Visual acuity in different intensities of light.
* To evaluate the association between intensity of light and visual acuity.
* To evaluate the optimum intensity of light for carrying out better perception of vision.
MATERIALS AND METHODS: A comparative study comprising 100 literate subjects of both the genders 50 each in the age group of 15-45 yrs who acts as controls in day light and cases in 6 different intensity of light. Written informed consent was taken and ethical clearance was obtained. A detailed eye examination including anterior segment, Posterior segment and refractive errors was done by an Ophthalmologist. Vision status was evaluated and those with h/o of acute or chronic ocular causes, h/o recent or past head injuries, tuberculosis, diabetes, and refractive errors were excluded. A written informed consent was taken and visual acuity was measured for far vision in bright day light and in an enclosed room with controlled light at different intensities 15W, 20W, 40W, 60W, 100W, 200W and the illuminance levels were chosen to be appropriate and to appreciate the ambient intensity of light by using incandescent light in a dark enclosed room. The no of characters read correctly at day light and different intensities was noted, compared and statically analyzed.
STATISTICS: Descriptive and inferential statistical analysis has been carried out in the present study. Results on continuous measurements are presented on Mean [+ or -] SD (Min-Max) and results on categorical measurements are presented in Number (%). Significance is assessed at 5 % level of significance. Student t test (Two tailed, independent) has been used to find the significance of study parameters on continuous scale between two groups (Inter group analysis) on metric parameters.
RESULTS: Number of choices read incorrectly was more with reduced illumination 100 W -15 W and was statistically significant (P < 0.05). Visual acuity was best in 200 W in comparison with day light but was not statistically significant.
DISCUSSION: Retina acts as a transducer to convert light energy to neuronal signals and which is directly propotinal to illuminance Light sensitive photo receptors cones hyperpolarize in response to light and these cells translate the visual image impinging upon the retina into continuous action potentials which propagates along the optic pathway to the visual centers within the brain. (1)
CONCLUSION: 200 Watts or natural day light is best for visual perception and no need to go for higher light intensities thereby conserving energy.
Visual acuity is associated with intensity of light however regulation of the amount of light that enters varies with the size of pupil that is constricted in bright light and dilates in dim light as the photoreceptors get bleached out by too much light. (6)
LIMITATIONS OF THE STUDY: Hence the limitations of this study is to further see at what luminance does the bleaching of photoreceptors occur and to define the suitable range of intensity of light for better perception.
(1.) Fauci, Braunwald, Kasper, Longo Hauser, Jameson, Loscalzo. Harrison's principles of internal medicine. 17th edition. vol 1. Mc Graw Hill Publisher (2008);180-81.
(2.) Macleods clinical examination. 12th edition. Churchill Livingstone (2009); 318.
(3.) Godnig Edward C, O.D., FCOVD. Visual acuity under various illuminance lighting conditions. Optom Vis Sci. 2004 Sept-Oct; 20 (5):484-488.
(4.) Pal GK, Pal Pravati. Textbook of Practical Physiology. 3rd edition. University Press (India) 2010; 318-319.
(5.) http:// en.m.wikipedia.org/wiki/visual acuity, last accessed on 2/9/2014.
(6.) German. j. will, L Lindy, Stanfield. Principles of Human Physiology. 2nd edition. Pearson Benjamin Cummings.
Shruthi K , Suresh Babu Gangasagara , Venkatesh S 
[1.] Shruthi K.
[2.] Suresh Babu Gangasagara
[3.] Venkatesh S.
PARTICULARS OF CONTRIBUTORS:
[1.] Post Graduate Student, Department of Physiology, Bangalore Medical College and Research Institute.
[2.] Associate Professor, Department of Ophthalmology, Minto Ophthalmic Hospital, Bangalore Medical College and Research Institute.
[3.] Associate Professor, Department of Physiology, Bangalore Medical College and Research Institute.
NAME ADDRESS EMAIL ID OF THE CORRESPONDING AUTHOR:
Dr. Shruthi K, Department of Physiology, Bangalore Medical College & Research Institute, K. R. Road, Bangalore-560002, Karnataka, India.
Date of Submission: 25/11/2014.
Date of Peer Review: 26/11/2014.
Date of Acceptance: 08/12/2014.
Date of Publishing: 13/12/2014.
Table 1: Gender distribution of patients studied Gender No. of patients % Female 50 50.0 Male 50 50.0 Total 100 100.0 Table 2: Comparison of total read characters (Alphabets) Right eye STUDY GROUP CONTROL P VALUE 15 W 16.43 [+ or -] 4.00 23.99 [+ or -] 2.51 <0.001 ** 25 W 19.24 [+ or -] 4.20 23.99 [+ or -] 2.51 <0.001 ** 40 W 20.71 [+ or -] 4.00 23.99 [+ or -] 2.51 <0.001 ** 60 W 22.03 [+ or -] 3.65 23.99 [+ or -] 2.51 <0.001 ** 100 W 22.91 [+ or -] 3.29 23.99 [+ or -] 2.51 <0.001 ** 200 W 23.71 [+ or -] 3.05 23.99 [+ or -] 2.51 0.312 Table 3: Comparison of total read characters (Numbers) Left eye STUDY GROUP CONTROL P VALUE 15w 17.14 [+ or -] 4.82 23.66 [+ or -] 3.29 <0.001 ** 25w 19.58 [+ or -] 5.05 23.66 [+ or -] 3.29 <0.001 ** 40w 21.24 [+ or -] 4.77 23.66 [+ or -] 3.29 <0.001 ** 60w 22.15 [+ or -] 4.52 23.66 [+ or -] 3.29 <0.001 ** 100w 23.04 [+ or -] 3.74 23.66 [+ or -] 3.29 0.006 ** 200w 23.49 [+ or -] 3.55 23.66 [+ or -] 3.29 0.328 Right eye STUDY GROUP CONTROL P VALUE 15w 24.41 [+ or -] 4.74 32.19 [+ or -] 2.31 <0.001 ** 25w 27.34 [+ or -] 5.08 32.19 [+ or -] 2.31 <0.001 ** 40w 29.10 [+ or -] 4.38 32.19 [+ or -] 2.31 <0.001 ** 60w 30.46 [+ or -] 3.87 32.19 [+ or -] 2.31 <0.001 ** 100w 31.18 [+ or -] 3.35 32.19 [+ or -] 2.31 <0.001 ** 200w 32.11 [+ or -] 2.97 32.19 [+ or -] 2.31 0.243 Left eye STUDY GROUP CONTROL P VALUE 15w 25.33 [+ or -] 5.69 31.79 [+ or -] 3.53 <0.001 ** 25w 27.76 [+ or -] 6.06 31.79 [+ or -] 3.53 <0.001 ** 40w 29.41 [+ or -] 5.52 31.79 [+ or -] 3.53 <0.001 ** 60w 30.27 [+ or -] 4.91 31.79 [+ or -] 3.53 <0.001 ** 100w 31.25 [+ or -] 4.26 31.79 [+ or -] 3.53 0.011 * 200w 31.61 [+ or -] 3.97 31.79 [+ or -] 3.53 0.289
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Shruthi, K.; Gangasagara, Suresh Babu; Venkatesh S.|
|Publication:||Journal of Evolution of Medical and Dental Sciences|
|Date:||Dec 15, 2014|
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