Your visual acuity is what people will use to help refer to the clarity of your vision. This is often dependent on many neural and optical factors such as the sensitivity of your interpretative part of your brain, the function and health of your retina and how sharp the focus of your retina is in your eye.
You may also have a common cause of low acuity which is called by ametropia or a type of refractive error. These are issues that cause differences in how light will be refracted in your eye. There are many causes of these errors which could be done by the shape of your cornea or eye or even having flexibility in your lens.
There may be some neural factors that could cause low vision which could be located within your brain, the retina or the pathway that is between the two. Examples of this are macular degeneration or a detached retina, and these are often common types. Another common form is amblyopia which is caused by the visual part of your brain by not having be able to develop properly during early childhood. There are some cases where this could be caused from a brain injury such as a strong or traumatic brain injury. Whenever the optical factors are corrected, then it could be considered to be a measure of well-functioning neural ability.
Normally, this can be measured while a person fixates which is a type of measure for central vision and that is because it will be highest here. But, when it comes to peripheral vision, it can be equal or sometimes higher when it comes to the importance of your daily life. This acuity will start to decline near the periphery using an inverse linear type of fashion.
When it comes to the visual processing system, visual acuity is a type of measurement. However, it is often referred to as just VA by many optical professionals. This can be tested by getting someone who is having their vision tested to identify optotypes or a type of stylized letters, symbols for those who are illiterate, Landolt rings, standardized Cyrillic letters found on the Golovin-Sivtsev table, or pediatric symbols or even other types of patterns that are on a printed chart or something similar that must be read from a certain viewing distance. These optotypes are often represented by a black letter or symbol against a white background, as this is for maximum contrast. The distance that is between your eyes and the testing chart are set so that there is an approximate optical infinity as to how the lens is attempting to focus or it will be a defined reading distance.
The most common value for VA to be considered normal will be 6/6 vision, and this is the equivalent of 20/20. So at 6 meters or 20 feet, the eye with this type of performance will be able to separate the contours that are 1.75 mm apart. Vision that happens to be 6/12 is considered to have a lower VA while 6/3 will be much better. Most people will have a score of 6/4 or better and this is based on age as well as other factors.
You can also measure VA by a type of psychophysical procedure, and this could relate to the type of physical characteristic of certain stimuli that a person can percept and the resulting responses. This measurement can be done by done using optical instruments, FrACT testing, or using the Monoyer eye chart.
When it comes to the viewing conditions, there must be care taken that all of the conditions are corresponding to the standard, like the right type of lighting for the room, and the right type of eye chart, the right type of distance for viewing, and enough time for the person to respond, and that there is enough allowance for any errors, and so on.
Now your VA also has a lot to do with your photopic vision, which is how you see in daylight. This is caused by cone receptor cells that have a spatial density that is high and allows you to have a high level of 6/6 or better. However, in scotopic vision which is low light vision, these cones will not have enough sensitivity for a person and then the vision will have been done by rods. This means that the resolution for spatial density will be much lower. This is caused by these rods or the number of rods that will merge to form a type of bipolar cell which makes a cell called the ganglion which have a resolution that is large and the acuity level quite small. You should know that in your visual field that are not any rods and the best performance for any low light instances will be achieved in your peripheral vision.
So, it could be said that your VA is a property of these cones. In order to create details, your eye has to be able to project a focused image inside of the macula of your eye and have a high density in these photo receptor cells and that means that the higher the resolution and the best color will be achieved. Even though color vision and acuity are done by the same cells, they are very different functions and they may be affected in different ways.
This measurement also means that you need to be able to see more than just the optotypes. You need to be cooperative and have an understanding of these and then be able to communicate with your doctor. If these factors are not there, then the measurements will not show your real visual acuity. This testing is also subjective and means that if you don’t cooperate, then the test will not be done. If you have had anything to intoxicate you, if you are sleepy or if you have a disease that can alter your mental status or consciousness, then you will not have a good reading.