ANISOCORIA Part 2 In part I of anisocoria we discussed the pupil light response, examined the PLR anatomy and also looked at different causes of both
ANISOCORIA Part 2
In part I of anisocoria we discussed the pupil light response, examined the PLR anatomy and also looked at different causes of both mydriasis and miosis. In part 2 we will discuss pharmacologic testing, basic diagnostic work up and look at some common examples.
Pharmacologic testing – can help in distinguishing pre-ganglionic from post-ganglionic lesions. Testing the pupil depends upon denervation hypersensitivity which usually occurs in post-ganglionic neurons about two weeks after they are denervated.
Pharmacologic testing for Horner's Syndrome
▪ Diluted phenylephrine (1%) or epinephrine (0.1%) is applied to the affected eye. Postganglionic lesions are supersensitive to the direct-acting mydriatics and the pupil will dilate within 20 to 40 minutes. Pre-ganglionic lesions are not hypersensitive and mydriasis does NOT occur. ▪ Pharmacologic concentrations can also be applied (2.5% phenylephrine, 1% epinephrine), but the results are more difficult to interpret. Post-ganglionic lesions usually show mydriasis within minutes, while pre-ganglionic lesions may take up to 20 minutes to dilate.
Pharmacologic testing for Efferent Mydriasis
▪ Diluted direct-acting miotics are used. Pilocarpine 0.1% is applied to the affected eye. Post-ganglionic lesions will show miosis within 20 to 40 minutes, while pre-ganglionic lesions remain dilated. ▪ If pupil dilation persists, it is then necessary to distinguish pre-ganglionic lesions from iris sphincter disease. Pilocarpine 2% can subsequently be applied to the eye. Pre-ganglionic lesions will constrict within 20 to 40 minutes. If the iris sphincter is diseased, it will be unable to respond to the miotic agent and mydriasis will persist.
Diagnostic work up
1. Confirm the anisocoria and determine which eye is abnormal.
2. Perform complete physical, ophthalmic and neurologic exams.
3. Rule out exposure to drugs.
4. Perform pharmacologic testing.
5. Consider laboratory and diagnostic imaging.
Case 1
7 year old Golden Retriever presents for anisocoria. The left eye has a constricted pupil. In addition to this the left eye has ptosis of the upper eyelid, third eyelid protrusion and slight enophthalmos. The most likely cause would be idiopathic Horner’s syndrome that should resolve in 6-8 weeks.
It is important to remember the pathway of the sympathetic nerve in Horners disease is very long and a lesion anywhere along this pathway may result in clinical signs.
Case 2
5 year old cat presents with anisocoria. The right eye is fixed and dilated. Both eyes are visual. The right eye has NO PLR but a positive consensual to the left eye. Whilst the left eye has normal PLR but no consensual to the right eye. There are no other abnormal physical, ophthalmological or neurological findings. The most likely diagnosis is oculomotor nerve dysfunction affecting the right eye.
Case 3
A 15 year old Poodle presents with aniscoria. Both eyes are semi-dilated in ambient room light. The right more so than the left eye. Both eyes are comfortable, the dog has normal vision but both eyes have poor pupil light response. There intraocular pressure is normal and there is no perilimbal hyperaemia. On closer examination the iris in both eyes has a scalloped pupil margin. The owner reports that sometimes the Poodle squints in very bright light. The most likely diagnosis is iris atrophy.
Case 4
A 14 year old Persian presents with anisocoria. The right eye is fully dilated with no direct or consensual PLR. The left eye appears normal with a normal direct and indirect PLR. The cat has no vision in the right eye but is visual in the left eye. Both eyes have a normal eye pressure. Physical examination shows the cat to be thin and the owner reports the cat has been drinking excessively. Blood pressure is measured and found to be 220 mmHg. The most likely diagnosis is hypertensive retinopathy. Although both eyes are affected one eye has detached its retina first. Full bloods and urine should be performed and treatment with Amlodipine commenced.
Case 5
A 2 year old Beagle presents with anisocoria and vision loss of the left eye. The left pupil is extremely miotic and the right eye is completely normal. The left has no direct or indirect PLR. On ophthalmic examination the left eye has deep perilimbal hyperaemia, aqueous flare with mild hyphaema, corneal oedema and an intraocular pressure of 4 mm Hg. The most likely diagnosis is uveitis. The owner reports the dog ran into a tree.