Eye Health Knowledge
Types of Vision
Normal Vision (Emmetropia)
Normal vision occurs when the eye’s focusing power is balanced with the length of the eyeball. The cornea has an ideal curvature, allowing light to focus directly on the retina. As a result, vision is clear at both near and far distances.
Myopia
Myopia occurs when the eye has too much focusing power relative to the length of the eyeball. This may be due to a steeper-than-normal cornea or an elongated eyeball. Light focuses in front of the retina, causing blurred distance vision while near vision remains clear.
Hyperopia
Hyperopia occurs when the eye’s focusing power is too weak compared to the length of the eyeball. It may be caused by a flatter corneal curvature or an eyeball that is too short. Light focuses behind the retina, resulting in blurred vision both near and far, especially when uncorrected.
Astigmatism
Astigmatism occurs when the eye’s focusing power differs between various meridians. The cornea is not perfectly spherical—its shape resembles the side of an egg—causing light rays to focus at multiple points instead of a single focal point.
This leads to distorted or blurred vision at all distances.
Common Eye Conditions Vision problems or blurred vision can result from:
Eye diseasesThese are abnormalities affecting parts of the eye that light must pass through before reaching the retina. Eye diseases that may impair vision include:
- Conjunctiveitis
- Corneal ulcer
- Hyphema
- Uveitis, Glaucoma
- Vitreous
- Retinal diseases
Refractive error In normal vision, light passing through the cornea and natural lens focuses directly on the retina. If the focus falls in front of the retina (myopia) or behind the retina (hyperopia), the image becomes blurred. The four main types of refractive errors include:
- Myopia
- Hyperopia
- Astigmatism
- Presbyopia
Treatment Options
General Correction Methods
Refractive errors are corrected by adjusting the eye’s focusing power: Reducing the focusing power for nearsightedness Increasing the focusing power for farsightedness Traditionally, there are two primary methods of correcting refractive errors:
1. Eyeglasses
Eyeglasses are the most common and safest method of correction. However, some people cannot wear glasses comfortably due to: Significant prescription differences between both eyes Occupations where glasses are inconvenient (e.g., flight attendants, public relations staff)
2. Contact Lens
Contact lens are also a popular choice. However, many individuals cannot tolerate contact lens due to: Allergic reactions to the lens material or cleaning solutions Environmental factors such as dust or smoke Activities where contact lenses are impractical (e.g., swimming or diving)