Dr. SANITHA SATHYAN

Dr.MATHEW KURIAN

Semi Finals

Abstract

AIM: To compare near stereoacuity(TNO) versus visual acuity tests(Lea Symbols/ Sheridan Gardiner) for amblyopia risk factor detection among preschoolers. METHODS: In this comparative observational study, 525 preschoolers, 3 to 6 years, were screened for amblyopia risk factors, using TNO steroacuity test and visual acuity (LS/ SG). Cut off for LS and SG was 0.3 log MAR and TNO was 120 sec. The data was analyzed using descriptive methods and Chi Square test. Results: The methods agreed in 388 (72.9%) subjects. Only 32 children who passed TNO failed LS/SG; while 112 children who passed LS/SG failed TNO test; (p=0.51). Differences in age wise comparisons was also not significant: 3 years (p=0.50), 4 year (p=0.59), 5 year(p=0.11) and 6 year (p=0.51). Conclusion: There is no significant difference in detection rates of LS/SG and TNO, though detection with TNO was greater. TNO is easier and faster and therefore can be used as a standalone test to improve screening process efficiency.

Full Text

 

ABSTRACT:

AIM: To compare the efficacy of preschool visual acuity charts (Lea Symbols/ HOTV) with TNO stereoacuity chart for the detection of amblyopia risk factors among preschoolers. METHODS: In this comparative observational study, 634 preschoolers between 3 to 6 years of age underwent screening using TNO near stereoacuity and Lea symbols/ HOTVcharts and the screening efficacy was analyzed using Chi Square test. RESULTS: The methods agreed in 537 (87.70%) children and did not agree in 97 (15.30%). In the total population, 48 children (7.57%) missed in visual acuity screening were detected by TNO test (p=0.00). Forty-nine children (7.72%) who were missed in TNO test were detected by visual acuity screening (p=0.00). Age wise comparisons between detection rates of the two tests were also significant: 3years (p=0.005), 4years (p=0.007), 5years (p=0.002) and 6years (p=0.00). CONCLUSION: Combination of visual acuity and stereoacuity screening is the preferred intervention. As standalone, TNO is preferred in the 3- and 4-year-olds. In 5- and 6-year-olds, either of the tests can be used with comparable screening efficacy

INTRODUCTION:

Preschool vision screening is an important public health intervention aimed at timely detection of amblyopia and its risk factors. The United States Preventive Task Force recommends screening all children between 3 to 5 years to detect amblyopia and its risk factors ^(1,2) as they are old enough to co-operate and within the window for effective interventions. ⁽³⁾

Screening for risk factors of amblyopia among preschool children is challenging. Conventional methods of screening involve distance visual acuity estimation using age-appropriate visual acuity charts. Popular among these are Lea Symbols chart, HOTV chart etc. Visual acuity estimation using these charts requires good comprehension, relatively good attention span and skills for naming/ matching the optotypes. This is also a resource/ labor intensive and time-consuming procedure, to be done by trained professionals. ^(4,5,6) Though useful for large scale screening, vision screeners and photorefractors, are more expensive and may not be viable in smaller eye care facilities and in developing countries. ⁽³⁾

Stereoacuity tests measure the quality of binocular vision. In potentially amblyogenic conditions like childhood refractive errors, strabismus and media opacities, binocular vision fails to develop normally. This failure in binocular vision development can be detected even in young children, who may not co-operate for formal screening with conventional visual acuity charts used for pre-school children.

This study was done to compare the efficacy of amblyopia risk factor screening using near stereoacuity chart and pre-school visual acuity charts, among preschoolers in an urban setting.

AIM: Aim of this study is to compare the efficacy of visual acuity screening using Lea Symbols/HOTV charts and TNO stereoacuity chart, in screening for amblyopia and its risk factors among preschool children, between 3 to 6 years of age.

METHODS:

In this comparative observational study, a total of 702 children from 12 preschools in an urban locality were enrolled. The study was done as a part of the preschool outreach screening conducted by a tertiary care eye facility and the study period was from November 2019 to January, 2020. All children between 3 and 6 years of age, who succeeded the pre-test and from whom reliable screening measurements could be obtained were included in the study. Those with unreliable measurements, neurological deficits, mental retardation, and multiple disabilities were excluded. The study adhered to the tenets of the Declaration of Helsinki and informed consent letter was obtained from parents/ guardians of all children before the screening procedure.
Procedure:
All the participants were tested at the preschool premises during the working hours, in a dedicated space with illumination more than 300 lux. Near stereo acuity screening was done first in all patients to avoid the effect of mono-ocular occlusion on stereoacuity values. Near stereoacuity testing was explained to each child using a single stereogram card with a “popping out” cartoon image. After familiarizing the child with the concept of stereovision, near stereoacuity estimation was formally done. TNO stereo test (Lameris Intrumenten, Groenekan, the Netherlands, 10th edition), held at a distance of 40 cm was used for near stereoacuity estimation. After wearing red/green anaglyph stereo glasses, the child was first presented with plate I and the response was recorded. When correct response was obtained, plates II and III were shown. After this threshold stereoacuity measures were obtained using plates V–VII and levels of disparity from 480, 240, 120, 60, 30, and 15 arc sec were tested and the results recorded. Those children who could identify the level of disparity corresponding to 240 sec of arc were denoted as ‘pass’ and those who could not identify it were denoted as ‘fail.’

Pretesting using Lea Symbols chart (LS) / HOTV chart (HOTV) was done to ascertain whether the child could identify the optotypes. A card with a single large symbol in LS or letter in HOTV was held at 60 cm from the child and the child was instructed to match the optotype with the key card. This was repeated for the four symbols and six letters and a maximum of two chances to respond were given. Only those children who responded correctly were selected for further examinations and others were excluded.

Those who passed the pretest underwent formal vision screening using Lea Symbols Chart (LS 10-line folding pediatric eye chart and key card (250200, Good-Lite Co; Elgin, IL) and HOTV and the corresponding key cards (2204-P-1004, Keeler, Windsor, The United Kingdom). The examination distance was 3 meters. Right eye was tested first followed by the left eye.

Testing with Lea Symbols was initiated at a line where the child instantly recognized the optotypes. Only when the first three optotypes at a particular level were answered correctly, was the next higher line introduced. If only two of the three symbols were answered correctly in a particular line, was the fourth symbol asked. If correct response was obtained, the examiner proceeded to the next line. If there were fewer than three correctly identified optotypes in a particular line, the previous line was taken as the visual acuity estimate. With HOTV chart, children who could identify all the letters in a row were tested for the next line. If the child could not identify all the letters in a line, the value of the previous line was considered as the visual acuity. Visual acuity cut off score for both the charts was taken as the line corresponding to 0.4 logMAR for 3-year-olds, 0.3 logMAR for 4-year-olds, 0.2 logMAR for 5-year-olds and 0.1 logMAR for 6-year-olds. Those who could identify the cutoff line were denoted as ‘pass’ and those who failed were denoted as ‘fail.’

All the children underwent corneal reflex test, evaluation of ocular movements, cover test, non-mydriatic retinoscopy and flash light examination. Those who failed any of these tests were referred to the base hospital for detailed evaluation.

Statistical analysis: Statistical analysis was performed using SPSS software for Windows version 20.0 (SPSS Inc., Chicago, Illinois, USA). Descriptive tests were used to analyze the visual acuity and stereoacuity estimate. The Chi Square was used for significance testing and p< 0.05 was taken as significant.

RESULTS:

Of the 702 children enrolled, 634 (90.31%) children who were judged by the observers as successfully comprehending the pre-tests for visual acuity and stereoacuity were included in the final analysis. Sixty-eight (9.69%) children who failed to comprehend/ respond to the pre-tests were excluded. Out of the 634 children in the final sample, 33 children (5.21%) were 3 years of age, 63 (9.94%) were 4 years of age, 203 (32.02%) were 5 years of age and 335 (52.84%) were 6 years of age. There were 322 males (50.79%) and 312 females (49.21%).

The mean visual acuity was 0.18±0.08 logMAR in 3-year-olds, 0.17±0.04 logMAR in 4-year-olds, 0.08±0.02 logMAR in 5-year-olds and 0.06±0.02 logMAR in 6 year olds. The mean near stereoacuity estimated was 747.00±134.22 sec of arc in 3-year-olds, 306.88±95.42 sec of arc in 4 year olds, 197.44±233.91 in 5 year olds and 263.58±189.37 in 6 year olds.

Using the criteria for ‘pass’ and ‘fail,’ 8 patients (24.24%) of the 3-year-olds, 6 patients (9.52%) of the 4 year olds, 29 (14.29%) of the 5 year olds and 42 (12.54%) of the 6 year olds, failed the visual acuity screening. Using the TNO stereoacuity cut off, 14 patients (42.42%) of the 3-year-olds, 11 patients (17.46%) of the 4 year olds, 28 (13.79%) of the 5 year olds and 31 (9.25%) of the 6 year olds failed the stereoacuity screening. (Table: 1)

Table: 1 Mean visual acuity and stereoacuity estimates

Age	Mean presenting visual acuity	Mean stereoacuity (sec of arc)
3 years	0.18±0.08 logMAR	747.00±134.22
4 years	0.17±0.04 logMAR	306.88±95.42
5 years	0.08±0.02 logMAR	197.44±233.91
6 years	0.06±0.02 logMAR	263.58±189.37

Table: 2 Age wise cross tabulation of visual acuity and stereoacuity estimates

Age group		TNO fail	TNO pass	Total	P-value (Chi Square test)
3 years	Visual acuity fail	7	1	8	0.005
	Visual acuity pass	7	18	25
	Total	14	19	33
4 years	Visual acuity fail	4	2	6	0.007
	Visual acuity pass	7	50	57
	Total	11	52	63
5 years	Visual acuity fail	10	19	29	0.002
	Visual acuity pass	18	156	174
	Total	28	175	203
6 years	Visual acuity fail	15	27	42	0.000
	Visual acuity pass	16	277	293
	Total	31	304	335
Total	Visual acuity fail	36	49	85	0.000
	Visual acuity pass	48	501	549
		84	550	634

The screening outcome according to the pass/ fail criteria (visual acuity charts based/ TNO stereoacuity based) agreed in 537 (87.70%) children; but did not agree in 97 (15.30%) children. In the total population, 48 (7.57%) children who failed the visual acuity screening, passed the TNO screening. and 49 (7.73%) children who failed in visual acuity test passed the TNO test (Figure:1).

Figure: 1 Pattern of agreement between the visual acuity estimate and the TNO estimate

Subgroup analysis was done as the younger age group (3 and 4 years) and the older age group (5 and 6 years). In the younger age group (3 and 4 years), methods agreed in 79 (82.29%) children and did not agree in 17 (17.71%). Among the 3-year-olds, 25 (75.76%) children would have the same screening outcome if either of the tests was used, 8 (24.24%) would have different outcome with the tests. In the 4-year-olds, 54 (85.71%) children would have the same outcome if either test was used for screening, and 9 (14.29%) would have different outcome.

In the older age group (5 and 6 years), methods agreed in 457 (84.94%) patients and did not agree in 80 (14.87%) children. Among the 5-year-olds, 166 (81.77%) children would have the same outcome if either test was used for screening, and in 37 (18.23%) the outcome would have been different. In the 6-year-olds, 292 (87.16%) children would have the same outcome if either test was used for screening, 43 (12.84%) would have different outcomes.

Among the 3-year-olds, 8 (24.24%) children would be referred for further evaluation if visual acuity screening criteria alone was used and 14 (42.42%) children would be referred if TNO test screening criteria alone was used. In the 4-year age group, 6 (9.52%) children would be referred for further evaluation if visual acuity screening criteria alone was used and 11 (17.46%) children would be referred if TNO test screening criteria alone was used. The referral rates would be 29 (14.29%) and 28 (13.79%) in the 5-year age group and 42 (12.54%) and 31 (9.25%) in the 6-year-old age group, for visual acuity screening and stereoacuity screening respectively. Figure: 2 represents the referral rates by the visual acuity and stereoacuity screening criteria.

Figure: 2 Referral rates by visual acuity and stereoacuity tests