Prevalence determination of the lost of visual acuity and severe amblyopia performed for students with limited resources
Carlos Carrión Ojeda. Ophthalmologist “OPELUCE” EYE CLINIC- Lima Perú
Flor Gálvez Quiroz. Ophthalmologist INSN
Raphael Jaramillo. Ophthalmologist INSN José Morales de La Cruz MD
Merí Gazani Meza. Nurse of Ophthalmology
Susana Guerrero Ocampo. “Aid in Action” Foundation
TRANSLATION: Eugene Fedeiko
INTRODUCTION: In Peru, where there are nearly 12 million children, reporting of studies of lost of visual acuity, associated ametropia and amblyopia in students has just started.
OBJECTIVE: To determine the prevalence and epidemiologic characteristics of lost of visual acuity and severe amblyopia in the students of the South of Lima, Peru.
METHODS: There are 120,000 students in 42 schools of five districts in this area of Lima. The study was performed on 12,364 students in their schools in three stages.
The first stage consisted of cross-sectional and observational evaluations of visual sharpness and refracting examinations.
The second stage consisted of ophthalmologic examinations for determine moderate and severe lost of visual acuity, and make respective cicloplegic refraction to these students.
The third stage consisted of detecting the amblyopic students if visual sharpness did not improve with corrective lenses, associating severe lost of visual acuity and amblyopia, and evaluating the existence of initial eyeglasses treatment for them. Excel 2003 was used to calculate sample and analyses results.
RESULTS: A high prevalence (46.3%) (p <0.01) of lost of visual acuity was discovered in the general student population and a high prevalence of amblyopia in students whit severe lost of visual acuity (39%). Four of each 10 students with severe lost of visual acuity had developed amblyopia (p< 0.029) and of these, 90.25% had not used lenses (p< 0.045).
CONCLUSIONS: It is urgent to take measures to help prevent visual amblyopia in children before and until age 5 since amblyopia diminishes student academic yields. It is, indeed, highly necessary to work to prevent these diseases to improve the future of our students.
KEY WORDS: Visual acuity, Ametropia, Amblyopia, Refraction.
In Peru there are no investigations related to the frequency or incidence of lost of visual acuity or amblyopia in students. The American Academy of Ophthalmology defines lost visual acuity as visual sharpness below 20/20 in one of the eyes in children older than five, 20/30 or less in four-year-olds, and 20/40 or less in one eye in three-year-olds. In Peru’s population of approximately 29 million, almost 11,600,000 are children. In the world population, the mean incidence of ametropia, almost always inherited, is about 30% to 35%.
Lost of visual acuity and ametropia associated is fundamentally diagnosed by means of measuring visual sharpness with standard “ directional E” Snellen cards positioned 6 meters from and at the same height of the visual axis of the patient. Severe lost of visual acuity and consequent amblyopia (sluggish eye) are general public health problems and whose prevention are great priorities in the global initiative for the elimination of avoidable visual incapacity. The World Health Organization and The American Academy of Ophthalmology define amblyopia as the incapacity to improve eye visual sharpness even after the use of correct prescription lenses. Over the whole world amblyopia is apparent in 3% to 4.5% of the population. Amblyopia limits learning capacity and impairs normal activity development, so special preventative attention is necessary including monitoring and properly controlling of visual sharpness in different stages of growth. Closely observing children in their games and book and whiteboard reading helps reveal effects of visual deterioration.
Classification of ambliopía according to lost of visual acuity.
• Deep <0,1.
• Moderate 0,5-0,1.
• Slight >0,5.
MATERIALS AND METHODS
This is a cross-sectional investigation revealing the frequency of lost visual acuity, ametropia associated and severe amblyopia in the schools of some districts in the South of Lima.
We used a snellen chart of the “E” letter to evaluate the sharpness of visual acuity and a autorefractometer “Unicos” trade mark.
• Operational definitions: Because ofthis, we define for our study the variable lost of visual acuity and severe amblyopia like.
Slight lost ofvisual acuity: Slightly impaired visual sharpness of minus 20/20 unto minus of 20/50 in one or both eyes.
Moderate lost of visual acuity: Visual sharpness from 20/50 unto minus of 20/70 in one or both eyes.
Severe lost of visual acuity: Reduced or equal visual sharpness of 20/70 in one or both eyes.
Severe amblyopia: Incapacity to improve eye visual sharpness even after the use of correct prescription lenses in students that present severe lost of visual acuity.
• Type and design of investigation: 3-stage prevalence investigation.
Stage I: study Observational and cross-sectional, whit diagnoses of individual visual sharpness and individual refraction in the school environment.
Stage II: Visual sharpness control, qualification of type of ametropia, and cicloplegic refraction.
Stage III: Detection of severe amblyopia and individualized remedial action with corrective lenses.
Population of the study:
The subject population of the study included the 120,000 students who study in the schools of the five districts in the South of Lima. The sample frame of 28,452 students corresponds to the overall total student population of the 42 schools, called Healthy Schools, which participated in this study.
Sample population for the first stage:
For an undetermined number of the population and a proportion of 50% of those diagnosed with lost acuity vision and ametropia associated - 5,6,17, Z =1.96 (α =0.05), maximum error β=0.01. The calculated student sample size was 9,604. To maintain a good degree of accuracy in the study and to step up to the great demand, 12,364 students aged 3 to 15 were enlisted in the first stage. The 42 Healthy Schools are spread over the five districts and constitute a significant sample for this study.
Sample population for the second stage: This sample was calculated on an undetermined size of the population. A proportion of 5% of amblyopia has been reported in different world studies - 9,25. Z =1.96 (α =0.05), maximum error β=0.045. The calculated student sample size was 90; however, this study revealed 105 students with severe ametropia in the first stage of this cicloplegic examination in search of amblyopia.
Sample population for the third stage: This sample was calculated in the same manner as the second sample, in this stage eyeglasses were employed. The students came up with their own eyeglasses after which the study checked each student for ambliopia. In the cases of the students thereafter whose ambliopia did not diminish, they were referred to other healthcare professionals for further treatment.
Criteria of inclusion:
Stage I: Students up to age 15 who studied in the healthy schools were identified between March and June of 2007. Students with good vision (20/20) in both eyes were excluded.
Stage II: The patients evaluated in this stage and diagnosed with moderate or severe visual acuity lost, agreed with paternal consent to be clinically treated (informed consent).
Stage III: The patients who passed through Stage II and whose vision did not improve with eyeglasses were passed into this further stage of sending on for more ophthalmologic care.