A man lost partial sight in his eye following a "vigorous" morning sex session with his partner, doctors have revealed.

The 29-year-old was enjoying an extended romp at home when the incident occurred, resulting in the loss of sight in his left eye. He presented his symptoms to doctors at an emergency eye clinic later in the day, it was reported in the British Medical Journal.

The publication suggested that a burst blood vessel caused by an orgasm was to blame. Doctors said that the Valsalva manoeuvre, or holding breath before climax, caused an excessive amount of pressure to build up behind his retina. This in turn caused a haemorrhage, which resulted in obstruction of his vision.

"During orgasm the Valsalva manoeuvre can produce a sudden increase in retinal venous pressure resulting in vessel rupture and haemorrhagic retinopathy," the journal stated.

The report noted that men are more likely to hold their breath during sex to delay ejaculation, making them more prone to this type of injury.

"The autonomic effects of orgasm on the eye are well-known and have been associated with other ocular pathology, including angle closure glaucoma [damage to the optic nerve due pressure build up]," the report concluded.

"Prior to ejaculation, retinal vascular tone decreases, allowing vessels to dilate and become engorged."

Thankfully for the man his symptoms were only temporary – a follow-up appointment three days later confirmed that his vision had returned to normal.

The paper also said this case illustrated why it is important to obtain a full sexual history from patients.