clogged.

The pressure builds up.

That is the fundamental mechanism of glaucoma.

And the third chamber.

Then behind the lens, you have the big one, the vitreous chamber.

That's filled with vitreous humor, which is much more gelatinous and viscous.

Its job is to maintain the shape of the eye and, critically, keep the retina attached to the back wall.

Let's move to that back wall.

The part we see with that very difficult ophthalmoscope exam.

The fundus.

The optic fundus.

When you look in there, you are looking at several key structures.

The retina, the choroid, the fovea, the macula, the optic disc, and all the retinal vessels.

When we look for the optic disc, what specifically are we looking at?

The disc is the entry point of the optic nerve.

It's usually yellowish orange to a creamy pink color.

It's also where all the blood vessels enter and exit the eye.

Okay, so that's the main landmark.

It is.

And just lateral to that is the fovea.

That is the point of our sharpest central vision.

And surrounding the fovea is a slightly larger area called the macula.

Okay, we've built the eye.

A beautiful, complex structure.

Now let's talk about how it actually works.

Visual fields and pathways.

This can get a little abstract for students, but stick with us.

It really helps to visualize it.

A visual field is the entire area that's seen by an eye when it looks at a central point.

So everything in your periphery.

Exactly.

And normally your field is limited by your eyebrows above, your cheeks below, and of course your nose medially.

And there's a blind spot.

Why do we have a blind spot?

It seems like a design flaw.

Well, everyone has one.

It's located about 15 degrees temporal to your line of days.

And it exists simply because there are no retinal receptors, no rods or cones at the optic disc where the nerve itself enters the eye.

So there's no way to sense light there?

None at all.

The brain usually just fills in the gap so you don't notice it, but it's definitely there.

Now trace the path of light for us.

It hits the eye.

Then what?

What's the wiring?

Okay, so light hits the retina.

The impulse then travels through the optic nerve, which is cranial nerve too.

It goes to a crossover point called the optic chiasm, where the nasal fibers cross over to the other side.

From there, it's the optic tract.

Then a fan -like structure called the optic radiation.

And finally, it all ends up in the visual cortex, way in the back of the brain in the occipital lobe.

And along the way, some of those signals are used for pupillary reactions.

Bates distinguishes between the light reaction and the near reaction.

Let's start with light.

The light reaction is absolutely key for checking nerve function.

You shine a light in one eye.

That pupil should constrict if that's the direct reaction.

Okay.

But the other pupil, the one you're not shining the light in, should also constrict.

And that's the consensual reaction.

And the wiring for that is a two -part loop, right?

It is.

The sensory path is the optic nerve, CN2, is the wire that tells the brain is bright in here.

The motor path, the signal to constrict, comes back out via the oculomotor nerve, CN3, and goes to both eyes.

So that's why the other eye constricts too.

That's the consensual part.

It's a shared motor response.

Then there's the near reaction.

When I look at something close up, like my phone.

Right.

When you shift your gaze from a distant object to a near object, three things happen almost simultaneously.

One, your pupils constrict.

Two, your eyes converge.

The medial rectus muscles pull them in toward your nose.

And three, accommodation.

The lens gets thicker to refocus the light.

We talked briefly about the sympathetic nervous system with the eyelid, but it plays a huge role in the pupil too, doesn't it?

This is critical to remember.

The parasympathetic system that travels with CNE3 causes constriction.

The sympathetic system causes dilation.

And the sympathetic pathway is famously long and complex.

It really is.

It starts way up in the hypothalamus, goes all the way down the brain stem to the cervical cord in your neck, travels out and over the apex of the lung, and then comes all the way back up along the carotid artery to the eye.

Wow.

Which is why a lung tumor at the very top of the lung can actually affect your eye.

Pancos tumor.

Right, causing Horner syndrome.

That anatomical path is just a long road where so many things can go wrong.

Precisely.

It's a great example of integrated anatomy.

Let's round out the anatomy with the extraocular muscles, the EOMs.

There are six of them moving each eye.

Yep.

Four rectus muscles,

superior, inferior, lateral, and medial.

And then two oblique muscles,

superior and inferior.

And the nerves that drive them.

This is a classic exam question.

I feel like there's always a mnemonic for this.

There is.

SO4LR6R3, superior oblique is cranial nerve the fourth, the trochlear.

Lateral rectus is cranial nerve six, the abducens.

And all the others are cranial nerve three, the oculomotor.

SO4LR6R3, got it.

So adducens, CNZI, innervates the lateral rectus.

It literally abducts the eye, pulls it outward.

That's the easy one to remember.

And trochlear, CNIV, just does the superior oblique.

Just that one.

And the workhorse, oculomotor, CN3, does all the rest.

Does everything else.

And these muscles are yoked.

What does that mean, yoked?

Like a team of oxen, they're paired up.

So when you look to your right, the right lateral rectus has to contract at the exact same time and with the same force as the left medial rectus.

They have to work together perfectly.

And if they don't?

If they don't, you get diplopia double vision.

The images don't land on the same spot on the retina for both eyes.

OK, anatomy class is dismissed.

That was a lot, but it's the foundation for everything else.

Let's put on our white coats.

We're walking into the patient's room.

Part two of the chapter, health history.

How do we start?

As with any system, you really want to start with open -ended questions.

How is your vision?

Have you had any trouble with your eyes?

Just let them talk.

And if they say yes, we immediately have to start differentiating.

Is it one eye or both?

Unilateral or bilateral?

Was the onset rapid or was it gradual?

And perhaps most importantly,

is it painless or is it painful?

That single distinction is huge for building your differential diagnosis.

OK, let's break down some of those vision changes.

If a patient says, I can't see things close up anymore, what are we thinking?

Well, the first question is how old are they?

If they're over 40, it's very likely presbyopia.

That's the age provision where the lens just loses its flexibility.

If they're younger, you're thinking more about hyperopia or farsightedness.

And if they have trouble with distance, seeing the boarding class.

That's myopia or nearsightedness.

Now let's get to the scary stuff.

Sudden unilateral painless vision loss.

The patient wakes up and can't see out of their right eye.

That is an emergency list.

And the fact that it's painless is a huge clue.

You have to think about things like vitreous hemorrhage from diabetes,

macular degeneration, a retinal detachment or a central retinal artery or vein occlusion.

That painless nature often points to vascular or retinal issues in the back of the eye.

And if it's painful,

sudden unilateral and painful.

Pain usually points to the front of the eye, the anterior chamber or the cornea.

Now you're thinking corneal ulcer, uveitis, which is inflammation inside the eye, acute angle closure, glaucoma or maybe optic neuritis.

Optic neuritis, inflammation of the optic nerve.

Often seen in conditions like multiple sclerosis, right?

Yes, it's a classic presenting symptom for MSS.

Pain with eye movement is a big clue there.

What about gradual loss?

Things that creep up over months or years.

That's usually cataracts, glaucoma or macular degeneration.

The slow, insidious decline.

The text also mentions the importance of location,

central loss versus peripheral loss.

Right.

A slow loss of central vision, like a smudge in the middle of what you're looking at, suggests a nuclear cataract or macular degeneration.

But a loss of peripheral vision, like you're looking through a tunnel,

that is the hallmark of advanced open angle glaucoma.

Let's talk about the floaters and flashers.

Patients complain about this all the time.

They do.

Moving specks or cobwebs are usually just vitreous floaters, which are common and benign.

But if a patient reports seeing flashing lights, like a camera flash, with a shower of new floaters, that suggests traction on the retina.

Which means?

Which means it could be the prelude to a retinal detachment.

That requires a prompt ophthalmology consultation.

Okay.

Diplopia, double vision.

The text gives a great clinical tip for figuring out where the problem is.

This is such a simple and elegant test.

You just ask the patient if the double vision goes away when they close one eye.

Either eye.

And what do the answers tell us?

If the diplopia persists with one eye closed, the problem is in the eye itself.

We call that monocular diplopia.

It's usually a cornea or a lens issue, like a cataract.

But if it disappears completely when one eye is closed.

Then it's binocular diplopia.

Exactly.

It means the problem is a nerve or muscle issue.

The eyes aren't aligning.

You're looking at a problem with cranial nerve, the third 46.

Brilliant.

Okay, let's move on.

Part three, physical examination techniques.

First thing on the list, we need to measure visual acuity.

The Snellen chart.

Right.

You position the patient 20 feet away from the chart.

And an important point, if they wear glasses for distance, they should keep them on.

You are testing their best corrected vision.

And can you explain the numbers for us?

Like 2200.

What does that actually mean?

Of course.

The first number is always the patient's distance from the chart.

So 20 feet.

The second number is the distance at which a person with normal vision can read that same line.

So 2200 means?

It means the patient sees at 20 feet what a normal person can see from 200 feet away.

That is significantly reduced acuity.

And what's the threshold for legal blindness?

In the United States, legal blindness is defined as 2200 or less in the better eye, even with correction.

Or an alternative definition is a visual field of 20 degrees or less.

Okay.

Next, after acuity, we test visual fields by confrontation.

The textbook calls it the static finger wiggle test.

I love the name.

It's a great screening test.

You stand at arm's length from the patient.

You close your right eye while the patient covers their left eye.

You are essentially mirroring them.

So your visual field should overlap.

And then you wiggle your fingers.

And you wiggle your fingers.

You bring your wiggling fingers in from the periphery, from all the different quadrants, and ask the patient to say now as soon as they see them.

You're comparing their field to your own.

And we are looking for field cuts.

We are.

For example, a patient might have a homonymous hemianopsia.

That's a mouthful.

But it just means they've lost the same half of the visual field in both eyes.

So they can't see anything on their left side with either eye.

Correct.

And that pattern usually indicates a lesion that's happened after the optic chiasm.

So in the optic tract or the optic radiation in the brain, the brain problem, not an eye problem.

The text also mentions testing color vision and contrast sensitivity.

Yeah, the pseudo -isochromatic plates, the ones with the color dots, are used for this.

And this isn't just for congenital color blindness.

It can be a very sensitive way to detect optic nerve damage, which often shows up as deficits in red -green color vision or something called red desaturation.

What's red desaturation?

It's when a red object, like the cap of a pen, looks faded or washed out in the affected eye compared to the normal eye.

It's a subtle sign of optic nerve dysfunction.

Now let's move to inspecting the eyes themselves.

Position and alignment.

You want to check for protrusion.

If you suspect the eyes are bulging, the technical term is exothelmos or proptosis, you can view them from above.

You stand behind the patient and look down.

It's sometimes called the worm's eye view.

Or you can just look for lid retraction where you see white sclera above the iris.

Exactly.

And this is all very common in Graves' disease or thyroid eye disease.

And we also look for deviations.

Right.

Exotropia is an inward deviation toward the nose.

Exotropia is an outward deviation.

Hypertropia is up and hypertropia is down.

When inspecting the eyebrows and eyelids, what are some of the key things we're looking for?

For eyebrows, scaliness could be something simple like seborrheic dermatitis.

But lateral starciness, losing the outer third of the eyebrow, is a classic textbook sign of hypothyroidism.

And for the eyelids?

You're looking for pitosis, which is drooping.

You're looking for edema or swelling.

And you're looking for failure of the eyelids to close completely, which is known as legothelmos.

That can lead to corneal damage.

And the conjunctiva and sclera.

How do we best inspect those?

You gently depress the lower lid with your thumb.

You're inspecting the color.

You're looking for injection, which is that redness, antinodules, or jaundice, which is yellowing of the sclera.

Here's a technique I think is really cool and often underutilized.

The shadow test for the iris.

This is a great screening tool for the risk of narrow angle glaucoma.

What you do is you shine your pen light from the temporal side, from the side across the front of the eye.

Okay.

And normally the iris is flat, so it should light up fully.

It should light up fully.

But if it's not normal,

if the iris is bowed forward, it actually blocks the light from reaching the other side.

Ah, so it casts a shadow.

It casts a crescent -shaped shadow on the nasal side of the iris.

And that tells you the angle is narrow.

It increases the risk for acute narrow angle glaucoma, a sudden, dangerous increase in pressure.

Moving on to the pupils.

We check size, shape, and symmetry.

Right.

And we should measure them in both dim and bright light to see how they react.

Meiosis is constriction.

Midriasis is dilation.

And if the pupils are unequal in size, that's anisocoria.

Is anisocoria always a bad thing?

Not always.

There's something called simple anisocoria, where the difference in size is less than 0 .4 millimeters, and it's constant in all lighting conditions.

That's benign and seen in about 20 % of healthy people.

But if the difference changes with light?

If it changes, it's pathologic.

You have to figure out why.

We check the extraocular muscles again in the physical exam, this time more directly.

Let's start with the corneal light reflection.

This is a quick screen for alignment.

You shine a light at the bridge of the patient's nose, and you look at the reflection of that light on their corneus.

The reflection should be in the same spot on both pupils.

If it's asymmetrical, you have a deviation atropia.

And the cover -and -cover test.

That's a bit more sensitive.

It's really useful for detecting a latent muscle imbalance, aphoria, especially in kids.

You have the patient stare at a point, you cover one eye, and you watch the other eye to see if it moves to fixate.

And if it moves, it means it was drifting when it wasn't the primary seeing eye.

Exactly.

It reveals a hidden misalignment.

And then the big one, the six cardinal directions of gaze, the H test.

Right.

You have the patient follow your finger as you trace a wide H in the air.

You are specifically testing the recti and oblique muscles in their primary fields of action.

And while you're doing this, you're also watching for nystagmus.

You are.

Nystagmus is a rhythmic oscillation of the eyes.

A few beats at the very extreme of lateral gaze can actually be normal, but sustain nystagmus.

We also check for lid lag during this test.

We do.

As you bring your finger down from the upper part of the H, you ask the patient to follow it.

The upper lid should smoothly follow the iris downward.

If you see a rim of white sclera above the iris as they look down, that's lid lag, another sign of hyperthyroidism.

And lastly, checking convergence.

Right.

You have the patient follow your finger as you bring it in towards the bridge of their nose.

Their eye should converge or cross, and normally they can maintain that convergence until the finger is within about five to eight centimeters of their nose.

All right.

This is it, part four.

The main event, the ophthalmoscopic examination.

Bates acknowledges this is one of the most challenging skills for a novice to master.

It absolutely is.

You are trying to look through a tiny hole, the patient's pupil, into a dark room, the back of the eye, using a bright flashlight.

It takes a lot of practice.

So let's break it down.

First, the instrument.

We're talking about the traditional direct ophthalmoscope here.

And the setup is key.

The room needs to be as dark as possible to help the pupil dilate naturally.

You want to use the large, round, white beam of light.

And you should set the focus wheel, the diopter wheel, to zero initially.

And the right -to -right rule.

Safety first and comfort first.

You hold the scope in your right hand and use your right eye to examine the patient's right eye.

Then you switch for the other side.

This keeps you from bumping noses with the patient and maintains a professional distance.

Step one, the red reflex.

The red reflex.

You shine the light into the patient's pupil from about 15 inches away and at a slight angle, about 15 degrees temporal.

You should see a beautiful orange glow in the pupil.

And if you don't, if it's absent or white.

An absent red reflex is a major red flag.

It suggests an opacity somewhere along the visual axis, like a dense cataract or a vitreous hemorrhage.

In children, a white reflex, leukocorrhea, could be a sign of retinoblastoma.

So that's a critical first check.

Step two, move in.

Yes, you keep that red reflex in your view and you move in closer like you're on a monorail until your forehead is almost touching your hand on the patient's forehead.

And you adjust the focus wheel as you go.

You do.

If you or the patient are nearsighted, you'll need to dial down into the red or minus numbers.

If you're both farsighted, you'll need the green or plus numbers to get the retina into focus.

And what are you looking for first?

What's the main landmark?

You're hunting for the optic disc.

It's the first thing you should try to find.

It's usually a round yellowish orange structure.

And you want to look at a few key characteristics.

The margins, are they sharp and clear?

And the physiologic cup.

The cup, that's the little depression in the center of the disc.

Why does the cup size matter so much?

Because if the cup is enlarged,

if the cup to disc ratio is greater than one half, that is a primary sign of chronic open angle glaucoma.

It means the nerve fibers are dying off and the cup is getting bigger.

And what if the disc is swollen with blurred margins?

The opposite of a big cup.

That is papillodema.

It's a sign of increased intracranial pressure.

Something is pushing on the brain meningitis, a mass lesion, brain swelling.

It usually also involves a loss of spontaneous venous pulsations, or SVPs, which you can sometimes see in a healthy eye.

Moving out from the disc now to the retina and vessels.

Right.

You need to follow the vessels out from the disc.

And you need to distinguish the arteries from the veins.

How do you do that?

Arteries are a light red color and they're smaller, about two thirds the size of the veins.

The veins are a darker red and larger.

And we look for hypertensive changes in those vessels, right?

Yes.

Chronic hypertension really damages the arteries in the eye.

You might see AV nicking, where a thickened artery crosses over a vein and makes it look like the vein stops abruptly.

Or copper wiring, where the artery gets a full coppery look.

In severe cases, silver wiring, where the wall becomes totally opaque.

And we're also looking for any lesions on the retina itself.

Exactly.

Hammerages, for one.

Dot and blot hammerages are very common in diabetic retinopathy.

And also cotton wool spots, which are these white or gray fluffy patches that represent areas of retinal infarction.

And finally,

the macula and fovea, the center of vision.

You inspect this last because looking directly at the light is really uncomfortable for the patient.

You just ask them to look directly at your light for a second.

And you're looking for drusen.

Drusen.

They're yellowish cellular debris that accumulate.

Hard drusen are small and well -defined.

Soft drusen are larger and fuzzier.

And these are associated with age -related macular degeneration.

Okay, that covers the standard exam.

It's a lot to remember.

Part five of the chapter focuses on special techniques.

First, checking for exothelmus properly.

Right.

If the eyes look prominent, you can get a better assessment by standing behind the seated patient and looking down from above that worm's eye view we mentioned.

For a precise measurement, you'd use a Hurtel exothelmometer.

Normal protrusion is generally less than 20 to 22 millimeters.

Next, nasolacrimal duct obstruction.

This is for a patient who has excessive tearing.

You press gently on the lower lid at the medial campus right near the nose.

You're basically compressing the lacrimal sac.

If mucocurulent fluid regurgitates out of the punca, that's a positive sign for an obstruction.

Everting the upper eyelid.

This sounds painful, but it's necessary if you suspect a foreign body.

It's a bit uncomfortable, but it's crucial.

The technique is to grasp the upper lashes, pull gently down and forward.

Then you place a small stick, like a cotton swab, just above the tarsal plate.

Then you push down on the stick while you lift the lashes up and back to flip the lid inside out.

And that exposes the whole palpable conjunctiva.

Exactly.

So you can find that trapped piece of dust or that eyelash that's been driving them crazy.

And finally, the swinging flashlight test.

This is for detecting an afferent pupillary defect.

Right.

Also known as a Marcus Gunn pupil.

It is a very sensitive test for optic nerve damage.

Walk us through the mechanism of this.

It can be a little confusing.

Okay.

So in a dark room, you swing a bright light back and forth between the two pupils.

You hold it on each eye for about two to three seconds.

Let's say the left eye is normal and the right eye has optic nerve damage.

Okay.

You swing the light into the normal left eye.

Both pupils constrict briskly.

Good.

Then you swing the light quickly over to the affected right eye.

And normally they should stay constricted because there's still light hitting an eye.

Correct.

But if the optic nerve in that right eye is damaged, it can't send a strong, it's bright signal to the brain.

So the brain perceives less light coming in from the damaged eye than it did from the normal eye.

So what happens to the pupils?

So paradoxically, the pupils dilate or appear to dilate when you move the light from the good eye to the bad eye.

It's because the afferent signal is too weak to maintain the strong constriction that the good eye caused.

That is such a fascinating physiological glitch.

A beautiful test.

It's a very sensitive and specific test for optic neuritis or any significant optic nerve damage.

Part six is briefly about recording findings.

Bates really emphasizes precision here.

Yeah, the main point is don't just write normal or WNL.

Be descriptive.

Visual acuity, 2020 bilaterally.

Sclera is white, conjunctiva are pink, disc margins are sharp and distinct.

And the text specifically mentions avoiding the acronym PIRAL -A unless you actually test for accommodation.

Right.

PIRAL -A stands for Pupils Equal, Round, Reactive to Light, and Accommodation.

If you didn't check the near reaction by having them look at your finger up close, you can't write the A.

Just write, Pupils are equally round and reactive to light, or PIRAL -A.

Good point.

Part seven, health promotion and counseling.

Why should we care about routine eye exams beyond just acute issues?

Well, the statistics are pretty heavy.

Visual impairment affects quality of life, it dramatically increases fall risk in the elderly, and it even correlates with cognitive decline.

Early detection is everything.

What about glaucoma screening specifically?

Primary open -angle glaucoma is often called the silent thief of sight.

It causes a slow, gradual loss of peripheral vision.

And the patient doesn't notice until it's very far advanced.

Exactly.

By the time they notice their tunnel vision, the damage is severe and irreversible.

So screening is key, especially for high -risk groups.

Who's high -risk?

Risk factors include being over the age of 65, being of African -American descent, having diabetes, high myopia, or an elevated intraocular pressure, which usually defined as over 21 millimeters of mercury.

The American Academy of Ophthalmology strongly recommends comprehensive exams to catch this early.

And UV protection?

Seems simple.

It is, but it's important.

Simple advice.

Wear sunglasses and sunscreen.

UV light is linked to cataracts, skin cancers on the eyelids like basal cell carcinoma, and solar retinopathy.

Finally, let's hit part eight, the tables.

These are fantastic for rapid -fire diagnoses.

Let's start with the red eye.

Differentiating them is absolutely key.

It is.

OK, so if you see a subconjunctival hemorrhage, it's a bright red patch, very sharply demarcated, but it's painless, and the vision is totally fine.

It looks scary, but it's usually harmless.

OK.

What about viral conjunctivitis?

That's going to be a red eye with a grittier, sandy sensation.

There's usually a watery or mucoid discharge, and it's highly contagious.

Corneal injury or infection?

Now we're talking about pain.

Moderate to severe pain is the key feature.

Vision is usually decreased, and the pupil might be affected as well.

And the big one.

The true emergency.

Acute angle closure glaucoma.

Severe, deep, aching pain.

Decreased vision.

Nausea and vomiting are common.

And the key sign.

The pupil is dilated and fixed in a mid -dilated position.

The cornea often looks cloudy or steamy.

This is an immediate, urgent referral to an ophthalmologist.

Let's do the same for eyelid lumps.

A stye versus a chelation.

What's the difference?

A stye, or hordeolum, is a painful, tender red infection right at the margin of the eyelid.

Usually an infected hair follicle.

A chelation, on the other hand, is usually painless.

It's a blocked myobomian gland that's a little bit inside the lid.

It tends to point inward, not on the lash line.

Benzanthalasma.

Those are the slightly raised, yellowish cholesterol plaques you sometimes see.

They're often on the nasal portion of the eyelids.

They're a big clue that you should probably check the patient's lipid panel.

Lastly, a quick review of the key pupillary abnormalities.

We already mentioned Horner's syndrome.

Right.

The classic triad.

A small pupil, meiosis.

A droopy lid, perptosis.

And a lack of sweating on that side of the face.

And hydrosis.

That's a loss of sympathetic nerve supply.

What is a tonic or AD pupil?

That's where the pupil is large, regular, and usually just on one side.

The key is that its reaction to light is severely reduced or even absent, but it does react very slowly to accommodation.

It's a parasympathetic denervation.

And the famous Argyle Robertson pupil.

The classic.

Small, irregular pupils that accommodate, meaning they constrict when the patient looks at a near object, but they do not react to light at all.

The old mnemonic, prostitute's pupil, accommodates but doesn't react.

That is the denonic often used, yes.

And it's the classic sign of neurocephalus.

Wow.

We have covered a massive amount of ground today.

All the way from the bony orbit to the optic radiation.

We have.

We've traced the path of light, the flow of tears, and the pressure of the aqueous humor.

We've looked at the retina and interpreted the story the blood vessels tell us.

It really just emphasizes the point we started with.

The eye exam is not just about checking if someone needs glasses.

Not at all.

It is a neurological exam and a vascular exam all wrapped into one.

Absolutely.

And mastering these techniques, especially the ophthalmoscope, it just takes practice.

But the diagnostic yield is incredibly high for your patients.

You can learn so much.

So next time you pick up that ophthalmoscope, remember the layers, remember the pathways, and please remember to check that red reflex first.

And remember the right -to -right rule so you don't bump noses.

Essential advice.

Thank you so much for listening to this deep dive into Bates chapter 12 on the eyes.

Keep practicing those skills.

You'll get it.

This has been the Last Minute Lecture Team.

Good luck with your studies.

Bye.

See you next time.