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Visual acuity in different intensities of light.

INTRODUCTION: The visual system provides a supremely efficient means for the rapid assimilation of information from the environment to aid in the guidance of behavior, the act of seeing begins with the capture of images focused by the cornea and lens upon the light sensitive membrane in the back of the eyes the retina which acts as a transducer which converts the patterns of light energy to neuronal signals (1) and focusing of a clear image requires adaptation of focal length of the optic lens by altering the curvature of the lens to suit the varying distance of the entering rays. (2) which requires good ambient lighting and is directly influenced by the intensity and amount of ambient light luminance which falls upon an object, (3) which resolves the power of the eyes to perceive the details and contours of an object which has to be perceived by the eye, (4) this functions is taken by the 5 million cones present in the human which function under day light conditions (Photopic) retina. Humans have a limited capability to identify object detail under diminished light conditions, it is seen that visual acuity decreases linearly with reductions in luminance and an greater increases in luminance is necessary to provide better changes in acuity hence visual changes over a range of back ground of luminance levels, Measurement of visual acuity assesses the health of the eyes, and the visual pathway to brain (5) and luminance levels are necessary at various common areas such as road lighting, vehicular head lights, reading with artificial lights, sign hoardings and advertisements and intactness of visual acuity is mandatory for selection posts related to driving and traffic services. This study was undertaken to determine the effect of different intensities of light on visual acuity.

OBJECTIVE:

* 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.

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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.

DOI: 10.14260/jemds/2014/4010

REFERENCES:

(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 [1], Suresh Babu Gangasagara [2], Venkatesh S [3]

AUTHORS:

[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.

Email: shruthi89@gmail.com

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
Words:1388
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