Basic farsightedness, or hyperopia, is not the simple opposite to nearsightedness, or myopia. More appropriately, it is the obverse, the complete flip side of a basic principle of human visual function. A recent study confirmed once again that basic visual strain at near distance is not simply a matter of blur, but that there is much more involved.
Hyperopia is common, and appears in higher proportions in some populations. Because most sight testing occurs at distance, most significant hyperopia goes unnoticed and continues to impact on child development, health, and learning. Hyperopia is essentially invisible, it becomes a masquerader, showing up as common childhood concerns:
- Where nearsighted children see poorly at distance, they tend to do well in school because their vision is tuned to the near distance: It is clear and easy for them to read and work at a desk.
- Farsighted children work especially hard to see at any distance, but it is physically harder for them to see at near distance, where most schooling takes place in the neotraditional classroom.
- Hyperopia and myopia are measured in diopters, and most often this is interpreted as depth of blur. Hyperopic children do have worse eyesight at near distance, while myopes are naturally adapted to the near environment and see blur at distance.
- The study below shows how 3D hyperopia is sufficient to impact on reading development.
- Hyperopia in the range of 2D is commonly associated with chronic eye strain and headache.
- The degree of hyperopia as measured in diopters is also a useful measure of accommodative strain (i.e. focusing effort). So, a +3D hyperope must engage focusing effort starting with a need to provide 3 diopters, they are in other words starting at a deficit and must provide muscular effort simply to hit the baseline distant clarity of sight. As the target draws nearer, more effort is required. The -3D myope, on the other hand, has a 6D advantage at near distance with respect to accommodative strain. For the child in Grade 1, working at 25-30cm, the difference is a major impediment to the farsighted child.
- Hyperopia causes excess convergence and this adds additional strain to near tasking.
- Given the near tension associated with school work, hyperopic children are more prone to distraction, headache, emotional outbursts, and other muscular pain in the head, neck, shoulders, and back.
It should be no surprise that nearsighted children tend to excel in academics compared to their nearsighted counterparts.
This recent review of an NEI study on hyperopia confirms once again that visual dysfunction is indistinguishable from physical disability. Furthermore, this particular disability engenders visual, muscular, emotional, and cognitive deficits. The lack of uptake to child vision exams means that most significantly hyperopic children will be left to struggle. Thanks to Dr. Len Press for the post.