1. INTRODUCTION

Astigmatism is a type of refractive anomaly in which no point focus of light is formed on the retina. This is due to the unequal refraction of the incident light by the dioptric system of the eye in different meridians. Studies have shown that about one in three people suffer from astigmatism, Asians and Hispanics having the highest prevalence of 33.6% and 36.9%, respectively.1

Although a person may not notice mild astigmatism, higher amounts of astigmatism may cause visual deficits. An individual who has highuncorrected astigmatism at a young age may later have reduced vision due to permanent visual deficits like amblyopia.

2. NEED FOR THE STUDY

Astigmatism is a common refractive error among ophthalmic patients. There is a paucity of Indian literature on both immediate and long term visual deficits induced by astigmatism. Literature on meridional amblyopia is meager. There is also no available literature on astigmatism induced visual deficits that can alter the quality of life in adult patients. In this study we will also correlate the amount of astigmatism with visual deficits and evaluate effect of early correction of astigmatism on vision.

In our country there is no systematic school screening programme. Hence astigmatism missed in preschool and school children could have a detrimental effect on vision and later, their quality of life.

3. REVIEW OF LITERATURE

E M Harvey et alconducted a study in Tohono O’odham reservation located in South Arizona to characterize the pattern of visual deficits resulting from uncorrected astigmatism in childhood. A total of one thousand forty eight children from second to sixth grade were enrolled in the study and completed the examination, of which two hundred and fifty three children were excluded due to various reasons. The rest eight hundred and five children were sub divided into non astigmatic, hypermetropic astigmatic, mixed and myopic astigmatic. The effects of astigmatic defocus in the development of visual function were evaluated. This was done through use of a comparison of the effects of astigmatism across a variety of visual functions (letter acuity, grating acuity, vernier acuity, contrast acuity and stereo acuity) relative to a normal (non astigmatic) age matched control group from the same population tested in the same way. The results indicate that astigmatic elementary school children show a deficit in best corrected letter acuity, grating acuity, vernier acuity, contrast sensitivity and stereo acuity.2

M.Abrahamsson selected three hundred and tenpatients with an astigmatism of more than or equal to one diopter in at least one eye and without strabismus or ocular disease for three year follow up. At the age of four years amblyopia was found in twenty three children(7%). They found that an increasing astigmatism during the test period was associated with an increased risk to develop amblyopia. Increasing refractive errors as well as amblyopia were more frequent among the cases with with-the-rule astigmatism or oblique astigmatism. All cases with oblique astigmatism in combination with increasing refractive error developed amblyopia. Considering the proposal that hypermetropia equal to or greater than +3.5D in the most hyperopic meridian at the age of one year is related to later development of amblyopia, they concluded that no one who had a hypermetropia of less than or equal to 2.5D at the age of four years or less than or equal to one diopter at the age of three years developed amblyopia.3

E M Harvey et al compared the effectiveness of eyeglass treatment of astigmatism related amblyopia in children younger than eight years versus children eight years of age and older. Four hundred forty six non astigmatic and three hundred ten astigmatic children in kindergarten were included in the study. Eyeglass correction of refractive error was prescribed for full time wear in astigmatic children and the change in mean best corrected visual acuity was assessed after short (six week) and long (one year) treatment interval. Astigmats showed significantly greater improvement in mean best corrected visual acuity (0.08 logMAR unit, approximately one line), than the nonastigmatic children (0.01 logMAR unit) over the six week treatment interval. No additional treatment effect was observed between six week and one year. Hence the conclusion that sustained eyeglass correction results in significant improvement in best corrected visual acuity in astigmatic children, including those previously believed to be beyond the sensitive period for successful treatment.4

V.Dobson et al conducted a study on seventy three astigmatic children of five to seven years of age, all having with the rule astigmatism. Thirty nine children received spectacle correction based on eye examination that indicated a refractive error. Thirty four children had no prior correction. The two groups were compared for mean best corrected right eye visual acuity with ETDRS chart and the lea symbols chart, for grating visual acuity, measured with modified teller acuity card stimuli, and for meridional amblyopia based on grating acuity results. He concluded that there is a significant improvement in letter recognition acuity in astigmatic children by the time they reach kindergarten if spectacle correction was given during the early preschool years. However no improvement in grating acuity or reduction in meridional amblyopia was noted. 5

R.Thad Goodwin and Paul E Romano conducted a study on fourteen normal individuals aged twenty three years and older to establish a relation between visual acuity and stereo acuity. Visual acuity was tested with Snellens chart and titmus stereo test was used for the latter. He established that there is a significant correlation between the performance of visual acuity and stereo acuity. The degree of stereo acuity reduction was slightly more marked with monocular decrements than with binocular at Visual Acuity between 20/25 to 20/50.6

4. OBJECTIVES OF THE STUDY

Primary

To estimatevisual deficits(letter acuity, stereo acuity, contrast sensitivity, vernier acuity)in patients with astigmatism more than or equal to one dioptre.

Secondary

  1. To evaluate the correlation between amount and axis of astigmatism (uniocular /binocular) with visual deficits.
  2. To study the correlation between age of correction of astigmatism and visual deficits.
  3. To evaluate the effect of astigmatism related visual deficits on vision related quality of life.

5. MATERIALS AND METHODS:

Study design—The study will be a prospective cross sectional type of study.

Sample size- Using data from an article by E M Harvey et al1 and programme “n master-hypothesis testing for two means (equal variances)”, the total number of sample size proposed is two hundred patients.

Inclusion criteria-

  1. Patients of age group twelve to thirty five years with regular astigmatism of more than or equal to one dioptre of either sex of Indian origin. The significance of the selected age is as follows—.Twelve years is well above the amblyopiogenic age and subjective testing is more accurate in children above this age. In a patient equal to or more than forty years, there is a conversion of with the rule astigmatism to against the rule astigmatism, which can occur as early as 35 years in a hypermetrope. Hence if a patient is considered above the age of 35, there may be a chance of missing the primary astigmatic error.7

Exclusion criteria-

  1. All refractive errors and conditions other than astigmatism.
  2. Astigmatism induced by ocular pathologies like keratoconus.
  3. Any patient with previous history of ocular surgeries.

5.2 METHOD OF COLLECTION OF DATA

Patients of either sex between the age of 12-35 presenting to the OPD in department of Ophthalmology in St.Johns Medical College and Hospital from April 2010 to March 2012 with regular astigmatism more than or equal to one diopter will be included in the study.

A detailed history including demographics, information regarding blurring of vision, distorted vision, photophobia, headache, eye strain following focus for long period and previous use of spectacles will be recorded in a proforma. The effect of these visual deficits on quality of life will be recorded using Proposed WHO/PBD Visual Functioning Questionnaire (20 item).8

Ophthalmological examination will be done in both eyes after written informed consent:

Visual acuity with anilluminated ETDRS chart,slit lamp examination, fundus evaluation and applanation tonometry. The patients will be subjected to cycloplegic refraction using tropicamide (one drop every five minutes for three times, refraction being carried out after 20 minutes) by Autorefractokeratometer-Humphrey ARK model 599. Two days later, patients are corrected with spectacles of appropriate power following which contrast sensitivity by Pelli Robson chart and stereo acuity testing by Titmus fly test and vernier acuity testing will be done.

The percentages along with the confidence intervals for the occurrence of each visual deficit will be calculated. Chi square test or Fisher’s exact test for categorical variables and ANOVA for quantitative variables will be done to correlate factors which affect the visual outcomes in astigmatism.

5.3 Does the study require any investigations or interventions to be conducted on patients, other humans or animals?

The various tests enumerated as a part of study are routinely done as a part of work up for a patient presenting to OPD with a complaint of diminution of vision.

5.4 Was ethical clearance obtained in this case?

Yes

6. LIST OF REFERENCES:

  1. Kleinstein RN, Jones LA, Hullett S, Kwon S et al (2003). “Refractive Error and Ethnicity in children”. Arch Opthalmol .121(8):1141-7.
  1. Harvey EM, Dobson V, Miller JM, Clifford-Donaldson CE. Amblyopia in astigmatic children: patterns of deficits. Vision Res. 2007;47:315-326.
  1. Abrahamsson M, AnderssonAK, Sjostrand J. A longitudinal study of a population based sample of astigmatic children. Acta ophthalmol. 1990;68:428-440.
  1. Harvey EM, Dobson V, Clifford Donaldson CE. Miller JM. Optical Treatment Of Amblyopia in Asigmatic Children:The Sensitive Period for Successful Treatment. Ophthalmology 2007;114:2293-2301.
  1. Dobson V, Clifford Donaldson CE, Tina K. Green, Miller JM, Harvey EM. Optical Treatment Reduces Amblyopia in Astigmatic Children Who Receive Spectacles Before Kindergarten. Ophthalmology 2009;116:1002-1008.
  1. R.Thad Goodwin, Paul E Romano. Stereoacuity Degradation by Experimental and Real Monocular and Binocular Amblyopia. Invest Ophthalmol Vis Sci 1985;26:917-923.
  1. Jane Gwiazda, Mitchell Scheiman, Indra Mohindra, Richard Held. Astigmatism in Children: Changes in Axis and Amount from Birth to Six Years. Invest Ophthalmol Vis Sci 1984;25:88-92.
  1. Consultation On Development Of Standards For Characterization Of Vision Loss And Visual Functioning, WHO Geneva 4-5 September, 2003.

7. SIGNATURE OF THE CANDIDATE:

  1. REMARKS OF THE GUIDE:

Refractive errors are the most common of ophthalmic cases seen in our out patient department. Surprisingly very little Indian literature exists on astigmatism and its correlation to amblyopia. Not much information exists on how amblyopia affects the quality of life in the context of studies and work.

Astigmatism also confuses our undergraduates and postgraduates as a subject and I hope this postgraduate will master the subject of astigmatism and refraction errors by the time of completion.

9. NAME AND DESIGNATION OF:

9.1 GUIDE: DR.COLIN A.S. NAZARETH

PROFESSOR

DEPARTMENT OF OPHTHALMOLOGY

9.2 SIGNATURE:

9.3 CO GUIDE: DR.USHA VASU

PROFESSOR

DEPARTMENT OF OPHTHALMOLOGY

9.4 SIGNATURE:

9.5 HEAD OF DR.REJI KOSHI THOMAS

DEPARTMENT: PROFESSOR

DEPARTMENT OF OPHTHALMOLOGY

9.6SIGNATURE:

10.1REMARKS OF THE CHAIRMAN AND THE PRINCIPAL:

10.2 SIGNATURE:

Rajiv Gandhi University of Health Sciences, Bangalore

PROFORMA FOR REGISTRATION OF SUBJECTS FOR DISSERTATION

1.Name of the candidate: Dr. Deepti .P

Address: Department of Ophthalmology

St. JohnsMedicalCollege

John nagar

Bangalore-560034

2.Name of the institution: St. JohnsMedicalCollege

Course: M.S.Ophthalmology

Date of admission to the course: 25-03-2010

3.Title of the topic: ASTIGMATISM RELATED ALTERED QUALITY OF VISION IN INDIAN PATIENTS.