Assessment of colour vision, contrast sensitivity, estereopsis.

Colour vision

pruebas-de-daltonismo-numerosThe alteration of colour vision is called discromatopsia and it consists in partial chromatic blindness; it may be due to hereditary and congenital or acquired disorders.

Cones are the cells in the retina responsible for colour vision and they are classified according to the type of pigment (red, green and blue).

Congenital defects of these cells can be classified by the alteration of the pigment:

  • Protanopia: absence of red pigment.
  • Deuteranopia: absence of green pigment.
  • Tritanopia: absence of blue pigment.

In the case the pigment is present but deficient, it will be called protanomalous, deuteranomalous or tritanómalo. When you suffer from total blindness to any color, it is called achromatopsia.

The pathological mechanisms that can cause chromatic defects can be also acquired:

  • Alterations of the lens (cataract, blue-yellow color blindness);
  • Macular Degeneration;
  • Optic nerve’s Pathologies (neuropathy, glaucoma… etc.);
  • Neurological Injury;
  • Choroidal pathologies.

Diagnosis Method

Ishihara Test

Ishihara plates are the most commonly used diagnostic test for the detection of colour vision abnormalities.

These pseudoisocromáticas sheets contain coloured pigments as dots, with variable size and intensity, which delimit numbers or lines impossible to distinguish for a pathological eye, allowing the detection and classification of chromatic alteration.

Mars Test Form 1 with contrast boost Contrast sensitivity

Contrast sensitivity measures the ability of visual system to discriminate an object from its background. It is an indicator which gives information about the actual patient’s true vision.
This diagnostic test can also be useful in the early detection of certain eye disorders such as cataracts, amblyopia, glaucoma, macular degeneration, diabetic retinopathy… etc.

Currently lenses with selective filter improve contrast sensitivity and reduce the level of glare, favouring visual activities such as reading, seeing steps, distinguishing sidewalk curbs, etc.

Diagnosis Method

Pelli-Robson Test

The Pelli Robson Contrast Test measures the visual ability to detect letters that are gradually less contrasted with a white background.

Stereopsis

Having stereopsis is a good indicator of having a well-developed visual system and is useful in many activities of daily life: to park a car, to pour liquid into a cup, to thread a needle, etc.
Depth perception, also called three-dimensional or stereoscopic vision, is a process in which different pathways are involved; visual sensory pathway, brain and motor. To make effective this process it is necessary having a similar monocular acuity and a good binocular vision, due to the superposition of both eyes images on slightly disparate retinal areas, resulting in a “relief view” feeling.

 

Diagnosis Method

  • 15358_titmus test girlTitmus Test: consists of three tests (fly, circles and animals), using 2 sheets with a three-dimensional polarized vectógraph. It consists in looking binocularly drawings with polarized glasses and a distance of 40cm. The drawings measure the depth threshold which is noted in arcseconds. Better is stereopsis, lower will be the value measured in arcseconds.
    • The Fly: right sheet, studies stereopsis rudely, 3000 arcseconds.
    • Animals: bottom left sheet, they confirm children’s finest perception, between 400 and 100 arcsec.
    • Circles: top left sheet, studies the finer depth perception, between 800 and 40 arcsec.

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