Developmental Disorders and Mental Health Disorders

Visual impairment refers to any vision condition that makes it difficult to perform daily activities that rely on visual perception. Visual perception is the ability to interpret the surrounding environment based on visual information. It is defined by visual acuity and the visual field. Visual acuity is the eye's ability to discern fine details and clearly see two separate points. The visual field is the area visible while looking straight ahead without moving the head or eyes. Based on severity, visual impairments are classified as low vision or blindness.

• Low vision (sometimes associated with amblyopia) includes visual acuity ranging from 10 % to 40 % of normal vision in the better eye with corrective lenses (glasses or contact lenses). It also includes visual acuity greater than 40 % if the condition is progressive, or less than 10 % if the person is able to use that vision effectively.
• Blindness refers to visual acuity of less than 5 % of normal vision in the better eye with corrective lenses. It also includes cases where central vision is less than 25 % of normal acuity, accompanied by a visual field reduced to less than 20 degrees.

A visual impairment does not necessarily result in deviations in emotional or social development; however, real barriers do exist. Limitations in visual observation and tracking lead to limitations in visual learning. A lack of visual information can cause delays in cognitive development. Individuals with low vision read standard print (inkprint) that is enlarged according to their needs. Blind individuals read Braille, and their success depends on intellectual development, fingertip sensitivity, motor dexterity, teaching methods, and practice. Motor development is affected not so much by the visual impairment itself, but by the inability to practise and visually imitate the movements and actions of others. Communication and socialisation are also made more difficult (URIHO, Visual Impairments).

Colour blindness is a condition that affects a person's ability to distinguish certain colours. People with this disorder most often have difficulty distinguishing specific shades. The condition is hereditary and affects men (about 8 %) significantly more often than women (about 0.5 %). Each eye has three types of photoreceptors (cones) that activate in various combinations to enable colour perception: receptors for red, green, and blue. In colour blindness, one or more of these receptors do not function correctly, leading to problems distinguishing certain colours.

There are different types of colour blindness depending on which photoreceptor is affected:

• Deuteranopia: The most common form; individuals have difficulty recognising green and often confuse it with red.
• Protanopia: Individuals have difficulty recognising red and often confuse it with green.
• Tritanopia: The rarest form; individuals have difficulty recognising blue and may confuse it with yellow.
• Monochromacy: An extremely rare condition in which a person cannot recognise any colours and sees the world exclusively in shades of grey.