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W4254313013 abstract "Purpose: To assess eye movements and binocular function in 14-year-olds with very low birthweight (VLBW: birthweight ≤ 1500 g) and 14-year-olds born at term but small for gestational age (SGA: birthweight < 10th percentile) in a population-based study. Methods: Ophthalmological examinations including measurements of heterophoria/tropia, near point of convergence, accommodative amplitude, stereopsis, nystagmus, saccades and smooth pursuit were performed in 51 adolescents with VLBW, 58 adolescents born SGA and in a control group consisting of 75 subjects of the same age. Results: Latent or manifest strabismus, poor stereopsis, poor convergence and nystagmus were all more frequent in the VLBW group than in the control group. The VLBW group did not differ from the control group regarding accommodative amplitude or saccades and smooth pursuit. The SGA population did not differ from the control group in the measured variables. Conclusions: Premature birth with VLBW affects binocular visual functions negatively in adolescence, whereas birth small for date at term does not appear to be a risk factor for impaired eye movements and binocular function. A wide range of everyday activities, from reading to running down stairs, are made more difficult by impaired stereopsis, defective accommodative amplitude, poor convergence or other defects in ocular motor ability (Skordilis et al. 2004; Abdi & Rydberg 2005; Sterner et al. 2006). Full function of these visual systems requires the cerebral structures involved to be undamaged. Both prematurity and intrauterine growth restriction can cause damage to the infant’s central nervous system (Jacobsson & Hagberg 2004). Several studies have shown that defects in ocular motor control and binocularity are frequent in premature children (McGinnity & Bryars 1992; Robinson & O’Keefe 1993; Fledelius 1996; Darlow et al. 1997; Powls et al. 1997; Jacobson et al. 2002; O'Connor et al. 2002; Cooke et al. 2004), but little has been published regarding these systems in adolescence or in subjects of any age born small at term. The aim of this study was to investigate the ocular motor ability and binocular function in prematurely born adolescents, as well as in adolescents born small for gestational age (SGA) at term and to compare these with functions in a control group. We describe a population-based, follow-up study of two groups of adolescents with low birthweight, comparing teenagers born prematurely with very low birthweight (VLBW, birthweight ≤ 1500 g) and adolescents born small for gestational age (SGA, birthweight < 10th percentile adjusted for gestational age and sex) at term with a control group of teenagers born at term with normal birthweight (birthweight > 10th percentile). The VLBW children were born to mothers living in the two Norwegian counties of North and South Trøndelag. Small for gestational age birth was used as a proxy for intrauterine growth restriction. The SGA and control children were born of para 1 or para 2 mothers living in the Trondheim area. The subjects were born between January 1986 to December 1988 and the study was carried out from January 2001 to June 2003. Further details of the study, including data on visual acuity (VA) and refraction, have been reported in a previous article (Lindqvist et al. 2007). Demographic characteristics of the study populations, as well as some data on VA and refractive errors, are shown in Table 1. There were no large differences regarding refractive errors between the groups; the only statistically significant differences found were a slight increase in anisometropia in the VLBW group and a slight increase in hypermetropia > 1 D in the SGA group (Lindqvist et al. 2007). In the VLBW cohort of 69 eligible children, 51 adolescents agreed to participate in the study. Two of the VLBW adolescents (birthweight 550 g and 690 g, both with cerebral palsy) did not manage to complete all aspects of the examination. The SGA group comprised 92 subjects, of whom 58 participated in the ophthalmological examination. In the control group of 110 adolescents, 75 completed the eye examination. Subjects with congenital anomalies diagnosed at birth were excluded. In the control group this comprised one subject with Goldenhaar syndrome and one with congenital anomaly of the urinary system. In the SGA group, four subjects (with, respectively, congenital cataract, cleft palate and/or cleft lip, congenital anomaly of the urinary system and atresia of the oesophagus) were excluded. Finally, one subject in the VLBW group with trisomy 21 was excluded. Participants and non-participants within each group did not differ in regard to mother’s age at childbirth, duration of pregnancy, or the infant’s weight, length or head circumference at birth. The study was carried out in keeping with the guidelines of the Declaration of Helsinki. The study protocol was approved by the Middle Norway Regional Committee for Medical Research Ethics. The Norwegian Data Inspectorate assigned a license to maintain a register of data including personal information. Written informed consent was obtained from both adolescents and parents. All examinations were performed by the same examiner and at the same time of day (early afternoon). The examiner was blinded to group assignment. Subjects used best correction after subjective refractioning. Results are, unless stated otherwise, given for all participants, with no exclusions. The alternating prism cover test was used to measure horizontal and vertical heterophorias/tropias in prism dioptres (PD). Measurements were made at distance (4 m) in the primary position, with gaze up, down, right and left, and at near (0.4 m) in the primary position. Subjects’ heads were rotated in order to make an extreme gaze possible (up, down, right and left). Care was taken to make this rotation as extreme as possible while maintaining the subject’s ability to fixate the target with both eyes. The alternating prism cover test is a reliable test for the detection of heterophoria (Rainey et al. 1998). However, although it may be used to evaluate both heterophoria and heterotropia, the test does not differentiate between them (Rainey et al. 1998). Thus all non-orthophoric results of the alternating cover test are reported as heterophorias/tropias or strabismus in this study. Figure 1 shows the magnitude and direction of all horizontal heterophorias/tropias at distance (any ≠ 0 PD) in five directions of gaze. Results of the alternating cover test in two groups of low birthweight adolescents and a control group. The figure shows the magnitude (in prism dioptres) of horizontal phoria/tropia at distance. Each bar represents one subject. Orthophoric subjects (i.e. those with no deviation on the alternating cover test) are not included in the graphs. The height of the bar denotes the size of phoria/tropia in that subject (y-axis: esodeviations positive and exodeviations negative) in one of five directions of gaze: primary position; right; left; up, and down. The figure shows that deviations were more common in the very low birthweight group than in the control group. VLBW = very low birthweight; SGA = small for gestational age. The results of the alternating cover test were classified as ‘physiological’ or ‘non-physiological’. Non-physiological exophoria/tropia was defined as exodeviation larger than the fifth percentile in the control group. Non-physiological esophoria/tropia was defined as an esodeviation larger than the 95th percentile of the control group. This produced the following cut-off values for non-physiological deviations: any esodeviation (> 0 PD) at distance or near, exodeviation of > − 2 PD at distance, or > − 8 PD at near and any vertical phoria/tropia (> ± 0 PD) or dissociated vertical deviation (DVD). Near point of convergence, break, was determined with an Royal Air Force (RAF) ruler, push-up technique, and defined as the distance at which the subject first reported diplopia, or as the distance where convergence was visibly broken, whichever came first. The shortest near point of convergence measurable with the RAF ruler is 6 cm. Poor convergence was defined as a near point of convergence larger than 10 cm. Binocular vision was primarily measured with the TNO test (Lameris Ootech BV, Nieuwegein, the Netherlands). If a subject did not manage the easiest stereograms on the TNO test (480 ”), the Titmus test (Stereo Optical Co., Chicago, IL, USA) was used. Those who did not manage a Titmus fly test were tested with Bagolini striated glasses at distance and near. A positive Titmus fly test was given a value of 3600 ” and a positive Bagolini, either near or distance, was given a numerical value > 3600 ” in order to make calculations of ranking possible. ‘Good’ stereopsis was defined as ≤ 60 ” and stereopsis > 240 ” was defined as ‘poor’. Subjects were asked if they had ever been treated for amblyopia with occlusion. Accommodative amplitude was measured monocularly in both eyes with an RAF ruler, using the push-up technique. The adolescents focused on the smallest letter they could comfortably see. The target was moved slowly towards the subject, who reported when the image became consistently blurred. The best available reading with the RAF ruler is 20 D, which is higher than the best recorded result in any subject in the study (17 D). Accommodative amplitude of < 6 D in at least one eye was defined as ‘poor’. Nystagmus was evaluated during the alternating cover test, when following and fixing an object in up, down, right and left gaze, and during examination in the slit-lamp. Nystagmus was categorized as either physiological end-point nystagmus or pathological nystagmus (latent, manifest latent or other). Smooth pursuit was evaluated by observing the subject fixating an object moving slowly either horizontally or vertically. A jerky pursuit or one that was difficult in other ways was noted as abnormal, and a comment was made about the nature of the problem. Horizontal and vertical saccades were evaluated by holding two objects (pens in different colours) approximately 20 cm apart and 40 cm away from the subject, in front of the subject and commanding the subject to look at one or the other alternately. Saccades were noted as abnormal when they were hypo- or hypermetric, or when they were slow or difficult in some other way. Both smooth pursuit and saccades were tested under binocular conditions. Participants were asked if they often got tired or experienced discomfort when reading or doing other near work. Those who confirmed this were given some follow-up questions to ensure this was an asthenopic problem. Mean, standard deviation, minimum and maximum values were used to measure location and spread in data with a normal distribution. For non-parametric data, median, minimum and maximum values were used. Comparisons were made between the VLBW or SGA groups and the control group with independent samples t-test for data with a normal distribution and Mann–Whitney U-test for non-parametric data. Paired t-test was used for comparisons of results of the alternating cover test in primary position and the other directions of gaze within the groups. For differences in binomial proportions between groups, Fisher’s exact test was used. P-values (p) < 0.05 were considered statistically significant. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated and used as an estimate of the relative risk that low birthweight adolescents had impaired functions compared with control adolescents. Non-physiological deviation (distance or near) was seen in every third (18 of 50) VLBW subject. Heterophorias/tropias were four times as common at distance and five times as common at near among VLBW subjects as among control adolescents. Dissociated vertical deviations and vertical deviations were seen only in the VLBW group. The analysis was also carried out for all deviations, without excluding the so-called non-physiological deviations. The VLBW group continued to have statistically significantly more deviations at distance, and at distance and near combined. However, there was no longer a significant difference at near between the VLBW and control groups. All VLBW adolescents with cerebral palsy had non-physiological deviation. Excluding subjects with cerebral palsy from the analysis decreased the prevalence of heterophorias/tropias in the VLBW group from 36% to 27%, which was still higher than in the control group (p = 0.02) (Table 2). In the VLBW group there were less severe exodeviations in right gaze (p = 0.003, Wilcoxon signed rank test) and left gaze (p = 0.007) versus the primary position (Fig. 1). No such differences were found in the SGA and control groups. However, the proportion with a lateral exodeviation incomitance > 5 PD (i.e. primary position 5 PD more exodeviating than lateral gaze) did not differ between the VLBW (8%), SGA (3%) and control (3%) groups. In each direction of gaze, the absolute values of all eso- and exodeviations were separately added and divided by the total number of observations (i.e. the number of participants) in that group to produce a mean eso- and exodeviation for the group. The VLBW group had significantly larger mean exodeviations in every direction of gaze compared with the control group, whereas there were no differences in esodeviations (Table 3). The SGA adolescents did not differ from the control group subjects regarding strabismus. Median near point of convergence was 8 cm in the VLBW group (range 6–30 cm), 6 cm in the SGA group (range 6–16 cm) and 8 cm in the control group (range 6–14 cm) (not significant [NS], Mann–Whitney U-test) (Fig. 2). A higher proportion of VLBW adolescents, 15 (29%), had poor convergence, compared with eight (11%) control adolescents (p = 0.01, OR 3.4, 95% CI 1.3–8.9). The difference between the control and VLBW groups persisted when subjects with cerebral palsy were excluded (OR 3.1, 95% CI 1.2–8.3). Near point of convergence in two low birthweight groups and a control group. The cumulative proportion of adolescents is shown on the y-axis and near point of convergence in cm on the x-axis. VLBW = very low birthweight; SGA = small for gestational age. Only four (7%) of the SGA group had poor convergence (NS) (Fig. 2). Median level of binocular vision was stereopsis of 60 ’’ in all groups, ranging from stereopsis of 15 ’’ to positive Bagolini in the VLBW and SGA group, and from 15 ’’ to 400 ’’ in the control group. No subjects failed all these tests. In the control group 62 (83%) adolescents had good stereopsis, compared with 36 (74%) in the VLBW and 49 (85%) in the SGA groups (NS). However, poor stereopsis was seen in seven (14%) of the VLBW group, versus one (1%) of the control adolescents (p = 0.006, OR 12, 95% CI 1.5–104). Five of the seven children with poor stereopsis in the VLBW group had cerebral palsy; the difference between the VLBW and control groups was no longer statistically significant when these children were excluded. Poor stereopsis was seen in three (5%) SGA subjects (NS versus control group). In the VLBW group, four (8%) children had undergone occlusion treatment for amblyopia, compared with none in the control group (p = 0.02). In the SGA group, three (5%) adolescents had used occlusion therapy in childhood (p = 0.08). Accommodative amplitude was similar in all the three groups. Median accommodative amplitude (mean of both eyes) was 10 D (range 5–13.5 D) in the VLBW group, 10 D (range 6–14.5 D) in the control group and 11 D (range 4.5–15 D) in the SGA group. Mean accommodative amplitude in the six subjects with cerebral palsy in the VLBW group who managed to do the test was 10.7 D, which did not differ from the mean (9.9 D) in the 44 VLBW subjects without cerebral palsy. The proportions of subjects in each group with poor accommodative amplitude was similar across the groups, ranging from 3% in the control group, through 5% in the SGA, to 8% in the VLBW group. None of the four VLBW subjects with poor accommodation had cerebral palsy. Neither of the study groups’ proportions differed statistically significantly (Fisher’s exact test) to that of the control group. Pathological nystagmus was not observed in any of the control subjects, but was in five (10%) of the VLBW group (p = 0.01) and one (2%) SGA subject (NS). Three of the five VLBW adolescents with nystagmus had cerebral palsy; when they were excluded, the difference between the VLBW and control groups disappeared. The six subjects with pathological nystagmus (five in the VLBW and one in the SGA group) all had various other visual problems (Table 4). All had monocular VA < 1.0, and four also had binocular VA < 1.0. In addition a varied pattern of deficits in different functions was seen, with reduced stereopsis, non-physiological deviations and problematic smooth pursuit and saccades being the most common. All subjects with pathological nystagmus had latent/manifest latent nystagmus, or nystagmus of similar appearance (horizontal, conjugate and increasing with occlusion of one eye). In one of the VLBW subjects the latent nystagmus was manifest; in all the others it was latent. Physiological end-point nystagmus was seen in 17 (33%) of the VLBW, 31 (53%) of the SGA and 33 (43%) of the control adolescents (NS). The proportion of adolescents with abnormal smooth pursuit and/or saccades did not differ at a statistically significant level between the VLBW (16%), SGA (9%) or control (9%) groups. There were no significant differences between the groups concerning smooth pursuit and saccades. The most severe disability was seen in a VLBW subject who could not make vertical saccades above the midline and also had problems managing vertical smooth pursuit above the midline. None of the other subjects were unable to elicit saccades or make smooth pursuit. The subjects with abnormal pathological smooth pursuits were labelled as jerky and saccadic in all cases but two, one of whom was noted as moving too fast, and having to jump back to the target, and one of whom was noted as unco-ordinated, with a gaze paresis upwards. The abnormal saccades were observed to be hypometric in 10 subjects, hypermetric in one and to involve a gaze paresis upwards in one. Increased latency for saccades or smooth pursuit was not seen in any of the subjects. Few subjects were noted to have abnormal head posture (three in the VLBW group, four in the control group and none in the SGA group). One of the adolescents in the VLBW group with abnormal head posture had nystagmus in right gaze, and none in the preferred left gaze. This subject’s head posture was the only one likely to have ophthalmological origin. In all the other cases head posture was described as slight, and could not retrospectively be explained by strabismus or nystagmus. Asthenopia was reported in 11 (22%) VLBW adolescents, 14 (24%) SGA subjects and 22 (29%) participants in the control group (NS). Failure in at least two ocular motor/binocularity functions (non-physiological heterophoria/tropia, poor stereopsis, poor convergence, poor accommodative amplitude, pathological nystagmus, deficits in saccades/smooth pursuit) was seen in three (4%) control adolescents, compared with 19 (38%) VLBW subjects (p = 0.000, OR 15, 95% CI 4.0–53) and four (7%) SGA adolescents (NS) (Fig. 3). Abnormality scores showing proportions of adolescents (y-axis) in low birthweight and control groups with one or more of the following abnormalities (x-axis): non-physiological heterophoria/tropia; poor stereopsis; poor convergence; poor accommodation; impaired saccades/smooth pursuit, and nystagmus. VLBW = very low birthweight; SGA = small for gestational age. In this study we found increased incidences of strabismus (manifest and latent), poor convergence, poor binocular vision and pathological nystagmus in the VLBW group compared with the control group. The SGA group did not differ significantly from control adolescents in these aspects. The strength of this study is that it was based on geographically defined populations, did not exclude children with cerebral palsy, included a population-based control group, used an examiner blinded to group assignment, and ensured that all children were evaluated by the same examiner. Loss to follow-up amounted to approximately 30% and this may be a study weakness. Although attenders did not differ from non-attenders on known background data, other studies have shown that non-attenders are more often visually impaired (Pennefather et al. 1999). The level of dysfunction in our populations is therefore more likely to have been under- than overestimated. This may be particularly important in the SGA group, where loss to follow-up was largest. Being born SGA is an indication of intrauterine growth restriction. However, some children born SGA are only constitutionally small, and have not been growth restricted (Bamberg & Kalache 2004). Furthermore, some members of the control group may have been growth retarded, but constitutionally large, and therefore still within the normal weight range. Thus, possible adverse effects of intrauterine growth restriction may have been diluted by misclassification. Finally, real, but smaller, differences between groups may not have reached statistical significance in this cohort, but may have done if the sample size had been larger. It is questionable whether some of the differences between the VLBW and control groups may reflect group differences in pubertal development. However, there were no differences in pubertal development between the three groups based upon Tanner staging of pubic hair development (data not shown). The results of this study confirm the increased prevalence of strabismus (manifest and latent) and decreased binocular vision previously reported in younger children with VLBW (Cats & Tan 1989; Gallo & Lennerstrand 1991; McGinnity & Bryars 1992;Robinson & O’Keefe 1993,Pennefather et al. 1995, Fledelius 1996; Holmström et al. 1999; Snir et al. 2004) and show that this risk is also present in adolescence. The prevalence of strabismus will vary depending on which criteria and tests are used for diagnosis. Using results from the alternating cover test, as in this study, which includes both heterotropias and heterophorias, yields higher prevalences than reporting only heterotropias. Small heterophorias are often regarded as physiological (Fledelius 1976) and therefore, in order to examine the prevalence of abnormal deviations in the study groups, we wanted to exclude physiological deviations. However, there is no general consensus on one particular range of heterophoria which might constitute normality, partly because the ability to cope with a phoria varies depending on the fusional reserves of the individual (Fledelius 1976). In this study, we chose to base our definition of abnormality on the fifth and 95th percentile levels in the control group. This took into account the asymmetric frequency and magnitude in exo- versus esodeviations. Although this division was based on statistical grounds, the resulting limits coincided well with the functional limits reported by Saladin (1995), who found that exo- and esophoria affected stereopsis differently: exophoria under − 7 PD had little or no effect on stereopsis, whereas in esophorias, stereopsis was negatively affected at values above + 1 PD to 2 PD. Stereoacuity was diminished by any vertical heterophoria (Saladin 1995). However, using this method, any small heterotropias, although not physiological, will also have been excluded from the non-physiological group. Depending on the rate of tropias to phorias in the physiological range of deviation, our results will to some degree under-report the prevalence of non-physiological deviations. The calculations including all (both physiological and non-physiological) deviations showed that this uncertainty is not a problem for distance values, which were essentially the same whether or not the assumed physiological deviations were excluded (Table 2). However, at near the prevalence of heterophoria/tropia increased almost 10-fold (from 5% to 47%) in the control group when subjects with measurements of – 1 PD to – 8 PD (i.e. those with presumed physiological results) were included. It seems likely that a very large proportion of these presumed physiological results were indeed physiological phorias and not tropias. A very high prevalence of non-orthophoric results at near in a control group is in accordance with findings of other authors, who have reported over 80% phoria measurements larger than 0 PD at near (Junghans et al. 2002). Thus it seems likely that most subjects with a deviation at near of – 1 PD to – 8 PD in the alternating cover test were displaying a physiological exophoria, not a pathological tropia. Our finding in the VLBW group of 30% distance manifest or latent strabismus in the primary position is very similar to values reported by Fledelius (1996) who, also using the alternating prism cover test, reported 33% strabismus at distance (more than + 1 PD or − 7 PD in the primary position) in a sample of 7–10-year-old children born prematurely. At near Fledelius reported 28% with heterophoria/tropia greater than + 1 PD or − 4 PD, which is identical to our finding of near deviations > 0 PD and less than − 8 PD. Our results also concur well with those of Dowdeswell et al. (1995), who reported an overall incidence of latent and manifest squint in 34% of children born before the gestational age of 32 weeks. In the VLBW group there was less exodeviation in right and left gaze, compared with in the primary position. This might be reflect an under-action of the abducting eye. Another possible explanation is that a measurement artefact occurs if the prism is rotated with the head during the measurement of lateral gaze positions. If the prism is misplaced in this situation, the larger the original angle is, the larger will be the misreading (Repka & Arnoldi 1991). However, larger lateral incomitance (> 5 PD) was unusual and not significantly more common in the study groups. The increased prevalence of subnormal stereopsis/binocular vision in the VLBW group is in agreement with findings from other studies (Dowdeswell et al. 1995; Powls et al. 1997; Cooke et al. 2004). Our findings of normal stereopsis in the VLBW group when children with cerebral palsy were excluded are in accordance with those of some (Dowdeswell et al. 1995), but not all (Powls et al. 1997) other authors. Lack of stereopsis in VLBW children has been strongly linked to strabismus, but it has also been reported in VLBW children without such an obvious reason for it, and it has been suggested that undetected subtle neurological lesions may be the reason in these cases (Holmström et al. 1999). Strabismus and binocular vision in subjects born SGA at term has to our knowledge not been reported before. No significant differences in these variables could be demonstrated in the SGA group compared with the control group. We defined poor convergence as a near point of convergence more distant than 10 cm, a definition which has also been advocated by other authors (Duane 1926; Hayes et al. 1998). We found no difference in ability to converge well (≥ 7 cm) between the groups, which is in concordance with findings of other authors (Dowdeswell et al. 1995). We did, however, find a larger proportion of poor convergers among the VLBW adolescents than in the control group. This difference was still significant when subjects with cerebral palsy were excluded from the analysis. The near point of convergence was poorer among our control subjects than previously reported (Dowdeswell et al. 1995; Chen et al. 2000; Aring et al. 2005): our subjects showed higher median values and with a more frequent incidence of convergence > 6 cm. This may be reflect differences in measurement technique, and in the selection of the control group. Visible break of convergence may occur later (i.e. at a closer distance from the subject) than diplopia, which was the main determinant in our group. A study by Chen et al. (2000)excluded 24% of its potential control children based on ocular pathology, whereas our control group was not selected in this way. Furthermore, the measuring technique used in our study (the RAF ruler) does not allow measurements of better convergence than that at 6 cm, although values of < 6 cm are to be expected (Hayes et al. 1998). However, any differences in technique and method would be the same for all study groups and any measured differences between the groups would be reliable. This is, to our knowledge, the first study to report on accommodative amplitude in a VLBW group and in an SGA group. Somewhat surprisingly, we found no decrease in accommodative amplitude in the VLBW group, not even among VLBW subjects with cerebral palsy, although accommodative ability has previously been shown to be reduced in cerebral palsy (Leat 1996). Most (74%) of the participants with cerebral palsy in Leat (1996) were patients (in an optometry clinic), and had not necessarily been born prematurely, whereas our VLBW subjects were not selected from a patient material, which might explain the different findings. We speculate that the reason for the comparative normality of accommodation among the VLBW adolescents could be that the cerebral functions governing accomodation are not at their most vulnerable at the time most of these children suffer brain injury. Results in our control group concur well with findings from several recent studies (Chen et al. 2000; Jimenez et al. 2003; Sterner et al. 2004), which have shown that the Hofstetter equation, although often used to calculate expected accommodative amplitude at different ages (Hofstetter 1950), is too optimistic regarding expected values in children. We found pathological nystagmus in 10% of the VLBW group, and none in the control group. Other studies have reported a prevalence of 2–5% nystagmus among prematurely born 3–10-year-olds (Gallo & Lennerstrand 1991; Fledelius 1996; Holmström et al. 1999). Absence of nystagmus in the control population is in accordance with other studies (Gallo & Lennerstrand 1991; Aring et al. 2005). Nystagmus is commonly seen in prematurely born, visually impaired children with periventricular leucomalacia (Jacobson et al. 1998; Brodsky et al. 2002), as well as in term-born children with perinatal visual pathway injuries (Brodsky et al. 2002). Thus the relatively high prevalence of nystagmus in our population of VLBW adolescents, compared with those in the studies mentioned above, may reflect a higher prevalence of visual pathway injuries in our material. Nystagmus was a serious symptom in our VLBW subjects as it was consistently combined with not only reduced VA, but also with various other ophthalmological problems such as reduced stereopsis, reduced convergence and abnormal smooth pursuit/saccades. All our cases of pathological nystagmus were of the relatively constant, low-amplitude, high-frequency type with clinical features of latent/manifest latent nystagmus. This is most frequently seen when perinatal trauma has caused white matter damage (Brodsky et al. 2002), as is usually the case in prematurity (Skranes et al. 2005). The adolescent with nystagmus in the SGA group also had this kind of nystagmus, and not the more chaotic, variable nystagmus, which is seen as predominantly secondary to term anoxia with cortical brain damage (Brodsky et al. 2002). We might therefore speculate that a pathological process causing fetal growth restriction in this SGA-born adolescent also affected the fetal brain negatively at a time before term when white matter structures were most susceptible to injury. Problems with saccades and smooth pursuit are common in visually impaired children with periventricular leucomalacia (Jacobson et al. 1998) and cerebral visual impairment of any cause (Salati et al. 2002; Dutton et al. 2004). We were unable to find an increased prevalence of defective saccades and smooth pursuit in the two low birthweight study groups. However, the smooth pursuits and saccades were only evaluated clinically, without video-recordings or with any electro diagnostic help. This diminishes the accuracy of our measurements and makes it difficult to record subtle dysfunction. Furthermore, our study groups did not consist of visually impaired children; most of our study group subjects had good VA. Prematurely born children without visual impairment have been shown to have largely normal control of saccades and smooth pursuit, even when tested with more refined equipment (Newsham et al. 2007). Considering the higher incidence of poor convergence and strabismus (latent or manifest) in the VLBW group, we might have expected asthenopia to be more common among the VLBW than control adolescents (Abdi & Rydberg 2005); however, asthenopia was equally frequent in all groups. It may be that in the VLBW group some adolescents with a potential for it did not experience asthenopia because, for example, attention problems (Indredavik et al. 2004) do not permit reading or other near work to continue until asthenopia occurs. It is also possible that the normal accommodative amplitude and relatively normal refractive status (refractive errors reported earlier) in the study groups (Lindqvist et al. 2007) were important in keeping asthenopia at levels similar to those in the control group (Abdi & Rydberg 2005). As we have shown in this study, 38% of VLBW adolescents (versus 4% in the control group) had two or more impairments in ocular motor functions or stereopsis. Thus, it is likely that impaired visual function will compound the academic, social or motor problems often encountered by these children (Evensen et al. 2004; Indredavik et al. 2004). A multitude of separately minor dysfunctions in one or several faculties, be they cognitive, motor and/or perceptual, limits the adolescent’s compensatory possibilities. Clinicians and teachers seeing a VLBW adolescent with, for example, a mild cognitive deficit, will, if they are unaware that the adolescent also has other impairments, expect the VLBW subject to have a similar coping ability as other patients/students with the same, but isolated, dysfunction. If one or two compensatory systems are less than fully operational, coping may be difficult for the child. However, an impairment in the visual functions described in this article may easily be overlooked unless the child is evaluated by a specialist. This stresses the need for broad, multidisciplinary co-operation when working with patients born prematurely. Premature birth and VLBW are followed by an increased risk of latent or manifest strabismus, impaired stereopsis, poor convergence and nystagmus in adolescence. More than a third of the VLBW adolescents in this study had reduced function in two or more of these systems. Impaired visual functions seem likely to aggravate the academic, social or motor problems often encountered by these children. In this study, we were unable to demonstrate that adolescents born SGA were at increased risk for ocular motor problems or defects in binocularity. The study was funded by the Department of Ophthalmology, St Olav’s University Hospital, Trondheim, and research funds at St Olav’s Hospital, Trondheim. Part of the study population was recruited from a multicentre study sponsored by the US National Institute of Child Health and Human Development, National Institutes of Health (NICHD contract nos. 1-HD-4-2803 and 1-HD-1-3127). The authors gratefully acknowledge statistical advice given by Pål Romundstad PhD, Department of Community Medicine, Norwegian University of Science and Technology, Trondheim, Norway." @default.
W4254313013 created "2022-05-12" @default.
W4254313013 creator A5000598019 @default.
W4254313013 creator A5012905819 @default.
W4254313013 creator A5036707697 @default.
W4254313013 creator A5057251829 @default.
W4254313013 creator A5091088389 @default.
W4254313013 date "2008-05-01" @default.
W4254313013 modified "2023-10-17" @default.
W4254313013 title "Eye movements and binocular function in low birthweight teenagers" @default.
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