Light and the developing retina

Safety of neonatal phototherapy lamp exposure

A routine review of light exposure within a neonatal intensive care unit is described following the introduction of a new model of neonatal phototherapy lamp. Spectral measurements were undertaken using a Bentham Dmc150 spectroradiometer system. Safety assessments were undertaken based on likely exposure of parents at the cot side, neonates in adjacent cots and the effectiveness of eye protection for neonates with direct phototherapy. An aphakic eye response was used for assessment of neonatal risk and the blue-light response for estimation of adult exposure using current ICNIRP guidelines. Such estimations indicated exposure levels of parents at the cot side and neonates in adjacent cots were within current established safe limits. The level of light blocking provided by the available neonatal eye protection was estimated to be entirely adequate and presented no hazard to the infant when correctly positioned over the neonate. It is likely, however, that an increased safety factor is potentially present for the neonate due to the fact that the neonate's eyes will typically be shut for over 50% of the time. It is identified, however, that the aphakic response is essentially associated with mature adult retinal cells, and that the maturing cells of the neonate may exhibit additional light sensitivity, especially in the case of premature infants. Changes in neonatal physiology associated with neonatal phototherapy are discussed, which may influence mechanisms of light-induced retinal damage.

Early light reduction for preventing retinopathy of prematurity in very low birth weight infants

BACKGROUND

Retinopathy of prematurity (ROP) is a complex condition of the developing retinal blood vessels and is one of the leading causes of preventable childhood blindness. Several risk factors for ROP have been studied over the past 50 years. Among them, general immaturity (low birth weight and low gestational age) and prolonged oxygen therapy have been consistently related to disease onset. However, it is understood that the progression of the disease is multifactorial and may be associated with others risk factors, such as multiple gestation, apnoea, intracranial haemorrhage, anaemia, sepsis, prolonged mechanical ventilation, multiple transfusions and light exposure. Furthermore, the precise role of these individual factors in the development of the disease has not yet been well established.

OBJECTIVES

To determine whether the reduction of early environmental light exposure reduces the incidence of retinopathy of prematurity (ROP) or poor ROP outcomes among very low birth weight infants.

SEARCH METHODS

We searched the following databases: the Cochrane Neonatal Group Specialised Register, CENTRAL (The Cochrane Library), MEDLINE, EMBASE, CINAHL, HealthSTAR, Science Citation Index Database, CANCERLIT, the Oxford Database of Perinatal Trials and www.clinicaltrials.gov. We also searched previous reviews including cross-references, abstracts, conference and symposia proceedings, and contacted expert informants. This search was updated in October 2012.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that reduced light exposure to premature infants within the first seven days following birth were considered for this review. We also considered cluster-randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Data on clinical outcomes including any acute ROP and poor ROP outcome were extracted by both review authors independently and consensus reached. We conducted data analysis according to the standards of the Cochrane Neonatal Review Group.

MAIN RESULTS

Data from four randomised trials with a total of 897 participants failed to show any reduction in acute ROP or poor ROP outcome with the reduction of ambient light to premature infants' retinas. The overall methodological quality of the included studies was about evenly split between those in which the classification was unclear and those in which the studies were categorised as low risk of bias. There was no report on the secondary outcomes considered in this review: quality of life measures; and time of exposure to oxygen.

AUTHORS' CONCLUSIONS

The evidence shows that bright light is not the cause of retinopathy of prematurity and that the reduction of exposure of the retinas of premature infants to light has no effect on the incidence of the disease.

A comparison of the light-reduction capacity of commonly used incubator covers

PURPOSE

The use of incubator covers to enhance preterm infants' rest and recovery is common in the NICU. However, the kinds of covers used vary extensively among and within nurseries. Few data exist on the effectiveness of different types of covers in reducing light levels to the infant. This study compared several types of commonly used incubator covers as to efficacy of light reduction.

DESIGN

A descriptive, comparative design was used in this study.

SAMPLE

Twenty-three incubator covers were tested, including professional, receiving blanket, hand-crocheted, three-layer quilt, and flannel.

MAIN OUTCOME VARIABLE

The percentage of light level reduction of different incubator covers under various ambient light level settings.

RESULTS

The amount of light reduction provided by incubator covers varies depending on type of fabric as well as percentage of incubator surface shielded by the cover. Dark-colored covers provided greater light reduction than bright/light-colored covers when covers identical in fabric type were compared. The light-reduction efficiency of the covers varied depending on the level of ambient light. Covers provided less light reduction in higher ambient light levels.

Ocular significance of intraventricular haemorrhage in premature infants

AIM

To document ocular outcome in premature infants with intraventricular haemorrhages (IVH).

METHODS

68 preterm infants with IVH were examined.

RESULTS

Mean gestational age was 28.1 weeks (range 24-35). Mean birth weight was 1045.9 g (630-2240). Mean follow up was 54.6 months (6-150). IVH is graded from 1 to 4 based on the severity of haemorrhages. The incidence of ocular abnormalities was compared between low grade IVH (grade 1 and 2) and high grade IVH (grade 3 and 4). Of the 68 infants with IVH, ROP occurred in 33 infants (48.5%); 13 (43.3%) had low grade IVH; 20 (52.6%) had high grade IVH. Strabismus developed in 30 infants (44.1%); 14 (46.6%) had low grade IVH; 16 (42.1%) had high grade IVH. Infants with high grade IVH were at significant greater risk than infants with low grade IVH for the development of optic atrophy (31.5% v 16.6%), hydrocephalus (57.8% v 10%).

CONCLUSION

This study highlights the serious significance of all grades of IVH with the higher incidence of optic atrophy and hydrocephalus with high grade IVH.

Modification of glial-neuronal cell interactions prevents photoreceptor apoptosis during light-induced retinal degeneration

Prolonged or high-intensity exposure to visible light leads to photoreceptor cell death. In this study, we demonstrate a novel pathway of light-induced photoreceptor apoptosis involving the low-affinity neurotrophin receptor p75 (p75NTR). Retinal degeneration upregulated both p75NTR and the high-affinity neurotrophin receptor TrkC in different parts of Müller glial cells. Exogenous neurotrophin-3 (NT-3) increased, but nerve growth factor (NGF) decreased basic fibroblast growth factor (bFGF) production in Müller cells, which can directly rescue photoreceptor apoptosis. Blockade of p75NTR prevented bFGF reduction and resulted in both structural and functional photoreceptor survival in vivo. Furthermore, the absence of p75NTR significantly prevented light-induced photoreceptor apoptosis. These observations implicate glial cells in the determination of neural cell survival, and suggest functional glial-neuronal cell interactions as new therapeutic targets for neurodegeneration.

Early light reduction for preventing retinopathy of prematurity in very low birth weight infants

BACKGROUND

This section is under preparation and will be included in the next issue.

OBJECTIVES

To answer the question: "Among very low birth weight infants, what is the effect of reducing early environmental light exposure on the incidence of any "Acute ROP", or "Poor ROP Outcomes"?

SEARCH STRATEGY

Searches were made of the Cochrane Neonatal Group Register of Controlled Trials, Medline, EMBASE, the Cochrane Library, previous reviews including cross references, abstracts, conference and symposia proceedings, and expert informants. The search terms used were [retrolental fibroplasia or retinopathy of prematurity] and [light or light/ae or lighting or lighting/ae or light/tu or lighting/st].

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials that reduced light exposure to premature infants within the first 7 days following birth were considered for this review.

DATA COLLECTION AND ANALYSIS

Data on clinical outcomes including any Acute ROP and Poor ROP Outcome were excerpted by both reviewers independently and consensus reached. Data analysis was conducted according to the standards of the Neonatal Cochrane Review Group.

MAIN RESULTS

Data from four recent randomized trials, and one much older quasi-randomized trial failed to show any reduction in Acute ROP, or Poor ROP Outcome with the reduction of light to premature infants' retinas. The number of infants studied to date allows 95% confidence that IF there were a true difference being missed, it would be smaller than 7 percentage points on a background of 54% of all infants under 2 kg developing ROP.

REVIEWER'S CONCLUSIONS

Decreasing retinal light exposure in premature infants is very unlikely to reduce the incidence of ROP.

Pre-term delivery and subsequent ocular development. A 7-10 year follow-up of children screened 1982-84 for ROP. 1) Visual function, slit-lamp findings, and fundus appearance

An ophthalmic follow-up comprised 88 children aged 7-10 years who had regular screening for retinopathy of prematurity (ROP) after their pre-term delivery 1982-84. Mean values of birth weight and gestational age in the 88 were 1467 g and 31 weeks. Out of 28 with early evidence of ROP four had progressed to bilateral blindness; the remaining 24 had at least a corrected visual acuity of 0.4 at disposal. The corrected median binocular acuity for all 88 was 0.95; however, the cumulated frequency curve was significantly below a previously stated norm in full-terms. The same conclusion was valid for single eye vision. Within the material, the visual score of the 28 with early ROP was significantly lower than in the remaining 60 subjects. Ophthalmoscopy often showed tortuosity of vessels, but no specific central retinal or optic nerve lesion to explain the slight general depression of visual acuity, and opacities of media contributed in only two subjects. It is concluded, that very preterm delivery generally influences the potential for developing full visual acuity, also in individuals without evidence of early ROP. Evidence of CNS-damage negatively influenced visual acuity score.

A controlled clinical trial of light and retinopathy of prematurity

Bright continuous light has been implicated in the pathogenesis of retinopathy of prematurity. To investigate the influence of light on the incidence and severity of retinopathy of prematurity, we enrolled 127 preterm infants (birth weight < or = 1,500 g; gestational age < or = 32 weeks) in a controlled clinical study. Randomization was done separately for three birth-weight groups (< 1,000 g; 1,000 to 1,249 g; 1,250 to 1,500 g). The babies' eyes were patched all day and night from birth to a gestational age of 35 weeks. The infants in the control group were exposed to cycled lighting conditions (that is, reduced light level during the night). Of 62 infants with patched eyes, 26 (42%) developed retinopathy of prematurity. In the control group, 25 of 65 infants (39%) showed retinopathy of prematurity (P = .596). There were also no statistically significant differences in the incidences of retinopathy of prematurity in the birth-weight subgroups or in the severity of retinopathy of prematurity. Thus, patching of the eyes from birth to 35 weeks of postconceptional age does not decrease the risk of retinopathy of prematurity in preterm infants when compared to a control group exposed to cycled lighting conditions.

Ambient light, ophthalmic artery blood flow velocities and retinopathy of prematurity

Exposure to bright light was recently proposed as a possible risk factor for the development of retinopathy of prematurity. A semi-longitudinal Doppler ultrasound study was conducted of ophthalmic artery flow velocities at normal and increased ambient light in 22 preterm infants, at post-menstrual ages from 28 to 37 weeks. The aim of this study was to obtain relationships between ophthalmic artery blood flow velocities at various post-menstrual ages and lighting conditions and the occurrence of retinopathy of prematurity. A gradual increase in average blood flow velocities was seen between 28 and 37 weeks. A stepwise increase in flow velocity was seen in all cases when ambient light was increased from moderate to intense. Five of the 22 infants developed retinopathy. No association could be established between ophthalmic artery flow velocities or light-induced changes in flow velocity and the occurrence of retinopathy.