Fixation be hav ior and fixation preference testing can be described using the CSM (Cen tral, Steady, and Maintained) notation. Fixation during monocular viewing is described as central (foveal) or noncentral (eccentric), and steady (stable eye position) or nonsteady (rov ing eye movement or nystagmus). Maintained refers to fixation that is held during binocular viewing after the opposite eye is uncovered during fixation preference testing. Table 1-2 de scribes gradations of fixation preference and their corresponding CSM notation.
A child with a strong fixation preference is more likely to have amblyopia than a child with weak or absent fixation preference, but strong fixation preference does not necessar ily indicate amblyopia. Conversely, weak or absent fixation preference does not rule out amblyopia.
Cotter SA, Tarczy- Hornoch K, Song E, et al; Multi- Ethnic Pediatric Eye Disease Study Group.
Fixation preference and visual acuity testing in a population- based cohort of preschool children with amblyopia risk factors. Ophthalmology. 2009;116(1):145–153. Erratum appears in Ophthalmology. 2009;116(2):174.
Preferential looking tests
In infants and children who are too young to do optotype testing, quantitative vision can be assessed using forced- choice preferential looking techniques. The child is shown a card with a black-and-white grating (Teller Acuity Cards II, Precision Vision; Fig 1-3, T able 1-2 Examples of Fixation Preference Grading, in Order of Increasing Fixation Preference
| Fixation Preference | Examination Finding | CSM Notation |
| None | Child spontaneously alternates fixation or shows no fixation preference (eg, always prefers eye without prism on induced tropia testing) | CSM alternates |
| Weak preference, holds well with fellow eye | Fixation preference is present, but the child maintains fixation well with the nonpreferred eye during binocular viewing (>3 seconds, through smooth pursuit, through blinks) | CSM prefers right or left CSM through blink |
| Strong preference, holds briefly with fellow eye | Fixation preference is present; child can maintain fixation only briefly with the nonpreferred eye during binocular viewing (1–3 seconds, not through pursuit or blink) | CSM to blink CSM briefly |
| Strong preference, does not hold with fellow eye | Fixation preference is present, and the child cannot maintain fixation with the nonpreferred eye during binocular viewing (<1 second) Monocular fixation with the nonpreferred eye may be central and steady, central but unsteady, or eccentric and unsteady | CSnM CnSnM nCnSnM |
C = central; nC = noncentral; S = steady; nS = nonsteady; M = maintained; nM = nonmaintained.
Figure 1-3 Teller Acuity Cards can be used to mea sure visual acuity in a preverbal child. If the pattern is vis i ble to the child, the child looks toward the grating; other wise, the stripes blend into the gray background and the child shows no preference for looking toward the side of the card with the grating. (Left image courtesy of John W. Simon, MD; right image courtesy of Lee R. Hunter, MD.)
Video 1-2) or vanis hing optotype (Cardiff Acuity Test) on one half, and a homogeneous gray area of equal mean luminance on the other. The observer notes where the child looks upon being shown the card, then checks to see whether it was toward the stimulus. As the stripes in the grating or figure outline become finer (higher spatial frequency), fixation be hav ior approaches chance at the child’s resolution threshold. Other preferential looking tests of grating acuity include the LEA Grating Acuity Test (LEA Test Intl/Good- Lite Com pany), and Patti Stripes Square Wave Grating Paddles (Precision Vision). Table 1-3 shows the average grating resolution acuity at dif fer ent ages.
T able 1-3 Monocular Grating Resolution Acuity Test Results for Forced- Choice Preferential Looking Using Teller Acuity Cards
| Age (Mo) | Mean Grating Acuity (Cycles/Degree)a | Snellen Fraction Notation of Similar Spatial Frequencyb |
| 1 | 0.94 | 20/640 |
| 4 | 2.68 | 20/220 |
| 6 | 5.65 | 20/110 |
| 12 | 6.42 | 20/93 |
| 24 | 9.57 | 20/63 |
| 36 | 21.81 | 20/28 |
a One cycle = 1 pair of black- and- white grating stripes. The number of cycles per degree of visual angle is a mea sure of spatial frequency.
b Even for a similar spatial frequency, grating resolution acuity is not comparable to optotype recognition acuity. Snellen fraction notations are provided only as a familiar indicator of spatial frequency. Snellen fraction notation denominators are rounded to 2 significant figures.
Information from Mayer DL, Beiser AS, Warner AF, Pratt EM, Raye KN, Lang JM. Monocular acuity norms for the Teller Acuity Cards between ages 1 month and 4 years. Invest Ophthalmol Vis Sci. 1995;36(3):671–685.
VIDEO 1-2 Teller Acuity Card testing.
Courtesy of Lee R. Hunter, MD.