Appendix. Search Strategy

Database: MEDLINE®
Yrs: 1999-April 2003

Search No.	Search Terms
1	exp AMBLYOPIA/ (584)
2	limit 1 to (human and English language and yr=1999-2003) (286)
3	limit 2 to (all infant <birth to 23 months> or preschool child <2 to 5 years>) (169)
4	limit 3 to (clinical trial or meta analysis or practice guideline or randomized controlled trial or review) (34)
5	limit 1 to (human and abstracts) (446)
6	limit 5 to (all infant <birth to 23 months> or preschool child <2 to 5 years>) (257)
7	6 not 3 (118)
8	from 3 keep 1-169 (169)

 

Search No.	Search Terms
1	vision tests/ or vision screening/ or exp Vision Disorders/di (2888)
2	limit 1 to (human and English language and (all infant <birth to 23 months> or preschool child <2 to 5 years>) and yr=1999-2003) (281)
3	limit 2 to (clinical trial or meta analysis or practice guideline or randomized controlled trial or review) (53)
4	"Sensitivity and Specificity"/ (70623)
5	exp "Outcome Assessment (Health Care)"/ (139719)
6	2 and (4 or 5) (51)
7	3 or 6 (96)
8	from 7 keep 1-96 (96)

Database: Cochrane Library
- Controlled clinical trial registry (CCTR)
- Systematic reviews (CDSR)
Yrs: 1999-2003

Key Words:
"Amblyopia" and "Preschool"

Inclusion and Exclusion Criteria for Abstracts About Screening

Include:

Search No.	Search Terms
1	Amblyopia/Preschool (lazy eye and other terms may apply)

Exclude:

Search No.	Search Terms
2	Not an RCT
3	Surgery study
4	Treatment study
5	Not our Scope/Not amblyopia
6	Not Ages 0-5
7	High risk population
8	Screening test other than for amblyopia
9	Animal study
10	Non-English abstract
11	Other

Criteria for Grading the Internal Validity of Individual Studies^a

Randomized Controlled Trials (RCTs) and Cohort Studies

Criteria:

• Initial assembly of comparable groups:
  • For RCTs: adequate randomization, including first concealment and whether potential confounders were distributed equally among groups.
  • For cohort studies: consideration of potential confounders with either restriction or measurement for adjustment in the analysis; consideration of inception cohorts.
• Maintenance of comparable groups (includes attrition, cross-overs, adherence, contamination).
• Important differential loss to followup or overall high loss to followup.
• Measurements: equal, reliable, and valid (includes masking of outcome assessment).
• Clear definition of interventions.
• Important outcomes considered.
• Analysis: adjustment for potential confounders for cohort studies, or intention-to-treat analysis for RCTs.

Definition of ratings based on above criteria:

Rating	Definition
Good:	Meets all criteria: comparable groups are assembled initially and maintained throughout the study (followup at least 80%); reliable and valid measurement instruments are used and applied equally to the groups; interventions are spelled out clearly; important outcomes are considered; and appropriate attention to confounders in analysis. In addition, for RCTs, intention-to-treat analysis is used.
Fair:	Studies will be graded "fair" if any or all of the following problems occur, without the fatal flaws noted in the "poor" category below: generally comparable groups are assembled initially but some question remains whether some (although not major) differences occurred in followup; measurement instruments are acceptable (although not the best) and generally applied equally; some but not all important outcomes are considered; and some but not all potential confounders are accounted for. Intention-to-treat analysis is done for RCTs.
Poor:	Studies will be graded "poor" if any of the following fatal flaws exist: groups assembled initially are not close to being comparable or maintained throughout the study; unreliable or invalid measurement instruments are used or not applied equally among groups (including not masking outcome assessment); and key confounders are given little or no attention. For RCTs, intention-to-treat analysis is lacking.

In general, a "good" study is one that meets all criteria well. A "fair" study is one that does not meet (or it is not clear that it meets) at least 1 criterion but has no known fatal flaw. "Poor" studies have at least 1 fatal flaw.

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^a Harris RP, Helfand M, Woolf SH, et al. Current methods of the U.S. Preventive Services Task Force: A review of the process. Am J Prev Med 2001;20:21-35.

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Search and Selection of Literature About Screening

[D] Select for Text Description.

Definitions

Amblyopia

• Functional amblyopia: difference of 2 or more Snellen lines between the 2 eyes.¹
• More than 1 line difference between the 2 eyes.²
• Reduced visual acuity that is not instantly alleviated by wearing spectacles, in an otherwise apparently healthy eye.³
• Amblyopia A: difference in acuity between the 2 eyes is 2 or more lines on the chart (0.2 logMAR).
• Amblyopia B: visual acuity in the amblyopic eye is worse than 0.3 logMAR.
• Reduced visual acuity in 1 or both eyes due to abnormal binocular interaction.⁴
• Impairment of vision without detectable organic lesion of the eye.⁵ Types: alcoholic, arsenic, nutritional deficiency, color, nocturnal, quinine, reflex, stabismic (resulting from suppression of vision in 1 eye to avoid diplopia, tobacco, toxic, traumatic, uremic).
• A condition of reduced Snellen acuity for which there is no evidence of an organic cause. This clinical definition is restricted to 1 kind of visual loss, which is recognition acuity for high-contrast targets. Psychophysicists suggested a more useful definition of amblyopia as "a developmental anomaly involving primarily those cortical mechanisms involved in form and shape perception."⁶
• Reduced acuity in 1 or both eyes without any clear ocular lesion.⁷
• A form of defective central visual processing, manifested as decreased visual acuity in 1 eye.⁸

Squint

• Strabismus.⁵

Strabismus

• Deviation of the eye that the patient cannot overcome. The visual axes assume a position relative to each other different than that required by the physiological conditions. The various forms of strabismus are spoken of as tropias, their direction being indicated by the appropriate prefix, as cyclotropia, esotropia (cross-eyed), exotropia, hypertropia, and hypotropia.
• The most common cause of amblyopia.⁹

References

1. Atilla H, Oral D, Coskun S, Erkam N. Poor correlation between "fix-follow-maintain" monocular/binocular fixation pattern evaluation and presence of functional amblyopia. Binocul Vis Strabismus Q 2001;16(2):85-90.

2. Eibschitz-Tsimhoni M, Friedman T, Naor J, Eibschitz N, Friedman Z. Early screening for amblyogenic risk factors lowers the prevalence and severity of amblyopia. J AAPOS 2000;4(4):194-9.

3. Williams C, Northstone K, Harrad RA, Sparrow JM, Harvey I; ALSPAC Study Team. Amblyopia treatment outcomes after screening before or at age 3 years: follow up from randomised trial. BMJ 2002;324(7353):1549.

4. Kemper A, Harris R, Lieu T, Homer C, Whitener BL. Screening for Visual Impairment in Children Younger than Age 5 Years. Systematic Evidence Review No. 27 (Prepared by the Research Triangle Institute—University of North Carolina Evidence-based Practice Center under Contract No. 290-97-0011). Rockville, MD: Agency for Healthcare Research and Quality. May 2004. (Available at: http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hstat3.chapter.33443).

5. Dorland's Illustrated Medical Dictionary, 29th ed. WBS Company; 2000.

6. Demirci H, Gezer A, Sezen F, Ovali T, Demiralp T, Isoglu-Alkoc U. Evaluation of the functions of the parvocellular and magnocellular pathways in strabismic amblyopia. Pediatr Ophthalmol Strabismus 2002;39(4):215-21.

7. Adams GG, Sloper JJ. Update on squint and amblyopia. J R Soc Med 2003;96(1):3-6.

8. Tong PY, Bassin RE, Enke-Miyazaki E, et al. Screening for amblyopia in preverbal children with photoscreening photographs: II. Sensitivity and specificity of the MTI photoscreener. Ophthalmology 2000;107(9):1623-9.

9. Altemeier WA 3rd. Preschool vision screening: the importance of the two-line difference. Pediatr Ann 2000;29(5):264-7.

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