1. PUPILS
INTRODUCTION:
The pupil is an opening located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the
light entering the pupil is absorbed by the tissues inside the eye
OPTIC EFFECTS:
When bright light is shone on the eye, light sensitive ganglion cells in the retina, containing the pigment melanopsin, will send signals to
the oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular
iris sphincter muscle.
When this muscle contracts, it reduces the size of the pupil.
This is the pupillary light reflex, which is an important test of brainstem function
Miosis
Constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological
conditions, microwave radiation exposure, and certain drugs, especially opiates
Mydriasis
An excessive dilation of the pupil due to disease, trauma or the use of drugs.
Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from
sunlight damage during the day.
A mydriatic pupil will remain excessively large even in bright light.
Adie's Tonic Pupil
Named after the British neurologist William John Adie.
It is caused by damage to the postganglionic fibers of the parasympathetic innervation of the eye, usually by a viral or bacterial infection
which causes inflammation
Characterized by a tonically dilated pupil
Adie syndrome presents with three hallmark symptoms, namely at least one abnormally dilated pupil, loss of deep tendon reflexes and
diaphoresis.
Other signs may include hyperopia due to accommodative paresis, photophobia and difficulty reading.
Argyll Robertson pupil
Bilateral small pupils that constrict when the patient focuses on a near object (they “accommodate”), but do not constrict when exposed
to bright light (they do not “react” to light).
They are a highly specific sign of neurosyphilis.
Parinaud syndrome (Dorsal midbrain syndrome)
This uncommon syndrome involves vertical gaze palsy associated with pupils that “accommodate but do not react”.
The causes of Parinaud syndrome include brain tumors (pinealomas), multiple sclerosis and brainstem infarction
Marcus Gunn pupil (relative afferent pupillary defect)
It is named after Scottish ophthalmologist Robert Marcus Gunn.
Pupils constrict less (therefore appearing to dilate) when the light swings from the pupil of the unaffected eye to the pupil of the affected
eye.
The affected pupil still senses light and produces sphincter constriction to some degree, albeit reduced.
The most common cause of Marcus Gunn pupil is a lesion of the optic nerve (distal to the optic chiasm) or severe retinal disease.
Horner's syndrome
Clinical syndrome caused by damage to the sympathetic nervous system.
The clinical features of Horner's syndrome are Ptosis, Anhydrosis, Miosis, Enophthalmos and Loss of ciliospinal reflex.