{Practical 4...Pupils!}

Thursday, February 11, 2010

Above is a video instruction of how to measure a person's pupil size by using PERRLA.
PERRLA is also used to check if the pupils are functioning properly and that the subject does not have any ocular diseases that affects the pupils.

Results for subject (Ke Yi):

PUPILS:

- To make sure that the patient has pupils to begin with

- Pupils are present in both eyes

EQUAL:

- To check if pupils are equal in size in both scoptopic and photopic conditions

- Scoptopic (dim) conditions: 6mm for both right and left eyes

- Photopic (bright) conditions: left eye is 4mm and right eye is 3mm

ROUND:

- To check if the pupils are of normal shape, which is round.

- Both pupils are round

REACTIVE TO LIGHT:

- This is to check the pupils reaction to light

- Using a pen torch, shine at the left eye to check constriction of pupils for direct pupillary reflex

- Shine the pen torch on the left eye again but observe the right eye for constriction for consensual pupillary reflex

- Both pupils are reactive to the light introduced

ACCOMMODATION:

- Check if accommodation for both pupils are working when subject focuses on a distant object and a near object

- Focusing at a far object, pupil would dilate

- Focusing at a near object or reading, pupil would constrict

- Subject’s pupils are accommodating as per normal

Ocular Physiology Practical 4, 7:09 AM

Wednesday, February 10, 2010

1. The Pupillary Light Reflex Pathway

--- afferent pathway
__ efferent pathway

Pupillary actions are controlled via the secondary pathway. The pupil has two actions, dilation and constriction. Dilation is controlled by the dilator muscle innervated by the sympathetic nervous system. Constriction is controlled by the sphincter muscle which is innervated by the parasympathetic nervous system.

Afferent Pathway

The pupillary light reflex starts at the retina, when light hits on the retina, photoreceptors (rods and cones) will absorb the light and transmit impulses. The impulse then travels through the optic nerve. The nasal nerve fiber goes to the opposite optic tract at the optic chiasm while the temporal nerve fiber continues in the ipsilateral optic tract. The impulse is transmitted to the pretectal nuclei. Axons from each pretectal nucleus pass ipsilaterally and contralaterally to the Edinger Westphal nucleus (EWN), found in the brain. The EWN processes the information about the level of light received. (With reference to Figure 1)

Efferent pathway

Figure 2. Sympathetic Pupillary Pathway (Oculosympathetic)

In the efferent pathway, there are two exits for the impulses to travel, through the EWN and the hypothalamus.

1) The efferent parasympathetic pathway starts from the EWN. The impulse is sent from the EWN via the oculomotor nerve to the cavernous sinus and finally to the orbit. The parasympathetic components synapse in the ciliary ganglion in the orbit. Then enters the eye through the short posterior ciliary nerves innervating the ciliary body (includes lens accommodation) and the iris’s pupilloconstrictor muscles. (With reference to Figure 1)

2) The efferent sympathetic pathway starts from the hypothalamus. The nervous system is alienated into three parts, central neuron being first, preganglionic neuron as second, and, lastly, postganglionic neuron. The central neuron (1st), which is located in the brainstem and cervical cord, innervates from the hypothalamus down the cervical spinal cord. The preganglionic neuron (2nd), is found in the chest and in the neck, journey upwards to the superior cervical ganglion at the carotid bifurcation. The postganglionic (3rd) fibers travel to the iris through the carotid plexus, the cavernous sinus and the long ciliary nerves. The postganglionic fibers are joined with the ophthalmic division of the trigeminal nerve after the fibers run upward around the internal carotid artery into the cavernous sinus. The orbit is entered through the nasociliary branch of the ophthalmic division, allows the entering of the emerged nerve fibers from the cavernous sinus. Finally, the innervation terminates at the iris dilator muscle after entering the eye. (With reference to Figure 2)

2. Near Pupillary Reflex Pathway:

The near pupil reflex is not stimulated by the change of the intensity of luminance, but looking at near and distant object. Convergence, accommodation and pupillary constriction occurs when looking at near and distant object.

The afferent pathway of the pupillary near response is the same as the visual pathway, which is to the striate cortex. The information is then relayed to the front eye fields, the oculomotor nucleus and the EWN from the striate cortex, avoiding the pretectal nuclei in the dorsal midbrain. When the dorsal midbrain and pretectal nuclei are damaged, light-near dissociation occurs as the arrangements of light and near pupillary pathways are near. Finally, the medial rectus muscles are innervated via the oculomotor nerve while the parasympathetic pathway innervates the iris sphincter and ciliary body muscles.

References
Spector, R. H. The Pupils [online]. Available from: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cm&part=A1745 [Accessed 2 February 2010].
Weon Jun. Pupil Anomalies: Reaction and Red Flags [online]. Oregon: Pacific University. Available from: http://www.pacificu.edu/optometry/ce/courses/19433/pupilanompg1.cfm [Accessed 2 February 2010].

Ocular Physiology Practical 4, 6:56 PM

Marcus Gunn pupil is also known as relative afferent pupillay defect. (RAPD)
It was named after a Scottish opthalmologist, Robert Marcus Gunn, who was an excellent ocular surgeon and he introduced systematic teachings of eye disorders.

Marcus Gunn pupil is a medical sign observed during swinging flashlight test, and this pupillary defect generally occurs with significant optic nerve or retinal disease.

Test to perform on patients with Marcus Gunn pupil

1) Shine a long steady light into one eye, and quickly switching to another eye

2) Since light shone on one pupil will cuase both eyes to constrict, switching quickly from one eye to another will give an indication of the functioning of each eye.

3) To start with, check the direct reflex of one eye, constriction of that pupil is expected

4) Observe the fellow eye for consensual reflex, it should constrict as well.

5) Next, the pentorch would be held infront of the defected eye to observe for a direct response,
and it should be absent.

6) Observation for the unaffeced eye's consnsual reflex would still be present.

This is a short testing guide video.

Conditions leading to RAPD

Optic Nerve disease

Optic Neuritis -Very mild optic neuritis with minimal loss of vision can lead to strong RAPD
Ischemia Optic neuropathies
Glaucoma
Optic Nerve Tumour
Optic Nerve inflammations or Infections
Optic atrophy

Retinal Causes