Defective vision

Eye care

Defective vision


What is Myopia?
It is a refractive defect of the eye in which parallel light rays converge at a focal point in front of the retina, rather than converging on the retina; it is the opposite of hyperopia, in which light rays reach the retina before converging.

It may also be defined as an excess in refractive power of the transparent media of the eye with respect to its length, so that the light rays from objects at a distance from the eye converge towards a point before the retina.

What are the symptoms of myopia?
Difficulty distinguishing objects from having blurred vision, having to squint in order to see details more clearly. Accompanied by intense eyestrain, redness of the eyes, and headaches.


What is farsightedness?
Farsightedness is a refractive eye defect that is characterized by the fact that the light rays coming from infinity affect the human eye, converging behind the retina, thereby forming the focus or image, where it is not correctly perceived. This is due mostly to the eye being too short in its anteroposterior axis.

What are the symptoms of farsightedness?
A farsighted person has vision problems at short distances, and can see more clearly in the distance. The eye cannot focus on objects closer than a certain distance, called the “next point” or “near point” (or cannot do so for long periods of time). In a young adult person without optical defects, the near point is 25 cm from the eye. In a hyperopic person, the near point moves to a greater distance out.


What is astigmatism?
It is an eye defect characterized by the fact that there is a different eye refraction between two meridians, which prevents the clear focus of objects, and generally to an alteration that involves the anterior curvature of the cornea. The cornea is the transparent region that is in the anterior pole of the eye and acts as a lens through which light passes, which is then focused onto the retina at the back of the eye. The surface of the cornea must be symmetrical and regular in its curvature, otherwise astigmatism occurs.

What are the symptoms of astigmatism?
There may be no symptoms in mild cases, and generally up to half a diopter of astigmatism is usually asymptomatic. When the disorder is important, the primary symptom is decreased visual acuity for both distance and near sight, vision is blurred and objects are distorted. There may be headache and dizziness, as the eye tries to compensate for the defect by accommodation, resulting in muscle strain. Astigmatism usually occurs associated with myopia or hyperopia, so the symptoms overlap with those of these conditions. In children, astigmatism which affects only one eye and is left untreated can cause a major difference in visual acuity between the two eyes. The child tends to use only the eye of greater acuity, while the other eye ends up being muted functionally, although its physical structure remains intact; a phenomenon known as lazy eye, or amblyopia.


What are cataracts?
The clouding of the crystalline lens and opacification thereof is known as a cataract. This situation makes people who suffer from the condition notice, among other things, a progressive loss of vision, increased susceptibility to glare, distorted vision, frequent changes of graduation in eyewear, etc.

Cataracts are the leading cause of blindness globally, and it is estimated that approximately 45% of people over 60 have cataracts. It is not uncommon for them to appear even prior to this age.

What are the symptoms of cataracts?
The main symptoms are blurred or hazy vision,  greater difficulty seeing at night or in low light, sensitivity to light and glare, the presence of halos around lights, perception of faded or yellowed colors, the need for a brighter light for reading and other activities, frequent changes in prescription glasses or contact lenses; or double vision in one eye.

At any rate, the only way to know for sure if you have cataracts is through a dilation exam, in which the pupil is dilated with eye drops. Your ophthalmologist can detect early signs of developing cataracts by observing the lens of the eye.


What is glaucoma?
Glaucoma is a progressive optic nerve atrophy, which as a rule is associated with increased intraocular pressure. The condition evolves slowly and progressively, damaging the optic nerve fibers irreversibly, making early detection extremely important, as it can lead to irreversible blindness.

What are the symptoms of glaucoma?
The most common forms of glaucoma often have no symptoms, as vision loss occurs very slowly and often peripheral (side) vision is first affected. In the less common varieties of glaucoma, symptoms can become severe and include:

  • Blurred vision
  • Sore eyes and headache
  • Nausea and vomiting
  • Appearance of halos around bright lights
  • Sudden loss of vision


What is Presbyopia?
Presbyopia, which literally means ‘eye strain’, is an eye condition related to age in which it is difficult to see things up close. It occurs naturally in all people from 40-45 years of age, and after 50 it is present in 100% of people, regardless of whether or not there is preexisting farsightedness. It is estimated that in Spain about 23 million people suffer from it, and 1,700 million people worldwide rely on reading glasses as a result.

How does presbyopia occur?
Presbyopia occurs as a result of two effects, (1) loss of elasticity of the lens and (2) loss of power of the ciliary muscle, so that the eye exhibits a reduced capacity of accommodation.

When the eyes are young, the lens is very elastic. This lets one change its optical power (magnification) and be able to focus objects on the retina which are located at any distance, near or far. But over time, this capacity is weakened as the lens gradually loses its elasticity, becoming more rigid, which prevents people from modifying the focus of the eye. Once we reach 40, the lens is already so stiff that we then start to notice that we have difficulty reading, and increasingly move objects away more so that they can be seen clearly.


What is strabismus?
It is a disorder in which the two eyes do not align in the same direction and, therefore, do not look at the same object at the same time. The condition is more commonly known as ‘crossed eyes’ (convergent strabismus). Strabismus can cause the eyes to cross inwardly (esotropia) or outwardly (exotropia). Sometimes amblyopia is caused when one eye is more myopic (nearsighted), hyperopic (farsighted), or astigmatic than the other eye. Sometimes amblyopia is caused by other eye conditions, such as cataracts.

How does strabismus occur?
Six different muscles surround each eye work as a team, which allows both eyes to focus on the same object. In someone with strabismus, these muscles do not work together. As a result, one eye looks at an object, while the other eye turns in a different direction to focus on another object. One image from each eye: when this occurs, two different images are sent to the brain, confusing it. In children, the brain may learn to ignore the image from the weaker eye.

If strabismus is not treated, the eye that the brain ignores will never see well. It is closely linked to the concept of amblyopia, or lazy eye.

AMBLYOPIA, or lazy eye

What is amblyopia, or lazy eye?
The brain and eye work together to produce vision. Light enters the eye and becomes nervous signs that travel through the optic nerve to the brain. Amblyopia is the medical term used to describe when the sight of one eye is reduced because the eye and brain are not working together in the right way. The eye is seeing normally, but not being used normally because the brain is favoring the other eye. This condition is also known as lazy eye.

How does amblyopia, or lazy eye, occur?
Amblyopia can be caused by any condition that affects the development of normal vision or use of the eyes. Amblyopia is usually caused by strabismus, an imbalance in the position of both eyes, or when the visual acuity of one eye is very different from the other, and no correction with glasses or contact lenses is used.


What is retinal detachment?
Retinal detachment is an eye disease caused by the spontaneous separation of the neurosensory retina (inner layer of the retina) from the pigment epithelium (outer layer). As this separation occurs, fluid accumulates in the space formed between the two layers, and the detached retina cannot function and does not receive proper nutrition. If left untreated, retinal detachment eventually leads to total loss of function of the eye (blindness).

How does retinal detachment occur?
Since this condition does not cause pain and, in many cases, is not accompanied by the onset of vision loss, it is important to be alert to the symptoms even if they are apparently harmless. These symptoms, which usually appear successively, are:

  • Seeing spots (black dots that move when you move your eye). They are caused by changes in the vitreous fluid.
  • Seeing flashes. This is a very important symptom, reflecting as it does the existence of traction on the retina. It usually occurs when separation has already been produced.
  • Perception of a black curtain that falls somewhere in the visual field. This occurs when there is a detached retina, so that consultation with an ophthalmologist should be sought immediately.
  • Distortion in images and subsequent significant decrease in visual acuity. This symptom appears if the central area of the retina is damaged (macula).