The sensitivity of the 2- to 4-month-old human infant accommodation system

The Performance of Spot Photoscreener in 6 to 10 Weeks Infants in China: A Cross-Sectional Study

Purpose

To compare the refractive errors measured by the Spot photoscreener (with or without cycloplegia) to cycloplegic retinoscopy in 6- to 10-week-old infants.

Materials and Methods

101 right eyes from 101 healthy infants aged 6 to 10 weeks were recruited for this cross-sectional observational study. Refractive errors were measured using Spot photoscreener before and after cycloplegia, as well as cycloplegic retinoscopy. Comparisons between the refractive measurements were performed using one-way ANOVA with the post hoc Tukey HSD test or Kruskal-Wallis test with the Steel-Dwass test according to the data normality. Pearson's correlation test and 95% confidence intervals were calculated. The agreement was evaluated using a Bland-Altman plot with 95% limits of agreement of the differences.

Results

Spot photoscreener was found to underestimate the spherical equivalent by 2.33 Diopters (D) in these infants. Following the induction of cycloplegia, the spherical equivalent measured by Spot photoscreener was in excellent agreement with cycloplegic retinoscopy with the mean difference of 0.01 D. Spot photoscreener overestimated cylindrical parameter by 0.2 D with poor agreement with cycloplegic retinoscopy no matter whether cycloplegia was induced. It had good agreement with cycloplegic retinoscopy in the J0 vector than the J45 vector measurement.

Conclusions

With the induction of cycloplegia, Spot photoscreener can accurately evaluate spherical equivalent in hyperopic infants with mild-to-moderate astigmatism. While it may provide valuable measurements of astigmatism, discrepancies in cylinder and axis should be taken into account.

Newborn and infant vision screening in primary care: A clinical review

PURPOSE

Newborn and infant vision screening is an essential component of the health promotion visit, where the provider screens for ocular risk factors and abnormalities that may cause future impairment or vision loss. Providers may underestimate the importance of screening or find neonatal vision assessments difficult due to poor patient cooperation or time-consuming exams, but the reversibility of vision impairment in infants makes early detection paramount to proper treatment. This article provides a clinical review of evidence-based, practical guidance to providers who care for infants from birth through 6 months of age in the primary care setting.

CONCLUSIONS

The comprehensive eye exam in infants should include a thorough history and physical examination of eye structures, visual acuity, evaluation of extraocular movements and alignment, and assessment of the red reflex. Recommended exam maneuvers differ with age as visual acuity improves and development advances through infancy.

PRACTICE IMPLICATIONS

Early detection of ocular pathology is critical to avoid permanent vision loss, serious morbidity, and even mortality. The seemingly complex vision screening exam can be completed with little to no cooperation from the patient when a competent pediatric healthcare provider prioritizes opportunistic exam maneuvers. The opportunistic exam allows providers to maximize efficiency while maintaining thorough technique during vision exams and screenings.

How Do Most Young Moderate Hyperopes Avoid Strabismus?

Purpose

Uncorrected hyperopic children must overcome an apparent conflict between accommodation and vergence demands to focus and align their retinal images. This study tested hypotheses about simultaneous accommodation and vergence performance of young hyperopes to gain insight into ocular motor strategies used to maintain eye alignment.

Methods

Simultaneous eccentric photorefraction and Purkinje image tracking were used to assess accommodative and vergence responses of 26 adult emmetropes (AE) and 94 children (0-13 years) viewing cartoons. Children were habitually uncorrected (CU) (spherical equivalent refractive error [SE] -0.5 to +4 D), corrected and aligned (CCA), or corrected with a history of refractive esotropia (CCS). Accommodative and vergence accuracy, dissociated heterophoria, and vergence/accommodation ratios in the absence of retinal disparity cues were measured for 33- and 80-cm viewing distances.

Results

In binocular viewing, median accommodative lags for 33 cm were 1.0 D (AE), 1.33 D (CU), 1.25 D (CCA), and 1.0 D (CCS). Median exophorias at 80 and 33 cm were 1.2 and 4.5 pd (AE), 0.8 and 2.5 pd (CU), and 0 and 1.2 pd (CCA), respectively. Without disparity cues, most response vergence/accommodation ratios were between 1 and 2 meter angle/D (∼5-10 pd/D) (69% of AE, 44% of CU, 60% of CCA, and 50% of CCS).

Conclusions

Despite apparent conflict in motor coupling, uncorrected hyperopes were typically exophoric and achieved adultlike accuracy of both vergence and accommodation simultaneously, indicating ability to compensate for conflicting demands rather than bias to accurate vergence while tolerating inaccurate accommodation. Large lags and esophoria are therefore atypical. This analysis provides normative guidelines for clinicians and a deeper mechanistic understanding of how hyperopes avoid strabismus.

Language Experience Is Associated with Infants' Visual Attention to Speakers

Early social-linguistic experience influences infants' attention to faces but little is known about how infants attend to the faces of speakers engaging in conversation. Here, we examine how monolingual and bilingual infants attended to speakers during a conversation, and we tested for the possibility that infants' visual attention may be modulated by familiarity with the language being spoken. We recorded eye movements in monolingual and bilingual 15-to-24-month-olds as they watched video clips of speakers using infant-directed speech while conversing in a familiar or unfamiliar language, with each other and to the infant. Overall, findings suggest that bilingual infants visually shift attention to a speaker prior to speech onset more when an unfamiliar, rather than a familiar, language is being spoken. However, this same effect was not found for monolingual infants. Thus, infants' familiarity with the language being spoken, and perhaps their language experiences, may modulate infants' visual attention to speakers.

The Importance of the Interaction Between Ocular Motor Function and Vision During Human Infancy

Numerous studies have demonstrated the impact of imposed abnormal visual experience on the postnatal development of the visual system. These studies have provided fundamental insights into the mechanisms underlying neuroplasticity and its role in clinical care. However, the ocular motor responses of postnatal human infants largely define their visual experience in dynamic three-dimensional environments. Thus, the immature visual system needs to control its own visual experience. This review explores the interaction between the developing motor and sensory/perceptual visual systems, together with its importance in both typical development and the development of forms of strabismus and amblyopia.

Sensitivity of vergence responses of 5- to 10-week-old human infants

Infants have been shown to make vergence eye movements by 1 month of age to stimulation with prisms or targets moving in depth. However, little is currently understood about the threshold sensitivity of the maturing visual system to such stimulation. In this study, 5- to 10-week-old human infants and adults viewed a target moving in depth as a triangle wave of three amplitudes (1.0, 0.5, and 0.25 meter angles). Their horizontal eye position and the refractive state of both eyes were measured simultaneously. The vergence responses of the infants and adults varied at the same frequency as the stimulus at the three tested modulation amplitudes. For a typical infant of this age, the smallest amplitude is equivalent to an interocular change of approximately 2° of retinal disparity, from nearest to farthest points. The infants' accommodation responses only modulated reliably to the largest stimulus, while adults responded to all three amplitudes. Although the accommodative system appears relatively insensitive, the sensitivity of the vergence responses suggests that subtle cues are available to drive vergence in the second month after birth.

Why do only some hyperopes become strabismic?

Children with hyperopia greater than +3.5 diopters (D) are at increased risk for developing refractive esotropia. However, only approximately 20% of these hyperopes develop strabismus. This review provides a systematic theoretical analysis of the accommodation and vergence oculomotor systems with a view to understanding factors that could either protect a hyperopic individual or precipitate a strabismus. The goal is to consider factors that may predict refractive esotropia in an individual and therefore help identify the subset of hyperopes who are at the highest risk for this strabismus, warranting the most consideration in a preventive effort.

Pupil responses to near visual demand during human visual development

Pupil responses of adults to near visual demands are well characterized but those of typically developing infants and children are not. This study determined the following pupil characteristics of infants, children and adults using a PowerRefractor (25 Hz): i) binocular and monocular responses to a cartoon movie that ramped between 80 and 33 cm (20 infants, 20 2-4-yr-olds and 20 adults participated) ii) binocular and monocular response threshold for 0.1 Hz sinusoidal stimuli of 0.25 D, 0.5 D or 0.75 D amplitude (33 infants and 8 adults participated) iii) steady-state stability of pupil responses at 80 cms (8 infants and 8 adults participated). The change in pupil diameter with viewing distance (Δpd) was significantly smaller in infants and 2-4-yr-olds than in adults (p < 0.001) and significantly smaller under monocular than binocular conditions (p<0.001). The 0.75 D sinusoidal stimulus elicited a significant binocular pupillary response in infants and a significant binocular and monocular pupillary response in adults. Steady-state pupillary fluctuations were similar in infants and adults (p = 0.25). The results suggest that the contribution of pupil size to changes in retinal image quality when tracking slow moving objects may be smaller during development than in adulthood. Smaller monocular Δpd reflects the importance of binocular cues in driving near-pupillary responses.