Differential Diagnosis for Anisocoria (Unequal Pupil Sizes)
Single Most Likely Diagnosis
- Physiological anisocoria: This condition is characterized by a small, benign difference in pupil size that is constant in different lighting conditions. It is a common and harmless variation found in many people.
Other Likely Diagnoses
- Iris damage or trauma: Injury to the iris can cause anisocoria due to scarring, bleeding, or other damage affecting the iris's ability to constrict or dilate.
- Third cranial nerve (oculomotor nerve) palsy: This nerve controls several of the extraocular muscles and the constriction of the pupil. Damage to this nerve can lead to anisocoria, often accompanied by ptosis (drooping eyelid) and outward deviation of the eye.
- Adie's pupil (tonic pupil): A condition where there is damage to the nerves that control the pupil, leading to a dilated pupil that reacts slowly to light.
Do Not Miss Diagnoses
- Subarachnoid hemorrhage or intracranial aneurysm: These are life-threatening conditions that can cause third cranial nerve palsy, leading to anisocoria. Prompt diagnosis is crucial for survival and recovery.
- Brain tumor or stroke: Certain tumors or strokes can affect the areas of the brain that control pupil size, leading to anisocoria. Early detection is vital for effective treatment.
- Horner's syndrome: Caused by disruption of the sympathetic nerves supplying the eye, leading to miosis (constricted pupil), ptosis, and anhidrosis (lack of sweating). It can be a sign of serious underlying conditions such as a stroke or tumor.
Rare Diagnoses
- Syphilis: In its tertiary stage, syphilis can cause a range of neurological symptoms, including anisocoria due to damage to the nerves controlling the pupils.
- Diabetic third nerve palsy: Diabetes can cause nerve damage, including the third cranial nerve, leading to anisocoria.
- Congenital conditions: Certain congenital conditions can affect the development of the iris or the nerves controlling the pupils, leading to anisocoria from birth.