Sleeping with eyes half-open, also known as nocturnal lagophthalmos, occurs for various reasons, including anatomical, medical, and environmental factors. Here are some of the main causes:

Damage to the facial nerve (cranial nerve VII), which controls eyelid movement, can prevent the eyes from fully closing. This is often seen in conditions like Bell's palsy, stroke, or trauma.

Weakness in the orbicularis oculi muscle (responsible for eyelid closure) can also contribute.

People with prominent eyes (e.g., due to thyroid eye disease or genetic factors) might struggle to fully close their eyelids during sleep.

Poor sleep posture or disorders like sleep apnea may contribute to incomplete eye closure.

Conditions like Graves' disease, which causes bulging eyes, or scarring of the eyelid from injuries or surgeries, may lead to partial eye opening.

Lagophthalmos can also develop as a side effect of surgery, such as eyelid or cosmetic procedures.

For some, it may simply be a genetic trait. Babies often sleep with their eyes partially open, but most outgrow it.

Dry environments or overly tired eyes might lead to temporary lagophthalmos, as the eyelids fail to close completely during rest.

Sleeping with eyes partially open can result in dryness and irritation, leading to potential long-term damage to the cornea if untreated. Symptoms often include redness, discomfort, and excessive tearing upon waking.

Lubricating eye drops or ointments.

Using a sleep mask to protect the eyes.

In severe cases, medical treatments like surgery or botox might be recommended to correct eyelid closure.

If you or someone you know experiences this persistently, consulting an ophthalmologist or neurologist is advisable to identify and address underlying causes.