CPEO is a rare disease that may affect those of all ages, but typically manifests in the young adult years.

[1] The first presenting symptom of ptosis is often unnoticed by the patient until the lids droop to the point of producing a visual field defect.

The ptosis is typically bilateral but may be unilateral for a period of months to years before the fellow lid becomes involved.

[citation needed] Ophthalmoplegia (the inability or difficulty to move the eye) is usually symmetrical, therefore, patients are not affected by diplopia (double vision).

Patients will move their heads to adjust for the loss of peripheral vision caused by inability to abduct or adduct the eye.

This includes mild, focal pigmentary abnormalities on funduscopy and widespread granular pigmented fundus alterations.

As a result of the orbicularis oculi weakness, patients may suffer from exposure keratopathy (damage to cornea) from the inability to close the eyes tightly.

[citation needed] Additional symptoms are variable, and may include exercise intolerance, cataracts, hearing loss, sensory axonal neuropathy, ataxia, clinical depression, hypogonadism, and parkinsonism.

[citation needed] Kearns–Sayre syndrome is characterized by onset before 15 years of age of CPEO, heart block and pigmentary retinopathy.

[1] Mitochondrial DNA which is transmitted from the mother, encodes proteins that are critical to the respiratory chain required to produce adenosine triphosphate (ATP).

[citation needed]In most cases, PEO occurs due to a sporadic deletion or duplication within the mitochondrial DNA.

[citation needed] Polymerase chain reaction (PCR) from a sample of blood or muscle tissue can determine a mutation of the mtDNA.

[citation needed] Elevated acetylcholine receptor antibody level which is typically seen in myasthenia gravis has been seen in certain patients of mitochondrial associated ophthalmoplegia.

[9] It is important to have a dilated eye exam to determine if there is pigmentary retinopathy that may signify Kearns–Sayre syndrome which is associated with cardiac abnormalities.