The term glare is sometimes used to refer to any visual aberration resulting from refractive surgery. 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 another phenomena reported by some laser eye surgery patients, particularly at night. Halos are usually seen as 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. From a simulation perspective, starbusts and halos exist on a continuum, with starbursts shading into halos as the rays become less distinct and diffuse into each other.
Some laser eye surgery patients see rays or fine filaments coming off lights, even during normal daytime lighting conditions. At night, these rays can become dramatically longer and denser, something referred to as starbursting. Starbursts are highly variable between patients, differing in size and shape, length of rays, the density of the rays, and transparency (whether the light source is visible through the starburst.)
Starbursts differ along at least the following dimensions:
- Size: The first thing to notice is that starbursts differ in terms of size.
- Transparency: If you compare Starbursts 2 and 3, you can see that some starbursts are smaller and denser, whereas others are bigger, but more transparent.
- Shape: If you compare Starbursts 5 and 6, you can see that starbursts aren't necessarily circular... Sometimes the starbursts are just more high than wide. But sometimes, as shown in 5 and 6, the rays tend to go off more in one direction than another. Starbursts 5 and 6 also differ in terms of their size and transparency.
- Fine versus Thick Rays: In contrast to the top picture, the bottom picture shows that some starbursts do not consist of a fan of fine filaments, but instead are best described as a huge twinkle. If the arms shoot off in only a few directions, patients may refer to these as 'flares,' or laser rays.
- Degree of Internal Halo: Some starbusts have a large internal halo, whereas others consist mainly of rays.
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. Unfortunately, blurred vision after refractive surgery may not be correctable, and 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. The perceptual effects of LASIK complications are often similar, but here, signal reflection results from irregularities in the corneal surface. Ghosts vary in terms of transparency, size, and colors ghosted.
Contrast sensitivity is something that individuals with normal vision take for granted. When contrast sensitivity is lost, the ability to distinguish between variations of hue and brightness is diminished. Perceptually, this effect is similar to turning down the contrast adjustment on your television or monitor. Sharp boundaries are lost and objects merge together as if a haze of grey soup had been poured over the visual field.
Copyright 2005 by Greg Gemoules, O.D