Most Common Visual Impairments

How does the eye work?

The eye or eyeball is the organ that detects and transforms light into electrical impulses that the brain translates into colours, sizes, shapes and distances, thus composing an image of the object or scenes being observed.

The light reflected or emitted from the objects around us penetrates the eye through the frontal structures (cornea, iris and lens) where the refractive process begins.

In a normal, healthy eye, the cornea is a clear membrane that serves to refract the beams of light towards the iris. The iris controls the amount of light that pierces the eyeball. The lens is behind the iris. It is flexible and transparent and can adapt its thickness and curvature (accommodation) to focus on objects no matter how near or far they are. This refracts the light and projects it on the retina.

The retina is in the back of the eyeball. It is made up of millions of photosensitive cells, known as cones and rods. The central region of the cornea or macula houses the cones. These are cells allow for a clearer perception of detail. The rods are responsible for night vision and the perception of movement. These photoreceptors convert beams of light into electrical impulses that travel to the brain through the optic nerve. The brain then interprets these electrical signals as visual images.

The deterioration of any of the eye’s structures would cause a visual impairment and images would not longer de seen clearly.

Most Common Visual Impairments

An inadequate refraction caused by the alteration of the lenses (the cornea and the crystalline) is the main cause of visual impairments such as myopia, hyperopia and astigmatism.


Is a refractive defect in which collimated light produces images focus in front of the retina. This makes it difficult to see distant objects. This refractive defect can be caused by:

  • Genetic factors.
  • Overly lengthy eyeball.
  • Excessively steep cornea.
  • Cloudy crystalline lens.

Myopia is developed in childhood and tends to stabilise around the age of 20. Blurred sighting of distant objects, headaches or ocular tension are the symptoms of myopia or short-sightedness.


Occurs when the beams of light converge behind the retina. It causes inability to focus on near by objects. The causes of this refractive error may be:

  • Genetic factors.
  • A small eyeball.
  • A flat cornea.
  • The main symptom of hyperopia is blurred close up vision. Headaches are also frequent, caused by the compensatory effort of the eye muscles.


Is a refractive defect that is caused by an irregularly-shaped cornea or crystalline lens that prevents the correct refraction of light. Images are blurred, both from a distance and nearby.

Astigmatism usually appears in childhood. The most common symptoms are blurred vision at any distance, ocular discomfort and migraines.


Are caused by the loss of clarity in the crystalline lens, responsible for focusing images on the retina. As time goes by, the proteins in the crystalline lens clump together, causing clouding in a small area of the eye and then degenerating its structure. The symptoms of cataracts are:

  • Blurred vision.
  • Double vision.
  • Viewing of halos around bright objects.
  • Loss of night vision.
  • Altered perception of colours.

Cataracts tend to affect people of advanced age although they can also originate from congenital factors, diseases such as diabetes or certain drugs such as cortisone.


Consists of an increased pressure in the papillary region that damages the optical nerve. It is the main cause of total loss of vision. If drainage of the humours fails, the intraocular pressure increases and damages the optical nerve.

The loss of peripheral vision, blurred vision, headaches, excessive secretion of tears and even nauseas are the symptoms of glaucoma.


Is the loss of alignment in focusing the eyes. While one eye focuses, the other deviates in the other direction, causing a reduction in visual acuity y one of the eyes and therefore making it difficult to judge distances and perceive depth.

Presbyopia or Eyestrain

Is the inability to focus on near objects caused by the loss of elasticity of the crystalline lens' accommodation capacity. The ciliary muscle controls the accommodation of the crystalline. This muscle loses its elasticity over the years. The crystalline begins to harden. This is why it becomes harder and harder to focus on nearby objects.

The main symptom of presbyopia or eyestrain is difficulty in reading at a short distance.

Diabetic retinopathy

Is a complication associated with diabetes that deteriorates the blood vessels that irrigate the retina. The blood or liquid leaks out of the weakened vessels and create fibrous tissue in the retina that prevents the correct projection of light needed to view images.

The symptoms can show up as small spots floating in the person’s visual field. Diabetic retinopathy is one of the main causes of total loss of vision and sometimes may not present any symptoms at all. Therefore, an annual eye check up should be performed.

Macular degeneration

Is an alteration of the macular area of the retina that causes loss of central vision or the inability to see fine details. Macular degeneration causes a reduction in sight that prevents reading, facial recognition o watching television.

In the initial stage of macula degeneration, the patient may notice distortions or even not notice any symptoms at all. It is therefore crucial to have annual eye examinations in which an Optometrist can monitor the retina’s condition.

Treatment of Visual Impairments

Personalised treatments area now available for each of these refractive imperfections. First of all, a diagnosis is performed through general eye examinations in which the Optometrist check parameters such as visual acuity, light refraction on the retina, visibility of colour or the state of the ocular muscles, amongst others.

Myopia, hyperopia and astigmatism can be treated with Refractive Surgery using three different surgical techniques according to the needs of each patient: Lasik Surgery (conventional surgery) and Intralase (laser) corrects myopias, hyperopias and astigmatisms by reshaping the cornea.

In the event that the cornea can not be treated by laser -as in the case of dry eye syndrome or a very high number of diopters- the solution is in the surgical implantation of Intraocular Contact Lenses behind the iris. The procedure lasts 30 minutes under topical anaesthetic in which the patient experiences no pain or discomfort.

Clear Lens Surgery replaces the cloudy crystalline lens and is capable of correcting refractive defects (myopia, hyperopia and astigmatism), eyestrain and even multiple correction cases where several visual defects are present.

Presbyopia or eyestrain surgery with multifocal intraocular contact lenses can also correct associated myopia or hyperopia, reaching a complete correction of near, mid and distant vision.

Combined cataract and presbyopia surgery can simultaneously correct cataracts and eyestrain. The patient will not require the use of spectacles after the procedure since these are replaced by the implantation of a lens doubly adapted to correct the cloudy crystalline and the accommodation of near vision.

Retinal surgery and photodynamic surgery have managed to dramatically reduce the anaesthesia and operating theatre time for the treatment of macular degeneration. Optical fibre laser avoids cuts and scars in tear duct surgery.

The Ophthalmological Unit at IML comprises a team of expert ophthalmologists and installations equipped with the latest technology to offer its patients the highest quality service in eye surgery. All procedures are simple and painlessly performed using topical or local anaesthetic.

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