When having an eye exam done you might have been told that you have 20/20 vision, but what exactly does that mean? To put it simply, having 20/20 vision indicates that at a distance of 20 feet, you are able to see the smallest letters that should be seen at 20 feet. If you have 20/40 vision, it indicates that you need to be at 20 feet to see what a person with 20/20 vision can see at 40 feet. On the other hand, if you have 20/15 vision, you can see at 20 feet what a person with 20/20 vision can see at 15 feet.
How do we measure our visual acuity?
There are many ways to measure a patient’s visual acuity, but the most common way is through using a Snellen chart that presents with numerous lines of letters above one another. Letters found at the top of the chart are larger and easier to see but become smaller and difficult to read as you move down the chart. Patients are tested by covering one eye and reading the letters from top to bottom at which point they repeat these steps while covering the other eye. Afterwards, patients will use both eyes together to determine the lowest line they are able to read clearly.
The retina plays an important role in providing us our vision. Sometimes we can have a retinal detachment which results in the retina pulling away from its normal position resulting in vision loss. It is also possible to have retinal holes and tears which results in a break in the retina and the accumulation of fluid resulting in a detachment occurring. This can result in someone having symptoms of blurred vision, flashes of light, a curtain veil blocking some of their vision and floaters covering their vision.
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Who is at risk and how do you treat it?
Individuals who have had previous eye surgeries, high nearsightedness, or trauma to the eye or head will also increase the chance of a retinal detachment occurring. Age also plays a factor in this as the vitreous gel found in our eye shrinks overtime and can pull away from the retina resulting in a possible hole or tear. Yearly dilated eye exams are done to help detect and prevent retinal detachments from occurring. It is especially important that you see an optometrist if you have any symptoms of flashes of light or floaters in your vision. Different treatment options exist such as laser therapy, cryopexy and surgery which are chosen depending on the severity of the detachment, hole, or tear.
Tears are needed to keep the eye’s front surface healthy and to maintain clear vision. It is common to temporarily produce excess tears when you are emotional, laughing, coughing, vomiting, experiencing strong taste sensations, or yawning.
Types of Tears
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Different types of tearing consist of basal tears, emotional tears, and reflex tears. Basal tears are your basic functional tears. They are released in tiny amounts to lubricate your ocular surface and keep it clear of any dust. These are vital for good vision and comfort. Emotional tears are triggered by strong feelings such as joy or sadness. Reflex tears result from irritation in the eye by foreign bodies, or from the presence of irritant substances in the environment. They can also occur with bright lights hot or peppery stimuli to the tongue and mouth, when we yawn, cough or even vomit. These types of tears are released in larger amounts than basal tears. Their goal is to protect one’s eye.
How can I have Dry Eyes if my eyes are so watery?
The two common causes of watery eyes are blocked tears ducts and excessive production of tears. The common cause of excessive production of tears is dry eye syndrome. This occurs due to the glands around our lid margins not producing enough oil resulting the tears drying up very quick. This lack of lubrication results in our eyes producing an abundance of tears to compensate.
It is often said that eating carrots will help you see better due to the high amounts of vitamin A. Although vitamin A plays an important role in our vision, it is unable to improve the quality of our vision. Vitamin A is able to prevent diseases such as macular degeneration which can result in severe vision loss if left untreated.
What is Vitamin A?
Vitamin A is derived from beta-carotene which acts as an antioxidant. This is essential in protecting our cells against heart disease, cancer, and many other diseases. Deficiency in vitamin A is the leading cause of preventable blindness in children across the world. Due to this, it is important to have some type of source for vitamin A such as carrots, eggs, spinach, or broccoli.
What does Vitamin A do for our eyes?
Vitamin A allows us to produce pigments needed in-order for the retina to function properly. Without these pigments, it would become much more difficult to see in the dark leading to eventual night blindness. Lack of vitamin A can also lead to a lack of nourishment to the cornea resulting in the eyes not producing enough moisture to keep the cornea lubricated. This can lead to our eyes becoming dry which can result in severe complications such as ulceration of the cornea and eventual blindness if not appropriately treated.
Color vision is an important part of human visual perception, and it is possible due to the photoreceptors in the retina. The human eye consists of two basic photoreceptor cell types, rods, and cones. Rods are responsible for vision in dim light, and cones are responsible for bright light and enable perception of color. Individuals with normal color vision have three subtypes of cones with different wavelengths corresponding to their peak absorption. Found in the central part of the retina are the cones that are sensitive to either red light (long wavelengths ~555nm), green light (medium wavelengths ~530nm) and blue light (short wavelengths ~ 426nm). Normal color processing consists of the cones registering different colors and sending information through the optic nerve to the brain. This enables us to distinguish countless shades of color.
Color Vision Deficiencies
Color vision deficiency or known as color blindness could be congenital or acquired. Congenital color deficiencies are typically bilateral and non-progressive, and acquired is more likely unilateral and progressive. The types of color deficiency include red-green deficiency and blue-yellow deficiency. Individuals with severe color vision defects lack the photopigment to see color completely while others with a mild color vision defect have a reduced sensitivity to certain colors. The degree of dysfunction varies between individuals, mildly affected individuals may pass some of the less sensitive color vision tests such as Farnsworth D-15 hue test. The most common type of color deficiency is red- green deficiency. Color vision deficiency can be diagnosed through a comprehensive eye examination. Testing that can be performed in clinic include, pseudoisochromatic tests, arrangement tests (ex. Farnsworth D-15) and anomaloscope.
Color vision deficiency can be frustrating and may limit participation in occupations that include being able to differentiate between colors. Few examples include pilots, truck drivers, law enforcement, and policing. There is no cure for inherited color deficiency. However, using specifically tinted eyeglasses or wearing red-tinted contact lens on one eye can increase some people’s ability to differentiate between colors.
