Chapter 38: Vision Loss Assessment & Diagnosis

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Welcome back to the Deep Dive.

We are doing something a little different today, shifting gears to specifically support the students in our audience.

We are putting on our last minute lecture hats.

That's right.

We know you're out there.

Maybe you're an advanced practice nursing student.

Maybe you're in med school.

Or maybe you're a PA student with a terrifying board exam coming up on Monday morning.

Oh, that Monday morning feeling.

Exactly.

You've had three coffees.

You're staring at a mountain of textbooks and you just need someone to, you know, open up your brain and pour the information right in.

We have all been there.

The panic is real.

So consider us your study partners who have actually done the reading thoroughly and are ready to break it down.

We are.

And today we are laser focused on Chapter 38 from Advanced Health Assessment and Clinical Diagnosis in Primary Care, the sixth edition.

The subject is vision loss.

And it is a beast of a chapter.

It's one of those topics that can feel really intimidating.

It's a high stakes chapter for sure, because unlike a lot of things in primary care where you can maybe watch and wait,

vision loss often has a countdown clock attached to it.

That's a good way to put it.

Yeah.

If you miss a red flag here, the patient doesn't just stay sick.

They can go permanently blind or in some of the cases we're going to talk about, it can actually be life threatening.

So here's our mission statement for this session.

We are going to walk through Chapter 38 in the exact order it appears in the text.

We aren't going to skip around or bring in outside guidelines that might confuse you on an exam.

No, we're sticking to the source material.

The goal here is to translate that dense clinical text into a narrative that you can actually remember when you're sitting in that exam room.

Okay, so let's get started.

The book opens with a topic overview.

It sets the stage by defining vision loss very broadly.

It's not just lights out.

Right.

It's a spectrum.

It ranges from minor impairment where things are just a little blurry all the way to total blindness.

A huge range.

And right away, the author hits us with a list.

The big five.

I feel like anytime a Oh, absolutely.

If you're writing a multiple choice question for a board exam, this list is gold.

These are the most common causes of vision loss in adults.

And it's interesting because this list really tells a story about, well, about aging in the modern world.

It really does.

Let's walk through them.

Number one is refractive errors.

That sounds almost too simple, doesn't it?

Yeah, like just needing glasses.

Just needing glasses.

But statistically,

uncorrected refractive error is the leading cause of visual impairment worldwide.

It's a huge public health issue.

Okay, that makes sense.

Then we have cataracts.

Right.

The classic clouding of the lens.

We'll get into the mechanism of that later, but it's a huge one.

Then glaucoma.

Which is all about pressure and optic nerve damage.

A silent thief of sight, as they say.

Then we have age -related macular degeneration, or AMD.

That's the one that has central vision, right?

That's your central vision killer.

It takes away your ability to read, to see faces.

The fifth one on the list.

Is diabetic retinopathy.

Which is kind of the odd one out, in a way.

The first four are primarily eye diseases.

Diabetic retinopathy is a systemic disease that's just manifesting in the eye.

It's a vascular problem.

It's a microvascular disaster happening on the retina.

Those are your big five.

If you get a question on your exam asking what's most likely causing vision loss in, say, a 65 -year -old patient, statistically, it's one of those five.

The text also gives us some context on what is not on that list anymore, which I found interesting.

It mentions infectious causes, like trachoma or entrosercesis.

River blindness, yeah.

River blindness.

And this gives us a little bit of a global health perspective.

Historically, and still in many developing nations, infection is a massive cause of blindness.

But in the context of this textbook, which is focused largely on primary care in developed countries, those numbers have just plummeted.

So you're not likely to see river blindness in a suburban clinic in Ohio?

Not very likely, no.

But you might see what the text calls functional causes.

Ah, yes.

This is tricky territory.

The old school terms were malingering or hysteria.

Exactly.

Basically, the patient says they can't see, but all the plumbing, all the wiring,

it works fine.

The physical exam is normal.

I feel like there's a huge trap here for the new clinician.

A massive trap.

And the text is very, very emphatic about this.

Functional vision loss is a diagnosis of exclusion.

You do not, I repeat, do not assume a patient is faking it or that it's psychosomatic until you have rigorously ruled out every single organic cause.

Because the consequences are just too high.

Think about it.

If you label someone a malingerer and they actually have a tumor pressing on their optic nerve, a retro bulbar tumor, you have failed that patient in the worst way.

So rule everything else out first.

Always.

Always.

So before we get into the nitty gritty of the history, let's just define our role here.

I think a lot of students get intimidated by eyes because they think, I'm not an ophthalmologist.

I don't have the fancy lasers and slit lamps.

And the chapter acknowledges that anxiety.

It says pretty clearly that in all cases of impaired vision, the patient requires an evaluation by an ophthalmologist.

Right.

They are the treaters.

They do the surgery.

They manage the long -term care.

But, and this is a big but, the primary care provider is the triage officer.

The detective.

You're the detective.

Your job is to use your knowledge of the causes to find the clues in the history and physicals that tell you who needs to go to the ER right now and who can get an appointment next week.

So we are the filter.

We're the safety net.

You are the safety net.

Exactly.

Okay.

Let's do it.

Let's turn to section one.

Diagnostic reasoning and the focused history.

A patient sits down and says, doc, I can't see.

That's a huge vague statement.

How do we sharpen that?

You have to define the complaint.

The text draws a really hard line here between total absence of vision and blurring.

Yeah.

The textbooks view they are not degrees of the same thing.

Yeah.

They are fundamentally different categories.

Okay.

So how does the text define total absence?

It is absolute.

It's defined as the complete lack of form and light perception.

So the test for this isn't the eye chart.

No.

The test is you shine a pen light in their eye and you ask them is the light on or off.

If they cannot tell you, that is total absence of vision.

And that points to a very specific kind of pathology.

A very severe one.

The text associates this level of severity specifically with diseases of the optic nerve or the retina itself, like a massive retinal detachment or CREO.

The signal cable is completely cut.

Whereas blurring?

Blurring is a change in acuity.

The signal is getting through, but it's distorted.

It's fuzzy.

The text notes, as we said, the most common cause here is a simple refractive error.

But you have to ask the question, is it dark or is it just fuzzy?

It's a critical first step.

Now let's shift gears to pediatrics.

Taking a history in PEDS is, well, it's mostly observation and interrogating the parents, right?

It's detective work on a nonverbal subject, 100%.

The text brings up a term here that every student needs to know cold.

Nostagmus.

The rhythmic twitching of the eye.

Yes.

Now adults can get Nostagmus from things like vertigo or certain drugs, but in an infant, it means something very, very specific.

The text gives a hard and fast rule here.

Which is?

If you see Nostagmus in the first year of life, it suggests bilateral vision loss until proven otherwise.

Bilateral vision loss.

Wow.

Why?

What's the connection?

Why does vision loss cause the eyes to shake?

Okay.

Think about how your own eyes work.

You look at something and you lock onto it.

That's called fixation.

That locking mechanism is what keeps the eyes steady.

Like an anchor.

A perfect analogy.

It's an anchor.

If a baby can't see well enough to find an anchor to lock onto a target, the eyes just,

they wander.

They search.

And that searching movement manifests as that rhythmic twitching we call Nostagmus.

So Nostagmus is literally the eyes searching for a signal they can't find.

That's a great way to visualize it.

And that brings us to the next point in the chapter.

Visual fixation.

This is a key developmental milestone.

The text mentions that the visual system isn't fully cooked at birth.

It's not.

It takes time to develop.

But it is functional enough that a newborn should demonstrate visual interest in a human face.

By two months, that fixation should be well -developed and solid.

So if you have a two -month -old whose eyes are just roving around the room and never locking onto mom or dad's face.

That is a major red flag.

And the text really emphasizes that parental concern is key here.

He doesn't look at me.

Yes.

If a parent says that he just doesn't look at me, believe them.

That is a critical, critical history finding.

Don't dismiss that.

Okay.

Let's talk about the scary stuff.

The emergency assessment, the red flags.

This is where we need to know when to hit the panic button.

And the first pivot point in the history according to the text is the onset.

Sudden versus gradual.

This is your first branch in the decision tree.

And the text gives a very specific, very dramatic scenario for sudden loss.

It really paints a picture.

It describes a patient who says their vision was lost instantly and light cannot be distinguished from dark.

So if you hear sudden and total darkness, the textbook directs your brain straight to central retinal artery occlusion, C -R -A -O.

Let's unpack that a little.

What is actually happening in a C -R -A -O?

Think of it as a stroke of the eye.

You have the central retinal artery, which is the main pipeline of blood and oxygen to the retina.

The retina has an incredibly high metabolic rate.

It is unbelievably hungry for oxygen.

So it can't survive long without it.

Not even for minutes.

If an embolus from the heart or a plaque from the carotid artery breaks off and plugs that pipeline, the lights go out immediately.

And the tissue starts dying.

And that's irreversible.

It can be.

That's why the text emphasizes that this is a minutes matter emergency.

You cannot wait for a consult next week.

This is a 911 call.

Okay, so onset is pivot number one.

The next pivot point is pain.

The text suggests this helps us localize the problem anatomically.

This is a really useful heuristic, a good rule of thumb.

The text suggests that if there is pain associated with the vision loss, the pathology is likely in the anterior structures of the eye, the front of the eye.

So the cornea, the iris, the ciliary body.

Exactly.

Those structures have a lot of nerve endings.

The retina, on the other hand, does not.

So red painful eye should make you think front of the eye problem.

And the big emergency here.

Acute angle closure glaucoma.

We'll talk about the mechanism later, but the classic clinical presentation is sudden vision loss with excruciating, deep,

boring pain, often with nausea and vomiting and a red eye.

What about a more specific kind of pain?

The book mentions pain on movement.

Like it only hurts when I look to the left.

Ah, yes.

That is the hallmark symptom of optic neuritis.

This is inflammation and demyelination of the optic nerve itself.

And why does moving the eye hurt the nerve?

It's a great anatomical connection.

The optic nerve is sheathed in the same structures as the muscles that move the eye.

So when you pull on those muscles to look side to side, you're essentially tugging on the sheath of that inflamed angry nerve.

And that causes pain.

That makes perfect sense.

Now, what if the loss is sudden but painless?

That almost feels more insidious, more sneaky.

It definitely can be.

The text gives a differential for painless sudden loss.

We already mentioned CRAO, which is typically painless.

But it also vividly describes vitreous hemorrhage.

This description in the book is very cinematic.

I won't forget this one.

It is.

The patient might describe a sudden shower of floaters drifting in their vision, followed by what the text calls a red glow.

And then the vision just fades to black over minutes.

What is that red glow?

It's blood.

They are literally seeing the blood fill the vitreous chamber of their eye.

It's filtering the light, turning everything red before it becomes so dense that no light can get through at all.

A red glow before the darkness.

That is unforgettable.

It really is.

Other painless causes the textless include macular degeneration, if one of the vessels bleeds suddenly, retinal detachment, and of course diabetic retinopathy.

Okay, before we move on from the history, we have to tackle the anatomy.

Figure 38 .1, localization.

This is the part of the board exam where everyone starts to sweat.

Chiasmal lesions, post -chiasmal lesions.

It doesn't have to be hard, I promise.

The text simplifies it into a geography problem.

You have the two optic nerves coming from the eyes, and they meet at the optic chiasm.

That's the crossing point in the brain.

The big intersection.

The big intersection.

The rule is simple.

If the vision loss is in one eye monocular vision loss, the problem has to be anterior to the chiasm.

It's in the eyeball itself or in the optic nerve before it gets to that crossing point.

That makes sense.

If the wire is cut before the junction box, only one light goes out.

Exactly.

But if you have what the text calls hemianopic field defects, which is a fancy way of saying you've lost half the vision in both eyes, that tells you the lesion is post -chiasmal.

It's after the crossing point.

So if the problem is after the junction box, it affects the wiring going to both sides.

Right.

And specifically, the classic finding is a homonymous hemianopsia.

Let's say you have a stroke in the right side of your brain, in the occipital lobe, which is way behind the chiasm.

You will lose the left visual field in both of your eyes.

Got it.

One eye equals anterior.

Both eyes with a field cut equals posterior.

That's the rule of thumb.

It'll get you through most test questions.

All right.

Moving on to section two in the chapter,

specific symptoms and trauma history.

The text highlights a very specific symptom here,

photopsia or flashes of light.

This is a classic, classic symptom.

The patient will say, I saw a lightning bolt in the corner of my eye, or a camera flash went off.

Sometimes they describe a veil or a curtain coming down over their vision along with it.

What is physically happening to cause a flash of light inside your own eye?

There's no actual light.

No, it's mechanical stimulation.

The retina is like wallpaper that's pasted to the back wall of the eye.

If that wallpaper starts to peel off, which is a retinal detachment, or if the vitreous gel that fills the eye shrinks and pulls on it, it physically tugs on the photoreceptors.

The rods and cones.

The rods and cones.

And the brain doesn't know how to interpret tugging.

The brain only speaks one language for the eye, light.

So when the retina gets tugged, the brain just screams light, even if you're in a pitch black room.

The text also includes an important warning here, distinguishing between a retinal tear and a full detachment.

Yes, it notes that a retinal tear, where it just rips a little bit, causes the exact same flash as a full detachment.

You cannot tell the difference by history alone, both are emergencies, because a tear is often the first step to a full detachment.

Got it.

What about transient loss?

A patient says, I went blind for a minute, and then it came back.

That almost always points us toward either a vascular issue, like a TIA of the eye, or a migraine.

The text describes a scotoma, which is an island of impaired vision.

In a migraine, this can be positive, seeing things that aren't there, like sparkles or zigzags, or it can be negative, which is just a blind spot, a missing patch of vision.

OK, let's talk trauma.

This is a huge section in the chapter.

And it's broken down by mechanism, which is helpful.

Let's start with head trauma.

The text notes that an injury to the occiput, the very back of the head where the visual cortex lives, can cause a sudden, complete blindness that often returns as the brain swelling goes down.

But there's a critical pediatric note here.

Yes.

Shaken baby syndrome, or abusive head trauma.

The mechanism is a violent acceleration deceleration force.

This shears the delicate blood vessels in the eye.

The text is explicit.

If you see retinal and vitreous hemorrhages in an infant, you must consider abuse.

It is a hallmark sign.

That's a heavy one.

Then we have direct eye trauma.

Blunt versus sharp.

The text has a very specific warning about high -velocity injuries.

It gives the example of a metal worker using a grinder.

This is what I call the deception of the small wound.

A tiny shard of metal flying at high speed can pierce the cornea in the lens, leaving a microscopic entry wound that looks exactly like a simple corneal abrasion.

So you look at it, you stain it with fluoresce, and you see a tiny little scratch, and you send them home with some eye drops thinking, you're fine.

And meanwhile, there's a piece of rusting metal sitting inside their vitreous, causing a massive inflammatory reaction that will destroy the eye.

The text warns that these small perforations are very easily missed, if you aren't suspicious of the mechanism of injury.

Finally, chemical and thermal trauma.

This is the one place where the text pretty much screams at us to stop being a doctor and start being a firefighter.

Crete first, examine later.

That is the golden rule.

Print it in bold.

You do not check visual acuity.

You do not ask about their allergies or their past medical history.

You grab the saline or the tap water and you wash that eye copiously.

And we really need to talk about the chemistry here.

The text makes a big distinction between acid and alkaline burns.

I think most people, myself included, always assumed acid was worse.

It just sounds scarier.

Everyone does.

It's the movie villain trope, right?

Yeah.

But the text explains exactly why alkaline burns.

Things like drain cleaners, lye, cement, even airbag residue are actually the nightmare scenario.

So why is that?

It comes down to how the cells react at a molecular level.

When acid hits the proteins of the cornea, it causes protein precipitation.

It basically cooks the proteins on the surface instantly, turning them into a hard coagulated crust.

A scab, essentially.

Exactly.

It forms its own eschar.

And that crust actually forms a barrier.

It stops the acid from penetrating deeper into the eye.

It limits its own damage.

But alkaline is different.

Alkaline is completely different.

Alkaline substances cause a process called saponification.

They interact with the fatty acids in the cell membranes and literally turn them into soap.

They liquefy the tissue.

They melt it.

That's a terrifying image.

There is no crust.

There's no barrier.

So the chemical just keeps melting its way right through the cornea into the anterior chamber and destroying the lens and the iris.

It just keeps going.

Saponification of the eye, OK, that is a high yield takeaway.

Alkali equals melt equals bad.

You've got it.

That's why the text emphasizes you irrigate, and you keep irrigating until the pH of the eye is neutral.

And that can take liters and liters of fluid and a long time.

OK, that's a great section.

Let's move to section three, progression, family history, and systemic disease.

Right, so we're back to the history.

The speed of progression helps us sort our differential list.

If it's slowly progressive, happening over months or years, we're thinking about degenerative diseases.

Like cataracts or macular degeneration.

Exactly.

The slow burners.

The text mentions night blindness, specifically as a presenting symptom.

Yes.

If the patient says, I'm fine during the day, but I just can't drive at night anymore,

that's often the very first symptom of retinitis pigmentosa, a genetic degenerative disease.

Or in a global health context, severe vitamin A deficiency.

What about dimming a vision when standing up?

I've had that happen.

Right, and it's a great fake out.

The patient says, my vision goes black, but the trigger is postural change.

That's not an eye problem.

That's orthostatic hypotension.

It's a blood pressure issue.

It's a pump problem, not a plumbing problem in the eye.

Let's look at pediatric tumors.

The text brings up optic gliomas.

Right, and the classic presentation here is progressive vision loss plus a loss of color vision.

But the key connection you need to make for the boards is the association with neurofibromatosis.

The text says 25 % of patients with optic gliomas have NF1.

So if you see one, you have to look for the other.

Family history.

This seems massive in ophthalmology.

It's genetic roulette.

It's huge.

Take retinoblastoma, the childhood eye cancer.

If there's a positive family history, a child has a 12 % chance of developing it.

It's an enormous risk.

And congenital cataracts.

The text says 10, 25 % of congenital cataracts are familial.

And they're often autosomal dominant, which means if a parent has it, each child has a 50 % chance.

A coin flip.

The text also references the torch complex.

We hear this in obian peds all the time.

It's a classic mnemonic for maternal infections that can cross the placenta and affect the fetus.

Toxoplasmosis, other like syphilis, rubella, cytomegalovirus, and herpes simplex.

And the relevance for vision.

These are the infections that cause blindness at birth or soon after.

If a baby is born with cataracts or corioretonitis or retinal scarring, you have to check the mom's two or shade status.

Systemic disease.

We have to talk about diabetes.

It's unavoidable.

You cannot talk about vision loss in the developed world without talking about diabetes.

It is the leading cause of blindness in the working age population.

The risk correlates directly with two things.

The duration of the disease and how uncontrolled the sugar is.

What's the mechanism the text describes?

What's actually happening to the blood vessels?

The text uses the term incompetent arterials.

The high blood sugar damages the endophilia lining.

The walls of the tiny blood vessels in the retina, they get weak.

They get leaky.

They start to leak fluid and fats, we call those exudates, into the retinal tissue.

That's the early stage.

Later, they just close off completely, causing ischemia.

And steroids.

We prescribe them all the time for so many things.

We do.

And we should be careful.

The text notes that prolonged use of systemic steroids, like prednisone, almost invariably results in the formation of a very specific kind of cataract.

A posterior sub -capsular cataract.

It's a direct drug -induced pathology.

OK, so we've got the history.

We know the risks.

Now we actually have to touch the patient.

Section four, physical examination part one.

We start just by looking.

Appearance and alignment.

And the concept you must understand cold here is amblyopia.

Which laypeople call lazy eye.

But clinically, it's much more complex than that.

So much more.

Amblyopia is a brain problem, not just an eye problem.

The definition is impaired vision in a structurally normal eye.

The hardware is fine.

The software is the issue.

The brain is literally turning off the input from that eye.

And the text classifies it into three distinct types.

We really need to be able to distinguish these for an exam.

Absolutely.

First is strabismic amblyopia.

This is the one you can see.

The eyes are misaligned.

One is crossed in or out.

The brain sees two different images.

It hates double vision, so it does something amazing.

It deletes the image from the deviating eye.

Type two.

Refractive amblyopia.

This word is much sneakier because the eyes look perfectly straight.

But one eye might be very near -sighted or very far -sighted.

And the other eye is normal.

The brain gets two images.

One is sharp and one is blurry.

Guess which one it pays attention to.

The sharp one?

Of course.

It tunes out the blurry one.

And if you don't catch this early and put glasses on that kid, the brain will permanently disconnect the wiring to that blurry eye.

That's wild.

The brain just gives up on it entirely.

It is use it or lose it, in the most literal sense of the phrase.

And the third type.

Deprivation amblyopia.

This is the most severe.

This is when something physically blocks the light from reaching the retina.

A congenital cataract.

A droopy eyelid, which we call a ptasis, that's covering the pupil.

If no light hits the retina in those first few years, the visual cortex for that eye never develops its wiring at all.

Let's talk about some other appearance terms.

The text mentions exothelmos versus enothelmos.

Right.

Exothelmos is bulging eyes.

You can see the whites of the eyes, the sclera, all the way around the iris.

You should immediately think of Graves' disease or hyperthyroidism.

Enothelmos is the opposite.

The eye is sunken in.

Think of severe dehydration in a child.

Or a blowout fracture where the floor of the orbit has collapsed and the eyeball has literally dropped into the maxillary sinus.

The text also mentions squinting.

We all do it in the sun.

Right.

It's a compensatory mechanism.

It creates a pinhole camera effect, blocking straight light rays, and sharpening your focus.

But the text has a very specific pediatric red flag here.

Excessive squinting in bright light.

And what does that mean?

It says you should think glaucoma.

Kids with congenital glaucoma are extremely sensitive to light.

That's photophobia.

They squint constantly to try and block out the painful light.

Okay.

Let's talk acuity testing.

We all know the Snellen chart.

But practically, as a primary care provider, how do we know when to refer?

The text has table 38 .1 for this.

This table is your cheat sheet.

It's gold.

The general rule for kids is asymmetry.

If the right eye tests at 20 -20 and the left eye is 20 -30, that's just one line difference on the chart.

That is a referral.

Why is one single line such a big deal?

Because of amblyopia.

That difference, however small, suggests the brain is starting to favor one eye over the other, and you have to intervene before it becomes permanent.

And what about the absolute age cutoffs?

According to the table, a five -year -old should be seeing at least 20 -50 or better.

A six -year -old should be at 20 -40 or better.

But, and here is the last minute lecture pro tip from the text retest before you refer.

Why is that?

Because kids are kids.

The first time you test them, they're distracted.

They don't understand the game.

They're shy.

If they fail the first time, take a minute, explain it again, and retest.

The text says they almost always do better the second time once they understand what you want from them.

That's a great practical tip.

Okay, moving to section five.

Physical examination part two.

Pupils, nystagmus, and fields.

And we have to start with the single most critical finding in a pediatric eye exam.

The white pupil.

The cocoria.

Instead of the red reflex, that red eye you see in flash photos, you look in with your ophthalmoscope, and the pupil looks white or yellow.

This is a drop everything and call ophthalmology now finding.

The text lists the causes, and they're all serious.

Cataract, retinoblastoma, which is cancer, or a retinal detachment.

If you see white, that kid needs to be seen by a specialist today.

No exceptions.

What about pupil size?

Anycocoria?

Unequal pupils.

The text does reassure us that about 5 % of the normal population has this, it's called physiologic anisocoria.

But you can't assume that.

You have to look at the context.

Is the pupil fixed, dilated, and is the eye red and painful?

That's acute glaucoma.

Is there a droopy eyelid?

Etosis?

And the pupil is small and constricted.

That could be a Horner's syndrome, which might mean a tumor in the chest.

We're back to nystagmus.

We said it's a huge red flag in babies.

But is any twitching in an adult's eye bad?

No, not at all.

The text describes something called endpoint nystagmus.

If you make someone look all the way to their far left or far right, their eye might twitch a little bit.

That's just normal muscle fatigue.

It becomes pathological when the eye twitches in the same direction, regardless of where they're looking.

That suggests a central neurological problem.

Let's get technical with the cover -on -cover tests.

These always confuse me in school.

There are two of them, and they test for different things.

You are not alone.

Let's break it down really simply.

There are two tests for two different problems.

A lazy eye that's lazy all the time, and one that's only lazy when it's bored.

Okay, I like that.

Test one, the cover -on -cover test.

This is for manifestribismus, also called a heterotropia.

The eye is lazy right now.

You can see it's misaligned.

So the test is you cover the good eye.

You force the bad eye to do the work.

If that bad eye was wandering off to the side, it will have to move to pick up the target.

You see it snap back to the center to fixate.

That's a positive test.

And test two, the alternating cover test.

This is for latent strabismus or a heterotropia.

This is an eye that really wants to wander, but the brain is working hard to keep it in check, as long as both eyes are open and working together.

So how do we trick it into showing its true colors?

We break that connection.

We break binocular fusion.

You swing the cover rapidly back and forth between the eyes.

By doing that, the brain never gets to use both eyes at the same time.

Without that binocular lock keeping it straight, the lazy eye will drift out.

When you uncover it, you'll see it snap back into place.

That's the clearest explanation I've ever heard.

Thank you.

Section six, advanced examination techniques.

Let's start with the AMSR grid.

Right, figure 38 .2 in the book.

It's so simple.

It looks like a piece of graph paper with a black dot in the middle.

And what is it for?

It's a test for macular degeneration.

The macula is responsible for your fine central vision.

You have the patient cover one eye,

stare at the central dot, and you ask them a simple question.

Do all the straight lines on the grid look straight?

And if they don't, if they say the lines look wavy.

That is the definition of metamorphopsia.

The lines look wavy, bent, or distorted.

That means the macula, the film at the center of the camera,

is either buckling because of dry AMD, or there's fluid underneath it from wet AMD.

It's a very sensitive test for macular disease.

Okay, now for the big one, the aphthalmoscope.

The fundoscopic exam.

The bane of every medical and nursing student's existence.

It is so hard.

The text admits it requires a ton of practice.

But for newborns, the goal is simpler.

We're just focusing on getting a good look at the red reflex.

And the text describes a specific technique to get the baby to open their eyes.

I love this tip.

It's called the parachute, or doll's eye maneuver.

How does it work?

You swaddle the infant snugly so their arms can't flail.

Then you hold them upright, facing you, and you gently but quickly swing them downward,

as if you were a parachute landing.

And that does what, exactly?

It triggers a vestibular reflex.

The baby automatically opens their eyes wide.

That is your window of opportunity to shine the aphthalmoscope in from about an arm's length away, and check for a symmetric, bright red reflex in both eyes.

That is a gem of a clinical tip.

OK, once we're actually looking inside an adult's eye, what are we seeing on the optic disc?

The text points out three main pathologies.

Right, you're looking for three big things.

Number one, pallor.

The disc should be a healthy pinkish orange.

If it looks pale and white, like a full moon, that's optic atrophy.

The nerve is dead.

Number two.

Capillodema.

This is the opposite.

The disc is swollen.

It's red or hyperemic.

And the margins, the edges of the disc, are blurry and indistinct.

That means there's increased pressure in the brain, increased intracranial pressure, pushing on the back of the nerve.

And number three.

The glaucoma disc cup.

There's a little depression in the center of the disc called the cup.

In glaucoma, as the nerve fibers die, that cup gets bigger and deeper.

The cup -to -disc ratio increases.

That's a sign of chronic nerve damage.

What if you look in and you just see nothing, just blackness where the red reflex should be?

Well, first you check the batteries in your ophthalmoscope.

Fair enough.

And if the batteries are working?

Then it's almost certainly a vitreous hemorrhage.

The light from your scope goes into the eye, it hits the wall of blood, and it just stops.

It can't reflect back out.

This is extremely common in patients with advanced diabetic retinopathy who have a sudden bleed.

Okay, moving on to section seven.

Laboratory and diagnostic studies.

There aren't many labs, but there are a few useful in -office tests.

Primary care can and should use fluorescein dye.

You touch a little strip of orange dye to the inside of the eyelid, have the patient blink, and then you look with a cobalt blue light.

And it makes corneal abrasions glow a bright green.

Exactly.

But there is one specific pattern that you need to memorize.

That if you see it, you should get a little jolt of adrenaline.

The dendritic pattern.

The dendritic pattern.

It looks like a little lightening bolt or the branching of a tree.

If you see that pattern on the cornea, you must put the steroid drops away.

That is pythognomonic for herpes simplex keratitis.

Giving steroids will make the virus replicate like crazy and can cause the cornea to melt.

That is a critical do not miss.

Dendrite equals herpes equals no steroids.

You got it.

That's the formula.

All right, section eight begins the differential diagnosis proper.

The chapter synthesizes the pediatric conditions first.

Right.

We've talked about strabismus and amblyopia.

The main takeaway from this section is the concept of the critical window.

The text says the risk for developing permanent amblyopia is highest in the first two to three years of life.

That is when the brain is actively wiring the visual cortex.

So that's when we have to intervene.

That's the window.

Yeah.

But it also notes that recurrence of amblyopia is possible until about age nine.

So you're not fully out of the woods until they hit the double digits.

What about retinopathy of prematurity?

This is a fascinating and tragic disease of medical progress.

We save these tiny premature babies by giving them high concentrations of oxygen.

But that oxygen, while life -saving, can be toxic to the developing blood vessels of the retina.

Who is most at risk?

The text specifies infants weighing under 1 ,500 grams or born before 40 weeks gestation.

In these babies, the peripheral retina hasn't finished growing as blood supply yet.

The high oxygen can cause those vessels to stop growing correctly, then later grow wildly and abnormally, forming scar tissue that can pull on and detach the retina.

Okay, section nine, adults.

Let's do a deeper dive on glaucoma.

Glaucoma is the leading cause of irreversible blindness.

But it's confusing for students because there are two main types that act in completely different ways.

Open angle versus closed angle.

Can you use the sync analogy?

I find that helpful.

The sync analogy is perfect.

Think of the inside of your eye as a sink.

The faucet is always running.

That's the ciliary body producing anqueous humor.

The drain is a spongy structure called the trabecular meshwork.

In open angle glaucoma, which is the common slow kind, the drain is just clogged with gunk.

It drains, but very slowly.

So the water level, the pressure,

rises slowly and painlessly over many years.

You don't know you have it until you've already lost a lot of peripheral vision.

And closed angle.

In acute angle closure glaucoma, someone just slammed the rubber stopper in the drain.

The iris physically bunches up and blocks the drain completely.

The faucet is still running, but nothing can get out.

Pressure spikes dramatically and instantly.

That's the painful red eye emergency we talked about.

Now here's a curve ball.

The chapter includes an evidence -based practice box regarding glaucoma screening in primary care.

And this surprises a lot of people.

The text states that routine screening for glaucoma by primary care providers is not recommended.

Why not?

We scream for high blood pressure all the time.

Because the tools we have in primary care, like the puff of air test or a simple tonal pen, aren't accurate enough on their own.

Glaucoma diagnosis isn't just about pressure.

You have to look at the optic nerve, measure the corneal thickness.

We just don't have the tools to do it well.

So the recommendation is to refer patients, especially those at high risk, to an optometrist or ophthalmologist for proper comprehensive screening.

Okay, let's talk macular degeneration, AMD.

This is the leading cause of permanent blindness in the elderly.

People over 50.

Two types,

dry and wet.

Dry is the slow one.

It's atrophy.

The cells of the macula are slowly dying.

You look in and see these little yellow deposits called drusen.

Wet is the fast one.

Abnormal, fragile new blood vessels grow underneath the macula.

They're leaky.

They bleed and leak fluid, causing rapid and severe vision loss.

And the AMSLA grid is a home monitoring tool for this.

Exactly.

It helps patients detect the change from dry to wet AMD early.

Let's review the stages of diabetic retinopathy.

The book divides it into non -proliferative versus proliferative.

In non -proliferative, the existing vessels are just weak and leaky.

You see micro aneurysms, which look like little red docks, and cotton wool spots, which are fluffy white patches that represent areas of infarction or ischemia.

In proliferative, the eye is so starved of oxygen that it panics and tries to grow new blood vessels.

That process is called neovascularization.

But new blood vessels sound like a good thing, right?

More blood flow.

You'd think so, but they're garbage vessels.

They're fragile, they grow in the wrong place, and they burst easily, causing massive vitreous hemorrhages and retinal detachments.

Proliferative disease is a very advanced, very dangerous stage.

Finally, we're in section 10, the other conditions.

The text brings back central retinal artery occlusion, CRAO.

We know it's painless, sudden, profound vision loss.

But the exam finding is famous.

The cherry red spot.

So why is it red?

What's happening?

It's actually a bit of an illusion.

The spot itself, the fovea, at the very center of the macula, is the only normal part.

It has a separate blood supply from the corroid underneath.

The rest of the entire retina, which is supplied by that blocked artery, is dead and ischemic, so it turns a pale, milky white.

So that normal red fovea stands out against the pale background like a cherry on white icing.

Tumors.

The text mentions a specific one, craniopharyngioma.

Right.

This is a type of pituitary tumor,

and its location is key.

It sits right underneath the optic chiasm.

As the tumor grows, it pushes up from below and compresses the crossing nerve fibers.

And that compression creates a very specific visual field defect.

A pathognomotic one by temporal hemianopsia.

Because it's hitting the fibers that cross from both eyes, you lose the outer temporal peripheral vision in both eyes.

It's like having blinders on.

If a patient comes in complaining that they keep bumping into doorframes on both sides, you have to think about a pituitary tumor.

Wow.

We have covered a lot of ground.

The anatomy, the history, the exam, the red flags, and the pathologies.

It is a marathon chapter, no doubt about it.

So let's wrap this up by looking at the summary table review.

The text connects the dots one last time, which is really helpful for studying.

It is.

It reinforces that if -then logic that you need for clinical reasoning.

If the history is a curtain falling over my vision, then the exam finding should be a gray elevated retina, which means retinal detachment.

If the history is pain with eye movement, then the exam finding to look for is an afferent pupillary defect, which points to optic neuritis.

It connects symptom to sign.

And bringing it all back to our main mission today, defining the role of the primary care provider.

We are the early warning system.

Yeah.

That's our job.

We don't need to know how to surgically fix the retinal detachment.

We just need to recognize that the flashing lights the patient is describing aren't just a migraine.

We don't need to operate on the congenital cataract.

No, but we have to be the one who catches the leukocuria in that six -month -old during a well -child check before the brain shuts off that eye for good.

We save sight and sometimes lives by paying attention to the details.

That's the job.

To all the students listening to this, take a deep breath, go back through the chapter you know more than you think you do.

Trust the red flags.

And if you remember nothing else, remember this.

Sudden loss is bad.

Pain is usually anterior.

And a white pupil is an immediate referral.

You've got this.

Thanks for diving deep with us.

From the entire last -minute lecture team, good luck on your exams.

Go crush it.