Deaf People Develop Better Vision

But only if their deafness occurs early in life:

...The research, which was funded by RNID -- Action on Hearing Loss and published June 1, 2011 in the journal PLoS ONE suggests that the retina of adults who are either born deaf or have an onset of deafness within the very first years of life actually develops differently to hearing adults in order for it to be able to capture more peripheral visual information.

Using retinal imaging data and correlating this with measures of peripheral vision sensitivity, a team led by Dr Charlotte Codina and Dr David Buckley from the University's Academic Unit of Ophthalmology and Orthoptics, have shown that the retinal neurons in deaf people appear to be distributed differently around the retina to enable them to capture more peripheral visual information. This means that in deaf people, the retinal neurons prioritise the temporal peripheral visual field, which is what a person can see in their furthest peripheral vision, i.e. towards your ears.

Previous research has shown that deaf people are able to see further into the visual periphery than hearing adults, although it was thought the area responsible for this change was the visual cortex, which is the area of the brain that is particularly dedicated to processing visual information. This research shows for the first time that additional changes appear to be occurring much earlier on in visual processing than the visual cortex -- even beginning at the retina.

The team also found an enlarged neuroretinal rim area in the optic nerve which shows that deaf people have more neurons transmitting visual information than hearing...

It's remarkable that hearing deficiency can cause better development in system that is physically remote from the hearing apparatus, and suggests that the brain is capable of sensing it's own sensory environment, recognizing a deficit and directing adaptions to other systems to help compensate.