Birds found to be naturally evolving blindness

At BBR Optometry we aim to prevent any avoidable sight loss through regular eye examinations and screening but found fascinating new research finding that New Zealand’s native kiwi birds are naturally going blind because they do not need sight to survive.

A study of 160 brown kiwi in the Okarito forest in New Zealand's South Island found a "very high prevalence of birds with eye lesions" making scientists believe natural evolution could be responsible as its habitat and way of life renders sight unnecessary.

Three kiwi have been found to be profoundly blind in a South Island forest and an article in the New Scientist has suggested this could be an indication that the flightless nocturnal birds may be evolving to lose their eyesight.

Te Papa Museum researcher Alan Tennyson, who carried out the study, said: "Kiwi are flightless and generally nocturnally active, and have very good senses of smell, hearing and touch, so it seems that vision is not essential for their survival, at least for some individuals."

The New Scientist said other researchers have speculated that a gene called Sonic hedgehog might be responsible for the loss of vision and that this gene could also enhance the touch and smell sensors in the birds' long beaks. This means normal, functioning eyes are not a necessity.

Nick Black, BBR’s chief executive, who himself hails from New Zealand, said: “I find it fascinating that no human wants to lose their sight because of the enormous impact they believe it would have on their lives.

“And, of course, here at BBR we aim to ensure all of our patients have healthy eyes, are screened for any potential sight-threatening conditions and achieve their full vision potential with corrective lenses or spectacles.

“But, in the natural world, we are finding many animals such as these kiwi birds, moles and cave-dwelling fish who are evolving blindness because vision is not essential for their own survival.

“I’m sure many of our patients and members of the wider community know people who have lost their sight, whether at birth or later in life, especially as Hereford is home to the renowned National College for the Blind.

“The College works to ensure all young people who have lost their sight can be supported to achieve their full potential, an aim we very much support.

“I am constantly amazed, however, by the natural world and it will be interesting to see if any more animals such as the kiwi evolve blindness because sight is also unnecessary for their survival,” he added.

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