Glare - Dr. Sanjay Dhawan

1 URL E-mail: Dr. Sanjay Dhawan MBBS, MS (Gold medallist ) DOGlareHigh beam of head-light of a on-coming car has blinding effect anddecreases visibility dangerously. A fielder in the outfield of a cricket matchmisses a crucial catch because of Glare from the flood lights or the one knows what is Glare and every one has experienced it too, butwhen asked to describe or define most are can be really troublesome in patients of cataract or after can be defined as the contrast lowering effect of stray lightin a visual scene. Glare forms a veil of luminance which reduces thecontrast and thus the visibility of a target is decreased. We cannot seeintensity differences efficiently in the presence of a high background oflight intensity.

2 And the sensitivity to Glare is amplified as scattering incornea or lens Light Scatter in Normal EyesCornea30 %Lens 70 %Aqueous & vitreous < 1 %Types of GlareGlare can be divided into two glareDiscomfort Glare refers to the sensation one experiences when theoverall illumination is too bright on a snow field under bright Glare refers to reduced visibility of a target due to thepresence of a light source elsewhere in the field. It occurs when light fromglare source is scattered by the ocular media. This scattered light forms aveil of luminance which reduces the contrast and thus the visibility of can be defined as the difference between the luminance of thetarget and the background relative to the average luminance of the =Target illuminance-Background illuminanceTarget illuminance+Background illuminanceusually expressed as percentage (%) or as a light raises the luminance of both the target and the backgroundto same extent thereby reducing the Dr.

3 Sanjay Dhawan MBBS, MS (Gold medallist ) DOURL E-mail: of GlareI. Discomfort pigmentosaII. Disability Glare1. Old age - The intraocular scatter of light and Glare are fairly constant untilabout 40 to 45 years of age, after which they increase rapidly. Following arethe factors responsible:o lens fluorescence which converts incident ultraviolet light (invisible) into scattered blue light (visible).o yellowing of senile miosis which reduces target illumination at the retina and adds to scatter from the edge of the subclinical lens Cataract - Glare sensitivity is markedly increased in cataract compared tonormal eye, even when adjusted for age, visual acuity and contrast is related to the degree of diminution of vision in case of nuclear andcortical cataract but not in posterior subcapsular cataract where it isdisproportionately higher.

4 Glare increases as the cataract advances and when80 % of the lens is cataractous the contrast drops and Glare Posterior Chamber IOL - Glare sensitivity is higher in eyes with posteriorchamber IOL when compared to normal eyes, even when the posterior capsuleis absolutely After Cataract - Posterior capsule opacification increases Glare which isimproved by Nd:YAG Keratoconus6. Corneal edema - Epithelial edema leads to more scattering of light and ismore visually debilitating than stromal Radial Keratotomy (RK) - RK increases Glare sensitivity especially undermesopic conditions or when the central optical zone is very Vitreous opacities9. Macular edema (controversial)URL E-mail: Dr.

5 Sanjay Dhawan MBBS, MS (Gold medallist ) DOMeasurement of GlareI. Discomfort GlareIt can be measured under experimental conditions by having a patientadjust brightness of a light source until it reaches an ill-defined threshold ofunpleasantness. However, it does not seem to have any clinical relevance Disability GlareA conventional visual function test, usually acuity or contrast-sensitivity, isadministered in the presence of a Glare source. Following tests are Glare Acuity Test (BAT) simple method which the author uses is to first record thevisual acuity of a patient using Snellen s chart and then repeatingthe same while shining a bright light of an ophthalmoscope or atorch on patient s eye. A drop of visual acuity of two lines or moredenotes significant degree of UtilityTo measure visual disability in mild cataract especially: decreased vision outdoor in bright disability with night time distinguish decreased vision because of anterior segment pathology (mediaopacity) from retinal pathology.

6 Glare sensitivity is markedly increased inanterior segment disease but is unaffected in retinal disorders. Glare sensitivitytests are more sensitive and more specific for anterior segment Recovery TimeIt is a measure of the speed with which the visual system regains functionfollowing exposure to bright light. Factors and diseases affecting light and darkadaptation will affect Glare recovery. This is used to predict predisposition of apatient to conclude, Glare is an important factor in visual disability with anteriorsegment disease and sensitivity tests are useful in evaluating the visualproblems of a patient with early cataract. It also forms a convenient and non-invasive method of differentiating anterior segment pathology from retinaldisease.

7 Glare recovery time is useful in predicting the possibility ofdevelopment of retinopathy in diabetics.