Vision for Doing
Assessing Functional Vision of Learners who are Multiply Disabled
Chapter 7 Assessing Vision for Doing
Section 13 Responses to Objects in Visual Field
Aims of Section 13
In this section we try to explore a little bit more the learner's field of view. In Section 10 you did this in passing. However, Section 10 still concentrated on the area of the learner's field of view which is around the centre. In this section we move away from the centre to the periphery. Because we are interested in looking at the periphery, to consider peripheral vision and what is known as peripheral visual field testing.
For most tasks, it is helpful to know whether a learner is seeing all positions or only certain areas of his surroundings. As we will discover, restriction of the visual field may result in only a small area at the centre in front of the learner being seen, with the learner not perceiving any position surrounding this central area. Or, as is common with learners who have severe physical disabilities, there may be certain areas of the periphery which are 'blank'.
How to use section 13
Try to avoid using materials that are so large that they take up too much of the visual field. At the same time you need to use materials that you have found may be seen by the learner. You need not use a ball, instead use any object which is well contrasted. Often it is best to begin with a small light source such as a pen torch. Use different coloured filters if you like. If successful try smaller objects. Other objects might include a ping-pong ball stuck on a thin rod, finger puppets or a favourite toy. You may have to suspend the object on invisible thread. You can always come back and try again using a smaller size of object you find (from Section 15) that he is able to see. Be flexible and be prepared to try again another day.
What to observe
Turn to diagrams 13a and 13b. These are very similar and we will shortly deal with them together. Later on we will deal with Section 13c. It has a slightly different emphasis, and we will therefore return to it immediately after discussion of Sections 13a and 13b.
To carry out these you will require a helper. One person stands behind the learner and presents the objects. The second person tries to gain the learner's attention. If this is not possible, the second person needs to notice the direction of the learner's gaze at the time the object is presented.
For your observations of the learner you will be using those parts of both diagrams which lie above the dotted line. Each diagram consists of two drawings. The one on the left shows how to bring an object into the visual field. The diagram on the right shows a person's head, surrounded by the Numbers 1 to 6. These numbers indicate positions in space. For 13a, the positions are above eye level. For 13b, the positions are below eye level.
Stand behind the learner. Slowly introduce the object from above or below on the left or the right side, around 20 cm from the eyes. Choose the side of presentation randomly so he does not anticipate on which side it will be presented. Repeat to vary the distance of the object from the learner's head.
Gain the learner's attention. If you cannot gain his attention, try to notice the direction of his gaze as the object is introduced. Watch for any response indicating that the object has been noticed. The response might consist of a flick of the eye in that direction, a head turn or something more obvious such as reaching out to the object. Note the position of the object at the time it was noticed by the learner (Numbers 1 to 6).
Belowthe dotted line there is a little table. On it record the results of your observations. This is where to record whether the learner responds to the object and in which positions. If you are sure the object has been noticed, tickConsistently. If inconsistent, tickOccasionally ; if not noticed, then tick Never. (If you find it easier you may want to ignore the table and record the results of your observations alongside the numbers themselves). So,
ticktick to indicate Consistently;
tick to indicate Occasionally;
0 to indicate Never.
Choose the system that is most convenient to you.
The most difficult instruction to follow is that while making observations, you need to take into account the direction of the learner's eyes. If the direction of eyes is pointing off to one side, then you will need to think of the Numbers 1 to 6 in positions corresponding to this direction of gaze. This may lead to inconsistent results, so take your time and, if necessary, return to try again.
As we stressed before, remember not to allow previous items to influence subsequent items.
Transferring Results to Section 18:
As with the other sections, you now have to decide what the results of your observations mean for the Summary Chart in Section 18. In that Summary Chart, you will find that in the row for Section 13a and 13b there is only space to tick under Aware, and Attend. Section 13c allows Aware, Attend and Localise. The other boxes are shaded. This is because any general response by the learner to an object's position in the visual field cannot tell us.
Restriction to an area of the visual field means that, should the learner respond to areas outwith the restricted area, this may occur because it is the only area in which he is aware of objects. It does not follow that he can Localise. He may still only Attend.
Of course, if he should make a very specific response (eg; naming the object being presented), this would mean he could Recognise through vision. Additional information would be needed if you are to tell that he is doing more than Attending. If you have that kind of extra information by all means tick boxes in the filled areas as appropriate.
No response in visual field?
If the learner Never shows any visual response to any of the positions in 13a and 13b, try again on subsequent occasions with different objects and in different lighting conditions (that is in other Settings). You should still try the remaining sections in this chapter. If these too result in Never you should refer back to the curriculum suggestions in Sections 9, 10, 11 and 12. You may also want to try Section 14, 15, 16 and 17.
OR score attend if:
OR score attend if:
he notices objects Consistently in one or more of the positions shown. In this case go to the Summary Chart (Section 18), find row 13a or b, and tick Attend. Note for your own records any positions that present difficulties. You will probably want to return to the suggestions for curriculum development given in this present Section. But you should still try Section 13c.
OR score aware if:
the learner shows no consistent responses, but there are tick Occasionally. If so, go to the Summary Chart and tick Aware . Then move on to Section 14. In this case you may well want to return and use the curriculum suggestions given in this present Section.
Where to go now?
Having noted the results of your observations and transferred these to the Summary Chart, you are then ready to make a choice. The choice you make will depend on the results you obtained.
you can skip the suggestions offered for developing the curriculum,and move on to carry out Section 13c. By doing this you will continue your assessment of the learner's use of Vision.
postpone further assessment and read the remainder of this section. In it we suggest activities for curriculum development.
Developing a curriculum
What is a visual field?
For learners who are multiply disabled, it is quite common to find gaps in the 'visual field' of one or both eyes. Visual Field means simply that part of the surroundings the learner can see without moving eyes or head. It extends up and down, from left across to right, and from near to far. (Usually the latter is ignored and, in any case, different parts of this chapter deal with distance).
Often no indication of visual fields is mentioned in any background information on a learner (you can refer to Section 2 to find out if this was true for your learner). The reason why a measure of 'visual fields' is not usually available for learners with multiple disability, is that it is often extremely difficult to obtain an accurate measurement. The kind of accurate measurement which is aimed for by ophthalmologists requires a fair degree of cooperation on the part of the 'patient'. It may also require a high level of understanding, consistent and reliable responses, and often rather quick reaction times. You can therefore see why accurate measurement of visual fields is not often available for the learner who is multiply disabled.
The method you are using offers no more than an approximation. That approximation will, none the less, be useful in your identification of any significant field losses. This in turn will help you to understand why it is that the learner displays certain unusual behaviour or has difficulties in particular tasks. Using the procedure outlined will also assist you in optimal design and presentation of materials.
This question is a bit like asking "How long is a piece of string?" Impairment to one's visual field can have a number of effects on everyday activities:
- on reading and writing;
- on perceiving a whole object or picture;
- mobility may be affected; tripping over obstacles or falling down stairs;
- if communication by signing is used, the person may only see the other's hand movements within a very small area.
Different visual field defects will produce different effects. A few of the most common visual field defects are shown in Figure 7.13.1.
This is a common type of visual field defect known as hemianopia (from the Greek where hemi = half; an = not; opia = sight). Notice that it is the same area of both eyes that is blanked out. This is because the visual field defect is located in the brain. This can be the result of a stroke in which, if the right side of the brain is affected, the left side of both fields of view will be lost.
The hemianopia can occur to the right or left side as well as to either the top or bottom half of the visual field. So for example your results for Section 13a might show Never or Occasionally being Ticked. Whereas results for Section 13b might show Consistently being Ticked. This would indicate an hemianopia in the upper half of the visual field.
Here we see that instead of half of the visual field being affected, a quarter of the field is affected. Again the defect is the same in both eyes. If this was the case with your learner then you might find that for Section 13a Numbers 1, 2, 3 Never applied. For Section 13a and Numbers 4, 5, 6 Consistently would be Ticked. For Section 13b Numbers 1 to 6 would all read Consistently.
In this Figure there is a subtle visual field defect. It is where a small part of the visual field has a blank spot. This is usually known as a scotoma. It is one that you may not detect as its discovery requires sophisticated equipment, cooperation and a good level of understanding by the learner. Even with sophisticated extremely expensive equipment, it may go undetected. In some instances, more than one, or indeed several, such scotomas may exist. This is commonly known as "Swiss cheese vision" for obvious reasons. In the latter case, it is usually easier to test, and such results may be available from medical records.
A scotoma may be present in one or in both eyes. If in both eyes, the scotoma may occur in the same place or in different places. It may be present in the eye or in part of the network sending messages to the brain, or even in the part of the brain itself which deals with vision.
Just as the site of the scotoma may vary so, too, the effect on the person's visual field may vary. A scotoma may only be noticeable in unusual circumstances, such as when the person is extremely tired. Or it may be noticeable and affect the person's reading ability. Even a small blind spot in the area of the eye which deals with reading (known as the macular area) may have a significant effect. For instance here we have the effect on reading a paragraph of text of a small blind spot in the macular area.
Eve a small lind s ot in the rea of the eye whi deal with re ing (kno as the acular a a) may ave a s nificant e ect. For insta e here we ha e the eff of a sma blind in the m ular a ea on a p agraph of text
What did you notice about the text?
You probably noticed it was difficult to read! With those who have only visual impairment, reading is aided by checking back, by familiar words being recognised without having to actually see the whole word, by using eye movements, and through past knowledge filling in missing gaps. An unfamiliar piece of text containing scientific jargon would be much more difficult to read. The learner who is multiply disabled, especially with severe learning difficulties, will be at a great disadvantage. What is true for reading words and letter is also true when looking at symbols or pictures. Bits of the picture or symbol will be missed. If the learner has experienced this from birth or from a very early age, he will be even less likely to be able to tell you that there is a problem.
Another point to note is that the effect will change as distance from objects being looked at changes. The same scotoma which at normal reading distance blanks out 2 letters will, at 400 yards, blank out an area the size of a bus!
It is a popular misconception that the areas which are not functioning are like holes or black spots. This is not true. Instead it is as if the brain 'fills in' the area. In fact we all have a blind spot in each eye. This happens because the optic nerve, which carries the visual messages to the brain, has to leave the eyes at some point. This point becomes 'blind'. Yet you do not experience blind spots, except in very artificial conditions. Your brain has filled in the area1.
Because many learners who are multiply disabled have impairment to cognitive abilities it is likely that this "filling in" will be affected. To what extent the "filling in" is affected is not, however, clear. After you have read the rest of this section, you may wish to return to the short list above and consider what effects would be produced by different visual field defects.
Presence of other disabilities
Another important point to note is that the same visual field defect will have different effects in two different learners. This is because the severity of the visual field defect will depend on the particular combination of additional disabilities. Someone with a severe short term memory disorder, coupled with a visual field defect, will not be able to remember one part of a picture already looked at while he looks at another part of that picture. Whereas a learner who has no short-term memory problems will be able to integrate the whole picture in his memory. You may like to consider the different ways in which the field defects shown in Figure 7.13.1. would be compounded by different types of disability.
Having set out briefly the nature of visual fields along with some examples of different defects, we are now in a position to be a little more specific on suggestions for curriculum development.
To have an interest in this topic you will have found from the completed Summary Chart that the learner is only Aware. Vision will be limited to perception of reflected light. Similarly the learner's use of 'The Other Senses' will be functioning at the level of Awareness. Those most interested in this part of Section 13 will be working with people who have very severe difficulties in learning about the world. For the most part intervention will have to begin using Sections 9, 10, 11, 12 and 14. However, there are some general points that are worth mentioning at this point.
Compensate or Rehabilitate?
What we mean by this question is that you can either adjust materials and activities to suit the area which is missing from the visual field - compensating. Or else you can try to restore the part of the visual field that is absent by appropriate stimulation. A good analogy is to think of an orchestra. Suddenly, just before a concert, all the members of the string section die. What can the orchestra do?
It could compensate by changing the repertoire, avoiding pieces which demand a contribution from the string section. That is it could compensate. Or it could find new members who play strings and carry on with their original repertoire. That is it could rehabilitate2.
This is more straightforward, and would involve you avoiding presenting objects in the parts of the visual field that showed no response in your assessment. It is not so easy to do in practice as it entails keeping a constant vigil over how objects are introduced; from which side to approach obstacles; where to present pictures, symbols and words. The presence of physical disability to the same side as the field defect also compounds problems. For it may be that not only does the learner have difficulty moving an arm or hand, say, but lack of vision to that side means he cannot even see the arm or hand. It is truly a case of 'out of sight, out of mind'.
So although compensation is a valuable approach to take, it should not be done to exclusion. As a rule of thumb, unfamiliar events should be brought to the 'good part' of the visual field.
The reason why compensation is often emphasised with visual field defects is that most assume that a visual field defect is 'here to stay'. After all, if part of the brain is affected, what would be the point in trying to make it work? However, two examples should suggest that this view might be over pessimistic.
The first piece of evidence comes from California, the second from England.
The girl with no visual cortex
This child's eyes seemed to the ophthalmologist to be fine, but she was found to have no visual cortex. According to accepted opinion, the visual cortex interprets and makes sense of the information coming from the eyes to the brain: it is the part of the brain that 'sees'. Therefore without a visual cortex, the child should have been totally blind. But she is not blind. Her vision is by no means perfect, but she can use it for moving around her surroundings, for recognising many objects and for a number of other tasks. How can this be possible? It would be possible if other parts of this child's brain had taken over the function normally carried out by the visual cortex.
(Our second example, contained in the caption, describes animal experiments. Some readers may therefore wish to pass it over.)
You will be interested in this topic if the learner showed consistency in responses to one or more areas of the visual field. In addition the Summary Chart will have pointed to this as being the appropriate "level" of intervention.
Field defect or attention problem?
In the previous topic we indicated that there was another good reason for trying to establish seeing within areas of visual field defect. It is worthwhile because difficulty in attention can lead to apparently similar difficulties as a defect of the visual field. The learner acts as if the object is not there.
The best ways to try to improve attention difficulties of this type are to use:-
- events that are of interest (referring to the learner's preferences in Section 3). Occasionally introduce these events in the area corresponding to the visual field defect;
- pair the visual object with other sensory information - a simple trick is to use cat bells (from the pet shop) with a mirror or pen torch or other object;
- in the same vein don't forget passive movement of the hand (or foot) to touch the object.
Use of dark room
In a similar fashion to that described in Section 9, a dark room may be used to accentuate the presence of objects.
In this case, the Summary Chart will have suggested the learner to be functioning at Localising. You now want to ensure that intervention techniques are suited to this "level".
Using the learner's preferences
Refer to Section 3 and, using what you found the learner to prefer, try to arrange so that preferences are presented in various positions. Some of these should correspond to the areas for which you have observed defects in the visual field.
Use of computers
'Targets', which has been mentioned elsewhere, is a useful program for encouraging both location and recognition of objects. Use of a Touch Screen is optimal, offering a helpful routine for restricting the position of shapes on screen. This allows you to encourage visual scanning through head and eye movements to locate shapes on screen. By varying the foreground and background colours on screen you will also be able to identify appropriate colour contrasts. From this you will be able to arrange that some materials adopt these colour contrasts.
It is likely that many learners functioning at this level will not understand how to use a Touch Screen.
You will be interested in this topic if the learner showed consistency in responses to one or more areas of the visual field. In addition the Summary Chart will have pointed to Recognising as being the appropriate "level" of intervention.
When she drops an object out of her visual field then for that same object to reappear may seem to the learner like magic. Some have termed this the 'good fairy syndrome'. To avoid this and to help the learner understand that objects have permanence, encourage the learner to physically follow an object and recover it. This can be done by following the object with her hand; or have her move towards the object; or have her retrieve an object attached to a string. Note however, that you should not do this on every occasion. It is also important for the learner to understand that she can be rid of objects once she has tired of them.
You will be interested in this topic if the learner showed consistency in responses to one or more areas of the visual field. In addition the Summary Chart will have pointed to Understanding as being the appropriate "level" of intervention.
In this case, and with Recognising, it is less likely that an attention problem is masquerading as a visual field defect. It is more likely that it is a true visual field defect.
We mentioned earlier that a learner being signed to may have difficulty seeing signs made if there is a visual field defect. For instance, for those with dual sensory impairment ('deaf-blind who rely upon signing, visual field restrictions may mean problems in detecting sign language. One of the more obvious examples is that of a learner who has retinitis pigmentosa, a condition which often results in loss of peripheral vision. Unfortunately, around 3-7% of children born deaf will in later life (usually appearing first between the ages of 10 and 15 years) experience this kind of visual loss. The syndrome is known as Usher syndrome, and it is often characterised by poor balance. If you have a child who is congenitally deaf and who has poor balance, ask for a medical check, as this condition can be diagnosed through biochemical and electrical tests.
Without going into the details of visual angles, there is a useful and fairly straightforward way to determine the size of the communication field. Lea Hyvarinen, an ophthalmologist from Finland, suggests asking the learner to look at the signer's nose, and indicate when the signer's hands are seen moving from the periphery towards the middle. Repeat for each side and for above and below. In this way the signer more easily remembers the possible "working space" for signing to be carried out. Of course not all learners will understand that task. You may then resort to your observations carried out using the diagrams at the start of this section.
Relation of Visual Field to Mobility
One of the most important functions of peripheral vision is for safe navigation through the environment, thus avoiding sudden hazards. This is developed more fully in Section 17.
Section 13c Responses in Visual Fields (preferences)
How to do useSection 13c
Use a variety of objects. You will be using two at a time.
What to observe
It is also useful to determine whether the learner has a particular visual field which is preferred. Objects may be preferred in one area over others. Refer to the diagram on the previous page. During the course of several sessions, place two items in two different quadrants in front of the learner. This is shown in the diagram above the dotted line in 13c.
Try to distract the learner's attention while placing objects. Begin with a distance of around 50cm. Observe whether the learner consistently reaches for or fixates in a particular quadrant. This is another indication of preference for a particular field of vision. You can vary this routine by using two identical items placed in quadrants.
Where you do discover a distinct preference, the suggestions given in this section on encouraging attention will also apply.