The visual problems that affect a poor visual efficiency are:

  • Refractive errors.
  • Changes in binocularity.
  • Dysfunctions of the eye movement.
  • Accommodative problems.
  • Difficulties in visual perception skills.

Refractive errors.

They alter the normal visual acuity (VA) due to structural factors of the eye (axial length, corneal curvature) or aging crystalline lens. They are classified as myopia, astigmatism and presbyopia.

Myopia:

  • Distant objects look blurred because the image is formed ahead of the retina.
  • It is compensated wearing concave lens.
  • ts appearance depends not only on hereditary but also environmental factors.
  • Mainly associated with the greatest axial length of the eye, but also with a high power optical system of the eye.

Hyperopia:

  • It involves major difficulties in the focus of near vision because, if the crystalline lens does not compensate it by making an effort, the image is formed behind the retina.
  • It is compensated wearing convex lenses.
  • Mainly associated with short-axial length of the eye, but also with a low-power optical system of the eye.

Astigmatism:

  • It affects to far vision as well as to close vision.
  • It is compensated wearing toric lenses.
  • It can be associated with myopia or hyperopia.
  • It is usually due to a cornea with two principal radii of curvature and its orientation will determine the axis of astigmatism.

Presbyopia:

  • It makes look blurred in near vision due to sclerosis of the crystalline lens.
  • It usually becomes noticeable in the early to mid-40s.
  • It is compensated wearing convex lenses with bifocal or multifocal lenses (also called “progressive lenses”).

Binocularity alterations

To ensure that there is good coordination between both eyes (binocularity) images that arrive to them fuse in the brain and they are perceived as a single one. Both images are a little different, allowing three-dimensional perception (stereopsis). The binocularity alterations are classified basically in:

  • binocular dysfunctions.
  • Amblyopia.
  • Strabismus.

Main binocular dysfunctions: There is a constant effort to keep the eyes properly aligned to where the look goes. They are difficult to detect without a good optometric examination. They are mainly classified into:

  • convergence insufficiency: Difficulty in stimulating ocular convergence in order to maintain the alignment of the eyes at near distances, so fatigue and even double vision (diplopia) may appear.
  • Convergence excess: Difficulty in relaxing the ocular convergence after prolonged near tasks performing which can cause fatigue, headaches and possible blurred vision or diplopia at the moment to lift the look from the paper. This condition can be associated with pseudomyopia or spasm of accommodation.

Amblyopia (lazy eye): It is the condition when one eye is compensated with the appropriate correction and it fails to achieve a visual acuity (VA) just as well as that of the other eye. The origin of this problem can be organic (due to disease) or functional (due to different abilities of the eye which failed to develop because a vision problem was not detected at an early age). It may be associated with a squint.

Strabismus: It occurs when one of the two visual axes is not directed at the point of fixation so there is no fusion or simultaneous three-dimensional perception (stereopsis). Basically it is classified into different types according to where the eye turns and the moment it appeared.

Dysfunctions of the ocular motor function:

The control of ocular movements is essential to analyze visual information. Therefore it requires a good anatomical and functional integration of ocular muscles which depend on adequate binocular coordination and on a proper innervation and normal anatomy. A poor control of the ocular motor function:

  • makes visual searching difficult as well as the attention by interfering on the autonomy of the individual.
  • causes reading difficulties: losing place, skipping words, low comprehension and low reading speed, inversion, need to move head too much, loss of concentration...
  • Negative effect on athletic performance and more especially on those who play ball sports (hand-eye coordination and eye-foot coordination).

Accommodative dysfunctions.

When the ability to focus is altered, headaches, poor performance in reading, a tendency to myopia, etc. may appear. The most common disorders that cause these problems are insufficient accommodative insufficiency, accommodative excess and accommodative inflexibility.

Accommodative insufficiency: Difficulty focusing on near distances so the focus is placed behind the view plane.

Accommodative excess: Tendency to focus too much, so the focus is placed in front of the view plane.

Accommodative inflexibility:Difficulty to change focus efficiently and quickly at different distances.

Difficulties in visual perception skills.

The visual perception skills are what allow us to recognize what we see and to interpret it correctly according to our previous experiences. In daily activities it is necessary an adequate visual processing and a good ocular motility integration. To adapt to our environment it is necessary that vision allows us to anticipate information. That is why skills for visual perception are necessary. When the visual system does not analyze properly what can be seen the reasons are basically the following:

  • Immaturity in the development of visual skills.
  • Brain damage whether it occurs at birth as if it is the result of a skull-brain trauma or a stroke.