The most obvious is distance. Getting closer to or farther away from the object or person to be seen may make it easier. Some children tilt their heads to get the visual material at an ideal angle. They may also do this by moving the material. Lighting interacts with many other factors but most importantly with contrast.
Lighting can increase or decrease the contrast of visual materials.
In a dark environment increased lighting will increase contrast but in a bright environment it will reduce it. Natural light is good but it needs to be controlled due to glare. Light that comes from behind the individual is best as it minimizes glare and does not strike the person directly in the eyes. A lamp with an adjustable level of light is useful for this. Children who have trouble attending to material may benefit from shining light directly on it.