Measuring-Palpebral-Fissures

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Measuring Palpebral Fissures

 
 
 
 
Methods of Measurement

Palpebral fissure measurement has a troubling amount of importance in the FASD physical assessment. The most common method consists of direct measurement with a clear plastic ruler held as close to the eye as possible and parallel to the angle of the fissure in all dimensions. This is not challenging conceptually but since errors of 1 to 2 mm can result in misdiagnosis, practice is required in order to establish technical precision. Studies comparing various techniques of palpebral fissure measurement have shown discrepancies between measurements made by ruler, calipers, or computerized photographic analysis that are potentially significant, and clarified the need for a standardized approach.1-4 From a purely practical standpoint, many clinicians (and parents) are uncomfortable with the use of calipers to measure palpebral fissures, and physicians in busy primary care settings are unlikely to adopt computerized photographic analysis methods. For the purpose of this toolkit then, measurement by ruler is assumed to be the technique most likely to be used by primary care providers.

Standards for Measuring Length
In addition, there are several published sets of standards for palpebral fissure length, which sometimes causes confusion. One that is popular among experienced FASD diagnosticians is from Thomas et al.5 This is also published in a reference book in wide usage by dysmorphologists , neonatologists, and many pediatricians.6 It was constructed using centiles and is based on data from 348 white American children between the ages of 29 weeks’ gestation and 14 years. It was recommended for use only in children in that demographic group, and the specific measurement technique was not described. A chart based on this data and others was published in another widely used reference book,7 but due to discrepancies between that version, the original Thomas version, and more recent data,8 the principal editor recommended that its use be discontinued.9 Others have been developed recently using photographic techniques, notably including the work by Clarren et al.9 This is based on data from 2097 Canadian school children aged 6 to 14 years whose standardized photos were analyzed using computer software, and are expressed in standard deviations. This paper also analyzed data from several racial and ethnic subpopulations and compared standards for boys and girls. Gender variance was clinically significant, and separate charts for males and females were provided. Among ethnic groups they found clinically insignificant differences with means varying by a millimeter or less. Others have shown that racial and ethnic differences may be significant. 2,5,10,11 The Canadian standards were validated in 928 American school-aged children in Washington.2

Choosing the Right Standard
So which is the “right” standard to use? The Canadian standards are very attractive, particularly to those who prefer computerized photographic analysis. This is fitting in light of the sample size, the quality of the data analysis, and the attention given to analysis of previous data sets. They do not, however, provide standards for children younger than 6.  Primarily for that reason, many clinicians experienced in FASD diagnosis continue to use the chart by Thomas.5,6 The Thomas chart is based on direct physical measurement, and presents the standards as percentiles rather than standard deviations, which is consistent with the decision by the National Task Force on Fetal Alcohol Syndrome,12 to use palpebral fissure length at or below the 10th percentile as one of the diagnostic criteria.  Unless new standards are established for palpebral fissure lengths by ruler measurement among a sufficiently large population of children of varying racial and ethnic backgrounds, and plotted along percentiles, the Thomas chart is likely to continue to be used, especially in the community health setting.


References
 
  1. Cranston ME, Mhanni AA, Marles SL, Chudley AE. Concordance of three methods for palpebral fissure length measurement in the assessment of fetal alcohol spectrum disorder. Can J Clin Pharmacol. 2009;16(1):e234-e241
  2. Astley SJ. Canadian palpebral fissure length growth charts reflect a good fit for two school and FASD clinic-based U.S. populations. J Popul Ther Clin Pharmacol. 2011;18(2):e231-e241 
  3. Shaner DJ, Bamforth JS, Peterson AE, Beattie OB. Technical note: different techniques, different results–a comparison of photogrammetric and caliper-derived measurements. Am J Phys Anthropol. 1998;106:547-552 
  4. Shaner DJ, Peterson AE, Beattie OB, Bamforth JS. Facial measurements in clinical genetics: how important are the instruments we use? Am J Med Genet. 1998;77:384-390 
  5. Thomas IT, Gaitantzis YA, Frias JL. Palpebral fissure length from 29 weeks gestation to 14 years. J Pediatr. 1987:111(2):267-268  
  6. Jones KL. Smith’s Recognizable Patterns of Human Malformation. 6th ed. Philadelphia, PA: Elsevier; 2006:859 
  7. Hall JG, Froster-Iskenius UG, Allanson JE. Handbook of Normal Physical Measurements. New York, NY: Oxford University Press; 1989 
  8. Clarren SK, Chudley AE, Wong L, Friesen J, Brant R. Normal distribution of palpebral fissure lengths in Canadian school age children. Can J Clin Pharmacol. 2010;17(1):e67-e78 
  9. Hall JG. New palpebral fissure measurements. Am J Med Genet A. 2010;152A:1870  
  10. Fuchs M, Iosub S, Bingol N, Bromisch DS. Palpebral fissure size revisited. J Pediatr. 1980:96(1):77-78 
  11. Douglas TS, Viljoen DL. Eye measurements in 7 year old black South African children. Ann Hum Biol. 2006;33(2):241-254 
  12. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Department of Health and Human Services. Fetal Alcohol Syndrome: Guidelines for Referral and Diagnosis. Atlanta, GA: Centers for Disease Control and Prevention; 2004
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