Assessing visual function in children II: young children's vision Part 4 C-18705 O/D.
For very young children, cover test, evaluation of the Hirschberg reflexes (assessment of the alignment of the corneal reflexes) and prism fusion tests are the most useful measures of binocular vision, with stereopsis providing extra information. The benefit of measuring stereopsis extends beyond measuring binocular depth perception. Young children generally dislike occlusion for monocular acuity testing, but a study showed that as the success rate of accepting occlusion declines with age in infancy, the success rate of measuring stereopsis increases. (1) If monocular acuity cannot be measured but stereopsis is demonstrated, then providing binocular acuity is normal and there is no anisometropia, the practitioner can be reasonably confident in assuming no amblyopia. Possibly the most useful subjective test of stereopsis for young children is the Frisby Test, as it provides real depth in the display and does not require the child to wear dissociating spectacles. Simple modifications to the procedure have been described, including a 'reward' for correct choice, which allow infants as young as seven months to be examined (2) (Figure 1). Tests of convergence need an interesting target that the child will want to fixate. If the target approaches the child too slowly they may get bored and look away, giving the false appearance of reaching the convergence limit. Therefore, the test should be repeated with the target moving more quickly. The practitioner should also talk to the child to keep their attention. For more comprehensive descriptions of binocular vision assessment in older children, the reader is directed to the articles in OT by Bruce Evans (3,4) which can be viewed at www.optometry.co.uk
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Colour vision should be tested at least once in every child at as young an age as possible. Congenital colour vision defects cannot, of course, be treated, but they may have an impact on a child's educational experience, as well as their eventual career choice. A child's parents and teacher knowing of a colour vision defect avoids concern over delays in colour naming and prevents the child from being corrected for choosing 'wrong' colours in artwork or having difficulties with puzzles. In the early years in school, colour coding is often used to identify a child's belongings, their drawer or coat peg, and a child with a colour vision deficiency may need alternative approaches. In a child with visual impairment, colour coding and highlighting can be helpful in making tasks more visible, so a colour vision deficiency must be identified and appropriate advice given. Standard colour vision tests such as Ishihara plates can be used with ease for older children, while the "pathway" plates at the rear of the book can allow for assessment in younger children. If they are able to follow the pathway correctly, the practitioner can be confident that the child can discriminate the colour from the background and has "normal" colour vision. A new test has recently become available which makes colour vision testing easier with young children (even as young as two years of age). This is the Mollon-Reffin test, which requires a child to pick out a coloured chip from an array of grey ones of varying brightness (Figure 2). Using a paint brush and letting the child pretend to pick out the coloured paint pot turns it into an enjoyable game. The test identifies protan, deutan and tritan defects (the last of which cannot be detected by the Ishihara test), and has the added advantage of allowing the parent to understand what colour confusions the child experiences.
One of the pleasures of working in paediatric optometry is the time one gets to spend in toy shops. And it is for measuring ocular motility that the choice of toys is most critical. Very young children will, in general, fail to follow an uninteresting target (eg, the typical pen torch used with older children and adults) and all sorts of eye movement disorders may be (wrongly) suspected. Very young children may lose attention and glance away several times during a motility test, unless the target is sufficiently attention-grabbing. A target which incorporates movement and changes in colour may be needed, and it helps if the practitioner chatters away to remind the child to watch the target carefully. It is only if you see a difficulty in following the target when you know that the child is trying, that you can be confident in recording an eye movement problem. A child glancing to a distant target that happens to align with one eye may be mistaken for a divergent strabismus, or glancing to a nearer target mistaken for a convergent strabismus. Remember also that very young children can follow only slow moving targets, and ensure that the difficulty you are observing is not due to too fast a target movement.
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Most practitioners would consider visual field assessment only in children with unusual symptoms or children with particular special needs. It is worth noting that research suggests that 62% of children with unilateral cerebral palsy have a hemianopic-type visual field defect. (5) However, in order to become skilled in measuring visual fields in these few cases, the practitioner needs to gain experience with a number of typical children. Visual fields are difficult to measure in children, with only the older ones being able to co-operate with correct fixation for confrontation or an automated field screening. For many children, the tedious nature of the test precludes reliable results. Younger children may have an understandable reluctance to place their chin on the chin-rest of an automated machine, as well as having great difficulty in understanding the task at hand. Less high-tech procedures will be needed, limiting findings to only gross defects. Modifying the confrontation technique can be successful. One technique is for the practitioner to face the child and extend both arms so that the hands are invisible behind the child's head. Have a small toy in one hand and slowly bring the hands around in an arc whilst the child looks at you. Ask the child to tell you, or to point to, which hand is holding the toy. A second technique suitable for younger children relies on an assistant (which can be the parent) standing behind the child and bringing the toy around on one side or the other. The child begins by looking at the practitioner, but will hopefully spontaneously look towards the toy once it enters the visual field. Remember that if the child is sitting, this technique doesn't allow lower visual field defects to be investigated and it may be necessary to ask the child to stand up. Some 'well-behaved' children, when told to look at the practitioner, will do so no matter what target approaches, whilst other more distractible children find it impossible to keep looking ahead when they know that a toy is approaching. Hence the statement that visual fields assessment in children is difficult. The Lea Flicker Wand (Figure 3) is a flexible curved wand with a lighted end designed for visual field measurement in children. It can be held by the practitioner with the light initially behind the child's head and 'swung' so that the light enters the visual field along an arc.
Examining external aspects of eye health is usually straightforward. Allow the child to watch their eyes in a hand-held mirror as you examine them. Young children are naturally wary of putting their chin onto a chin-rest, so table-mounted slit lamp examination may be frightening. Consider investing in a hand-held slit-lamp for children (and domiciliary visits). Ophthalmoscopy presents a challenge. Imagine the procedure from the child's point of view. A stranger is going to get within touching distance of your face, in the dark. They will ask you to look at something and then they will put their head in the way so that you can't see it. They will shine a very bright light into your eye, which will dazzle you so that you can't see what this stranger is going to do next. Once you have grasped how the child feels, you will be able to modify your technique to make it less daunting. Use the parent standing in front of the child for fixation. If they keep talking, the child will know where to look even when your head is in the way. There is no need to complete the procedure in one marathon session. Try a quick glance to locate the disc, then pull away and praise the child. The next quick look allows you to examine the disc in more detail and then you can pull away again. You can proceed in this way, examining each part of the fundus in separate intervals. Few young children can keep their eyes still. An indirect ophthalmoscope can be useful in providing a larger field of view so that the practitioner can more easily keep track of the fundus landmarks. Whichever instrument is used, always keep your hand between the child's head and the instrument. Without this protection, if the child suddenly moves forward, they may unintentionally bang their head, or worse, their eye on the ophthalmoscope.
Planning the examination
Recording history and symptoms is clearly as important for a child patient as for an adult. Involve the child as much as possible, even if it is the parent who is reporting their concerns. Take all concerns seriously, don't appear dismissive. Make notes because it will be important at the end to return to the concerns and address each one. Check which eye a parent is referring to but be aware that some will get left and right mixed up. Check what a parent means by a particular word. To an eye care practitioner 'squint' means a deviating eye, whereas to some people it means "screwing up" one's eyes. As far as possible, try to observe the child doing what the parent describes. If the parent tells you that the child holds a book very close, then have a children's book to hand and give it to the child to check their preferred distance. If the parent tells you the child holds their head at a strange angle to look across the road, ask the child to look out of a window for you. Even before the talking begins, you can make a number of observations about the child's use of vision, as they walk into the room and explore their surroundings. Young children tend to have short attention spans. You may not be able to complete a full examination on one occasion, so be sure to prioritise the components of your examination according to the concerns expressed by the parent and to the mood of the child. If the parent is worried about an eye turn, then a binocular assessment and refraction are paramount. If the concern is lack of interest in reading then refraction and accommodation may take priority. The importance of the other components of the examination will become clearer as the results are obtained and the practitioner can decide whether they are best left to a second visit. A shy child may find visual acuity tasks daunting at first. It may be better to begin with more objective components of the examination until the child gains confidence. On the other hand, with an excitable, curious child, it may be better to begin with interactive tests like acuity and move on later to the more passive components when the child is calmer. Be sure to have a variety of formal and informal tests available. You may not be able to judge which tests are appropriate purely on the child's age. When examining children, there is no such thing as a "routine" and this is what many practitioners find so enjoyable about paediatric optometry.
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Preparing the practice
Optometrists wishing to attract young children to their practice should give consideration to the first impression created by the environment. There are no hard and fast rules, but try to see the practice through a child's eyes and create a welcoming atmosphere. Remember that children are small so imagine how your reception desk and furniture appear from very low down. You may want to consider a toy corner to occupy children while waiting. If so, place this well away from the children's frame display so that children don't confuse spectacle frames as toys. Restrict content to quiet activities (eg, puzzles and colouring) rather than allowing children to become excited by playing with active items. Remember that children may resent being dragged away from a toy corner to have an eye examination. Think about the equipment on display in your examination room. Is it unfamiliar and scary? Is it computerised and highly attractive to inquisitive fingers? Can you place unnecessary equipment behind a screen? Can you replace your information posters with children's pictures? Arrange your appointment book to avoid unnecessary waiting and to give flexibility. Some practitioners like to reserve one whole session per week for children. For older children, reserving after-school appointments can be useful. When the appointment is made, it may be helpful to discuss parental concerns and determine whether an extended or second appointment might be needed. Remember to allow time during the examination to explain what is going to happen and after the examination to discuss the outcome with both the child and the parent(s). Some children, particularly those with special needs, may be nervous. Consider allowing children to visit the practice before their first appointment, to meet the staff and see the room where the examination will take place. There are children's books about eye tests available so consider loaning a book at the time the parent makes the appointment. Some practitioners create their own leaflets especially for children. Staff training may be needed as not everyone has a natural rapport with children. Ensure that all members of staff are familiar with child protection issues and local protocols (see the College of Optometrists' guidelines on examining the younger child and consider studying the e-learning module on safeguarding children provided by DOCET). It is good practice to ensure that a child is never alone with a member of staff. This extends to the examination; ensure that a parent or guardian comes into the examination room with the child. This may not always be possible eg, a parent may need to take a distracting sibling outside, or an older child may not want the parent to accompany them. In this case leave the door open or have another member of staff join you.
In order to successfully test children, it may be necessary to purchase tests specifically designed for the age group. Of equal importance is the attitude of all staff, the practice environment and the approaches taken to make the entire experience child-friendly.
See www.optometry.co.uk/ clinical. Click on the article title and then on 'references' to download.
Module questions Course code: C-18705 O/D
PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on May 18, 2012--You will be unable to submit exams after this date. Answers to the module will be published on www.optometry.co.uk/cet/exam-archive. CET points for these exams will be uploaded to Vantage on May 28, 2012. Find out when CET points will be uploaded to Vantage at www.optometry.co.uk/cet/vantage-dates
1. Diagnosing a congenital colour vision defect in early childhood has the following benefits EXCEPT:
a) The defect can be treated
b) Teachers can understand a child's colour choice in artwork
c) Inappropriate career plans can be avoided
d) Alternatives to colour coding can be used
2. Measuring eye movements in children is likely to be more successful if the practitioner:
a) Moves the target very slowly
b) Avoids distracting the child by speaking
c) Uses a flashing colourful target
d) Uses a large target
3. Success in eye health examination of a young child may be improved if the practitioner:
a) Asks the child to sit as still as possible for as long as it takes
b) Asks the child to keep looking at an interesting picture on the wall, no matter what
c) Uses a slit-lamp and a Volk lens
d) Examines sections of the eyes in separate intervals
4. Practice preparation may include all of the following EXCEPT:
a) Allowing a child to visit beforehand to become familiar with the practice
b) Having toys in the dispensing area near the children's frames
c) Keeping computerised equipment out of sight or reach
d) Adapting the appointment system to allow extended examinations
5. When taking history and symptoms, it may be best to:
a) Talk only to the parent to ensure reliable answers
b) Correct any misunderstandings in the parent straight away
c) Record only the concerns that are likely to prove valid
d) Ask the parent to explain any ambiguous terms
6. During a child's examination, use the following guidelines EXCEPT:
a) Use a set order of procedures so that you cover all aspects reliably
b) Explain before each component what you will be doing
c) Do lengthy tests in small steps
d) Allow the child's mood and the symptoms to dictate the order of tests
Maggie Woodhouse is senior lecturer at the School of Optometry and Vision Sciences, Cardiff University, where she specialises in paediatric optometry. She runs the Special Assessment Clinic, which caters for patients of all ages with disabilities. Her particular interests are visual development in children with Down's syndrome and the impact of visual defects on education.
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|Title Annotation:||CONTINUING EDUCATION & TRAINING|
|Date:||Apr 20, 2012|
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