What is Emmetropia?
Emmetropia is a refractive state of an eye wherein it remains fully focused without any glasses or contact lens prescription. Emmetropia describes an eye with no refractive error (no nearsightedness, farsightedness, or astigmatism). People with emmetropia have clear vision at distance without any visual correction.
A person with emmetropic vision is considered to have an ideal vision that does not require any kind of vision correction. It occurs when there is a perfect balance between the optical power and length of the eye. Even though an emmetropic eye does not need any visual correction, people with emmetropia can develop other eye conditions that may require treatment.
Key Takeaways
- Emmetropia is the clinical term that defines an eye with no refractive error (no prescription for nearsightedness, farsightedness or astigmatism).
- An emmetropic prescription power is 0.00 diopters.
- People with emmetropia often can achieve 20/20 vision without glasses or contact lenses. However, they may still have other conditions that affect the health of the eyes.
Understanding Emmetropia
Emmetropia is the state of having no refractive error. With emmetropia, your eyes can view an object located far away and focus the light rays clearly onto the retina without any visual aid. With emmetropia you might have distance glasses or a contact lens prescription of 0.00 diopters, which means no corrective power is required at distance.
Although people with emmetropia have no distance prescription, it’s possible to have a reading prescription, especially as you age. Reading and viewing objects up-close require the focusing power of the lens. When you look at near objects like a smartphone, your eyes focus on the small text because the lens moves forward, the lens diameter decreases, and the lens thickness increases. These anatomical changes of the lens happen very quickly to focus objects up close.
It is also possible for your vision to be 20/20 at distance without having emmetropia. In some cases, people with low to moderate farsightedness (e.g. +2.00) can still see clearly at distance. This occurs because you are able to focus to make the vision clear. People with low amounts of astigmatism may also see clearly at distance without any glasses or contact lenses, even though they technically do not have emmetropia.
How Sight Changes with Age
When you’re young, your focusing system is robust and, for most people, uses no effort to focus on close-up objects. Around age 40, the lens of the eye is no longer as robust, and struggles to focus on objects up close.
Around the age of 60, the internal focusing ability of the lens is markedly decreased. You may need reading glasses to help magnify text and focus on small objects because of your reduced internal focusing power.
Therefore, someone with emmetropia and a 0.00 diopter distance prescription can still have a reading prescription if you have diminished near-focusing ability.
The Difference Between Emmetropia and Ametropia
Emmetropia and ametropia are opposites. Emmetropia is a visual condition where refractive errors are absent, whereas ametropia is a visual condition where refractive errors are present.
Some of the most common types of refractive errors causing ametropia are:
- Myopia (Nearsightedness)
In this condition, objects that are nearer appear clearer. However, objects that are located far away appear to be blurry. Myopia occurs when the eyeball is too long in length.
- Hyperopia (Farsightedness)
Hyperopia is the condition where objects far away appear clearer, whereas nearby objects appear to be blurred. In some cases of hyperopia, there are no symptoms of blurred vision. This is because the eye uses its near-focusing system to make the vision clear. Hyperopia occurs when the eyeball is too short in length.
- Astigmatism
Astigmatism is defined as an irregularly shaped cornea. This irregularly shaped cornea bends the light that enters the eye differently and cannot focus on a single point. Astigmatism causes blurry vision both at distance and near.
- Presbyopia
Presbyopia is defined as the loss of near-focusing ability which occurs normally with age. This condition causes blurry near vision, and starts around the age of 40 when the eye’s lens loses its flexibility.
Preventive Measures for People with Emmetropia
Although emmetropia does not require any special treatment or vision correcting lenses, the emmetropic eye still has risks. Eyes with emmetropia are still susceptible to getting eye diseases, and routine vision examinations should be completed.
The following are ways to keep eyes with emmetropia healthy:
- UV Protection
UV rays harm your eyes, causing various eye conditions such as eyelid cancers, cataracts, snow blindness, and macular degeneration. Always make sure to protect your eyes with 100% UV-protected sunglasses when outside in the sun. It is important to ensure that sunglasses have UV protection besides just being tinted dark. Tints alone do not guarantee UV protection.
- Routine Eye Checkup
No matter how healthy your eyes are, a routine eye checkup by a licensed ophthalmologist or optometrist is always important. Eyecare professionals use a multitude of clinical techniques to detect eye diseases and other conditions that affect the eyes. An annual comprehensive eye care checkup is crucial to avoid unwanted eye complications.
- Extra Eye Protection
Protective polycarbonate eyewear or safety eyewear should be worn when doing risky activities that can harm the eyes. For example, while playing sports, doing metalwork, or using chemicals like household cleaners. Safety glasses or goggles can also be worn when working with irritants in heavily polluted environments or dusty areas.
