Seeing brignt lights, for example a car headlight, in the dark sometimes makes me see strays of light spreading outwards from the light source. It looks similar with the image below, but much less. In my case, the 'rays' have changes in their direction, are much less brighter, and often disappear when observed from a different angle. I have decided to make several theories on why this phenomenon happens, find the answer by research, and compare it with my theories.
Characterizing
The first thing I did was characterize the 'light rays'. It occurred to me that I would be able to build more realistic theories if I knew more details of phenomenon.
1. (It is) observed usally in the dark
2. light source below eye level -> rays point downwards
3. light source above eye level -> rays point upwards
3. light source at eye level -> rays point in all direction
3. seen only near my eye
4. 'strays' of light are seen - the rays can be distinguished
5. observed as the same color as the light source
Analyzing Characteristics
feature 1≫ much less light than the direct light from the light source
feature 2≫ related to direction
feature 3≫ not due to scattered light by airborne particles
feature 4≫ might be because of an asymmetric property of the eye
feature 5≫ probably not chromatic aberration
※chromatic aberration: a mismatch at the focal point where the colors do not combine as they should, when colors are incorrectly refracted by the lens(digital-photography-school.com)
Theories
1. the curve of the lens or the cornea
If some parts of the lens/cornea are slightly asymmetric with the rest, 'rays' of light could be perceived.
2. chromatic aberration
Analyzing feature 5 does result to that these light rays are not due to chromatic aberration, but this theory came into my mind even before I started listing the characteristics to the phenomenon. Light with different wavelengths refract differently through matter. Long-wavelength light, like red, refract less. On the other hand, short-wavelength light like blue refract more. As a result, light with different wavelengths do not intersect at one point. I believed that this could explain the rays of light, but soon gave up because I never observed them in different colors than the light source.
3. slits in the iris
Similar light effects happen in camera images, too. They are often created when light passes through a small crack and reaches the camera lens. The six rays of light are a result of the shape of the lens. I thought that if there were small, irregular slits in the iris, light could pass through them and create similar phenomenons.
Research & Compare/Contrast
The rays of light that I experienced were "star bursts". It is a type of glare - light that enters the eye and interferes with vision - , along with haloes.
There are about three reasons to extreme glares. First is corneal abberation. Unlike my prediction, glares due to abberations did exist; it just didn't happen to me. What I learned from this is that when making theories based on existing phenomenons, it is important to look at a variety of different situations. Back to the point, corneal abberations occur usually with diseases related to the curvature of the conea, such as keratoconus.
The second reason is the presence of defects in the iris. The normal iris absorbs unnecessary light, but the irises of people with albinism, pigment dispersion syndrome, or cataract cannot do so. This results in unwanted light not being absorbed but perceived in vision.
The last reason is related to the retina. A healthy line of pigment epithelium cells absorb light that passed through the retina. But in some other cases, these cells don't work well and the light is reflected back towards the retina. This causes light in the retina to be scattered, making a star burst image.
To say the truth, these four reasons mentioned above are when glares of serious levels happen. But when glares happen in healthy people's eyes, 30% of the light scattering is due to the curve of the cornea, and the rest because of that of the lens.