Ocular Anatomy

Question 1

Which of the following provide parasympathetic innervation to the eye? (Pick 2)

CN III
CN V
CN VII
CN II

Answer 1

Correct Answer = CN 3 and CN 7 provide parasympathetic innervation (involuntary motor) to the eye.

CN III – uses ciliary ganglion (CG) for miosis and accommodation.
CN VII – uses sphenopalatine ganglion (aka pterygopalatine ganglion) for lacrimation.

Question 2

A patient with blunt trauma or a penetrating injury to the globe with iridodialysis is most likely to have pathology in what area of the iris? If this patient experienced a hyphema, where is the blood most likely coming from?

Answer 2

Correct Answer = Iris Root. This is the thinnest location of the iris. where the iris attaches to the ciliary body.
Correct Answer = Major arterial circle of the iris. Recall that this arterial network is actually located in the ciliary body stroma (not the iris, even though called major arterial circle of the iris), which is located right next to the iris root.

Question 3

What anatomical changes occur as you go from the cornea to the limbus?

Answer 3

Correct Answer = Two structures END and two structures BEGIN!

END = Bowman’s layer and Descemet’s layer.  Recall that Descemet’s layer becomes Schwalbe’s Line.
BEGIN = Conjunctiva and Tenon’s capsule

Question 4

Which of the following increases during accomodation? (Pick 3)

1. Lens zonule tension
2. Lens diameter
3. Lens thickness
4. Anterior lens curvature
5. Posterior lens curvature
6. Intraocular pressure (IOP)

Answer 4

Correct Answers = 3, 4, 5

The following changes occur during accomodation:

Increase = lens thickness, anterior lens curvature, posterior lens curvature
Decrease = lens diameter, IOP (temporary decrease)
Don’t confuse diameter and thickness on the exam. If you get confused on the exam, remember Diameter = Decreases (the d’s go together).

Question 5

What increases more during accommodation, anterior or posterior lens curvature?

Answer 5

Correct Answer = anterior curvature.

Question 6

Which of the following corneal layers will not regenerate after injury? (Pick 2)

1. Epithelium
2. Bowman’s layer
3. Endothelium
4. Stroma
5. Descemet’s membrane

Answer 6

Correct Answers = 2,3

Recall that the stroma regenerates new tissue after injury, but the replacement tissue has slightly different characteristics (and thus reveals a different color), which is evident as a scar.

Question 7

Which of the following structures would NOT be visible in a patient with Grade 2 narrow angles? (Pick 3)

1. Peripheral iris
2. Scleral spur
3. Trabecular meshwork
4. Ciliary body

Answer 7

Correct Answer = 1, 2, 4

As an angle becomes more narrow, the peripheral iris and most POSTERIOR structures in the angle (e.g. ciliary body, scleral spur, respectively) will NOT be visible.

Clinical Application = if you ever check an angle with gonioscopy and the trabecular meshwork is NOT visible, you have a big problem!

Question 8

Which of the following ocular effects is expected FIRST with uncal herniation?

1. Dilated pupil
2. “Down and Out” location of the pupil

Answer 8

Correct Answer = Dilated pupil

Recall that the pupillary fibers lie on the outside of Cranial Nerve 3. Compression on the midbrain during uncal herniation will initially push on the outside fibers of cranial nerve 3, affecting the pupil (e.g. dilated pupils, lack of pupil response to light) before affecting the EOM’s.

Question 9

A patient with traumatic brain injury (TBI), after a recent car accident, has increased intracranial pressure. The primary care physician is concerned about uncal herniation and consults with you for an ocular evaluation. Which of the following signs/symptoms are most likely if an uncal herniation is present? (Pick 3)

1. Lack of pupil responses to light
2. Location of the eyes in the “down and out” position
3. Dilated pupils
4. Corneal hypoesthesia

Answer 9

Correct Answers = 1,2,3

Uncal herniation results from an increase in intracranial pressure and the brainstem is compressed downward, with major emphasis on the lower brainstem (mainly the MIDBRAIN). The worst case scenario in this condition is the midbrain being squeezed through the foramen magnum, resulting in death. From a testing standpoint, UNCAL HERNIATION = MIDBRAIN = CN 3 DAMAGE.

The midbrain is responsible for controlling consciousness — damage to specific areas within the midbrain can result in coma. It is common to check pupils in brain injuries to determine extent of midbrain injury to assess risk of uncal herniation.

Answer choice 4 (corneal hypoesthesia) was not correct b/c CN5 originates from the PONS. Do you recall how to test for corneal hypoesthesia? Cotton-swab testing

Question 10

Touch your right superficial temporal artery. This is located on the right temple, correct? This artery is an external carotid artery branch, correct?
You know that temporal arteritis is an ocular emergency because both eyes can become blind very quickly. How can an artery that provides blood supply to superficial areas of the face lead to vision loss?

Answer 10

Temporal arteritis is a systemic disease that affects MEDIUM-SIZED blood vessels. The SPCA’s are branches of the ophthalmic artery (of the Internal Carotid) that provide blood supply to the optic nerve head. These arteries are also MEDIUM-SIZED blood vessels. The inflammation in this systemic condition spreads throughout the body attacking the medium sized vessels.

Definitely know the SPCA’s! They are SHORT b/c they enter the back of the eye (near the optic nerve) and stay posterior (they have a short course) — recall that the SPCA’s not only supply the optic disc, but they also provide for the macula and the majority of the choroid (especially throughout the posterior pole).

Question 11

Which portion of the optic nerve is NOT affected by the demyelinating inflammatory changes in optic neuritis?

1. Intraocular portion
2. Intraorbital portion
3. Intracanalicular portion
4. Intracranial portion

Answer 11

Correct Answer = Intraocular portion

Recall that the optic nerve becomes myelinated AFTER passing through the lamina cribosa. The intraocular portion of the optic nerve extends from within the eye to the lamina cribosa.

MYELINATION = begins just posterior to LAMINA CRIBOSA.

Question 12

Which of the following EOMs would not be affected with a tumor located on the Circle of Zinn?

1. Superior Rectus
2. Inferior Rectus
3. Inferior Oblique
4. Superior Oblique

Answer 12

4. Remember, the inferior oblique is the only EOM whose origin is anterior to the globe.

Question 13

Your patient has a tumor within the muscle cone behind the eye. Which of the following would you NOT expect?

1. Sensory loss to the cornea
2. Lateral rectus palsy
3. Sensory loss to the upper eyelid
4. Sensory loss to the tip of the nose

Answer 13

Correct Answer = Sensory loss to the upper eyelid

Recall that all of the recti muscles have their origin at the common tendinous ring (CTR). This forms a “muscle cone” behind the globe. Sensory to the upper eyelid comes from the frontal nerve, which courses above CTR. Recall that there are three branches of V1 of CN V — Nasociliary nerve, Frontal nerve, and Lacrimal Nerve — think of V1 like the National Football League (V1 = NFL). Again, the nasociliary nerve, which innervates the cornea, iris and tip of the nose, courses through the CTR. The frontal nerve, which branches into the supraorbital nerve and supratrochlear nerve, courses above the CTR and innervates the forehead.

Recall that three nerves course through the CTR – Nasociliary nerve, Oculomotor nerve, and Abducens nerve = NOA. Remember, all three are nerves… don’t just memorize NOA – think NOA Nerves!

Question 14

A tumor arises at the foramen ovale – what symptoms would you NOT expect? (Pick 2)

1. Difficulty with chewing
2. Loss of sensory innervation to cheek
3. Hearing loss on the contralateral side

Answer 14

2,3. You would expect difficulty with chewing. Recall that V3 goes through the foramen ovale. We remember CN V by SENSORY, SENSORY, SENSORY with a minor motor component – which is muscles of mastication through V3. Don’t forget that V3 also does sensory to the same area (mandible region).

Question 15

In what condition is the upper eyelid ptosis more severe, Horner’s syndrome or a Cranial Nerve 3 palsy? Why?

Answer 15

Correct Answer = Cranial Nerve 3 Palsy.

The superior levator palpebrae muscle is innervated by CN 3 and is the main retractor of the upper eyelid (15 mm).
Muller’s muscle, which is innervated by the sympathetic nervous system is the minor retractor of the upper eyelid (3 mm) and is damaged in Horner’s syndrome.
LEVATOR MUSCLE = 15 mm. MULLER’S MUSCLE = 3 mm.

Question 16

Upon examining a patient, you see a corneal defect that is suspicious for Herpes Simplex. If you were to test nearby areas for loss of sensation, which of the following would most likely be affected?

1. Mandible
2. Lower cheek
3. Upper eyelid

Answer 16

3. Herpes Simplex hides-out within the Trigeminal ganglion (of CN V) and can enter V1, V2, or V3. The question stated that the cornea was likely affected, so you would anticipate the other areas of distribution of V1 for the answer. I would definitely know V1 very well for your exam!

Remember, V1 has three branches: National Football League (NFL):

Nasociliary – goes to cornea
Frontal – goes to UPPER EYELID, forehead
Lacrimal – goes to lacrimal gland
Remember, V1 = NFL

Question 17

What condition results in ptosis of the upper eyelid and a reverse ptosis of the lower eyelid?

Answer 17

Correct Answer = Horner’s Syndrome = narrowed interpalpebral fissure (think squint appearance)

Recall that this condition results from sympathetic damage. The upper eyelid ptosis results from damage to Muller’s muscle. Lack of sympathetic innervation to the Muscle of Riolan (of the lower eyelid) results in a reverse ptosis (normally sympathetic innervation contracts the eyelid and pulls it away from upper eyelid). So remember, in Horner’s the upper and lower eyelids are, in essence, pulled toward each other. Why? All results from lack of sympathetic innervation! This can cause the patient to appear as though they have enophthalmos (opposite of proptosis) because of the narrowed lids.

HORNER’S = PTOSIS and REVERSE PTOSIS

Question 18

Why are myelinated fibers of the nerve fiber layer not typically present in most eyes?

Answer 18

Correct Answer = Normally, myelination begins after (posterior to) the lamina cribosa; this reduces scattering of light and optimizes transduction of the nerve signal. Imagine if myelination started anterior to the lamina (within the NFL); this would cause a huge problem, as a significant amount of the light entering the retina would be scattered within the NFL prior to reaching the photoreceptors.

Question 19

How is the forced duction test used clinically to differentiate between a muscle restriction and a muscle palsy?

Answer 19

Correct Answer = Forced duction testing helps differentiate a muscle paresis (palsy) from muscle restriction (e.g. trauma). The eye is grasped with forceps (after anesthesia of course) and moved in different directions, most notably in the area that you are suspecting an issue. If you are NOT able to rotate the eye in a area, the eye is “restricted” and this is called a POSITIVE FORCED DUCTION TEST.

For example, diagnosis of Brown’s syndrome is aided with a positive forced duction test. A blowout fracture would result in a positive forced duction test. A cranial nerve VI palsy will be non-comitant with a negative forced duction test.

MUSCLE RESTRICTION = POSITIVE FORCED DUCTION TEST

MUSCLE PALSY = NEGATIVE FORCED DUCTION TEST

Question 20

Name five clinical features of a blowout fracture?

Answer 20

Correct Answers = Crepitus, diplopia, enophthalmos, hypesthesia of the infraorbital nerve, positive forced ductions

Question 21

An orbital infection that involves the lamina papyracea can cause what dreaded ocular infection?

Answer 21

Correct Answer = Orbital Cellulitis

This question combines knowledge of several different concepts. Recall that the lamina papyracea is another name for the ethmoid bone. Recall that an ethmoid sinusitis (SINUS INFECTION) is the most common cause of orbital cellulitis. An orbital cellulitis is very dangerous because it can spread posteriorly and result in meningitis.

Question 22

Why is the eye “down and out” in a Cranial Nerve 3 palsy?

Answer 22

The eye will be displaced downward because the superior oblique (innervated by CN 4), is unantagonized by the paralyzed superior rectus and inferior oblique and displaced outward, because the lateral rectus (innervated by CN 6) is unantagonized by the paralyzed medial rectus.

Remember SO4 LR6 = Superior Oblique innervated by CN 4 AND Lateral Rectus innervated by CN 6. The remaining EOM’s are innervated by CN III.

Question 23

Which of the following is expected in a COMPLETE Cranial Nerve 3 palsy? (Pick 4)

1. Limitations with abduction on the involved side
2. Limitations with adduction on the involved side
3. Location of the eye in the “down and out” position on the involved side
4. Ptosis on the involved side
5. Limitations with abduction on the contralateral eye
6. Dilated pupil on the involved side

Answer 23

2, 3, 4, 6. Complete CN3 palsy means that all functions of CN3 will be affected, including:

Opening the eye (damage results in ptosis). Remember, CN 3 opens eye, CN 7 closes eye.
Operation of 4 of the 6 EOM’s (sup oblique, lateral rectus unaffected; thus eye in “down and out” position)
Pupil function impaired (damage results in dilated pupil that does not respond to light)

Question 24

Name one location where the globe is most likely to rupture with trauma?

Answer 24

Correct Answer = underneath a rectus muscle. Why? Recall that the sclera (0.3mm) is thinnest where the recti muscles attach.

Two other locations = the limbus, or at a previous surgical site.

Question 25

Name 2 functions of the medial and lateral palpebral arteries.

Answer 25

Correct Answer: 1. Provides blood supply to the internal portion of the EYELIDS. 2. Provides oxygen to the anterior cornea (epithelium to anterior stroma) when the eyes are CLOSED. So, the next logical question would be: Where does the back portion of the cornea obtain its oxygen from? Correct Answer = The aqueous humor. And remember: when our eyes are OPEN, the entire cornea receives its oxygen from the air/atmosphere.

Question 26

Which of the following are branches of the external carotid? (Pick 3) 1. Maxillary Artery 2. Short Posterior Ciliary Artery 3. Superficial Temporal Artery 4. Supratrochlear Artery 5. Supraorbital Artery 6. Facial Artery

Answer 26

Correct Answers = 1,3,6 are branches of the external carotid artery

Question 27

A. Where does Tenon’s capsule begin in relation to the limbus? B. Perforation of Tenon’s capsule in the posterior pole allows for passage of what important structures? C. Which of the following are posterior to TENON’S CAPSULE? (Pick 2) 1. Conjunctival epithelium 2. Conjunctival stroma 3. Sclera 4. Episclera

Answer 27

A = Tenon’s capsule begins 2 mm posterior to the limbus. B = Basically the optic nerve and a bunch of valuable arteries, veins, and nerves: Vortex veins, Posterior ciliary arteries, veins, and nerves (e.g. SPCA’s, LPCA’s, etc) C = 3, 4. Summary: Picture looking at the limbus under the slit lamp. Just 2 mm posterior to the limbus Tenon’s capsule starts by FUSING WITH THE BACK SIDE OF THE CONJUNCTIVA. That is a key sentence to remember. If you know it is just barely posterior to the conjunctiva, it should be fairly obvious that the conjunctival epithelium and conjunctival stroma are anterior to this structure and the episclera and sclera are posterior, respectively. As Tenon’s reaches the posterior pole, it has pores that allow for the axons of ganglion cells (optic nerve) to enter the eye.

Question 28

Which of the following cranial nerves exit from the Pons? (Pick 2) ``` CN V CN VI CN III CN IV CN X ```

Answer 28

Correct Answers = CN’s 5,6 Remember 1) CN’S 3,4 = exit from the MIDBRAIN 2) CN’s 5,6,7,8 = exit from the PONS 3) CN 9-12 = exit from the MEDULLA To be even more specific, recall that CN 6 exits from the pons and then courses between the pons and medulla towards the lateral rectus muscle. CN 6 is the only CN to course between the pons and the medulla.

Question 29

Which of the following provide blood supply to the eyelids? (Pick 3) 1. External carotid through facial artery branches 2. Short posterior ciliary arteries (SPCA’s) 3. Muscular arteries 4. Ethmoid arteries 5. Branches of the ophthalmic artery 6. Medial and lateral palpebral arteries

Answer 29

Correct Answers = 1, 5,6 The two main arteries that supply the eyelid are: 1) Internal carotid = “internal” portion of the eyelid. Utilizes branches of the ophthalmic artery (medial and lateral palpebral arteries) 2) External carotid = “external” portion of the eyelid. Utilizes branches of the facial artery. MEDIAL and LATERAL PALPEBRAL ARTERIES = OPHTHALMIC ARTERY BRANCHES

Question 30

Recall that the lacrimal gland has an orbital portion and a palpebral portion. If a malignancy is suspected in the lacrimal gland and biopsy is required, why is the biopsy always performed on the orbital portion?

Answer 30

Correct Answer = Because the PALPEBRAL PORTION contains the excretory ducts for secretion of the aqueous portion of tears. Please do NOT get too discouraged or caught up in the details of this question. This is likely way too difficult for boards. I asked the question to emphasize, once again, that the lacrimal gland has two portions in case a detailed question about this is asked on the exam. Do you recall what divides the gland into the two portions? Correct Answer = Tendon of the superior levator palpebrae muscle. What cranial nerve innervates the levator palpebrae muscle? Correct Answer = Cranial Nerve 3. Remember, CN 3 opens the eye, CN 7 closes the eye. What provides sensory innervation to the eye? CN 5.

Question 31

Why does Kocher’s sign occur in some patients with thyroid eye disease?

Answer 31

Correct Answer = Recall that Kocher’s sign = GLOBE LAG behind the upper lid movement in UPGAZE. An increase in sympathetic innervation to the sympathetic muscles of the eyelids results in contraction of the eyelid (opposite of ptosis). What are the sympathetic muscles of the eyelids? Correct Answer = MULLER’S MUSCLE and MUSCLE OF RIOLAN. In addition, in thyroid eye disease the EOMs behind the eye can swell and push the eye forward. This widening of the palpebral fissure, in combination with the eyelid retraction, leads to the “stare appearance” known as DALRYMPLE’S SIGN.

Question 32

What is the most likely cause of a CN 3 palsy that does NOT involve the pupil?

Answer 32

Correct Answer = Vascular etiology (DM and HTN) Clinical Application: Imagine you have a patient who comes into your office with the classic appearance of a CN 3 palsy. The patient reports double vision (because one eye is sitting “down and out”) and you notice ptosis on that side. as well. Immediately you want to check the pupil response. If the pupil responds properly to light this makes you much less concerned of a tumor or aneursym compressing the outside portion of CN 3. (Recall that CN 3 is a thick nerve, with the outer portion responsible for pupil innervation). Recall that the central portion of CN 3 is supplied by small blood vessels. In cases of HTN and/or DM that are not well controlled, ISCHEMIA can occur and the central portion of CN 3 (portion responsible for opening the eye and eye movements of 4 or 6 EOM’s) can be affected.

Question 33

What is the most likely location, within the Circle of Willis, for aneurysms that result in pupil-involving Cranial Nerve 3 palsies?

Answer 33

Correct Answer = Junction of the Posterior Communicating Artery and Internal Carotid Artery This is a difficult question. Please be sure to review the Circle of Willis prior to your exam! Because a pupil-involving CN 3 palsy is such an important condition that we can NOT afford to overlook, I would know this topic well.

Question 34

Your patient experiences a full-thickness corneal laceration. The patient is referred, receives prompt treatment and stabilizes with little to no vision loss. At the next examination, in what locations of the cornea would you expect to see scarring? (Pick 2) ``` Epithelium Descemet’s membrane Bowman’s layer Stroma Endothelium ```

Answer 34

Correct Answers = 3,4 = Bowman’s layer and Stroma are the corneal layers that scar with trauma. Recall that Descemet’s membrane is constantly growing and actually triples in thickness throughout a lifetime. Thus, when damaged it will quickly regenerate without scar formation. Clinical Application: You should never write the phrase “epithelial scar” in your chart because the epithelium does not scar. If the scar looks fairly superficial in location, it is either located within Bowman’s layer or the anterior stroma.

Question 35

Name a condition that affects sympathetic innervation to the eye and describe the expected clinical presentation?

Answer 35

Correct Answer = Horner’s syndrome Horner’s syndrome: Can affect sympathetic pathway anywhere along the 3 neuron tract. Regardless of the lesion location, expected clinical signs include upper eyelid ptosis, slight elevation of lower eyelid (upside down ptosis), miosis, and dilation lag. After reading the above you may be wondering about anhidrosis. Recall that this is absent or decreased sweating on the ipsilateral side of the face. Horner’s syndrome does NOT always result in anhidrosis. Lesions that affect the postganglionic portion of the sympathetic pathway (portion after synapse at superior cervical ganglion) will result in no anhidrosis or it will be limited to above the eyebrow.

Question 36

Overview the sympathetic nervous system pathway to the dilator muscle.

Answer 36

Correct Answer: The sympathetic nervous system to the dilator muscle occurs via a 1st order neuron, 2nd order neuron, and 3rd order neuron. 1st-order neuron: Starts in the ipsilateral hypothalamus and synapses within the spinal cord at the Ciliospinal Center of Budge. 2nd-order neuron: Leaves spinal cord, travels over the apex of the lung, and synapses in the Superior Cervical Ganglion (near angle of mandible) 3rd-order neuron: exits the superior cervical ganglion, now as postganglionic fibers, unites with the internal carotid artery plexus (on top of the internal carotid artery), travels through the cavernous sinus (with CN VI near its side) and joins V1 to enter the orbit. Now it travels with the Nasociliary divison of V1 and ultimately innervates the dilator through the long ciliary nerve (branch of Nasociliary nerve). V1 = SYMPATHETIC PATHWAY TO DILATOR MUSCLE

Question 37

Which area of the trabecular meshwork is most pigmented? Hint: Clinically, during gonioscopy we are advised to start in this angle because this extra pigment allows us to recognize the structures quicker and understand the patient’s anatomy quicker.

Answer 37

Correct Answer = Inferior Angle, because of gravity. Clinical Application: During gonioscopy, start by looking into the superior mirror.

Question 38

What is the link between damage to the Anterior Knee of Wilbrand and junctional scotomas?

Answer 38

Correct Answer = the Anterior Knee of Wilbrand consists of INFERIOR/NASAL fibers that cross ANTERIORLY in the chiasm and bulge into fibers from the contralateral optic nerve. Thus, a lesion located where these fibers meet that causes damage to the central fibers in one eye as well as the inferior nasal fibers in the other eye is called a JUNCTIONAL SCOTOMA. You know that nasal retinal fibers cross, correct? Good. Now you need to take your knowledge to the next level. Remember, that superior nasal fibers cross at the chiasm differently than inferior nasal fibers. Inf/nasal fibers cross anteriorly (Anterior Knee of Wilbrand), while the Sup/nasal fibers cross posteriorly (Posterior Knee of Wilbrand). The Knees of Wilbrand are especially relevant clinically with understanding how a visual defect could show central loss in one eye and a superior/temporal defect in the other eye. That is a very unique looking visual field don’t you agree? Understanding the Knees of Wilbrand allows you to understand how this could happen. JUNCTIONAL SCOTOMA = CENTRAL SCOTOMA in one eye with a SUPERIOR/TEMPORAL defect in the other eye.

Question 39

Where are orbital wall fractures most likely to occur (be specific)?

Answer 39

Correct Answer = Posteromedial orbital floor. Recall that the maxillary bone makes up the majority (“maxillary = majority”) of the orbital floor and is the weakest bone in the orbit. Orbital wall fractures are most likely to occur on the floor – specifically on the posterior and medial portion of the floor.

Question 40

When looking at a visual field printout, how do you differentiate the right eye from the left eye?

Answer 40

Correct Answer = location of blind spot. The right eye will have the blind spot on the right side (within temporal field) and the left eye will have the blind spot on the left side (within temporal field).

Question 41

On visual field testing, where is the physiological blind spot located?

Answer 41

Correct Answer = temporal visual field. Recall that the fovea marks the center of the visual field. The blind spot is 15 degrees temporal and slightly below the horizontal plane.

Question 42

Contrast the size and definition of the macula with that of the fovea. Is the macula temporal or nasal to the optic disc? Superior or inferior to the optic disc?

Answer 42

Macula = 5.5 mm area that contains xanthophyllic pigment and 2 or more layers of ganglion cells. Macula is located approximately 4mm temporal and 0.8mm inferior to the optic disc. Fovea = 1.5mm, which is approximately 1 disc diameter (DD) in size – that is a very helpful visual tool to allow you to picture the diameter of the fovea. Recall that the foveala (0.35mm) is found within the fovea. No ganglion or bipolar cells are found here, only CONES!