Vision Development: Ocular Motor

An irony of ocular motor development is that it is often overlooked. Efficient ocular motor skills keep eyes aligned at all distances of gaze, maintain clear vision, track a moving object smoothly, maintain visual attention, and accurately jump eyes to the next object or word. Vision development does not have obvious milestones such as rolling over for the first time or saying the first word, but it is just as dependent on engaged practice. The thousands of hours that children spend moving, reaching, climbing, and imitating may not be recognized for what they accomplish. Like other skills which must be developed, ocular motor skills are roughly prewired. They are refined and tuned through years of intentional movements and play.

It is common for the eyes of a newborn to wander independently. The coordinated movements required to align the eyes and to maintain their precise alignment must develop from visual feedback. The newborn’s visual acuity is limited, particularly at a distance. Binocularity is driven by the coordination of the visual fields of both eyes so that the spatially synchronous retinal receptors of each eye receive information from the same object and send signals to the same receptors in the visual cortex.

When people consider sight, what comes to mind is seeing clearly, recognizing objects and the ability to read. These are skills of our focal visual system, but our ambient, peripheral, primarily subconscious visual system is just as important. Our focal visual system is dependent on our ambient visual system to maintain eye alignment. The ambient system also directs our eye movements, senses our motion and the motion of objects around us, stabilizes the image we perceive of the world (particularly as we move), and contributes to our balance. These may be dysfunctional due to faulty development, can be severely impaired by head injuries and must be recalibrated as we adjust to new glasses.

The speed, accuracy, and coordination of eye movements is unique. Eye alignment is accurate to within hundredths of a degree and misalignments of as little as 1o create significant noise in the system. In reading, a 1o misalignment of the eyes cause them to be looking at different letters. In most of our motor systems, being off by 1o is trivial and does not interfere with function.

 Our nervous system functions through a balance between the amplification and depression of signals, so it is natural that when the information from the eyes conflict and do not augment visual function, information will be suppressed. This is beneficial to reduce confusion, but also reduces visual potential, compromising the input and the processing of visual information. Persistent suppression can cause amblyopia.

Since almost no children are born with a turned eye, the description for an eye turn in the first year of life has changed from congenital to infantile. While there may be genetic predispositions, the loss of control is primarily due to faulty development. There is a tendency for some children’s eyes to turn inward around three years of age as they are becoming increasingly interested in detail and small differences. This often correlates with being farsighted. It has also been observed to correlate with children who are precocious and whose activities and interests are outdistancing their visual development.

When children are brought into the office due to visual difficulties in school such as a convergence insufficiency or loss of place when reading, it is not effective to try to train those skills in isolation. Convergence and tracking to read are due to a combination of perceptual and ocular motor skills as is the ability to handle visually crowded spaces and pages. They emerge from the development of a hierarchy of visual skills including: planning and guiding movement, being aware of where we and our body parts are in space, being aware of where things are around us, exercising meaningful and accurate eye movements in our surroundings, being able to visually multitask (see more than one object at a time), and assist balance.

We are concerned about the accelerated visual demands in school which exceeds the visual development of many children. Not all children are visually ready to read in kindergarten. Many children are not ready to handle crowded pages of reading or math problems, write on the line, or copy from the board. We are creating unnecessary stress with no evidence that pushing children to read who are not ready will improve their lifelong reading skills or enhance their interest in reading. Visual development, and other areas of development, are stimulated by going outside to play with peers (made easier by not having homework).