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Hand Motion Vision
In normal, healthy eyes with good vision, blurry vision indicates a need for prescription lens that adds additional power or corrects astigmatism that distorts the natural optics of the eye. Blurred vision can coexist with ghosting, smeared vision, or other visual abberations.
The term 'ghosting' was coined around 1957, and originally referred to the false image on a TV screen, caused by signal reflection. Ghosts are caused by residual astigmatism, or irregularities in the corneal surface. They vary in terms of transparency, size, and colors ghosted.
The term 'glare' is sometimes used to refer to the perception of any higher-order aberration. Here, the term is restricted to situations in which light seems to overflow, or 'seep outside,' its normal boundaries around light sources, or sources of reflected light, such as shiny objects.
Halos are usually huge globes of illuminated fog surrounding sources of light. Sometimes the globes seem to contain other globes, brighter and denser, nested two or more levels deep.
Loss of Contrast
Contrast sensitivity refers to the ability to distinguish between variations of lightness and darkness. Perceptually, this effect is similar to turning down the Contrast on your television or monitor: Eventually sharp boundaries are lost, objects merge together, as if a haze of grey soup had been poured over the visual field.
Starbursting refers to rays or fine filaments coming off lights. At night, these rays can become dramatically longer and denser. Starbursts are highly variable between patients, differing in terms of their size and shape, length of rays, the density of rays, and transparency (whether the light source is visible through the starburst).
Floaters are typically seen as specks, threads, or filaments, sometimes isolated and sometimes interconnected, that seem to "float" across the visual field.
The receptors responsible for human vision are located on the retina, at the back of the eye. Information from these receptors is aggregated at the optic nerve, and sent on to the visual cortex for further processing and interpretation. Portions of the retina that are detached are no longer in communication with the brain, resulting in areas of blankness or blackness. Spatial distortions may exist at the margin of the detachment.
Glaucoma is a group of eye diseases that slowly steal sight, often with no immediately recognizable symptoms. Most often, vision loss is the result of increased pressure inside the eye, which causes damage to the optic nerve. As glaucoma progresses, peripheral vision becomes more and more compromised as the area of effective vision continues to shrink. How does pressure cause loss of sight? Think of the eye as a balloon filled with air. As more air is pumped in, the balloon expands. The eye, however, is too strong to expand. As the pressure increases, the eye gives at its weakest point, where the optic nerve leaves the eye.
Patients who complain of Visual Snow literally see what resembles "television snow," that is, specs or particles that blink on and off in their vision.
Hemianopia refers to loss of vision in one half of the visual field of both eyes, most commonly on the right side. Causes of hemianopia include injury to the brain (temporal or occipital lobe) or optic nerve pathways from accident, infection, stroke, or tumor. Hemianopia may also affect the upper or lower halves of the visual field.
Visual Quality Disparities
Patients with bilateral eye injury or LASIK complications may report different aberrations in each eye. With both eyes open, these aberrations are synthesized to yield a composite image. However, one eye usually contributes more to the resulting composite than the other, a phenomenon known as "ocular dominance." This simulation illustrates one possible scenario, in which vision in the left eye is blurred following LASIK, whereas vision in the right eye is ghosted.
Aberrations & Pupil Size
Patients with complications from refractive surgery often report that their vision seems much better in bright light than dim light. Not only does bright light help compensate for Loss of Contrast Sensitivity, it also shrinks the pupil, reducing the visual aberrations caused by an irregular cornea.
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