People who have central scotomas (such as those who have macular degeneration) are unable to see things when they look directly at them because the center of their vision is impaired.
However, their peripheral vision is usually intact, so they need to learn how to use their best area of vision (preferred retinal locus or "psuedo fovea"), which means
looking a little bit away from what they want to see, rather than look directly at it.
The main purpose of many programs to train people to do this is to help them be able to read.
Those who want to cross streets and do other mobility tasks need to also learn to use their preferred retinal locus to find things in the environment such as traffic signals, approaching vehicles, etc.
For example, many years ago I was working with a client who had macular degeneration and wanted to learn how to cross streets more safely.
As we approached the intersection, she looked up and said "I don't see the traffic signal -- OH! I see it! oops -- I don't see it -- Oh! I see it! Now I don't."
I knew what was happening -- when she looked at the signal, it was obscured because she was looking directly at it with her scotoma, and when she looked away she was able to see it with her peripheral vision that was still intact.
Of course as soon as she saw it with her peripheral vision, she tried to look at it directly but, again, she obscured it with her scotoma and it disappeared . . . and so it went.
I realized that before we worked on street-crossing, we should help her learn to use eccentric viewing -- seeing things with the preferred retinal locus in her peripheral vision.
This page describes a simple procedure for helping people find their preferred retinal locus and use it for mobility purposes, such as finding and following objects.
The procedure usually takes me less than half an hour -- any suggestions to improve the procedure or, more importantly, follow up on it would be welcome! Contact me at firstname.lastname@example.org
The procedure is illustrated in the video here.
The person who is posing as the "student" does not have any visual impairment, we are simply demonstrating the different procedures, so the size and distance of the targets and flash cards might not reflect what would have been used with an actual student.
As you experiment with this training procedure, you may want to have the target at a greater distance from the student so s/he can learn to see things at a distance.
To help discover the preferred retinal locus, you can use a board with a circle in the middle surrounded by targets of equal size and shape, like the one I made that is shown to the left (this one is about 10 inches across)
If you don't have a board, you can use your hands or other objects placed around your face, but it may not be as accurate.
For the training, you can use flash cards with letters or numbers, like the ones that I made which are shown to the left.
I like to have several sets of flashcards with different-sized letters or numbers, so I can choose one that is challenging for the client to see.
Find the preferred retinal locus:
Ask the client to look at the center of your board (or the center of your face, if you don't have a board).
Explain that by looking at the center (of the board or your face), it should disappear because of the scotoma.
If you are using a board, ask which symbol seems the most clear.
If you are using your face, hold your hand or an object above, below, and all around your head, and ask where the hand or object seems most clear.
Wherever the symbol or object is seen most clearly by the client is the preferred retinal locus for him or her.
For example, if the clearest symbol is above and to the right of the circle (or your face), then the client can see things best when s/he looks below and to the left of the object.
NOTE: There may be more than one area that has equally clear vision.
NOTE: If the target is just as clear when the client looks directly at it as it is when looking slightly away from it, the vision is probably not impaired enough to need to use eccentric viewing.
For your training, determine the size of your flashcards and the distance to hold them:
Try different sizes of numbers or letters on the flash cards and/or move them closer to or further away from the client.
Ask the client to look at the flash cards and report when the numbers or letters are too small to see when looking directly at them, but can be seen easily when looking
with the preferred retinal locus (for example, when looking below and to the left of it).
When you find that combination of size and distance for the flashcards (that is, when the client cannot see the numbers or letters when looking directly at them but can see them when using the preferred retinal locus), THAT is what you will use for the training.
To do the training:
NOTE: Do NOT encourage clients to move their head for these tasks, they should be moving their eyes.
Hold up the stack of flash cards at the distance that is challenging, and ask the client to look at the card in the manner that you had just determined was the preferred retinal locus.
Give the client time to find the card and look at it from the angle that is the best (e.g. "below and to the left of the object"), and read it.
Keep the stack of cards in the same position, and remove the top card to reveal another number, and ask the client to read it.
Continue to reveal new cards as the client maintains the eye position and reads the card.
Once the client is proficient with reading the cards in that position, lower the stack of cards, put a new one on top, and hold it up in a random position and ask the client to read it.
This gives the client practice with finding the oject and then moving the eyes to be in the best position to read it.
Once the client is proficient with finding and reading the cards, hold the stack of cards on one side, allow the client to find and read it, and then move it smoothly while removing the top card to reveal the next one.
The client must follow the moving card and keep it in the preferred retinal locus in order to read the next card.