The scientific definition of hardness is the ability to resist scratching, nothing more. If you ask most folks, theyâll say feathers are soft and glass is hard. In the world of gemology, however, glass is fairly soft. It can be scratched easily by a variety of what we gemologists consider hard substances.
convergence excess. Convergence excess is an over-convergence of the eyes at a near distance for extended periods of time, such as when reading, writing, drawing, or viewing a computer screen. Sometimes, the over-convergence can result in diplopia (double vision).nce a diagnosis of convergence insufficiency has been made, a simple visual therapy technique that may be helpful is pencil pushups. 1. Hold a pencil at arm s length, with the eraser about level with the tip of your nose.
From Wikipedia, the free encyclopedia. Convergence insufficiency or convergence disorder is a sensory and neuromuscular anomaly of the binocular vision system, characterized by a reduced ability of the eyes to turn towards each other, or sustain convergence.rom Wikipedia, the free encyclopedia. Convergence insufficiency or convergence disorder is a sensory and neuromuscular anomaly of the binocular vision system, characterized by a reduced ability of the eyes to turn towards each other, or sustain convergence.