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3 Frequent Reasons of Reduction or Loss in the Czech Republic

3 Frequent Reasons of Reduction or Loss in the Czech Republic

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Visual Impairment and Its Impact on Development



retina (ARMD)11 (Gubková, 2002). It is necessary to mention also eye injuries.

The injuries of one eye of various levels of seriousness prevail in clinical practice.

These are usually traumatic injuries caused by chemicals or perforation. Damage

may cause a reduction of visual acuity, amblyopia; in some cases, other complications can occur resulting in the development of other eye diseases (Řehůřek, 1997).

Moravcová (2004, 37) states that ‘it is possible to diagnose a significant deterioration of visual ability in 90 % of persons over 60 years as well as hearing ability in

30 % of persons over 60 years’.12 SONS research (In Jesenský, 2002, 15) published

the following data about the relative distribution of causes of visual impairments:

‘31 % congenital or hereditary visual disorder, 27 % eye disease, 11 % injury and 7 %

diabetes mellitus. In terms of time of origin, 17 % of persons reported a defect from

birth, the rest of the group developed visual disorders during the course of life’. The

data clearly show the significant superiority in numbers of persons over 60 years as

compared to other groups as well as the prevalent occurrence of persons with low

vision in comparison with the number of persons with complete loss of vision.

Vision is a very complicated and complex process based on learning. It must be

seen in three basic dimensions—visual perception, visual cognition and visual performance. Visual perception is the process of obtaining input information to the brain.

Visual cognition provides the processing of obtained data through the CNS and visual

performance is the level of skill to use visual abilities functionally in specific activities, especially in critical situations.13 (Dickinson, 2002) A sufficient level of understanding anatomy, physiology, neuropsychology and their pathology is necessary for

professionals to increase performance through education and rehabilitation.



1.4



Anatomical and Physiological Aspects of Vision



The knowledge of the rules of anatomy and physiology of vision and their pathology

applied to the specific eye disease diagnosis is very important starting information for

the professional worker in the area of special education and rehabilitation. Such information makes it easier to communicate with the ophthalmologist, to understand the

nature of limitation of visual ability in every specific case, and, last but not least, also

to choose optimal educational, training and supportive strategies and techniques.



11



WHO statistical data (2001) show that ARMD is the most frequent cause of visual acuity loss in

persons older than 60. It is estimated that in the developed countries more than 2.5 million persons

suffer from it, with the annual increase of approximately 200,000 persons. However, the ARMD

generally does not result in total visual impairment, more often it results in moderate to profound

reduction in vision, i.e. loss of central vision and visual acuity (Sosna, 2002).

12

Similar data about the structure of patients with visual disorders are given in the analysis of

patients by the Centre of Visual Impairment in Prague (Centrum zrakových vad v Praze, CZV)

conducted on the sample of 622 patients (Moravcová, 2004).

13

The term ‘critical situation’ must be understood as a situation which is for the person visually

demanding or difficult to manage.



1.4



Anatomical and Physiological Aspects of Vision



11



This chapter summarizes the importance of vision rehabilitation of persons with

low vision with reference to existing professional information resources. Because of

the wide reference field of this presented work, we do not include the issue of anatomy and physiology of vision, characteristics of eye diagnosis or the ways of clinical examinations which have been well described by a number of other authors.14



1.4.1



Basic Visual Functions and Disorders



Vision is a very complicated and complex process based on the synthesis of the

abilities of visual analyser. From the ophthalmologic point of view, the basic functions of vision are acuity, width of visual field, colour discrimination, contrast

sensitivity, spatial vision, resolution and adaptation to light and darkness. In terms

of rehabilitation, the basic precondition for every educational and rehabilitation

intervention is complex diagnosis of visual ability.

Central visual acuity is defined as the ability of the eye to perceive clearly and

sharply objects and their details. The key component is the ability to distinguish two

points. An important role is played by the correct ratio of refraction of optical environments and sagittal length of the eyeball. Deviations from the norm are called refractive

disorders (myopia, hypermetropia, astigmatism, etc.). The ability to have sharp vision

at various distances is ensured by the accommodation of the eye. Its basic function is

mainly the accommodation of near vision. The diagnosis of central visual acuity is

measured with acuity tests. In problematic cases, it is suitable to examine near vision

acuity with the help of special acuity tests (for instance, texts of graduated scale of sizes

or other non-alphabetic characters).15 Visual acuity also depends on other variables

such as intensity of illumination. With increasing intensity, acuity increases up to the

limit of glare, after it acuity decreases again (Pokorná, 2000).

Visual field (VF) represents the sum of all points displayed on retina when the

eye does not move. Boundary is defined by the rim of the orbit including the eyebrows, nose, cheeks and eyelids. Visual fields of both eyes overlap about 60° around

the fixation point, thereby enabling stereoscopic vision (Kolín et al., 1994). Visual

field can be classified into central (up to 30° from the fovea) and peripheral. The

function of peripheral vision consists mainly in spatial orientation and vision in low

light conditions (scotopic vision). Transition from photopic vision (retinal cones) in

the centre to scotopic vision (retinal rods) at the periphery is gradual. With closer

distance to the periphery, the ability to distinguish colours decreases (first the ability

disappears to perceive green, then red; blue and yellow are perceived for the longest

time); visual acuity is also gradually decreasing (Kvapilíková, 1999).

14

Kraus et al. (1997), Kolín et al. (1994), Řehůřek (1997), Divišová et al. (1990), Řehůřek, 1997;

Koukolík (2002), Kulišťák (2011), etc.

15

The most frequently used tests of visual acuity are: Snellen charts, LogMAR charts, Pfluger

hooks; for near acuity: Jaeger charts, LogMAR charts, Lea Hyvärinen test batteries (Kraus et al.,

1997; Moravcová, 2004).



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Visual Impairment and Its Impact on Development



Visual field disorders occur as the result of damage to retina, visual pathways or

brain centre, paralysis of upper eyelids or in connection with severe limitation or

exclusion of the function of one eye. Another reason of visual field limitation can be

the use of spectacle correction and special optical devices. Deviations in visual field

can have the following character: concentric narrowing (the number of degrees

decreases from the periphery to the point of fixation), central field loss (scotoma),

hemianopia (loss of one half of the VF), quadrantanopia (the loss of vision is located

in the area of brain damage). In other cases, it is possible to observe a variety of

shapes and locations of vision loss throughout the entire visual field (Kolín et al.,

1994). Central scotoma causes complications especially in near-distance activity;

concentric narrowing, on the other hand, causes difficulties especially in spatial

orientation and mobility. Scotoma can be relative (reduced quality of images) or total

(vision is excluded in the place of scotoma). For the examination of vision field,

kinetic and static perimetry is used.16 Some visual disorders can affect the reality

of image. In such case, image distortion (metamorphopsia) has to be examined17

(Kraus et al., 1997).

Eye movements are performed by six extraocular muscles, which control the

movements in nine visual directions. Binocular vision is defined by KvětoňováŠvecová (1999) as the coordinated sensorimotor activity of both eyes enabling to

create a simple spatial image (stereopsis). Such a connection is the prerequisite of

depth (spacial, three-dimensional) perception. Different visual acuity in the two

eyes (or other obstacles) causes the inability to link the images of both eyes into a

single binocular image (fusion) (Kraus et al., 1997). As a result of the perception of

image without stereopsis, the perception of objects becomes the most affected

area (secondarily also the formation of concepts is affected—especially perception

of space, sensorimotor coordination and fine motor skills of the hand) (Vítková,

2004). New researches into the functions of human brain show that the threedimensional perception of objects largely depends on visual learning from a very

early age (Koukolík, 2002).

The most common eye movement disorders are strabismus in childhood and

gaze palsies in adulthood. In case of strabismus, only one eye may be affected, or

both eyes alternate in fixation and deviation. ‘Eye movement disorders lead to the

reduction of sensation in one eye which is subsequently fixed as amblyopia or diplopia in adulthood’ (Kraus et al., 1997). If a visual disorder develops in the dominant

eye, spatial vision gets disrupted; often the problem is also the difficulty of the

patient to refocus on the use of non-dominant eye. In such case, it is necessary to

indicate the occlusion of the dominant eye for near-distance visual tasks (Moravcová,

2004). Binocular vision examination is performed by examining ocular fundus and



16



Modern kinetic perimeters include for instance Goldman chart and Hart chart. Both types allow

the adjustment of light intensity and colour of fixation point. They also allow the examiner to

observe the sequence of patient’s fixations (Kraus et al., 1997).

17

For a preliminary examination of deviations, Amsler Grid can be used.



1.4



Anatomical and Physiological Aspects of Vision



13



detecting deviations. Both diagnosis and actual training of simple binocular vision

are carried out on special devices by orthoptists (Květoňová-Švecová, 1999;

Divišová et al., 1990, etc.).

Colour perception is a process based on the activity of photosensitive cells in the

retina. The irritation of retina by the light signals of different wavelengths of visible

light stimulates cone cells. This means that colour perception is affected by the

impact of the distance of an image from the macula. The central part of retina allows

for a more accurate colour perception, towards the periphery the ability gradually

declines (Hofmannová, 1993). In terms of biochemistry, the pigment rhodopsin is

responsible for colour vision. It is found in cone cells and contains three components capable of reacting to various electromagnetic waves in the range of visible

spectrum. Researches have shown that humans are able to recognize more than 150

colours and altogether about 2000 shades.18 The diagnosis of colour perception can

be performed through various methods. The most frequently used include isochromatic and numerical methods, letter charts and test batteries of shades of colour

spectrum19 (Kraus et al., 1997).

The quality of colour discrimination is also influenced by external factors (light

intensity, hue, colour saturation, brightness and contrast) and related adaptation. In

this context, many persons with low vision lose the ability to accurately recognize

the subtle shades of colours. At very low levels of light, the eye cannot distinguish

colours at all (Macháček, 2002).

Adaptation of the eye is the ability to adjust to different light intensity, i.e. the ability of the eye to change the threshold of sensitivity to light. Adaptive capacity is

determined by the regeneration and synthesis of visual pigments in the retina. At a

higher light intensity, dominant function is taken over by cones (photopic vision);

during transitional period (in deteriorated lighting conditions), it is a synthesis of the

function of cones and rods (mesopic vision); at low levels of light, the function of

cones is being phased out and rods take over (scotopic vision). For the examination

of adaptation to darkness, adaptometers are used.20 The result of examination is

adaptation curve. During the examination of adaptation to glare, central acuity is

being tested under standard lighting conditions. It is followed by dazzling the eye

with the ophthalmoscope, and time is measured how long it takes for the patient to

read the same line of optotype (Kraus et al., 1997).

Permanently increased or decreased sensitivity to light and contrast occurs in

many persons with low vision. There are two types of the most frequent adaptation

problems: nyctalopia (night blindness) and photophobia. Adaptation process can be

disproportionally long or adaptation can take place only partially or not at all

18



Based on the research, two types of colour perception are further differentiated: dominator (irritated by the whole spectrum of wavelengths in visible spectrum) and modulator (responsive only

to a certain narrow range of wavelengths—blue: 450–470, green: 520–540, red-yellow: 580–

600 nm) (Oláh et al., 1998).

19

The Farnsworth Munsell 100 Hue Test, Lanthony 40 Hue Test, etc. (Kraus et al., 1997).

20

For instance, Hartinger adaptometer (Oláh et al., 1998).



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Visual Impairment and Its Impact on Development



(Jesenský, 1994). In such cases, it is necessary to use additional tests for diagnosis

to specify the quality of the recognition of faces, traffic signs, etc. in various lighting

conditions (Kraus et al., 1997).



1.4.2



Visual Cognition and Its Disorders



The process of vision, beginning on the retina of visual analyser, transforms the

image into a neural image; its final quality depends on the quality of information

processed in brain centres. An important role is played by learning, previous

visual and other experiences, but also other factors (emotional state, will, etc.).

The ability of visual perception and cognition and its disorders caused by brain

damage is considered a very important part of the comprehensive approach to vision

rehabilitation. The process of visual analysis proceeds in two stages. The lower

stage—discrimination—ensures the resolution and recognition of objects based on

their basic qualitative properties. The higher stage—differentiation—evaluates also

other features, reactions, position and complex properties of the object. Synthesis

concerns the developmentally higher process of generalization, which builds on the

analysis (Jošt, 1998). Disorders of the cognition of persons, things and their importance or spatial relations through an otherwise intact eye are clinically defined as

visual agnosia. Object agnosia has, according to Lissauer (in Koukolík, 2002), two

basic forms. Apperceptive agnosia: visual cortex distinguishes essential components of the observed stimulus, but cannot integrate them into a meaningful whole.

The difficulties are evident in distinguishing between simple and complex drawings

or fonts21 (the person is unable to perform tasks in imagination based on spatial rotation; however, he/she is able to distinguish the basic geometrical shapes). Associative

agnosia: the obstacle consists in the impossibility to assign a correctly identified

stimulus to the appropriate concept (the person can distinguish a stimulus and its

individual features; however, he/she cannot name it).

Recognizing shapes (geometrical, numeral, alphabetic symbols) When diagnosing such a disorder, it is necessary to eliminate the situation where the failure can be

caused by a poor quality of visual material.

Three-dimensional perception depends very much on visual learning in early

childhood, when visual system is still very pliable. To recognize specific shapes of

buildings, faces or letters, cortical areas were found at the border of occipital and

temporal cortex on the inner surface of hemispheres. Visual stimuli are processed in

such a way by the brain so that certain types of neurons respond to individual

features of the object (shapes, direction of movement, spatial depth, colours). There

are visual areas at the rear part of temporal cortex which perform synthesis and

compare it with the record in long-term memory.



21



One form of it is ‘word blindness’ (alexia). Such a person can write but not read written text

(Otradovec, 2003).



1.4



Anatomical and Physiological Aspects of Vision



15



Visual differentiation is a comparison of two or more two-dimensional or threedimensional shapes/patterns.22 The diagnosis of the ability of visual differentiation

from the point of view of functional assessment is focused at the first stage on the

ability to distinguish differences. At the second stage, it is performed under similar

conditions as in the previous case and is aimed at the determination of boundaries

of the ability to distinguish detail with regard to environmental conditions.

Recognizing colours An important quality of visual parts of the brain is the ability to attribute constant colour to the surface of various objects regardless of the type

of lighting. The existing research has shown that the brain processes colour stimuli

in three stages: stage 1 is characterized by the activity of primary visual cortex,

which registers the presence and intensity of the colour components of the stimulus

and distinguishes different wave lengths of light from the retina; stage 2 takes place

in the remotest area of visual cortex and is dealing with the problem of colour constancy; stage 3 deals with the colours of objects and takes place in the lower parts of

temporal cortex and frontal cortex23 (Šikl, 2012).

Recognizing movement When a movement is registered at the periphery of

visual field, the saccadic transfer of attention to this particular object occurs. This

brings the object into the central visual field where it is examined through slow

tracking movements. According to Atkinson et al. (1995, 181), ‘the human eye

can much better perceive movement on a structured background (relative movement) than on a dark or neutral background (absolute movement)’. Motion perception disorder (akinetopsia) is a rare disorder associated with a limited ability

to determine the direction of movement.24 A specific form is the unilateral spatial

agnosia in which everything is ignored which happens in one half of visual field

(Otradovec, 2003).

Recognizing face raises complex brain activity, part of which is also assigning

the name to the person. It has been proven that the ability to recognize faces has no

relationship to the ability to recognize other objects. ‘Prosopagnosia is the failure

to recognize human faces which is a consequence of brain damage’25 (Koukolík,

2002, 55). The corrective educational techniques are, in case of all types of agnosia,



22



The category of differentiation includes for instance the ability to recognize persons by appearance

(Koukolík, 2002).

23

Problems with colour recognition are described in professional resources as: cerebral achromatopsia (syndrome of partial or complete loss of the ability to see colours as a result of brain

damage); colour agnosia (the person sees colours but cannot distinguish them); colour anomia

(the person sees colours but fails to name them) and dyschromatopsia (person confuses colours)

(Koukolík, 2002).

24

Topographical disorientation is a diagnosis indicating loss of orientation in a familiar environment.

However, this is not a perception disorder but a cognitive one (Koukolík, 2002).

25

The person recognizes a face without being able to distinguish it from other faces. In some cases,

the recognition of parts of the face and facial expressions fail. Another time the failure occurs only

in relation to recognizing new faces. This category does not include face blindness disorder caused

by memory disorder.



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Visual Impairment and Its Impact on Development



based on the support of perception through other senses and the characteristic

context of recognized objects.

In visual images, two thirds of similar cortical areas are activated as in visual

perception and cognition. Regarding primary visual cortex, it is important what

kind of task is being solved here during the creation of visual image. However,

visual cognition and images still represent two different systems.26 Similar areas of

visual cortex are also activated by visual hallucinations (for instance, Charles

Bonnet syndrome and Alice-in-Wonderland syndrome).27 Recommended corrective

procedures for training visual imagination in persons with visual perception are

techniques of finding shapes or patterns in a tangle of dots or lines, filling in the

missing parts of letters, etc. (Koukolík, 2002).



1.4.3



Visual Attention



Visual attention is a part of the complex system of attention defined by Šikl (2012) as

a dynamic regulatory, control and coordinating function characterized by selectivity,

concentration and focus of mental activity of the person. According to the theory of

Treisman (1986), certain types of visual processing are carried out automatically;

other arrangements of elements in the reference field evoke the reaction of focused

attention. The first type of analysis is called ‘search for an outstanding feature’; the

second type ‘search for a combination of characteristics’. According to this theory, it

is possible to conclude that vision at early age saves some simple and useful properties of the observed scene into maps which can preserve the spatial relations of what

was seen; however, the maps are not able to use the information in subsequent processing stages. Instead, it is the focused attention which selects and combines the

characteristics presented in various locations. In later periods, integrated information

serves to create sets of perceived objects; the contents of set are compared with the

description stored in the cognitive network (Kulišťák, 2011). The assessment of extent

and quality variations in abilities belongs to the domain of neuropsychology. Apart

from determining the actual ability as such, the diagnosis of the use of functional visual

capacity is also important (it points to the level of effectiveness of the use of individual

abilities in activities of daily living). In rehabilitation of persons with cortical visual

impairment (CVI) developed in adulthood, it is necessary to respect the recommendations of neurologist (Moravcová, 2004).



26



This is proven by cases when persons cannot recognize objects visually but they can imagine

them visually, whilst others are not able to form the visual image of an object which they visually

recognize.

27

Bonnet syndrome develops after an eye disease. It is associated with several types of visual hallucinatory experiences: hallucinations of landscapes and persons wearing hats, hallucinations of

grotesque or distorted faces, etc. Visual hallucinations of Alice-in-Wonderland syndrome are characterized by a bizarre distortion of visual perception (Kulišťák 2003).



1.5



Psychosocial Aspects of Visual Impairment



1.5



17



Psychosocial Aspects of Visual Impairment



Vision is an important source of stimuli necessary for the harmonious development of human psyche. Reduction or exclusion of visual control causes sensory

deprivation with difficulties at the level of activity, cognition, understanding and

experience.

Vágnerová (215) defines personality as ‘a relatively stable system of interconnected somatic and mental functions which determines the experience, thinking

and behaviour of the person’. This determines the relationship of the person to

society and environment, both of which further affect person’s development and

position in society.

Psychology of persons with low vision (CZ—psychologie osob se zrakovým

postižením) deals with the specific influence of visual disorders on mental development of the person. The aim is to detect the patterns of optimal mental development

and to maintain mental health under the influence of various types and forms of

visual disorders or defects. It is specifically important for persons with acquired

disorders as it helps to overcome the negative consequences of the loss of perfect

vision.28

The understanding of the specifics of development of the personality of individuals with visual impairment can be approached on the basis of a number of criteria

which can facilitate an understanding of both internal and external determinants of

development: level of person’s development, characteristics, current conditions and

situational variables.29

Depending on the level of impairment, age at the time of its occurrence and

other indicators, tendencies can be predicted as to the changes in development of

cognitive processes as well as changes in lifespan emotional development. Such

changes can in turn influence self-esteem, performance, social relationships, career

and other important areas (Vágnerová, 1995).



1.5.1



Specifics of Cognitive Processes



Litvák (1979) states that the study of the psyche of persons with low vision can be

successful only when supported by the results of general, developmental and educational psychology. A number of patterns discovered by general psychology find its

confirmation in the development and manifestations of the psyche of persons with

visual impairment.



28



Souček (1992, 23) states that ‘severe visual impairment in adulthood should not have a major

impact on the change of personality’.

29

More specifically was the issue dealt with by Langrová (2005).



18



1.5.1.1



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Visual Impairment and Its Impact on Development



Perception



Visual perception provides most of the information on the basis of which the person

creates a more complex picture of the world. It is mainly the recognition of processes

associated with one’s own organism, objects and properties of the environment, relationship between them, occurring changes, movement, etc. The processing of sensory information is a prerequisite for purposeful activity enabling situational adaptation

(Nakonečný, 1998). If we understand perception as a complex process of selection, classification, interpretation of certain stimuli and their integration into an existing information system, then reduction in the quality of visual perception presents a problem

immediately in the initial stage of the described process.

The quality of visual images is based on the degree of globality and accuracy of

visual stimuli which a person can perceive and further specify on the basis of information obtained other than visual way. Nakonečný states: ‘For the description and

characterization of a perceived image, the term “phenomenal world” was coined to

express its individually typical depiction. The variable change of sensitivity may

then be reflected for instance in the group of persons with low vision, colour blind

persons, etc’, The development of vision on the basis of visual learning occurs differently in children with congenital disorder and persons with later acquired visual

disorder. Children may, at the level of inadvertent use of visual potential, get only

very little of sufficiently specific and structured information, which is often quite

insufficient for the development of visual imagination and memory. They therefore

have to learn how to build and use visual memory with the help of adaptive techniques.30 The level of imagination of an individual with congenital visual impairment depends not only on the degree of visual functions, but also on the level of

built-up capacity for visual learning, imagination and memory (Růžičková &

Hordějčuková, 2015).

With regard to learning and use of visual memory, persons with acquired disorders,

with their visual memory built on concrete and precise visual images, are in a different situation. They can use images perfectly well even in case of imperfect visual

sensations. It is therefore clear that an already existing visual memory has a distinctive potential which has to be supported by a purposeful, systematic training of

visual stimuli decoding and assigning to existing visual images. Persons with low

vision may have different threshold levels of sensations. The thresholds were classified by Nakonečný (1998) into four basic types: lower absolute threshold, upper

absolute threshold, difference threshold and movement registration threshold.

Sensation thresholds change during development; they correspond with the overall

level of activation and are influenced by learning and training. Extreme changes can



30



Barraga (1976) states that ‘the ability to create visual images and the development of visual

memory in children with low vision is a developmental issue. It is a complex pattern of learning

within which the child learns to track objects especially “for near”, with the support of information

modification and thus also stimulation of visual pathways in the brain. Accumulation of visual

information and their later differentiation enables also development at the level of reverse recalling

of previously acquired images and memories.’



1.5



Psychosocial Aspects of Visual Impairment



19



be achieved through the use of pharmacological therapies. Sensation thresholds can

also shift due to the irritation of other senses.

The issue of persons with low vision in the CR was specifically studied by

Ludíková, 2005; Langrová, 2005; Vágnerová, 1995. Sensation thresholds may be

affected by visual disorders especially in the area of visual perception. The lower

threshold can be shifted or is variable under environmental conditions. The upper

threshold is in many cases negatively affected by reduced adaptation to light and

darkness, high glosses, etc. Also the difference threshold and movement registration

threshold are in most cases less sensitive. Differences in stimuli must be more distinctive, movement must be slower and executed in a certain minimal range; very

fast movements often cannot be perceived at all. In contrast, sensation through other

senses tends to be more sensitive, particularly with increasing experience. The reason is the principle of compensation when a person perceives and focuses attention

on the stimuli which are accessible and understandable.

Reaction time tends to be prolonged in the process of perception of persons with

low vision. Nakonečný (1998, 171) defines it as ‘the time that elapses from emergence

of the stimulus to response to it’. The reaction time depends on the condition and function of the receptor, the current level of mental activation, the intensity of acting stimulus and other factors.31 The response must be preceded by orientation in the situation

and the choice of the type of reaction (Langrová, 2005). Even in the case of ‘slow’

decision, the person is disadvantaged because of the limited possibilities of visual

control and sensation. During a swift decision (which in a number of situations may

involve also security risk), persons with low vision are forced to respond on the basis

of an insufficient quantity and quality of both visual and compensation information;

therefore, a mistaken or imprecise response is more probable.

Objectivity of perception is defined as assigning perceptions to the already known

in the holistic context of the environment (Atkinson et al., 1995). If we relate this

theory to the reduced visual perception of persons with low vision, two reactions

may occur: If the person is able (using experience, cognition, etc.) to assign the

stimulus to a particular object through visual perception, then he/she can further

work with it in a more specific way (the information helps to analyse object’s characteristics); if the person is unable to assign the stimulus, he/she may attempt to gain

information by purposeful behaviour (by reducing relative distance, by lighting,

eventually by using other sensory analysers). If the stimulus remains in the area of

unassigned sensation, it cannot become a sensation with its above listed information

competences. Beliveau and Smith (1980) published a similar theory of visual cognition

of persons with low vision.32



31



For example, figure-ground contrast, speed of induction and remission extent of changes in stimulus (Nakonečný, 1998).

32

They rely on the research results which correspond to three conclusions concerning the recognition of objects and images: creation of an internal image of the object or memory of it is a very

slow process, proceeding in qualitative phases. Specifically, it is collecting single pieces of knowledge about the properties of the object; the properties of the object are what provide most information; memory traces recording these properties together form the overall internal image.



20



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Visual Impairment and Its Impact on Development



The influence of expectation and context of perception were described by

Vágnerová. The way how the object is perceived depends on the context which is

further specified in time and space. Based on temporal context, what scenes will

follow can be guessed; based on the context of space, for instance, the presence of

objects can be guessed, etc. (Atkinson et al., 1995). The described qualities of perception can make it easier for persons with low vision to perceive environment (for

instance, the person can guess on what he/she should focus their visual attention).

Spatial context greatly assists to perceive individual details, but only if the person

has enough sensations and information to use in the process of perception. In contrast, the tendency to perceive expected, not real, can cause errors in perception

(Nakonečný, 1995). Therefore, it is important to lead persons with low vision during their education to the targeted verification of vague perceptions through other

control mechanisms.

Synergy of perception is defined as the ability to perceive sensations through

more than one sensory analyser. Then, the perception at a particular time is usually

complex (a synthesis of sensations: visual, acoustic, olfactory, tactile, kinaesthetic).

The inadequacy of visual sensation is often accompanied by sensations from other

sensory receptors. The use of the synergy of perception in various situations of daily

living is the subject of learning and gaining experience (Jesenský, 2007).

Social perception is defined as a characteristic intervention in the perception of the

world through the environment of culture in which it occurs. Based on the experience

of recognition of other persons’ behaviour and their reactions and experiences, orientation structures emerge which influence judgements for the next similar experience.

The evaluation of an impression becomes a basis for taking a certain position and a

more or less adequate response. The ability to understand social expressions is called

social intelligence. The reduced possibility of visual control of social situations is

considered to be one of the major communication barriers.33 It is important to register

the specifics of perception based on social communication in both its components:

verbal and non-verbal. Language names the perceived and allows its categorization.

On this basis, conceptual logical thinking is developed. Through language and speech,

the process of communication, mutual exchange of information and sharing of experience occurs (Nakonečný, 1998).

For persons with severe visual impairment, the use of language is irreplaceable

compensation means; however, only provided that they can sufficiently understand the

content. Linguistic means can support the creation of images of an object, the understanding of ongoing processes and they can also help to understand the changes and

limits of persons’ vision and learn how to effectively compensate for them (Galvas,

2002). However, to bring verbally acquired knowledge into precise and complex relationships (for instance, through learning) is a very demanding process. The problem is

not only knowledge as such but also the creation of most accurate real image which is

necessary for the retention and recollection of an adequate response. A partial or total

unavailability of the perception of non-verbal components of communication affects

the form, process and significance of the message. Unless persons with limited visual

33



Similarly, sociological surveys also show that the fear of social communication is one of the most

frequent causes of the limitation of human activities (Pluhařová, 1999).



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3 Frequent Reasons of Reduction or Loss in the Czech Republic

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