Ocular Anatomy Flashcards
Which of the following provide parasympathetic innervation to the eye? (Pick 2)
CN III
CN V
CN VII
CN II
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.
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?
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.
What anatomical changes occur as you go from the cornea to the limbus?
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
Which of the following increases during accomodation? (Pick 3)
- Lens zonule tension
- Lens diameter
- Lens thickness
- Anterior lens curvature
- Posterior lens curvature
- Intraocular pressure (IOP)
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).
What increases more during accommodation, anterior or posterior lens curvature?
Correct Answer = anterior curvature.
Which of the following corneal layers will not regenerate after injury? (Pick 2)
- Epithelium
- Bowman’s layer
- Endothelium
- Stroma
- Descemet’s membrane
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.
Which of the following structures would NOT be visible in a patient with Grade 2 narrow angles? (Pick 3)
- Peripheral iris
- Scleral spur
- Trabecular meshwork
- Ciliary body
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!
Which of the following ocular effects is expected FIRST with uncal herniation?
- Dilated pupil
- “Down and Out” location of the pupil
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.
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)
- Lack of pupil responses to light
- Location of the eyes in the “down and out” position
- Dilated pupils
- Corneal hypoesthesia
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
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?
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).
Which portion of the optic nerve is NOT affected by the demyelinating inflammatory changes in optic neuritis?
- Intraocular portion
- Intraorbital portion
- Intracanalicular portion
- Intracranial portion
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.
Which of the following EOMs would not be affected with a tumor located on the Circle of Zinn?
- Superior Rectus
- Inferior Rectus
- Inferior Oblique
- Superior Oblique
- Remember, the inferior oblique is the only EOM whose origin is anterior to the globe.
Your patient has a tumor within the muscle cone behind the eye. Which of the following would you NOT expect?
- Sensory loss to the cornea
- Lateral rectus palsy
- Sensory loss to the upper eyelid
- Sensory loss to the tip of the nose
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!
A tumor arises at the foramen ovale – what symptoms would you NOT expect? (Pick 2)
- Difficulty with chewing
- Loss of sensory innervation to cheek
- Hearing loss on the contralateral side
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).
In what condition is the upper eyelid ptosis more severe, Horner’s syndrome or a Cranial Nerve 3 palsy? Why?
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.
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?
- Mandible
- Lower cheek
- Upper eyelid
- 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