2.5.2. Ocular Alignment

Very young toddlers, such as our toddlers, cannot fixate on a target long enough for a valid cover test. In such cases, the optometrist estimated the degree of ocular alignment with the corneal reflex test and diopter prisms (the Krimsky test) or without diopter prisms (the Hirschberg test and kappa angle) [34]. The kappa angle was described as the angle between the visual axis and pupil axis. Each eye has a different Kappa angle, usually less than five degrees. A positive Kappa angle (displacement toward the nose) is physiologic up to five degrees. A negative kappa angle represents a temporal displacement (toward the ear). A large kappa angle may cause ocular alignment disorders [35]. Angles that were zero or no differences between the visual and pupil axis were reported as centered.

### 2.5.3. Motor Fusion, Suppression, and Stereopsis

For convergence/divergence test, a fixed target was presented at 25 cm. First, a 20Δ base-out (BO) prism was placed in front of one of the child's eyes. Next, a 20Δ base-in (BI) prism was placed in front of one of the child's eyes. The child should direct his/her hand in front of or behind the fixed target [36]. The near point of convergence (NPC) was determined by placing a fixed target 30 cm from the eye in the midplane of the child's head. The child was asked to maintain fixation on the target. The toddlers were asked to describe the picture that they looked at during the measurement. The target was moved slowly toward the eyes until one eye lost fixation and turned out. The distance between the fixed target and the nose bridge was measured with a string and ruler. It was repeated twice for each child [37,38]. To test ocular motility using binocular fixation, the toddler fixed on a small dot for 20 s [17]. Next, smooth movement without restrictions was assessed via smooth pursuit to a moving target located 30 to 40 cm away [36]. Saccades eye movements were also studied. The toddlers were instructed to look at a target point as quickly and accurately as possible using their index finger. Target appeared randomly at four eccentricities ± 5 degrees or ± 10 degrees from central fixation in the horizontal plane [39]. The Lang stereo test II was used to measure stereopsis. The test consisted of three three-dimensional images, a moon, truck, and elephant, and one two-dimensional image, a star that is seen without stereoscopic vision (visible with only one eye) that serves to capture the patient's attention. The test was placed with the observer in front of the child to observe his/her eye movements. The toddlers were told to look at the picture lying perpendicular to approximately 40 cm from the child's face and asked if he/she saw anything, observing the eye movements. If the child was unable to name the images, he/she was asked to locate an area on the card where there appeared to be something different and try to describe their differences [40].

#### *2.6. Statistical Analysis*

The data were analyzed with SPSS statistical software (version 26.0 for Windows; SPSS Inc., Chicago, IL, USA). Descriptive analysis was conducted with values expressed as mean ± SD. The data

normality distribution was assessed with the Kolmogorov-Smirnov test. Gross, fine, and total motor quotients were divided into two groups (fast motor development when the GMQ, FMQ, and TMQ was ≥ 100 and slow motor development when the GMQ, FMQ, and TMQ was 100). Differences in visual development between the fast and slow motor development groups were assessed with Student's t-test for quantitative variables and the chi-squared test for qualitative variables. For all of the tests, the level of significance was established at 95% (P < 0.05).
