Blindness is something we can all appreciate simply by trying to navigate around our homes eyes closed. It’s inconvenient, frustrating and interferes with life, work, and fun. It also costs billions annually to healthcare, education, and the insurance industry.
We almost never see ‘pure blindness’ in clinic, that is, the same profound pitch black darkness of blindfolded and closed eyes, or the deafening blackness of a subterranean cave. Blindness comes in degrees, from mild distortions to large portions of lost visual field, and in most cases some vision remains.
In the case of macular degeneration, central vision is lost so we lose the ability to see fine detail, colour, read, recognise faces – but peripheral vision is intact in most cases, so walking around is not a problem. Glaucoma affects peripheral vision but not central vision, and so reading remains intact while stairs and curbs become a problem, and we’re more likely to bump into walls, get into T-bone accidents while driving.
This sort of blindness can be prevented or halted, but once damage is done, it cannot be repaired or vision restored. In some instances, there is a catastrophic failure of nerve or blood flow due to disease or injury, and most sight can be lost. In these cases, and in cases of advanced macular degeneration, the brain can exhibit what can be described as ghost sensations, or the appearance of objects and people that are not there. This is called Charles Bonnet Syndrome, or CBS.
Amblyopia is another form of blindness, but it is more of a functional nature, and not a matter of traditional disease where tissue is inflamed, or dying. Amblyopia, sometimes impolitely called ‘lazy eye’, exists when the the visual cortex does not receive a clear visual signal from the eyes. Both eyes must provide equally strong and clear signals to the brain tissue starting soon after birth for clear and binocular vision to develop. Binocular here meaning both eyes working together to overlap images to provide depth – so they must be pointing to the same object with equally sharp clarity. If one or both eyes cannot provide a clear signal, or if one eye is turned as in the case of strabismus, the brain does what it can to create a full view of the world given available information. In the case of eye turns, or strabismus, the brain will usually pick one eye as dominant and that eye-cortex pathway will be reinforced and strengthened. The fellow eye, the strabismic eye, will then be virtually ignored by the visual cortex and will not engage it as fully in seeking targets in the environment.
Amblyopia, like other functional visual disorders, can be caused by a variety of factors including very high or unbalanced refractive states, eye turns, cataracts and other medical conditions. Vision Mechanics, that is behavioural and rehabilitation optometrists and vision therapists, can retrain vision problems like amblyopia to restore function and retrain eye gaze to realign eyes without the need to resort to surgery, but like surgery, results will vary.
You can learn a lot more about eyes and vision and how it all works at VisionMechanic.net and through our courses online, so feel free to have a look. You’ll be especially interested in spending time with us if you’re a parent, a teacher, therapist or doctor working with reading, developmental, and learning disorders, or even brain injuries.
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