Why does bright light hurt my eyes so much?

[Andrew MacLean]

Why does bright light hurt my eyes so much?

The cornea of the normal eye focuses the light that comes through the pupil onto a cluster of cells at the back of the eye. These cells are light sensitive, they are either turned on or off by the light that hits them, and the mass of signals they produce is conveyed along the optic nerve to the occipital lobe of the brain (at the back of your head).

If you have keratoconus, your cornea does not manage to focus all the light onto this area at the back of your eye, so that some light hits parts of the inside of your eye that are not really suitable places for light to land. Hence the pain, and poor sight associated with KC.

This leads to light aversion in the person with KC, and many of us manage this problem by wearing rather stylish hats and/or sunglasses.

[itsallbroken]

Thanks for this info Andrew, i have wondered why for some time now

[Karl R]

The simplified answer, if I remember correctly, is that the refraction of light onto the retina is different in KC patients than that of non KC and the light falls onto areas which are not normally/little used in bright light. It is this that creates a sensation of pain via the receptors working in overload.

I'm sure that an optom or someone with more experience will come along later and correct me on this though, so please don't take it as read. Also the degree of light sensitivity will vary from person to person. Personally in all but the brightest of light reflecting back of a highly light reflective surface, I got no pain, and have actually not worn my shades since my operation.

PS, it has not affected my inability to read prior posts correctly No offence meant Andrew

Also welcome to the forum itsallbroken

<going away to sit in in the naughty corner for next couple of days >

[hannah+]

after years of struggling with bright light especially in the summer i found the following very helpful;
- using polarising sunglasses
- having allergy drops for my eyes - i never realised that the reason my yes were so bad in the summer was hayfeaver type symptoms that are mostly only preseent when i wear my lenses

all the best everybody

[Andrew MacLean]

hannah

Welcome to the forum!

Andrew

[rosemary johnson]

Hannah,
welcome from me too, and glad you're finding polarising shades a help. I wouldn't be without mine.
In response tot he original question:
Wht Andrew gives is one of the "standard answers" about KC an dlight sensitivity.
It isn't the only one though.
APparently, some people are just very light sensitive.
And people who already have an existing eye condition (of which KC is one) are ore likely than other people to develop hypersensitivity to bright light.
There's no particular reason for this - the existing condition doesn't cause the light sensitivity, nor vice versa. It's just that some people develop both.
I'm one of tthis type of people - I've "just" become hypersensitive. NOthing to do with the KC, nothing to do with my eye or my optic nerve per se. My brain just reactions with an AAARRGHHHHH!!! reaction to bright light.
This is according to the eye-neurologists, who say it just happens, and there's nothing that can be done about it.
This does explain one thing - why some people with KC find the light sensitivity gets better when they have contact lenses (or glasses) - they focus the lght better, on th the intended areas of the retina, so the normally obscure areas aren't getting doeses of light they don't normally get.
Whereas some of us, including me, find putting the lenses in makes the light sensitivity worse - as if focusing the light has just focused the pain. Literally, it has.
Rosemary

[mancity31]

This is something i ve never realised before .Occasionally on bright days i really struggle to adjust and can barely keep my eyes open unless i stare at the floor and i squint perminantly when i do eventually adjust .I ve had some of the effects of KC explained but have learned a lot from reading through the forum tonight

[Johan]

I've had KC for years and I have always been wearing sunglasses, even on overcast days. For me it's just second nature to put on my glasses when things get to bright.

Never knew the cause of the extreme sensivity to light was light being scattered to parts of the retina that don't receive a lot of light under normal circumstances.

By the way, I have one corneal graft in my right eye, and overal light sensivity hasn't really decreased. I can't feel whether the sensivity is caused by my left, untreated eye or both eyes.

I would certainly like some (official) in-depth explanation about light sensivity and KC...

[Andrew MacLean]

Johan, Welcome to the forum.

I really found that wearing contact lenses cut my photophobia by a great deal, so that the idea of light being scattered onto structures within my eye that was not designed to absorb light makes sense for me. Like most people with KC, I use sunglasses when the light is moderate, and I wear rather stylish broad brimmed hats.

Andrew

[GarethB]

In my case, no lenses meant no photophobia and when I was using RGP lenses this got really bad. Sincing moving over to soft silicone hydrogel lenses for Irregular Corneas, I now have no light sensitivity at all.

So in some cases it might be due to irritation from the lens, a but like when most of us that have had a graft find that for the first few weeks, light is a real problem and everyone I know that has laser eye surgery has been photophobic for a couple of weeks post surgery.