Showing posts with label Glare. Show all posts
Showing posts with label Glare. Show all posts

Glare after LASIK and Cataract surgery



Glare is visual sensation caused by excessive and uncontrolled brightness. It is difficult to see in presence of bright light such as direct or reflected sun light or artificial light such as car headlamp at night. It is subjective, and sensitivity to glare can vary person to person. 

            Glare generally caused by a significant ratio of luminance between object (that which is being looked at) and glare source. The angle between the task and glare source and eye adaptation have significant impacts on the experience of glare. 

            Glare can be discomfort glare and disability glare. Disability glare is the reduction in visibility caused by intense light sources in the field of view, and discomfort glare is the sensation of annoyance (inconvenience) or pain induced by overly bright sources. Disability glare is usually caused by inter-reflection of light within the eyeball which reduces the contrast between object and glare source to point where object cannot be identified easily. If glare is very intense that vision completely impaired and called dazzling. 

            Now-a-days most of us are complaining about night glare which is caused by opposite car headlamp. All cars has eclectically operated headlamp which is positioned in pairs, one or two each side of the front of a car. 

A headlamp has a system to produce a low and high beam. 

Low beam light have strict control of upward light and direct most of light downwards to provide visibility without excessive glare or back dazzling. Low beam with a sharp, asymmetric cut off preventing significant amount of light from being cast in to the eyes of driver of preceding or oncoming cars. Low beam headlamps provide a distribution of light designed to provide forward and lateral illumination, with limits on light directed towards the eyes of other road users to control glare. 

 


















        High beam light cast most of light straight ahead, maximizing seeing distance and producing too much of glare. In high beam there is no control of upward light and causes backdazzle from fog and rain. High beam is suitable for use when alone on the road, as the glare they produce will dazzle other drivers coming from opposite side. High beam headlamps provide a bright symmetrical distribution of light with no particular control of light directed towards other road users’ eye.

Uncorrected refractive error, cataract, eye allergies, multifocal intraocular lenses (IOL), post LASIK, post Radial keratotomy (RK), corneal scar, corneal ectatic conditions (keratoconus, pellucid marginal corneal degeneration), enlarged pupil (due to injury) are most common cause for glare.

Simple tips to reduce glare

First of all everyone should follow the rule that within the city they should use low light beam strictly and once they are out of city limits, can use high light beam. So that everyone can drive safely.

Glare can be reduced by using sunglasses or polarized sunglasses. Polarized sunglasses are designed to reduce glare caused by sun light, reflected from non-metallic surface such as water, coal tar roads, painted surface etc but these glasses are not useful in night driving.

Vehicle visor – available in cars – use this to avoid direct sunlight falling over eyes.

Cataract surgery – if someone is having cataract.

Radial keratotomy (RK), corneal ectatic conditions, corneal scar – glasses are the first choice and then rigid gas permeable (RGP) contact lenses etc are the next.

Multifocal IOL – If someone drives at nights should not select multifocal IOL (during cataract surgery). Best choice to use monofocal IOL.

Enlarged pupil (due to injury or neurological) – can use prosthetic contact lens to reduce glare.