Implications of Acquired Monocular Vision
Acquired monocular vision will affect vision and the individual in several ways. There are two main issues which are uniformly and predominantly addressed by the published literature and authorities. The two primary deficits are loss of stereoscopic binocular vision and reduction of peripheral field of vision. Most of the ramifications and symptoms of monocular vision are a result of these two deficiencies.
Literature
According to Borrish, monocular vision versus binocular vision results in approximately a 25% decrease in the size of the field of view. Monocularity causes an absence of stereopsis which comes from the lack of comparison of retinal disparity present in binocular individuals. Monocular individuals will have decreased visual acuity (compared to their binocular counterparts) because of their lack of binocular summation. Binocular summation is the phenomenon by which people see better with both eyes together than by either eye alone. Monocular people will have an impairment in their orientation (to space) which results from a lack of kinesthetic cues arising from convergence (binocular "eye aiming") and accommodation (focusing).
Gunter von Noorden writes that the monocular cues of motion parallax, linear perspective, overlay of contours, distribution of highlights and shadows, size of known objects and aerial perspective can be be used for spatial orientation. He states, "The nature of non stereoscopic clues is that they are experiential and can be meaningful only when they are capable of being related to past experience."
According to von Noorden the advantages of binocular vision (and conversely the disadvantage to monocular vision) are in visual motor skills, better exteroception of form and color, and better appreciation of the dynamic relationship of the body to the environment, thereby facilitating control of manipulation, reaching and balance.
Brady writes the main problems in monocular vision are primarily attributable to a loss of stereopsis and a reduction of the peripheral field of vision. According to Brady, the loss of peripheral vision is between ten and twenty percent. (I guessed at 25%) He says these problems will manifest as difficulties in eye hand coordination, clumsiness, bumping into objects and/or people, ascending or descending stairs or curbs, crossing the street, driving, various sports and miscellaneous activities of daily living which require stereopsis and peripheral vision. Brady believes people may develop an increased awareness because of the monocular condition and that there is a better prognosis with onset at a younger age.
Brady raises additional concerns and issues for monocular individuals. One, the need for eye protection and safeguarding the good eye. Two, the need to have back-up prescriptions on hand. Three, the need to employ driving aids and techniques such as special mirrors, scanning with the head and eyes, and heightened awareness. Four, the implications of cosmesis. And five, the concerns for a prosthetic device.
Schein writes, "Individuals limited by loss of vision in one eye have difficulties in depth perception." "Determining the distance within three feet from the eye is extremely difficult and highly unreliable." "Beyond three feet, other distance cues can substitute for loss of binocular disparity, provided monocularly impaired individuals are free to move their heads, which allows them to obtain information about relative distances by taking more time than they would when visual images from both eyes can be superimposed, as they are with binocular vision." "Mishaps can occur when monocularly impaired persons are in heavy traffic unless the head is constantly moving from side to side to increase the visual field". He believes that rehabilitation is easier with an earlier age of onset, that a gradual loss of vision in one eye allows for better adjustments to the condition than sudden onset and that rehabilitation is less complicated with a total loss of vision than a partial loss of vision. Regarding driving safety, Schein quotes a study by Keeney, et al. who state that, "nationwide, monocularly impaired individuals have seven times more accidents than the general population with which they were compared." Schein states, "Occupations most affected are those that require close work (e.g. barber, beautician, bartender, machinist, needle worker, surgeon); those that involve vehicle operation (e.g. airline pilot, bus driver, motorman); and any work demanding prolonged visual vigilance (e.g. air traffic controller)."