two retinae with foveae being the principle corresponding points. In spite of the normal anatomical development of both eyes, interruption of physiological development in visual acuity of one eye can lead to amblyopia. This definition is based solely on visual acuity; however, this definition does not take into account the qualitative differences in vision that an amblyopic often experiences resulting in poorer vision than that measured by Snellen’s chart. Amblyopia till date remains a diagnosis of exclusion.

Children constitute 35-40% of the general population. School going children.¹, therefore, form an important large target group and school vision screening plays an important part in early detection of amblyopia and institution of appropriate therapy, which is of immense value towards preventing the development of lifelong visual morbidity.

The time necessary for amblyopia to occur during the critical period.² is shorter for stimulus deprivation amblyopia than for strabismic amblyopia or anisometropic amblyopia. Around the age of two to four weeks, a period of dramatic developmental plasticity.³ is found to occur when the developing functional and anatomic organisation of the visual system is influenced markedly by visual experiences, which are both uniocular and or binocular. Visually significant conditions like monocular or binocular visual deprivation, anisometropia, strabismus or abnormal visual environment during this period results in significant electrophysiological and anatomic abnormalities in striate cortex and in the lateral geniculate nucleus (LGN).

There occur losses in the number of responsive cells to the deprived eye, a loss of binocularly responsive cells, shrinkage of cells in the LGN laminae serving the deprived eye and significant abnormalities in the response qualities of the cells that remain throughout life. Primate models of amblyopic have repeatedly shown the primary visual cortex (area VI) to be dysfunctional. Functional imaging confirms the presence of processing abnormalities in area VI of the human cortex and also hints at deficits within the higher cortical areas.

In the context of amblyopia, it has often been stated that treatment is ineffective after the age of 8 years. While this may be true for some types of amblyopia, for example, complete unilateral congenital cataract, where treatment must be commenced within a few weeks of birth to be effective, for other causes of amblyopia there is increasing evidence that treatment may be effective beyond this age.

METHODS

A cross-sectional and time bound study was conducted among 50 children aged 5-15 years attending the OP at Ophthalmology Department, GRH Madurai as well as the School Health Program screening camps. The children who had decreased visual acuity, complaints of asthenia and deviation of eye were thoroughly examined for their refractive status, anterior and posterior segment examination done to determine the prevalence and types of amblyopia among school going children in our area–their improvement after partial occlusion therapy.⁴ Patients aged 5-15 years with refractive errors were included in the study. Criteria for exclusion were patients with known cause of reduced visual acuity, patients with myopia greater than spherical equivalent of - 6.00 D, history of previous amblyopia treatment within one year, those who had undergone intraocular surgery, known skin reaction to patch or bandage adhesive and dropouts and noncompliant patients were excluded from final analysis.

Ethical Committee Clearance

Ethical committee clearance was obtained from Institutional Review Board/Independent Ethics Committee of Govt. Rajaji Hospital.

METHODOLOGY

A diagnosis of Amblyopia was made and they were further grouped into moderate and severe amblyopia according to their degree of visual loss. A few numbers of the patients who presented with temporal pallor on dilated fundus examination were further subjected to CT scan to rule out a possibility of the organic lesion. A thorough refractive correction.⁵ was done. Patients with high myopia and hypermetropia were excluded from the study. Treatment options like refractive error correction and partial occlusion were discussed with the patients. The duration of occlusion therapy was three hours where the patients were emphasised to do near activity tasks. Compliance to treatment.⁶ for more effective results was stressed to both the patient and his/her parents. Depending on the severity of amblyopia, children with moderate amblyopia were advised occlusion for three hours per day and children with severe amblyopia were advised occlusion for six hours per day. The importance of near vision tasks was instructed to the patients. Parents and teachers were asked to motivate the child to wear the occlusion patches.

Patients were explained the importance of treatment of amblyopia, where stress was given on early intervention, self-motivation and dedicated followup. They were asked to come for followup after three months of occlusion. Significant improvement in visual acuity was seen in younger patients with good compliance which was tested with Snellen’s visual acuity chart that showed an improvement in visual acuity by one or two lines. Patients whose visual acuity failed to improve after three months of occlusion therapy were counselled for better compliance and motivation was given to increase the duration of occlusion to six hours a day. However, a very limited number of patients who failed to improve even after six months were referred to an alternate method of treatment and explained about the use of low visual aids, etc.

Patients with a significant amount of ptosis or congenital cataract were explained about the possibility of stimulus deprivation amblyopia and were referred for surgical correction. In each case after analysis of the type of amblyopia, proper counselling was given and the prognosis for each case was discussed with both the parents of the patient and the teachers also.

OBSERVATION AND ANALYSIS

The number of patients in the younger age group (5-10 years of age) was 32, and those in the older age group (11-15 years of age) were 18. There were totally 50 patients of whom 26 were boys and 24 were girls. A higher incidence of amblyopia was detected among the younger age group 64% as compared to the older age group 36%. A proper understanding of complaints revealed that the patients who came to our OPD mainly complained of visual discomfort (50%) which was followed by deviation of the eye (30%) and a few patients had complaints of asthenia. A higher incidence of amblyopia was seen in the rural population (58%) as compared to the urban population (42%). Our study shows moderate amblyopia (72%) is more prevalent than severe amblyopia (28%). The response to occlusion therapy in severe amblyopia is less than moderate amblyopia with some reversibility (Table: 3).

A careful analysis of anterior segment in these patients revealed a normal anterior segment in nearly 70% of the patients and tropias in the remaining 30%. Posterior segment examination revealed normal fundus in the majority of the patients (94%) and with mild temporal pallor in 4% of the cases. The patients with temporal pallor were further evaluated with non-invasive imaging studies like CT scan to rule out any brain pathology. CT scan was found to be normal in these patients, helped us in the exclusion of amblyopia of organic aetiology.

Among the refractive errors prevalent in these patients (Table: 1), simple myopia at 20% and simple hypermetropia at 40% were commonly seen.

Myopic astigmatism was 8% more common than hyperopic astigmatism (2%). The prevalence of myopic among tropias was 10%, exotropia was more commonly seen than esotropia (5%). The duration of partial occlusion therapy was three to six hours per day.