PRACTICAL 4: PUPILS

CP 3032

OCULAR PHYSIOLOGY <;

Explanation of Pupillary Pathway

An example of the pupillary pathway of the eye is the reflex pathway.

Afferent pupillary pathway arises from the optic nerve, where nerve fibres that are not transmitted to the LGN will be sent to the ispilateral pretactal nucleus of the eye, at the midbrain region. From there, all the impulses will be further sent to the Edinger Westphal nucleus (EWN), which is the starting point for parasympathetic pathways.

PUPILLARY REFLEX PATHWAYS

(a) For example, when eye is subjected to bright conditions, efferent parasympathetic response occurs, whereby the EWN will transmit the nerve impulses through the lateral geniculate nucleus (LGN) to the cranial nerve III, oculomotor nerve.

These impulses will then synapse at the ciliary ganglion. After which the impulses will be sent to the target muscle through the short posterior ciliary nerves to carry out an action. In this case, the impulses will be sent to the sphincter muscle, which results in constriction of the pupil.

(b) If the eye is now exposed to a dark illumination, impulses from the brain will be sent to the eye through the sympathetic pathway. Nerve fibres will be transmitted by the hypothalamus instead of the EWN, then it will synapse in the superior cervical ganglion.

These fibres travel with the internal carotid artery, enter the cavernous sinus to enter the superior orbital fissue with cranial nerve V, the trigeminal nerve.
Then, nerve fibres will travel with the nasociliary branch of V, and pass through the ciliary ganglion, but without synapsing.

Finally, the nerve fibres will pass through the long ciliary nerves to activate the dilator muscle. This explains why our pupil will dilate in dark illuminations after being exposed to bright light.

How is pupil size is measured ( Include PERRLA)

Pupil size is measured using PERRLA.

P -pupils

E -equal

R -round

R -reactive (reactivity to light)

L -light

A -accommodation

R -shape of the eye. We have to check if it is round or abnormal(eg. keyhole shape).

R and L stands for reactivity to light.

PROCEDURE

With the aid of a pen torch, shine light into the subject’s eyes.

Check if the pupil constricts and dilates.

If it does, then the eye is reactive to light.

For accommodation, the subject is first asked to sit down.

Then, instruct her to look slightly up/far away.

Explain the test to the subject.

Next, hold a target a distance away from the subject.

Ask the subject to look at the target, and then look at something that is further away.

Do this a few times. If the pupil constricts and dilates, the eye is normal.

READINGS

1st subject, Kitru:(under normal situation)

Scotopic conditions: 5mm, Photopic conditions: 4mm

P: scotopic-5mm, photopic-4mm E: equal R: round R: 3++ L: 3++ A: eye accomodates

2nd subject, Venus: (under normal situation)

Scotopic conditions: 5mm, Photopic conditions: 3mm

P: scotopic-5mm, photopic-3mm E: equal R: round R: 3++ L: 3++ A: eye accomodates

Explanation of 1 chosen abnormal pupil condition

Condition: HORNER'S SYNDROME



Definition :
Horner's syndrome, also called oculosympathetic paresis, is a classic neurologic syndrome that interrupts the sympathetic nerves to the eye and face. This disease is very uncommon.

Etiology & Pathogenesis :
Horner's syndrome can be produced by a lesion anywhere along the sympathetic pathway that supplies the head, eye, and neck.

The sympathetic nerves connecting to the eye originate from the brain and it takes a long route. They descend along the spinal column to the chest, then ascend along the carotid arteries to the back of the eye. Therefore, a wide variety of conditions can cause a Horner's syndrome. The most concerning being the tumors.

Causes :
Horner’s syndrome can be congenital, acquired, or purely hereditary.
· Preganglionic Horner’s syndrome indicates a serious underlying pathology, and is associated with malignancy.
· Painful Horner’s syndrome suggests the possibility of internal carotid artery dissection.
· Postganglionic involvement has benign causes such as neck or thyroid surgery, or migraines.
. Brainstem stroke
. Posterior retroparotid space masstumor

• Parotid Gland Tumor
• Carotid body tumor
• Metastatic tumor
• Lymphoma

Rarely, Horner syndrome may be present at birth (congenital). In this case, the cause is not known. The condition may occur with a lack of pigmentation of the iris.

CLINICAL SIGNIFICANCE :
Horner's syndrome causes a droopy eyelid and smaller pupil on one side of the face.

Treatment:
No specific treatment for Horner’s syndrome as treatment depends on the cause of the problem.
Possible complications:
There are no direct complications of the syndrome itself. However, complications may arise from the disease that caused this syndrome.

References

http://www.westmetroeye.com/Disorders/Horners_syndrome.html
http://www.fpnotebook.com/Neuro/Autonomic/HrnrsSyndrm.html
http://www.umm.edu/ency/article/000708.htm
http://www.rarediseases.org/search/rdbdetail_abstract.html?disname=Horner
http://www.britannica.com/EBchecked/topic/199272/eye/64951/Pupillary-pathways
http://emedicine.medscape.com/article/1220091-overview
http://emedicine.medscape.com/article/279394-overview
http://www.nlm.nih.gov/medlineplus/ency/article/000708.htm
http://images.google.com.sg/images?sourceid=navclient&rlz=1T4ADBF_en___SG332&q=visual+pathway&um=1&ie=UTF-8&ei=EHaOS4f3OpKmrQfRr4DRCw&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CBUQsAQwAA