For correct vision to occur, the cornea and lens (located at the front of the eye) must cause light rays to strike the retina (at the back of the eyeball) and transmit information to the brain through the optic nerve.
Several visual defects can occur that make it difficult for the eye to focus images of the outside on the retina, causing a faulty image of objects to form.
Refractive defects are myopia, hyperopia, astigmatism, or presbyopia. On the other hand, there is also an alteration in visual acuity due to total or partial occlusion of the passage of light in the case of cataracts.
All these refractive defects are measured in diopters, which represent the amount of correction that a lens requires to normalize sight.
To summarize, myopia, hyperopia and astigmatism are caused by differences in the length or shape of the eye, while presbyopia (or eyestrain) occurs when the crystalline lens, due to age, loses the ability to focus on nearby objects.
It is one of the most common visual problems. Light rays converge and focus before reaching the retina because the eye is longer than normal or the cornea is too curved. A blurry image is formed, mostly from afar.
The cause of myopia is not known exactly, although a primary reason is the genetic factor. Myopia usually occurs in infancy, during the school years, evolving during growth to stabilize by the age of 20.
- Decreased visual acuity in distant vision. Need to encircle the eyelids to clearly see objects located at a greater distance.
- Good visual acuity in near vision
- Eye fatigue
- Late onset of presbyopia
- Alterations of the binocular vision, bad convergence, being able to favor the appearance of strabismus.
Myopia is measured in negative diopters. Myopias of more than 6 diopters are considered “high” and require periodic retinal check-ups, as retinal detachments may occur more frequently than in a normal eye.
It is advisable to maintain good visual hygiene, during close work, lighting should be good, preferably natural, and should be properly located. It is recommended to take breaks, using distant vision during work in near vision.
These alterations can be solved with the use of glasses or contact lenses, as well as surgery. The ophthalmologist will decide the most convenient type of operation for each patient based on the number of diopters, the thickness of the cornea and other anatomical factors.
In this case, light rays converge behind the retina because the eye is shorter than normal or the cornea is too flat, resulting in a blurry image mainly close up.
The main cause of farsightedness is hereditary.
- blurred vision of nearby objects
- Headaches, usually at the end of the day, due to the eye’s continuous effort to accommodate vision.
Children at birth tend to be farsighted to a greater or lesser degree, as the eye grows and becomes longer, farsightedness decreases or disappears. Despite farsightedness, children usually see clearly both objects that are far away and those that are close, thanks to the great focusing power of the young crystalline lens.
Astigmatism is a visual defect produced by an irregular or abnormal curvature of the cornea, which prevents the convergence of light rays at a single point. In this way we will see “deformed” and blurred objects regardless of the distance of the objects. The focus of the image takes place in front of or behind the retina.
Some people with mild astigmatism do not notice large changes in vision, it is possible to have astigmatism and not know it.
- Blurred vision, difficulty distinguishing details and focusing on objects both near and far.
- Visual fatigue
- Excessive sensitivity to light
- Double vision
- Difficulty driving at night
The cause of astigmatism is unknown. It is usually present from birth and often occurs along with nearsightedness or farsightedness. It may run in families or occur after eye surgery, such as cataract surgery.
With age, the muscles of the body lose elasticity and the lens becomes less flexible, making it increasingly difficult to accommodate vision and see close up clearly. This is called presbyopia or “tired eyesight.
This visual anomaly affects above all those over 45 years of age and progresses to approximately 60 years of age. It is associated with the ageing of the organs.
- Difficulty reading small letters
- Problems seeing near objects, especially when brightness is low and at the end of the day
- Visual fatigue
The ophthalmologist will make an assessment of the visual capacity to decide the need for glasses with a suitable prescription that usually ranges between 1 and 3 diopters. The problem can also be solved by surgery in which the lens is removed and replaced by a multifocal intraocular lens.
A cataract is the partial or total opacity of the lens, which causes light to scatter within the eye and cannot focus on the retina, creating diffuse images.
The primary cause is age, although cataracts can also occur from eye trauma, some diseases such as diabetes or treatment with some medications such as corticosteroids.
- In its beginnings, cataracts are very small and almost do not alter vision, with time the vision becomes blurred.
- Increased sensitivity to light and glare sensation
- Less contrast is perceived in the colors, they look faded
- Perception of halos around light sources
- Double vision in one eye
- Doesn’t look good at night or in low light
The only definitive treatment for cataracts today is surgery.
It is advisable to carry out a periodic ophthalmological check-up, at least once a year, to detect the previous alterations and correct them as far as possible.