Page 18 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

CHAPTER 1
eye movements are used to stabilize a moving stimulus on the retina. This test indicates whether there is coordination between both eyes, tests the cerebral development and tests the function of the eye muscles.
Visual acuity
Visual acuity is the ability of the eye to distinguish detail and can be assessed with optotype acuity charts. Visual acuity measurements can be performed from the age of three years with picture optotypes. These picture optotypes however measure not only VA but also recognition and cognitive skills. From the age of 4-5 years VA can be reliably tested with normal optotypes (logarithmic or Snellen) charts. Crowded VA charts have been shown to be more sensitive in detecting amblyopia. Each eye should be tested separately with the other eye covered.
Visual acuity testing has been shown to have very high sensitivity and specificity for detection of amblyopia.28,29 It is also sensitive to refractive errors, especially myopia, but myopia is uncommon in preschool children, and usually does not lead to amblyopia. Visual acuity testing is relatively easy to perform and it can be carried out by non- ophthalmologic personnel. Visual acuity screening, with re-screening of inconclusive cases, has moreover been shown to be favourable from a cost-benefit point of view. It is however time-consuming and sensitive to simple refractive errors.
Conditions not affecting VA might naturally elude observation in a setting with VA based screening, e.g. strabismus with normal VA, minor ptosis or small partial cataracts. On the other hand, without impact on VA these disorders do not require treatment in preschool children. Strabismus may represent a cosmetic problem, though, but that is beyond the aim for vision screening. Large-angled strabismus will be detected without screening and strabismus that is not cosmetically obvious is not easy to detect without expert testing. Most cases of microstrabismus will not require surgery.
In the Netherlands the Amsterdam Picture Chart (APK) and Landolt C charts are most often just at the CHC centres.
16