Strabismus, 17:20–23, 2009Copyright ©c 2009 Informa Healthcare USA, Inc.ISSN: 0927-3972 print / 1744-5132 onlineDOI: 10.1080/09273970802679006

Factors Affecting Development of MotorSkills in Extremely Low Birth Weight

Children

Anna R. O’Connor, PhDDirectorate of Orthoptics andVision Science, University ofLiverpool, Liverpool, UK

Eileen E. Birch, PhDRetina Foundation of theSouthwest, Dallas, Texas, USA;and Department ofOphthalmology, UTSouthwestern Medical Center,Dallas, Texas, USA

Rand Spencer, MDRetina Foundation of theSouthwest, Dallas, Texas, USA

ABSTRACT Purpose: The aim of this study is to analyze the impact of oph-thalmic and neonatal factors on motor development in extremely low birthweight (ELBW) children. Methods: Sixty-four ELBW children at least 3 yearsof age were recruited. Visual acuity (VA) was assessed using the Teller acuitycards (TACs) and a letter test, if possible. A validated questionnaire assessing 25fine (part A) and 20 gross motor (part B) skills was administered to the parents.Data were collected on retinopathy of prematurity (ROP) zone, intraventric-ular haemorrhage (IVH), length of stay in hospital, and number of days onoxygen. Results: Abnormal TAC acuity was associated with significantly lowerscores on both parts A and B (part A: 21.5 versus 11.8, p < 0.001; part B:17.5 versus 13.2, p < 0.001). Linear regression demonstrates a significant directrelationship between letter acuity and score A only (p = 0.03, r 2 = 0.179).Neither length of hospital stay, number of days ventilated, nor a history ofIVH were associated with score A or B. However, the presence of ROP zone1 was associated with a lower score A (p = 0.03). Conclusion: In this ELBWcohort VA and ophthalmic factors were the only factors associated with scoresof development, particularly fine motor development.

KEYWORDS extremely low birth weight; development; retinopathy of prematurity; visualacuity

INTRODUCTIONSurvival rates of extremely low birth weight (ELBW) infants, that is, those

with birth weight below 1001 g, have improved by almost 50% since the early1970s.1,2 However, the reduction in mortality has been accompanied by areciprocal increase in morbidity in multiple areas of development. Two ELBWbirth cohort studies reported that 64% to 80% of ELBW children had a disabilitywhen assessed at 6 to 8 years of age.3,4 One of the most prevalent categories ofdisability in the ELBW population is visual impairment,3−6 but in many casesthese deficits do not occur in isolation. However, how the ophthalmic deficitsimpact on functional ability and interact with other types of deficit (e.g., motorskills) is not fully understood.

Received 16 August 2008;Accepted 8 November 2008.

Correspondence: Dr Anna O’Connor,Directorate of Orthoptics and VisionScience, University of Liverpool,Thompson Yates Building,Quadrangle, Brownlow Hill, LiverpoolL69 3GB, UK. E-mail: annaoc@liv.ac.uk

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The aim of this study is to assess a range of factors,including visual acuity (VA), neurological deficits, andseverity of illness in the neonatal period, and determinewhether there is any association with the developmentof a child’s motor skills.

METHODSThis is a prospective observational longitudinal

study of a convenience sample of 64 children with birthweight less than 1001 g and aged 3 years or above. Partic-ipants with birth weight <1001 g referred to the RetinaFoundation of the Southwest by Dallas-area ophthal-mologists were enrolled in a prospective study of visualacuity development. Records of the retinopathy of pre-maturity (ROP) examinations were graded according tothe International Classification for ROP.7,8 The datawere summarized into the maximum stage of ROP andmost central zone of ROP.

Grating acuity was assessed monocularly with theTeller Acuity Cards (Vistech, Dayton, OH). A 2-down1-up forced choice staircase protocol was used, witheight staircase reversals.9 The visual acuity thresholdwas calculated as the mean of the last six reversals.Recognition acuity was measured with the ElectronicVisual Acuity system (JAEB Center for Health Re-search, Tampa, FL).10

A validated questionnaire assessing 25 fine (part A)and 20 gross (part B) motor skills was administered tothe parents. This questionnaire encompassed a range ofskills from very simple tasks, such as grasping an objector the ability to roll over, to more complex abilitiessuch as dialling a telephone or riding a bike.

Score comparisons were made between groups usinga t test with continuous variables assessed using a linearregression analysis.

The research was approved by University of TexasSouthwestern Medical Center Institutional ReviewBoard and complied with the tenets of the Declarationof Helsinki.

RESULTSData are presented for the right eye only as binocular

acuities could not be related to ROP outcomes as ROPcan be asymmetrical. The ages reported are adjusted forprematurity to allow comparison with normative data.The mean birth weight ± standard deviation (SD) was669 ± 137 g with the mean gestational age ± SD being

25 ± 1.92 months. The mean age was close to 7 years(mean ± SD was 82.3 ± 42.6 months, range 36–236months).

Teller acuity measures were possible on 55 subjects,with a further 6 subjects being classified as light percep-tion (LP; coded as 2.0 logMAR) and no light perception(NLP; coded as 2.5 logMAR). In addition, there werethree children who had vision but it was not possible,due to their disabilities, to measure their vision with theTeller acuity cards. The mean value of all 61 subjectswas 0.42 ± 0.71 logMAR, but after exclusion of thosewith LP or NLP this improved to 0.18 ± 0.28 logMAR.The results were compared to age-matched normativedata11 and divided into those with values within thenormal range (defined as being above the lower toler-ance limit, n = 44) and those below (n = 17). Table1 shows the mean values of the fine and gross motorskills for these two groups, the group with the acuitywithin the normal range has a significantly higher scoreon both parts A and B, which for the fine motor skills(part A) is an improvement of over 80% compared tothe low-acuity group.

The children with a known developmental delay (ex-cluding speech delay as this would not impact on thequestionnaire score) were identified (n = 39) and theabove comparison was repeated for this subgroup. Thefindings remained the same with a significant increasein the score for part A and part B associated with anacuity within the normal limits (part A: acuity abovelower limit = 20.6 ± 4.08, acuity below lower limit =11.6 ± 5.87, p < 0.001; part B: acuity above lower limit= 16.4 ± 3.99, acuity below lower limit = 13 ± 4.39,p = 0.02).

Fifty-four subjects were capable of identifying ormatching letters and linear regression analysis demon-strated a statistically significant relationship betweenthe VA and fine motor skills score (part A), r 2 = 0.179,p = 0.03, as shown in Figure 1. However there was no

TABLE 1 Mean responses of the motor skills scores divided bylevel of acuity

Teller acuity

Above lowerlimit

(n = 44)

Below lowerlimit

(n = 17) p value

Part A, mean ± SD 21.5 ± 3.8 11.8 ± 5.5 <0.001Part B, mean ± SD 17.5 ± 3.3 13.2 ± 4.1 <0.001

21 Development of Motor Skills in ELBW Children

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FIGURE 1 Letter acuity score plotted against the fine motorskills score (part A).

significant relationship between the letter acuity andthe gross motor skills (part B), r 2 = 0.027, p = 0.3.

Twenty-seven children had intraventricular hemor-rhage (IVH), with 11 cases being classified as severe.When comparing all those with a diagnosis of IVH (n =26) to those without, there was no significant differencebetween the groups on either score (part A: with IVH= 19.1 ± 5.7, without IVH = 18.9 ± 6.23, p = 0.9;part B: with IVH = 16 ± 4.62, without IVH = 16.75± 3.29, p = 0.5). When those with severe IVH (n =11) were compared to those with mild or no IVH, therewas still no significant difference between the groups.

Two factors were used as proxies to assess theseverity of illness of the child. Length of stay wascategorized as less than, or greater than or equal, to 4months, and number of days ventilated was dividedinto less than or equal to, or greater than, 60 days. Themotor skills scores were not statistically associated witheither factor as shown in Table 2.

Twenty-seven children had ROP in zone 1, 23reached zone 2, 2 cases reached zone 3, and no datawere recorded for 12 cases. The data were combined

TABLE 2 Proxies for severity of illness and the motor skillsscores

Length of stay in hospital

<4 months ≥ 4 months(n = 31) (n = 33) p value

Part A, mean ± SD 19.9 ± 4.8 17.9 ± 6.9 0.2Part B, mean±SD 17.2 ± 3.3 15.6 ± 4.3 0.1

Number of days ventilated

≤ 60(n = 33) >60 (n = 31)

Part A, mean±SD 19.2 ± 5.43 18.5 ± 6.6 0.7Part B, mean±SD 16.7 ± 3.98 15.97 ± 3.9 0.5

TABLE 3 Motor skills scores divided by ROP zone

ROP zone

1 (n = 27) 2 (n = 25) p value

Part A, mean ± SD 16.9 ± 6.88 20.68 ± 5 0.03Part B, mean±SD 15.85 ± 4.08 16.8 ± 3.79 0.4

for subjects with zones 2 and 3. There was a statisti-cally lower score on the fine motor skills tasks in chil-dren with zone 1 ROP compared to those with zone 2,but no difference was found on the gross motor skills(Table 3).

DISCUSSIONIn this ELBW cohort, the presence of zone 1 ROP

or poor acuity were the only measures associated with asignificantly poorer motor skills score, particularly forfine motor skills. Powls et al.12 reported a direct rela-tionship between contrast sensitivity (CS) and motorskills in a low birth weight cohort, where reduced CSproved to be a better predictor of reduced motor skillsthan VA. However, detailed testing of visual functionsis not always possible in ELBW children due to theirmultiple disabilities.

Preterm birth results in a multitude of problems andreports have found many factors to be statistically asso-ciated with measures of long-term outcome.13,14 How-ever, many of these factors are multifactorial in nature;for example, ROP and visual outcome15 and analyseshave found that no single factor, or group of factors,are good at predicting the long-term outcome.16 There-fore in this study two measures were used as proxies forseverity of illness, length of stay in hospital and numberof days ventilated. However, no significant relationshipwas found between these factors and the motor skillsoutcome.

The only factors found to be associated with a poorerscore on the motor skills questionnaires were vision re-lated (VA and zone of ROP). Although these data can-not determine whether the link between motor skillsand visual impairment is causal, it highlights the im-portance of vision in development and therefore theneed to continue to monitor ELBW children past theneonatal period.

A. R. O’Connor et al. 22

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