10.1.2. DEFECTS OF VISION AND THEIR CORRECTION

Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. A person with this defect has the far point nearer than infinity. Such a person may see clearly up to a distance of a few metres. In a myopic eye, the image of a distant object is formed in front of the retina. This defect may arise due to (i) excessive curvature of the eye lens, or (ii) elongation of the eyeball. This defect can be corrected by using a concave lens of suitable power.

Myopia, or near-sightedness, is a common vision defect where distant objects appear blurry while close objects are seen clearly. This happens because the eye focuses images in front of the retina, making it hard to see far away. It can result from an excessively curved lens or an elongated eyeball that changes how light enters the eye. To correct myopia, a concave lens (which diverges light rays) is used. This helps to shift the image focus back onto the retina, allowing for clear distance vision.

Imagine a camera that is out of focus for distant landscapes but perfectly focused for close-up shots like family photos. Like adjusting the camera lens, using concave glasses for someone with myopia helps them to focus on far away objects clearly, bringing distant landscapes into view.

Hypermetropia is also known as far-sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly. The near point, for the person, is farther away from the normal near point (25 cm). Such a person has to keep a reading material much beyond 25 cm from the eye for comfortable reading. This is because the light rays from a close object are focused at a point behind the retina. This defect arises either because (i) the focal length of the eye lens is too long, or (ii) the eyeball has become too small. This defect can be corrected by using a convex lens of appropriate power.

Hypermetropia, or far-sightedness, is where individuals can see distant objects distinctly but struggle with nearby ones. In this case, the near point (the closest distance at which objects can be seen clearly) is beyond the normal range of about 25 cm. This occurs because the eyeball might be too short, or the lens is too flat, causing light rays from close objects to be focused behind the retina. Convex lenses are used for correction since they converge light rays, moving the focus forward onto the retina for clearer near vision.

Think of a smartphone camera that struggles to capture sharp close-up pictures but does well with landscapes. For a person with hypermetropia, reading a book close-up is similar to that camera—it requires a specific lens (like a convex lens) to enable the eye to focus properly on the text.

The power of accommodation of the eye usually decreases with aging. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye glasses. This defect is called Presbyopia. It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bi-focal lenses. A common type of bi-focal lenses consists of both concave and convex lenses.

Presbyopia is an age-related vision change where the ability of the eye to focus on close objects diminishes. This is due to the ciliary muscles weakening and the lens losing its flexibility over time, making it hard to read small print. Some individuals may experience both myopia and hypermetropia, leading to the need for bi-focal lenses, which combine both corrective lenses in one. The upper portion typically uses concave lenses for distance vision, while the lower part utilizes convex lenses for near vision.

Imagine trying to stretch a rubber band worn out by time—it can no longer go back to its original shape. Similarly, as we age, our eye lens becomes stiffer, losing flexibility to accommodate for varied distances, prompting the use of bi-focal glasses to aid clarity for both near and far vision.

These days, it is possible to correct the refractive defects with contact lenses or through surgical interventions.

Correcting refractive errors such as myopia, hypermetropia, and presbyopia can now be achieved not only by traditional glasses but also by using contact lenses and surgical procedures. Contact lenses sit directly on the eye and can offer a beneficial cosmetic option, while surgeries like LASIK reshape the cornea to improve vision permanently. These advancements provide more options for individuals to see clearly without relying on glasses.

Just as we can choose between using reading glasses or upgrading to e-readers with adjustable font sizes, people with vision problems can shift preference from glasses to contact lenses or even surgical options to maintain clarity in their vision while enjoying a fashionable or convenient lifestyle.

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