Vision Stimulation of Visually Impaired Infants and Young Children
by Dr. L. E. Leguire
Columbus Children’s Hospital
Once an infant or child has been diagnosed with a vision loss, one of the first things that the parent(s) should do is find professionals and organizations that work with infants and children with vision loss. For example, services are provided by numerous programs including MRDD (Mental Retardation and Developmental Disability), BSVI (Bureau of Services for the Visually Impaired) and the local school system. Early infant vision stimulation programs are also sometimes available through other local and state agencies, so you’ll have to search and ask everyone you have contact with about the services available for the visually impaired (VI) child in your local area. Start with the doctors that diagnosed the vision loss; ask their opinion.
One of the most important pieces of information that will help in providing services to a VI child is to know his or her visual acuity – how small of an object can the child see? Visual acuity is usually listed as a “Snellen” fraction; for example, a normal 6 year old child sees 20/20. One way to think of the Snellen fraction is that the top number is how far away the VI child can see the object and the bottom number is how far away a normal child can see the same object. For example, if a VI child has 20/200 visual acuity this means that the VI child can see an object that is 20 feet away and a normal child can see the same object 200 feet away. Visual acuity can be measured in most, but not all, infants and children (usually by the Acuity Card Procedure/Preferential Looking Technique (ACP/PLT) or Visual Evoked Potential, VEP). Some VI children can only see light (light perception) and other VI children can see only see a light and the direction of the light (light projection).
The information detailed below is directed towards rehabilitation specialists, teachers and parents who work with VI infants and young children.
In order to maximize vision, a young VI child must have appropriate visual stimulation as well as physically interact with the visual stimulation to form the brain connections that will last a lifetime. Appropriate visual stimulation involves visual objects that are of sufficient strength to provide the visual centers of the brain and other brain areas with visual information for “seeing” and for action. However, visual stimulation alone is not enough – the young child must also interact with the visual object (e.g., reaching for the object, gazing at the object, walking through the doorway, etc.), in order to maximize vision.
Appropriate visual stimulation is possible with visual objects that can stimulate the brain of a VI child. For example, a VI child with 20/600 visual acuity can only see objects that are 20 feet away that a child with normal vision can see 600 feet away. Or, the VI child can only see an object that is 2 feet away that a child with normal vision can see 60 feet away. In this case, many objects would be too small for the child with 20/600 vision to see and these objects would not provide visual stimulation. To provide the VI child with appropriate visual stimulation, the object would have to be larger than 20/600. Remember, visual acuity only tells us the smallest object the child can see (i.e., discriminate from other objects). In order to maximize vision stimulation, objects must be much larger than that based on visual acuity alone.
Some of the most “powerful” visual objects include high contrast, black and white objects including alternating black and white bars (Figure 1), known as a grating, as well as checkerboards (Figure 2). More complex visual objects include faces (Figure 3). Contrast refers to the brightness difference between the light and dark parts of the visual object. The greater the difference between the light and dark areas of the object the higher the contrast and the more likely the object will provide appropriate visual stimulation. Low contrast objects (Figure 4), like an object drawn with a pencil on white paper, are difficult or even impossible to see for a VI child. This is one reason why older VI children should use thick black felt tipped pens for all writing and drawing.
To provide appropriate visual stimulation, gratings should have different orientations (vertical, horizontal, oblique 45o, 135o) and bar sizes. The white area should never be small than the black areas. Given a stroke width of 3/4″ for electrical tape, a child with 20/200 vision will be able to see the black and white stripes of the grating up to 6 meters away; however, at 6 meters this would the absolute minimum size that the child could see. To stimulate vision, bar or stripe size should be larger than that based on visual acuity (at least 2-3 times larger).
A checkerboard made from black electrical tape and white cardboard. Checkerboards should also vary in overall size and orientation in order to provide appropriate vision stimulation. Individual bar size can also be varied by making checkerboards with two and even three strips of electrical tape, particularly if the child has very low visual acuity (e.g., worse than 20/400).
More complex visual objects can include faces, squares, and stars…use your imagination. For older children, letters of the alphabet as well as numbers can also be constructed to teach the child the alphabet and numbers, accordingly. The white area should never be less than the black (tape) area or stroke width.
One of the easiest ways to create a high contrast powerful visual object is with the use of black electrical tape (3/4″) and white cardboard. Mobiles placed about 1/2 – 1 meter from the child, beyond arms reach, can be easily constructed with this material. The contrast between the black electrical tape and white cardboard is the highest possible. The tape and cardboard are also very inexpensive. Both sides of the white cardboard can contain objects (e.g., Figs 1-3) and a small fan or open window can even be used to give the mobile continuous movement. Posters constructed from black electrical tape and white cardboard can also be constructed for hanging on walls. However, in order for the VI child to see the object, as viewing distance increases the object must be larger and larger and the stroke width wider and wider.
Objects that are created with the tape and cardboard must be of sufficient size for the VI child. If the VI child has very reduced vision, several pieces of black electrical tape can be placed side-by-side to create larger stroke widths (e.g., 2 pieces of tape = 1 1/2″).
Table 1 provides guidelines for minimum stroke width of an object given a VI child’s visual acuity. For example, a child with 20/600 visual acuity would be able to just see a grating (Figure 1) whose black and white bars were 4 mm wide at a viewing distance of 18″. Table 1 DOES NOT provide the minimum size of an object that a VI child could see – just the width of the lines that make-up the object. For example, for Figure 3, a child with 20/600 visual acuity would have to have a minimum stroke width (black lines) of 4mm BUT THE FACE WOULD HAVE TO BE MUCH LARGER.
Relation between visual acuity (VA) and size (millimeters, mm) of the stroke width (width of 1 dark bar of a grating) at a viewing distance of 18 inches. The purpose of this table is to provide guidelines as to the minimum stroke width, of a much larger object, a VI child could discriminate from another, similar, object (e.g., letters).
We cannot emphasize enough that an object and the stroke width that makes-up the object must be easy for the VI child to see. If the object is difficult to see, for example because stroke width is too small or lines are of too low contrast, the child will have great difficulties in using the object for a motor task. If objects are difficult or impossible to see, performance may be affected on certain tasks (e.g., tracing, writing and even reading).
Figure 4 shows simple line drawings made by different types of writing instruments, to illustrate the importance of utilizing objects that are easy to see by the VI child in vision stimulation programs, as well as in a school setting. A VI child with, for example, 20/200 visual acuity would have great difficulty in seeing the pencil drawing but would easily sees the medium felt-tip pen drawing. A VI child with 20/600 visual acuity may have difficulty seeing the medium felt-tip pen drawing but more easily see the drawing made by the heavy thick felt-tip marker.
Figure 4 illustrates simple drawings made with different writing instruments (simulated, this figure did not scan well). For a VI child, the drawing made with the pencil (far left) may be difficult or impossible to see while the drawing with the medium felt-tip pen is easy to see, even though the drawings are of the same overall size.
To further illustrate the importance of a high contrast and thicker stroke width for older VI children with good communication skills, do the following exercises.
Exercise 1 – Test Yourself – Read the following lines, out loud.
Larry didn’t see the ball coming and it hit him in the chest. It startled him for a moment, but he soon recovered and picked-up the ball. The runner had already rounded second base and was heading for third. Larry threw the ball, but it went high and past the third baseman. The runner headed for home. The left outfielder threw the ball to the catcher at home plate. Home is where the buffalo roam.
Note your slow reading speed and how difficult it was to make-out some of the letters or words. Also, you probably held the page closer to your face in order to make the print larger and easier to read. In many ways, a VI child sees regular size print and perhaps even large size print with as much difficulty as you were having with the #4 font print as shown in the above lines. The point is – print should be of sufficient size and contrast (and font type) to be easily seen by the VI child. When in doubt make it BIGGER and BOLDER!
Exercise 2 – See How Large Stroke Width Makes a Difference – Tracing (older children)
Draw several simple figures (circle, square, triangle) with a No 2 or No 3 pencil. Make the figures about 3″ across on white paper. Have the child trace the figures with a pencil and time his or her performance. Also observe the child’s behavior while s/he is tracing the objects. Now, draw the same or similar figures but with the medium felt-tip pen. Also have the child trace the figures with a medium thick felt-tip pen. Many VI children will have difficulty with the thinner and fainter stroke widths made by the pencil, however, the children’s performance will be much faster and easier when the figures are drawn with the medium felt-tip pen. You can try different figures to make sure that the better performance is not simply due to practice or familiarity with the drawn objects.
Exercise 3 – High Contrast is Important – Naming Objects (older children)
Draw several simple figures with a pencil and with a medium felt-tip pen, similar to exercise 1. At a viewing distance of about 1 meter, have the child name the objects. Some VI children will not be able to name the objects when they’re drawn with the pencil but will have no problem naming the objects when they’re made with the medium felt-tip pen.
Exercise 4 – Employ High Contrast Stimuli – Learning the Alphabet (2 years and older)
For VI children who are 2 years old or older, construct all the letters of the alphabet using 5″x7″ white index cards and black electrical tape (single width). Use a block diagram that is about 5″ high and 3″ wide to construct all the letters. Or, use a computer and print the alphabet 1 or 2 to a page and cut the pages in half (only one letter to a card). Use a simple font (e.g., Arial Black) or another simple bold font with about a 300-font size (based on WORD.doc, 2 letters per page). Place a letter about 12 – 18 inches in front of the child as say the letter twice, about 2 seconds apart, slowly but clearly (do not use “baby talk”). Repeat the process for other letters, as long as you have the child’s cooperation and attention. You do not have to go through all the letters at the same setting – break them up into manageable time slots. ANY vocalizations, as if the child is trying to say the letter, should be immediately rewarded verbally (e.g., Good!). You can even touch or tickle the child to reinforcement each vocalization. Minimize other talking during the exercise. Never say anything negative if the child does not respond, just continue with the exercise.
Exercise 5. Discrimination of Letters
Once the child has had several months or more to learn the alphabet, see if s/he can discriminate letters. Place two letters side by side and say one of the letters while attending to the child’s eyes in terms of fixation. Reward the child whenever the child looks at the correct letter after you have said the letter. If the child does not respond, move or shake the correct letter while saying the correct letter. If the child does not fixate the correct letter, say nothing. Remove the other (incorrect) letter and verbally repeat the letter. Move to the next pair of letters. Repeat the process with other letters. NEVER give a child negative feedback (e.g., never say “No”, “Wrong”, etc.) if s/he gets the letter wrong or points or looks at the wrong letter. Reward correct responses and ignore incorrect responses. For older children with good motor skills, pointing or a head turn to the correct letter is sometimes possible.
LPr = Light Projection
The general guidelines as listed in Table 2 are for infants and young children with limited or no communication skills. For VI children with communication skills (e.g., child can fixate or visually follow an object) or with some form of motor or verbal response, the child’s response may be used as a guide to determine the general size, shape and type of the visual objects used for vision stimulation.
Again, the emphasis should be placed on high contrast, black and white objects that are easy to see by the child. Colored objects are generally not recommended because color contrast is much less than luminance (brightness) contrast and colored objects (e.g., drawings) are more difficult to discriminate from a colored background. However, sometimes children with “cortical blindness” or cortical visual impairment (refer to article on CVI here) may prefer colored objects to black and white objects.
Use these guidelines for constructing visual objects, with black electrical tape and white cardboard, for a VI child with limited or no communication skills. Viewing distance is 18″. Double object size and stroke width (number of pieces of tape) for each doubling of viewing distance. For example, if the object is 36″ from the child with 20/200 visual acuity, the minimum size is 6″ and the stroke width should be 1 or 2 pieces of black electrical tape.
Detection vs Discrimination of Objects
It is important to know the difference between detection and discrimination in a visual stimulation program. Detection refers to simply being able to tell something is there and discrimination is being able to tell what it is. For example, a VI child might be able to detect a flash of light but not be able to see the flashlight, itself (discriminate the flashlight from the flash). Along similar lines, Figure 1 presents a black-and-white grating. Detection refers to the ability to tell that something is there, for example, the overall grating may have lower luminance than the surround area and the child may be able to tell that something dark is there; however, the VI child might not discriminate the individual bars of the grating. Discrimination, in this case, refers to the ability to “see” the different bars that comprise the grating. In general, a visual object must be detected first and than discriminated from other objects (exceptions include children with cortical visual impairment, see below). This type of hierarchy, detection => discrimination, follows general development of the visual system. It is easy to detect a visual object (e.g., a light against a dark background). It is much harder to discriminate the object from other objects (this is the basis for visual acuity). Thus, a VI child may be able to see a very small light flash but not able to discriminate a large “C” from a large “O”.
We often see parents of VI children, for example, who say that the child can pick-up a very small object on the floor. However, our testing shows that the child’s visual acuity is, for example, 20/400. In other words, the child is legally blind. So how can a legally blind child see such small objects? This discrepency is due to the fact that the parents are referring to the child’s detection of an object while the eye doctors are referring to the child’s discrimination of the object; that is, visual acuity. It is much easier to detect that something is there vs to discriminate an object from other objects of the same size.
Light perception and light projection are somewhat analogous to detection – being able to see a light or the source of light but not able to tell what it is. Form perception (e.g., 20/1000 visual acuity) is analogous to discrimination – being able to tell a “C” from an “O”, albeit at a very close viewing distance or very large letter size. One goal of vision stimulation is to allow the child to discriminate the smallest visual objects possible. In other words, maximize visual acuity.
Children with Nystagmus (“Dancing eyes”)
Nystagmus is defined as involuntary eye movements that are usually very repetitive – a back-and-forth movement of the eyes. Nystagmus is usually in the horizontal direction, although vertical and even rotational nystagmus is possible. Some children with nystagmus have a “null zone” – a certain direction of gaze where the nystagmus decreases or stops altogether. Infants and children with nystagmus and who have limited or no communication skills pose a challenge to the eye doctor and to the rehabilitation specialist. Nystagmus makes it difficult to tell if the VI child is “looking” at the object of interest. We do know, however, that children with nystagmus will show certain signs that they’re looking at an object of interest:
VI children with nystagmus will attempt to use their null zone as much as possible for seeing. They may even turn their head in a certain direction in order to have their eyes pointing to the object of interest and to use their null zone so that their eyes don’t move or move minimally.
The size and frequency of nystagmus changes when a child attempts fixation on a visual object. Attempts at fixation cause nystagmus size to decrease and frequency to increase. As a consequence, if you place an object of interest in front of a VI child with nystagmus and the size of the nystagmus decreases and the frequency of the nystagmus increases, it is likely that the child is attending to the object.
For stimulating a VI child with limited or no communication skills and who has nystagmus, first you must get a feeling for how the eyes move. Then, place the object of interest ideally in the child’s null zone for maximum vision. If the child does not have a null zone, pay particular attention to the child’s eyes in terms of the size and frequency of the nystagmus. Present the object of interest directly in front of the child, no more than say 18″ away, and observe the nystagmus. If there is no change in the nystagmus try other objects until you’re confident that the child is responding. Again, however, it is important that the object of interest is of sufficient overall size, stroke width and contrast to be seen by the child. (click here or information on congenital nystagmus).
VI Children with Abnormal Head Posture (AHP)
Some VI children, particularly children with nystagmus and who have a null zone, will tilt their head a certain way when reading, writing or when doing close work. Such a child may have developed the AHP because it allows the child to maximize vision. You should inform your doctor about the abnormal head posture. However, you should NOT discipline the child for an AHP – after all, this is simply the best way for him or her to see objects and to minimize nystagmus. In general, the VI child should be free to look at objects any way possible to maximize vision!
VI Children and Holding Visual Objects Close
Depending on the amount of vision loss, some VI children may hold objects very close to their eyes or they may even watch TV only a few inches away. LEAVE THEM ALONE. Do not try to get the child to hold the book at a certain distance or watch TV from a certain distance. The child knows best in terms of how he or she can see. DO NOT impose your ideas of how he or she should hold a book, for example. Also, some VI children, particularly those who are near sighted (myopic), may take-off their glasses in order to see close objects clearly. LEAVE THE CHILD ALONE. In order to see close objects clearly, myopic VI children may have to remove their glasses. Again, they know best. If a VI child wants to remove his or her glasses for close work than let them!
VI Children with central vision loss – Can’t see straight ahead
For various reasons, a child may not be able to see straight ahead but may have perfectly normal peripheral (side) vision. In this case the child will actually look off to the side of an object in order to see the object. A prime example is a child with a macular degeneration. A child with a macular degeneration may look at your ear in order to be able to see your face. DO NOT discourage or try to prevent the child from looking at your ear when he is looking at you. The child has learned and knows more than anybody else how he or she can best see. DO tell your eye doctor about the child’s peripheral fixation. [When the child is older and is able to understand the importance of social interactions, then the child can learn to make “eye contact” when interacting with others.]
VI Children with Light Perception (LP) or Light Projection (LPr)
Children with LP or LPr vision, by definition, cannot see visual objects or can see only objects that are VERY large. However, children can tell if it is light or dark in the room (LP) or they can tell the direction of a light source (LPr). One strategy with such VI children is to use a dark room and provide a lighted object (the bigger the better) and try to teach the child to respond (e.g., head turn, or fixation) to the lighted object. In general, with LP or LPr children, a dark object against a lighted background (e.g., window) is not recommended. Light scatter will reduce the contrast of the object and make it difficult to see the dark object against the window.
Use of a light box is recommended for VI children, even when the child only has LPr. The light box can serve as the visual object of interest in a dark room. Very large, high contrast objects can be back-lighted, but again, the objects would have to be very big to elicit a response from a child with such low vision.
VI Children with Seizure Disorders
Children with seizure disorders require special considerations because certain environmental stimuli may pose a risk of triggering a seizure. Flickering light or flashing an object on-and-off should be avoided. In general, parents and the child’s doctor(s) know best in terms of what might trigger a seizure in a particular child – pay attention to the parents! Seizure disorders may cause cortical visual impairment – the eyes and optic nerves look normal but the child may exhibit abnormal visual behavior.
VI Children with Over Stimulation Syndrome (OSS)
Some children, particularly VI children diagnosed with cortical visual impairment (CVI) and with multiple handicaps, may not handle very much stimulation of the senses. VI children with OSS appear to be overwhelmed by visual, auditory and/or by things touching their skin. They may pull away when their hand is touched or they may actively look away from a powerful visual stimulus, like that shown in Figure 1. Children with OSS require special care and handling – they may require less stimulation, not more as is usually the case in early stimulation programs. OSS is a rare, previously unrecognized condition and we are gathering information on these children. See article on Over Stimulation Syndrome for more information on this topic (http://www.ohiolionseyeresearch.com/past.htm).
VI Children with Sensitivity to Lights (Photophobia)
Some VI children will be very sensitive to lights, particularly sun light. Children with photophobia will squint or close their eyes and allow only a little light to get to the eyes. VI children with photophobia prefer cloudy days, prefer to stay inside and like going outside at dusk and dawn – when the sun is not high in the sky. Photophobic children prefer to wear a hat and darker sunglasses. They will tend to shade their eyes with their hands. If the child has photophobia, when outside s/he should always wear a hat with a wide brim and sunglasses. Sometimes children with photophobia like wearing a hat and even sunglasses if inside lighting is bright. If a child sees better outside or inside with a hat and/or sunglasses than s/he should be allowed to wear a hat or sunglasses. Often, however, the photophobic child will remove the hat or/and sunglasses when inside because of peer pressure and to fit-in and not be different. Again, the child knows best. If s/he can see better inside with a hat or sunglasses than s/he should be allowed to do so to maximize vision.
While sunglasses are often recommended for children with photophobia, it is often the case that glasses that allow different amounts of light to reach the eyes work best, like photo-grays or so-called transition lenses. Our research has shown real benefits with the use of Corning Photochromic (CPF) lenses (511, 527, 550) in photophobic children, particularly in children with retinal disease (cone dystrophy, macular degeneration, achromatopsia). CPF lenses darken when the child is outside and lighten when the child is inside, much like photo-grays and transition lenses. Also, the CPF lenses block-out wavelengths of light that the photophobic child is particularly sensitive to, including UV and blue light. Be sure to tell the child’s eye doctor that the child is photophobic and ask about the different types of eyeglasses with light filters that might be available.
Moving vs Stationary Visual Objects for Vision Stimulation – What is it vs Where is it
Some children with cortical visual impairment (CVI) may actually see moving or flashing objects better than stationary objects. For example, one patient that we examined several years ago could run after a small ball as it rolled across the floor, but the child could not localize or see the ball once the ball stopped moving. We now know that the visual system is separated into two main pathways – one pathway is used for determining where an (moving) object is relative to the observe. The other pathway is responsible for identifying what the object is and assigning properties to the object like size, color, and shape. The child that we examined had a loss of the WHAT pathway, so that he could not see the object when it was stationary.
It is important to remember that moving and flashing visual objects stimulate the WHERE pathway. The WHERE pathway is sometimes called the “egocentric” (i.e., self-centered – where is the object relative to where I am) pathway. As a consequence, some VI children will do much better if the visual object is moving or flashing rather than stationary. Because of these differences, moving/flashing objects as well as stationary objects should be a part of visual stimulation programs. In general, VI children with a loss or impairment of the WHAT pathway will have 20/200 or worse visual acuity. If the VI child has 20/100 or better visual acuity it is unlikely that he or she has an impairment of the WHAT pathway. By capitalizing on moving or flashing a visual object, a VI child with an impairment of the WHAT pathway may do surprisingly well at identifying objects which, if stationary, are not even seen by he child.
Some children with an impairment of the WHAT pathway may see better when they’re moving (e.g., walking) in the environment rather than when they’re stationary. These children may not be able to tell, for example, where the doorway is, but they can walk through the doorway (this is one exception to the detection => discrimination hierarchy). Or, they may walk around and avoid objects that they cannot see when standing still. Children with a WHAT pathway impairment may have great difficulty in identifying objects or in naming attributes of a stationary object. Such unusual behavior should cue the rehabilitation specialist or parent of the possibility of a WHAT pathway impairment. [See section on VI children with seizure activity for precautions.]
Little is know about selective damage to the WHERE pathway (when the WHAT pathway is intact). Theoretically, children with a WHERE pathway impairment would have difficulty seeing objects that move or flash, and would have particular problems in orientation and mobility. Such a child might be able to see the doorway, for example, but would have great difficulty in walking through the doorway. Likewise, a child with a WHERE pathway impairment might be very bright, have great communication and verbal skills, but may have great difficulty in reading, for example, because placement on the page would be lost each time the child moved his or her eyes. Such a child might be able to see and identify small objects but have difficulty with large objects. There is some evidence that dyslexia may, in part, be attributed to a WHERE pathway deficit.
Interaction with other Children
By far, the best vision rehabilitation specialists for a VI child are other children. Within reason (and with safety concerns in mind), interactions between a VI child and other children should be emphasized. Other children will bring-out every bit of visual and motor potential of the VI child. Other children will continuously stimulate, aggravate and push the VI child to reach his or her maximum potential. Overprotection of a VI child by parents or caregivers should be actively avoided.
Interaction with the Visual Environment
As noted in the opening paragraph, it is not sufficient to just provide vision stimulation to a VI child. The child must also interact with the object or visual environment. Such interactions may take-on the simplest task like moving ones eyes to fixate on an object. More complex tasks may include reaching for an object or turning to a visual object that is also making a sound. Ideally, interactions with the environment ultimately involve orientation and mobility. Only though such motor interactions with the environment can a child form the brain connections necessary for using vision for motor responses and orientation and mobility tasks.
For a theoretical basis of some of the information contained in this handout, see the following references:
Fellows, RR, Leguire, LE, Rogers, GL, Bremer, DL. A Theoretical Approach to Vision Stimulation. Journal of Visual Impairment and Blindness. October 1986, p907 – 909.
Leguire, LE, Fellows, RR, Rogers, GL, Bremer, DL, Fillman, RD. The CCH Vision Stimulation Program for Infants with Low Vision: Preliminary Results. Journal of Visual Impairment and Blindness. January 1992, p33 – 37.
Dr. Leguire is the Director of Electrophysiological Testing and Eye Research at Columbus Children’s Hospital. Dr. Leguire is also a Clinical Associate Professor in the Department of Ophthalmology at The Ohio State University, Executive Director of the Ohio Amblyope Registry, Scientific Chair of the Ohio LIONS Eye Research Foundation and Immediate Past Chair of Prevent Blindness Ohio. He has worked “hands-on” with visually impaired infants and children for the past 25 years. He has published extensively in the field of low vision and vision rehabilitation, and is the Editor of three large print joke books for visually impaired children.