Methods on how to measure pupil size

Under Photopic conditions,

Steps:

1. Ensure subject is in a relaxed state, and instruct him/her to look in forward.

2. Make sure the overhead light is also turned on.

3. Use the Burton’s lamp to magnify the eye, specifically, the pupil of the eye.

4. Check the eye using PERRLA.

PERRLA

- Pupils
- Equal
- Round
- Reactive to
- Light and
- Accommodation

5. Check whether the subject’s pupils are there.

6. Check to see whether the subject’s pupils are both equal in size, and round.

7. Check that the pupils are reactive to light; when light is shone on the pupil, pupil would decrease in size.

8. Check for the accommodation of the pupils when eye is reading at near, or focusing something at near.

9. Place a ruler just above the pupil and measure the pupil size. Ensure free fingers are placed on subject’s face/cheeks to avoid shaky hands.

10. Read and record down the reading from the Burton’s lamp, since the magnifying glass on the Burton’s lamp can also be use to read off measurements from the ruler.

Marcus Gunn

Marcus-Gunn pupil is an alternative name for a condition of the eye known as Afferent Pupillary Defect (APD) which indicates a decreased pupillary response to light in the affected eye, and pupils fail to constrict fully. A Marcus Gunn pupil is said to occur when there is a unilateral lesion in the afferent visual pathway anterior to the chiasm.

In the swinging flashlight test, a light is shone into the left and right eyes. For a normal response, there would be equal constriction of both pupils, regardless whether the light is directed at the left or right eye. This indicates an intact direct and consensual pupillary light reflex. When the test is performed in an eye with an afferent pupillary defect, light directed in the affected eye will cause only little constriction of both pupils (due to decreased response to light from the afferent defect), while light in the unaffected eye will cause a normal constriction of both pupils (due to an intact afferent path, and an intact consensual pupillary reflex). Therefore, there will be lesser pupillary constriction in the affected eye when light is shone on it, than when light is shone in the unaffected eye.

Some symptoms of a Marcus-Gunn phenomenon are that the patient has a drooping eyelid and there is brief eyelid lifting when the patient opens his mouth.

Pupillary Pathway

The optic nerve is responsible for the afferent limb of the pupillary reflex which senses the incoming light. The oculomotor nerve is responsible for the efferent limb of the pupillary reflex which drives the muscles that constrict the pupil.

The pupillary pathway consists of two pathways which are the afferent pupillary light reflex and efferent pupillary light reflex.

AFFERENT:
In afferent pathway, neural fibers that relay visual and pupillary afferent stimulus contain in the retina, optic nerve, optic chiasm and the optic tract. Therefore, any damage would affect both pupillary light reflex and visual function. Afferent pathway goes through the optic nerve, optic chiasm and optic tract. The pupillary fibers follow the optic tract till it reaches the lateral geniculate body. The signals will then enter the midbrain to pretectal nucleus where they synapse. Then pupillary fibers leaves the pretectal nucleus and spilt to the two edinger westphal nuclei. This tract is called tectotegmental tract which carries the pupillary fibers from both pretectal nuclei. Then both pupils will constrict in the consensual light reflex.

EFFERENT:
The efferent pathway begins at the edinger westphal nuclei. Efferent pathway fibers in inferior division will pass through the superior orbital fissure to ciliary ganglion where it synapse.


http://library.med.utah.edu/kw/hyperbrain/anim/reflex.html