Retinopathy of prematurity

Effects of Hyperoxia on the Refraction in Murine Neonatal and Adult Models

Whether hyperoxia affects the refraction in neonatal and adult mice is unknown. The mice exposed to 85% oxygen at postnatal 8 days (P8d) for 3 days and the mice exposed to normal air were assigned to the neonatal hyperoxia and normoxia groups, respectively. The refraction, the corneal curvature radius (CR) and the axial length (AL) were measured at P30d and P47d. Postnatal 6 weeks (P6w) adult mice were divided into the adult hyperoxia and normoxia groups. These parameters were measured before oxygen exposure, after 1 and 6 weeks, and every 7 weeks. The lens elasticity was measured at P7w and P26w by enucleation. The neonatal hyperoxia group showed a significantly larger myopic change than the neonatal normoxia group (P47d −6.56 ± 5.89 D, +4.11 ± 2.02 D, p < 0.001), whereas the changes in AL were not significantly different (P47d, 3.31 ± 0.04 mm, 3.31 ± 0.05 mm, p = 0.852). The adult hyperoxia group also showed a significantly larger myopic change (P12w, −7.20 ± 4.09 D, +7.52 ± 2.54 D, p < 0.001). The AL did not show significant difference (P12w, 3.44 ± 0.03 mm, 3.43 ± 0.01 mm, p = 0.545); however, the CR in the adult hyperoxia group was significantly smaller than the adult normoxia group (P12w, 1.44 ± 0.03 mm, 1.50 ± 0.03 mm, p = 0.003). In conclusion, hyperoxia was demonstrated to induce myopic shift both in neonatal and adult mice, which was attributed to the change in the CR rather than the AL. Elucidation of the mechanisms of hyperoxia and the application of this result to humans should be carried out in future studies.

Enhancing Retinal Endothelial Glycolysis by Inhibiting UCP2 Promotes Physiologic Retinal Vascular Development in a Model of Retinopathy of Prematurity

Purpose

We address the hypothesis that uncoupling protein 2 (UCP2), a cellular glucose regulator, delays physiologic retinal vascular development (PRVD) by interfering with glucose uptake through glucose transporter 1 (Glut1).

Methods

In the rat 50/10 oxygen-induced retinopathy (OIR) model, retinal Glut1 and UCP2 were measured and compared to room air (RA)-raised pups at postnatal day 14 (p14). Pups in OIR and RA received intraperitoneal genipin, an UCP2 inhibitor, or control every other day from p3 until p13. Analyses at p14 included avascular/total retinal area (AVA), Western blots of retinal UCP2 and Glut1, and immunostaining of Glut1 in retinal cryosections. Intravitreal neovascular/total retinal area (IVNV) was analyzed at p18, and electroretinograms were performed at p26. Glut1 and phosphorylated VEGFR2 (p-VEGFR2), glucose uptake, adenosine triphosphate (ATP) production, and cell proliferation were measured in human retinal microvascular endothelial cells (hRMVECs) pretreated with genipin or transfected with UCP2siRNA, Glut1siRNA, or control siRNA when incubated with VEGF or PBS.

Results

At p14, OIR pups had increased AVA with decreased Glut1 and increased UCP2 in the retina compared to RA retinas. Intraperitoneal genipin increased retinal Glut1 and reduced AVA. Compared to control, treatment with genipin or knockdown of UCP2 significantly increased Glut1, glucose uptake, ATP production, VEGF-induced p-VEGFR2 and cell proliferation in hRMVECs. Knockdown of Glut1 inhibited VEGF-induced p-VEGFR2. Genipin-treated OIR pups with decreased AVA at p14 had reduced IVNV at p18 and increased amplitudes in a- and b-waves at p26.

Conclusions

Extending PRVD by increasing retinal endothelial glucose uptake may represent a strategy to prevent severe retinopathy of prematurity and vision loss.

Retinopathy of Prematurity in Denmark. Epidemiological Considerations and Screening Limits

The epidemiology of retinopathy of prematurity (ROP) in Denmark is analysed based on two sources. Regional experience is presented from 12 years' prospective ophthalmic control of infants at risk, in a Danish county with population 342,000 and 44,805 liveborns over the period 1982-93. Out of 127 subjects with ROP 101 reached stage 1 or 2 only; 26 progressed to at least stage 3. Seven with blindness due to ROP amounted to 15.6/100,000 liveborns, a high frequency. The trend over the twelve years was towards less serious sequelae. Currently, the national screening limits for ROP have been adjusted under guidance from the compulsory registration of childhood visual impairment; with birth years 1974-94 there were 157 ROP-children in the register. Blindness due to ROP is now seen only in the very immature. It is suggested that gestational age 30 weeks will soon replace the present limits of less than 32 weeks/1750 g.

Evaluating the association of autonomic drug use to the development and severity of retinopathy of prematurity

PURPOSE

To explore the association of autonomic agents with the development and severity of retinopathy of prematurity (ROP).

METHODS

The medical records of all preterm infants screened for ROP were retrospective reviewed. The association between development and severity of ROP and the use and dose(s) of autonomic agents was analyzed, after adjustment for the covariates gestational age, weight, development of septicemia, intraventricular hemorrhage, and respiratory distress syndrome.

RESULTS

A total of 350 infants were screened. Caffeine was used in 338 infants; dopamine in 98 infants. There was a significant association between the use of dopamine and development of ROP (P < 0.001; relative risk [RR] = 1.6 [95% CI, 1.23-2.06]) and the need for ROP treatment (P = 0.001; RR = 4.63 [95% CI, 1.82-11.79]). The number of dopamine doses was significantly associated with the development of any ROP (P < 0.001; RR = 1.07 [95% CI, 1.03-1.1]), the severity of ROP (P < 0.001; RR = 1.09 [95% CI, 1.05-1.14]), and the need for treatment (P < 0.001; RR = 1.09 [95% CI, 1.05-1.14]). The total dose of caffeine was significantly associated with the development of any ROP (P = 0.003; RR = 1.03 [95% CI, 1.01-1.05]) and the need for treatment (P = 0.006, RR = 1.073 [95% CI; 1.021-1.13]).

CONCLUSIONS

Although a causal relationship was not identified, the use of the autonomic agents caffeine and dopamine was associated with the development and severity of retinopathy of prematurity in this cohort.

Algorithms for the prediction of retinopathy of prematurity based on postnatal weight gain

Current ROP screening guidelines represent a simple risk model with two dichotomized factors, birth weight and gestational age at birth. Pioneering work has shown that tracking postnatal weight gain, a surrogate for low insulin-like growth factor 1, may capture the influence of many other ROP risk factors and improve risk prediction. Models including weight gain, such as WINROP, ROPScore, and CHOP ROP, have demonstrated accurate ROP risk assessment and a potentially large reduction in ROP examinations, compared to current guidelines. However, there is a need for larger studies, and generalizability is limited in countries with developing neonatal care systems.

Retinopathy of prematurity in very low birth weight infants and the potential protective role of indomethacin

BACKGROUND AND OBJECTIVE

To describe clinical features of very low birth weight (VLBW) infants and examine the effect of indomethacin on the incidence of retinopathy of prematurity (ROP).

PATIENTS AND METHODS

Medical records of all VLBW infants over a 4-year period were reviewed. Data regarding systemic and ophthalmic examinations were analyzed.

RESULTS

Forty-seven infants with ROP were evaluated. Most infants had bilateral stage 1 or 2 disease extending 5 clock hours. Infants with ROP had younger mean gestational age, had lower gestational weight, and demonstrated higher incidence of diseases of prematurity. These infants were exposed to increased doses of surfactant and higher oxygen concentration for a prolonged duration given their immature pulmonary status. Independent predictors of ROP susceptibility also included length of hospitalization and Apgar score at 5 minutes. Patent ductus arteriosus was more common among infants with ROP. Approximately half of the infants who received one or two doses of indomethacin had ROP, but the ROP rate was decreased in infants who received three doses.

CONCLUSION

Premature infants with younger gestational age, lower gestational weight, and severe morbidities were found to have an increased prevalence of ROP. Indomethacin treatment for patent ductus arteriosus may have a protective role in the development of severe ROP.

Frequency and natural history of retinopathy of prematurity (ROP). A prospective study in a Swedish city 1986-1990

Frequency and natural history of retinopathy of prematurity (ROP) were prospectively studied in 142 preterm infants with birth weight (BW) less than 1501 g and/or gestational age (GA) below 33 weeks, who were born in Malmö 1986-1990. ROP developed in 27 (19%) of the 142 infants. The frequency of the ROP was significantly higher in infants with BW < or = 1000 g (54%) and in those with GA < or = 28 weeks (40%) than above these values. Infants with ROP had, compared with those without ROP, significantly lower BW, lower GA, lower Apgar score at 1 and 5 min, longer period of oxygen-therapy and higher frequency of neonatal complications. Five infants with stage 3 ROP were treated with cryotherapy; four with moderate changes showed good regression, the fifth with a severe stage 3 progressed and became blind. Up to 5 years follow-up revealed a significantly higher frequency of strabismus (40% vs 8%), myopia (25% vs 4%), and amblyopia (33% vs 6%) in infants with ROP than in those without ROP. Astigmatism and anisometropia were also frequent in children with ROP.

Restricted versus liberal oxygen exposure for preventing morbidity and mortality in preterm or low birth weight infants

BACKGROUND

While the use of supplemental oxygen has a long history in neonatal care, resulting in both significant health care benefits and harms, uncertainty remains as to the most appropriate range to target blood oxygen levels in preterm and low birth weight infants. Potential benefits of higher oxygen targeting may include more stable sleep patterns and improved long-term growth and development. However, there may be significant deleterious pulmonary effects and health service use implications resulting from such a policy.

OBJECTIVES

To determine whether targeting ambient oxygen concentration to achieve a lower vs. higher blood oxygen range, or administering restricted vs. liberal supplemental oxygen, effects mortality, retinopathy of prematurity, lung function, growth or development in preterm or low birth weight infants.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group was used. An additional literature search was conducted of the MEDLINE and CINAHL databases in order to locate any trials in addition to those provided by the Cochrane Controlled Trials Register (CENTRAL/CCTR). Search updated to week two July 2008.

SELECTION CRITERIA

All trials in preterm or low birth weight infants utilising random or quasi-random patient allocation in which ambient oxygen concentrations were targeted to achieve a lower vs. higher blood oxygen range, or restricted vs. liberal oxygen was administered were eligible for inclusion.

DATA COLLECTION AND ANALYSIS

The methodological quality of the eligible trials was assessed independently by each review author for the degree of selection, performance, attrition and detection bias. Data were extracted and reviewed independently by the each author. Data analysis was conducted according to the standards of the Cochrane Neonatal Review Group.

MAIN RESULTS

In the meta-analysis of the five trials included in this review, the restriction of oxygen significantly reduced the incidence and severity of retinopathy of prematurity without unduly increasing death rates The one prospective, multicenter, double-blind, randomized trial investigating lower vs. higher blood oxygen levels from 32 weeks postmenstrual age showed no significant differences in the rates of ROP, mortality or growth and development between the two groups. However, this study did show increased rates of chronic lung disease and home oxygen use.

AUTHORS' CONCLUSIONS

The results of this systematic review confirm that (the now historical) policy of unrestricted, unmonitored oxygen therapy has potential harms without clear benefits. However, the question of what is the optimal target range for maintaining blood oxygen levels in preterm/LBW infants was not answered by the data available for inclusion in this review.

Retinopathy of prematurity in assisted versus natural conception and singleton versus multiple births

OBJECTIVES

To determine whether the incidence and severity of retinopathy of prematurity (ROP) differs between infants conceived naturally and those born after assisted conception, and to analyze the impact of singleton versus multiple gestation on ROP.

DESIGN

Comparative case series.

PARTICIPANTS

The study group consisted of 363 infants with a birth weight (BW) of < or =1500 g who were hospitalized in the neonatal unit of a single tertiary-care center between 1998 and 2000.

METHODS

Data on gestational age (GA), BW, type of pregnancy (singleton/multiple), and type of conception (natural/assisted) were recorded, in addition to the ophthalmological results. Ophthalmological examinations were performed routinely at 4 weeks and repeated later, depending on the severity of the findings.

MAIN OUTCOME MEASURES

Presence and stage of ROP were compared between infants conceived naturally and those conceived by assisted technology, and between singleton and multiple-birth infants.

RESULTS

Mean GA at birth was 29.4 weeks (standard deviation, 2.5; range, 23-36). Two hundred four neonates (56.2%) were conceived naturally and 159 were conceived by assisted conception, either in vitro fertilization (IVF) alone (n = 119 [32.85%]) or IVF combined with drug treatment (n = 40 [11%]). Sixty-four infants in the natural conception group were the product of multiple pregnancies, as were 103 infants in the assisted conception group. Retinopathy of prematurity was noted in 159 of 363 infants (43.8%): 89 conceived naturally (71% singletons, 28% twins, and 17% triplets) and 70 born by assisted conception (70% singletons, 47% twins, and 33% triplets). There was no significant difference in either occurrence or severity of ROP between the natural conception and assisted conception groups. Singletons had a significantly higher rate of advanced ROP (stages II-III) (30.2%) than twins (23.1%), triplets, and quadruplets (10.6%) (P = 0.024). On multiple regression analysis, low GA and BW were the variables most significantly associated with ROP.

CONCLUSIONS

In our sample, assisted conception per se did not appear to be a risk factor for ROP. Singleton babies with a birth weight of < or =1500 g were more prone to develop ROP stages II and III than twins or triplets. Gestational age and BW were the most significant factors associated with ROP.

Hypobaric hypoxia reduces the amplitude of oscillatory potentials in the human ERG

PURPOSE

To explore the retinal functions in healthy volunteers during acute hypoxic exposure, applying a set of electrophysiological tests.

METHODS

Standard electroretinograms (ERGs) of the retina (rod-(scotopic) ERGs, cone-(photopic) ERGs, maximal responses and oscillatory potentials (OPs)) and 30-Hz flicker ERGs were recorded according to ISCEV (International Society of Clinical Electrophysiology of Vision) recommendations in 14 healthy volunteers during a 15-min exposure to a simulated altitude of 5500 m.

RESULTS

The mean arterial oxygen saturation level was significantly reduced (P < 0.001) during the hypobaric challenge. It returned to the normal level very shortly after the end of the hypoxic exposure. No significant change in the latency or amplitude of the slow components of the ERG was found in any recording. The OPs of the ERG, however, revealed a significant decrease in amplitude during hypoxic exposure. Both OP1 and OP2 amplitudes were significantly different (P < 0.05) from the baseline values during hypoxia. Partial recovery of these waves occurred after termination of the hypoxia.

CONCLUSIONS

These results appear to support the notion that the inner layers of the retina presumed to be the main source of the OPs, display the highest sensitivity towards circulatory and/or hypoxic challenges.

Retinopathy of prematurity: recent advances in our understanding

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Retinopathy of prematurity: recent advances in our understanding

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Reduced incidence of retinopathy of prematurity

AIM

To audit the prevalence of retinopathy of prematurity (ROP) in a level 2 status neonatal unit.

METHODS

Data were collected prospectively over 9 years from September 1989 to September 1998. Preterm infants were examined according to the Royal College of Ophthalmologists' guidelines and retinopathy graded following the International Classification of ROP. ROP 3-5 was analysed using logistic regression in relation to time, and to gestational age and birth weight.

RESULTS

383 babies were examined. Mean gestational age fell over the 9 year period (p=0.051) as did mean birth weight (p<0.001). There was a decrease in the number of infants with ROP grades 3-5 over the 9 years (p=0.045 and, when adjusted for gestational age and birth weight, the decrease in ROP 3-5 was significant (p=0.03).

CONCLUSIONS

This study found a significant reduction in the incidence of ROP during the 9 years of the study period, despite a decrease in mean gestational age of and birth weight. The reduced incidence of ROP is attributed to improvements in ventilation techniques and overall care of the neonate, in particular the use of prenatal steroids and surfactant.

Expression of GAP-43 in the retina of rats following protracted illumination

Distribution of GAP-43 was studied in the retinas of rats after continuous illumination followed by different darkness periods. GAP-43 immunoreactivity was maximum in regenerating outer photoreceptor segments of rats kept in total darkness for 10 days, while in the inner plexiform layer, immunoreactivity was maximum immediately after illumination. Changes in GAP-43 expression could participate in retinal repair/regeneration after light-induced damage.

Evaluation of the prothrombin gene polymorphism in patients with advanced retinopathy of prematurity

It has been reported recently that a common genetic variant in the 3'-untranslated region of the prothrombin gene is associated with a significant fraction of premature births. The purpose of this study is to evaluate the prothrombin gene polymorphism in a large cohort of patients with preterm birth and advanced retinopathy of prematurity. For this purpose, the leukocyte DNAs were analyzed for the mutation (20210A) in the 3'-untranslated region of the prothrombin gene by PCR amplification, followed by restriction analysis and DNA sequencing. Our extensive analysis revealed a normal genotype (GG) in all patients as well as controls. These results suggest that the common genetic variant in the 3'-untranslated region of the prothrombin gene is not associated with advanced retinopathy of prematurity. Although more patients' samples should be evaluated, this genetic test does not support a relationship between prothrombin gene mutation and retinopathy of prematurity.

New developments in neonatology: less severe retinopathy of prematurity?

PURPOSE

To determine the effects of surfactant replacement therapy (SRT), high-frequency oscillatory ventilation (HFOV), and general improvements in quality of care on the incidence of severe retinopathy of prematurity (ROP).

METHODS

Retrospective comparison of the incidence and severity of ROP in two groups of preterm infants admitted to our neonatal intensive care unit (NICU) in two consecutive 5-year periods (1986-1995) and screened for ROP. During the second study period, natural surfactant was introduced in the treatment of respiratory distress syndrome (RDS) and HFOV was used for treatment of respiratory insufficiency of any origin. The effects of these developments and general improvements on the incidence of severe ROP were analyzed with stepwise logistic regression.

RESULTS

The overall incidence of ROP from 1986-1990 was not significantly different from the incidence of ROP from 1991-1995. The incidence of severe ROP (ROP stage 3 or greater) was significantly lower in the second period (15.7% versus 6.4%, P=.015). For infants <1000 g, the incidence of overall ROP was increased significantly during the second study period (47.6% versus 60.1 %, P=.045), although the incidence of severe ROP remained unchanged. Only SRT was associated with a decreased risk for severe ROP; HFOV and general improvements in quality of care had no influence on the outcome. In patients with RDS, the incidence of severe ROP decreased significantly during the second period.

CONCLUSION

Of the recent new developments in neonatology, only SRT was associated with a decreased risk for severe ROP.

Dopamine use is an indicator for the development of threshold retinopathy of prematurity

AIM

To assess whether treatment of premature infants with dopamine is a risk factor for development of retinopathy of prematurity (ROP).

METHODS

A retrospective case series analysis of two groups was utilised with a minimum follow up of 6 months. Clinical profiles and patient risk factors were identified along with an evaluation of ROP progression and an analysis of clinical outcome. All infants were seen in a single community neonatal intensive care unit (NICU). 41 consecutive high risk infants were identified during a 36 month period whose birth weight was less than 1000 grams and who remained in the NICU without transfer until at least 28 days of age. Dilated indirect ophthalmoscopy fundus examinations were performed on all infants to identify the degree of and progression to threshold ROP.

RESULTS

18 of 41 infants were treated with dopamine for hypotension. The group of infants requiring dopamine differed statistically from the non-dopamine treated group by having a slightly higher birth weight, a greater incidence of hypotension and colloid treatment, and in manifesting more advanced respiratory disease. Within the dopamine treated group, 12 of 18 infants (67%) reached prethreshold ROP and seven infants (39%) reached threshold ROP requiring laser treatment. In contrast, only three of the infants (13%) who did not require dopamine for hypotension progressed to prethreshold (p = 0.001) and only one of these infants (4%) progressed to threshold ROP (p = 0.02). Logistic regression analysis among other variables demonstrated that dopamine use and gestational age are important factors in this low birthweight population for predicting the development of threshold ROP (dopamine use: adjusted odds ratio = 119.88, p = 0.0061; gestational age: adjusted odds ratio = 0.061, p = 0.0043).

CONCLUSIONS

Dopamine use in low birthweight infants may therefore be a risk factor for the development of threshold ROP. More vigilant screening of high risk infants requiring dopamine therapy for systemic hypotension may be warranted.

Retinopathy of prematurity in multiple-gestation pregnancies

PURPOSE

To determine differences in incidence of retinopathy of prematurity between neonates of multiple-gestation and single-gestation pregnancies and to analyze differences in severity of retinopathy of prematurity among siblings of multiple-gestation pregnancies.

METHODS

We reviewed the records of 149 neonates of multiple-gestation pregnancies and 691 single-gestation neonates screened for retinopathy of prematurity at one hospital from January 1, 1992, through December 31, 1995. The peak stage of retinopathy of prematurity was recorded for all infants. The multiple-gestation infants were then separated into concordant and discordant retinopathy of prematurity groups, with discordance defined as a difference of at least 2 stages of retinopathy of prematurity between siblings. Between siblings with discordant retinopathy of prematurity, multiple factors were compared.

RESULTS

Retinopathy of prematurity was present in 69 (46%) of the multiple-gestation neonates. Retinopathy of prematurity was present in 312 (45%) of single-birth neonates. The percentage of multiple-gestation neonates with stages 1, 2, or 3 (prethreshold) or threshold retinopathy of prematurity was similar to that of single-gestation neonates. Stage 4 or 5 retinopathy of prematurity did not occur in either group.

CONCLUSIONS

There was no significant difference in stage of retinopathy of prematurity between infants of single-gestation pregnancies vs those of multiple-gestation pregnancies. The majority (84%) of infants of multiple-gestation pregnancies had concordant retinopathy of prematurity. In those infants with discordant disease, zygosity and postgestational factors other than lowest serum glucose were not related to severity of retinopathy of prematurity.

Myopia in children born premature or with low birth weight

PURPOSE

To evaluate the association of myopia or astigmatism in children without retinopathy of prematurity (ROP) born premature or with low birth weight.

METHODS

This cross-sectional study was conducted in Singapore where 527 children from three kindergartens aged 2 to 7 years without a history of ROP were recruited. Information on birth weight and gestational age at birth was obtained from a personal booklet and the refractive error in spherical equivalents was measured using distance photoretinoscopy. The data was analysed with univariate analysis and logistic regression models.

RESULTS

There was no difference in the prevalence of myopia in children born premature or with low birth weight. There was also no difference in astigmatism in children born premature or with low birth weight.

CONCLUSION

This study shows no relationship between astigmatism or myopia with prematurity or low birth weight in children born without retinopathy of prematurity.

Heme-mediated reactive oxygen species toxicity to retinal pigment epithelial cells is reduced by hemopexin

Catalysis of the formation of reactive oxygen species (RO2S) by low molecular weight complexes of iron has been implicated in several pathological conditions in the retina since photoreceptors and retinal pigment epithelial cells are likely to be especially sensitive to RO2S. Since protective proteins cannot cross the blood-retinal barrier, it is likely that the retina performs its own protective functions by synthesizing proteins that bind iron and nonprotein iron complexes, the major catalysts of RO2S generation. Investigations were carried out to determine whether pigment epithelial cells are themselves sensitive to iron-generated RO2S and whether apo-transferrin and apo-hemopexin, known to be made locally in the retina, can perform a protective function. In 51Cr release assays, the toxicity of exogenous RO2S including hydrogen peroxide or superoxide (generated by xanthine oxidase/hypoxanthine) to human retinal pigment epithelial cells was inhibited by the iron chelators, desferrioxamine and apo-transferrin. Free but not protein-bound ferric iron and heme exacerbated the toxic effect. The toxic effect of heme was abolished by the heme-scavenging, extracellular antioxidant, apo-hemopexin, and also by exogenous bovine serum albumin. In addition, heme toxicity was inhibited by a 3 h preincubation of cells with either heme, apo-hemopexin, or heme-hemopexin 24 h prior to the toxicity assay. It is concluded, first, that toxic effects of iron and heme can be prevented by apo-transferrin or apo-hemopexin and, second, that exposure of RPE cells to free heme or hemopexin sets in motion a series of biochemical events resulting in protection against oxidative stress. It is probable that these include heme oxygenase induction.

Hemopexin in the human retina: protection of the retina against heme-mediated toxicity

The existence of the blood-retinal barrier means that proteins that protect the retina from damage by reactive oxygen species must either be made locally or specifically transported across the barrier cells; however, such transepithelial transport does not seem to occur. Among the circulatory proteins that protect against iron-catalyzed production of free radicals are apo-transferrin, which binds ferric iron and has previously been shown to be made by cells of the neural retina (Davis and Hunt, 1993, J. Cell Physiol., 156:280-285), and the extracellular antioxidant, apo-hemopexin, which binds free heme (iron-protoporphyrin IX). Since hemorrhage and heme release can be important contributing factors in retinal disease, evidence of a hemopexin-based retinal protection system was sought. The human retina has been shown to contain apo-hemopexin which is probably synthesized locally since its mRNA can be detected in retinal tissue dissected from human donor eyes. It is likely that the retina contains a mechanism for the degradation of hemopexin-bound heme since the blood-retinal barrier also precludes the exit of heme-hemopexin from the retina. Retinal pigment epithelial cells have been found to bind and internalize heme-hemopexin in a temperature-dependent, saturable, and specific manner, analogous to the receptor-mediated endocytic system of hepatoma cells. Moreover, the binding of heme-hemopexin to the cells stimulates the expression of heme oxygenase-1, metallothionein-1, and ferritin.

Screening for retinopathy of prematurity: do former guidelines still apply?

Early detection of retinopathy of prematurity (ROP) in premature and very-low-birth-weight infants is crucial. In this retrospective study, 581 infants either with a birth weight below 1500 g or a gestational age of less than 32 weeks, or who did not fit these criteria but were judged to be at increased risk, were screened for ROP. ROP developed in 159 (27.4%). The incidence of ROP appeared to be inversely proportional to birth weight and gestational age. Infants with a birth weight below 750 g had a significantly higher risk of developing stage 3 and 4 ROP. The mean age at detection was 7.6 +/- 1.6 weeks. Nearly all of the ROP cases and all of the stage 3 and 4 cases were detected between the 5th and 10th week. Because screening should be focused on these vision-threatening stages, ophthalmic examinations should be concentrated in, but not limited to, the period between the 5th and the 10th postnatal week.

Late visual field changes following cryotherapy for retinopathy of prematurity stage 3

AIMS

The correlation between cryoscars and visual field defects following cryoablation was studied.

METHODS

A Humphrey 120 full field screening test was performed in 10 children (15 eyes) who were treated by cryotherapy between 10 and 14 years previously for retinopathy of prematurity (ROP) stage 3.

RESULTS

In eight eyes treated by cryoablation through 360 degrees in zone I or II, a moderate circumferential peripheral visual field constriction was found. In seven other eyes, cryotreated up to 180 degrees only in the temporal retina (zone III), a nasal field constriction was noted. There was no evidence of late development of retinal tears or retinal detachment. The correlation between the primary cryoapplications, late chorioretinal cryoscars, and the visual field changes was evaluated.

CONCLUSION

Late chorioretinal scars following cryotherapy for ROP stage 3 are associated with visual field defects, but as these defects are at the periphery of the visual field they do not cause any subjective derangements 10-14 years after treatment.

Regression pattern in retinopathy of prematurity

We characterized the regression pattern of retinopathy of prematurity (ROP) for 266 infants examined over a 22-month period. Infants were included in the evaluation with a birth weight of less than or equal to 1500 g. Regression of retinopathy was observed in all but 11 infants, who were treated for threshold ROP. ROP limited to the peripheral retina resolved around term (40 weeks postconceptional age). Posterior ROP and/or stage 3 ROP underwent a protracted course of resolution, often not reaching zone 3 until 42 to 45 weeks after conception. Permanent retinal/vascular sequelae of ROP were observed in 10% of infants with ROP. The most common abnormality was failure to completely vascularize the temporal retinal periphery. Overall, retinal morbidity from ROP was an infrequent occurrence (18 of 266 premature infants--6.8%).

Retinopathy of prematurity and bilirubin--no clinical evidence for a beneficial role of bilirubin as a physiological anti-oxidant

The prevention of retinopathy of prematurity (ROP) remains a persistent problem. A previous report has focused on the possible protective effect of bilirubin on the development of ROP. These results still await clinical confirmation by other research groups. Therefore, we undertook a retrospective clinical study trying to confirm this attractive hypothesis. Twelve premature newborns under 32 weeks of gestation with ROP stage 3-4 were matched for gestational age with 12 infants without ROP. Data were collected about the infant's characteristics, medical illnesses, ventilatory settings and treatments. The total serum bilirubin concentrations between the 1st and 8th postnatal day were also gathered. The two matched groups were comparable as to their basic data, clinical characteristics and treatment, except for a slight, but significant longer duration of phototherapy for group ROP 0 (mean, 50.2 h; SD 48,6 vs 31.6 h; SD 42.7 in ROP 3-4; P = 0.02). No statistical difference relative to bilirubin was found between the two groups, neither when expressed as daily mean concentrations, nor as area under the curve (AUC) (mean, ROP 0: 17876.7; SD 6077.3 vs 18888.4; SD 55552.7 in ROP 3-4; P = 0.404) or AUC/h (mean, ROP 0: 135.1; SD 36.3 vs 144.1; SD 23.2 in ROP 3-4; P = 0.515). Our findings do not confirm the hypothesis of a clinically measurable, beneficial role of bilirubin on the development of ROP.

Surfactant replacement therapy: a new risk factor in developing retinopathy of prematurity?

We documented the prevalence of retinopathy of prematurity (ROP) in a group of 46 infants suffering from a moderate or severe respiratory distress syndrome and treated with surfactant replacement therapy (SRT) and 61 controls admitted in the year prior to the institution of SRT. Mortality in the treatment group was lower than in the control group (15.5% versus 23.8; P = 0.29). The ROP prevalence in the treatment group was 47.8% and in the control group 27.9%. To analyse the contribution of SRT alone to the prevalence of ROP, multivariate analysis using logistic regression technique was used. The odds ratio for SRT was 5.2 with a 95% confidence interval of 1.3-20.7, P = 0.02. The prevalence of severe ROP in the surfactant treated group was not increased compared to the control group. From our data we conclude that SRT increases the risk of developing ROP but is not associated with more severe forms of ROP.

Perinatal predictors of ocular morbidity in school children who were very low birthweight

Two hundred children from one neonatal intensive care unit (NICU), who were very low birthweight (VLBW), were examined at approximately 9 years of age and compared with a control group of normal birthweight children. Visual morbidity was significantly higher among children who were very low birthweight. Binocular visual acuity of 6/9 or worse was noted in 21 (10.5%), strabismus in 38 (19%) and regressed retinopathy of prematurity (ROP) in 13 (6.7%) of these children. A history of seizures in the perinatal period was highly correlated with poor visual acuity. Independently significant factors associated with strabismus included clinically diagnosed intraventricular haemorrhage, a maternal history of neonatal death, transfer from another hospital, bronchopulmonary dysplasia and necrotising enterocolitis. Perinatal variables that correlated with regressed ROP included birthweight, time from birth to admission to the NICU, necrotising enterocolitis and a history of maternal smoking during the pregnancy. When screening for ocular abnormalities among children who were born preterm, particular attention should be given to children with these risk factors.

Recent developments in certain X-linked genetic eye disorders

Over the past few years, genetic diseases of the ocular system have become very active and fast-growing research areas in the vision field. The rapid development of the recombinant DNA techniques together with somatic cell genetics, during the last two decades has fueled this progress. As a result, many genetic disease genes have been localized in the human chromosome and several of them have been isolated and characterized. These and other studies have profoundly enriched our basic understanding of genetic eye disorders. Although gene replacement therapy, prenatal diagnosis and carrier detection have not been extensively tried for genetic eye diseases, such attempts will now be feasible. Molecular analyses made it clear that there are many challenging problems that need attention. This report highlights some of these initial developments, particularly on the X-linked major genetic eye diseases. In order to help the beginners and general audience, a brief description of the clinical pathology and the molecular probes used to locate the genetic defects of certain disorders are presented. Disorders are arranged according to their linkage from telomere to telomere on the chromosome to give a coherent structure. It is hoped that this information is useful and of general interest for the beginners, established investigators and ophthalmologists.

Diode laser for retinopathy of prematurity--early outcome

Diode laser treatment for retinopathy of prematurity was successful in 81% of 21 eyes with 'threshold' (zone 2, stage 3+) disease. This compares favourably with cryotherapy and argon laser photocoagulation. The retinal outcome and technique are discussed.

Glaucoma as a cause of poor vision in severe retinopathy of prematurity

Despite surgical reattachment of the retina in infants with severe retinopathy of prematurity (ROP), visual acuity may decline. We performed gonioscopy and applanation tonometry on 26 eyes of 17 infants with severe ROP who were randomly selected and followed prospectively for 2 years. Of these 26 eyes, one eye of one patient had only peripheral retinocryopexy for threshold stage III disease and had an attached retina before enrollment into the study. Sixteen infants subsequently underwent vitrectomy, scleral buckle, or both. Retinal reattachment of the posterior pole was present in at least one eye each of 10 of the 17 infants. Glaucoma was diagnosed in 5 of the 10 patients; all 5 showed a decrease in visual acuity of greater than 1 octave. Of the 5 infants without glaucoma, 3 showed visual improvement, and 2 remained the same. Although we studied a small number of cases, our results suggest that glaucoma may be a cause of visual decline in infants with severe ROP. A decline in visual acuity in infants with severe ROP and surgical retinal reattachment may warn us of glaucoma, as this diagnosis is difficult to make in these small infants.

Hyperbaric oxygen tolerance in newborn mammals--hypothesis on mechanisms and outcome

Newborn mammals, compared to adults, are extremely resistant to the CNS effects of hyperbaric oxygenation (HBO) induced by excessive generation of reactive oxygen species. This tolerance to HBO may be related to either physiological responses or the chemical characteristics of the immature brain, including a low cerebral blood flow and energy metabolism, and a low concentration of polyunsaturated fatty acids. In adult mammals the main protective mechanism against CNS oxygen toxicity, besides endogenous antioxidants, is a transient HBO-induced cerebral vasoconstriction. How cerebral vasculature reacts to HBO in the immature brain is not known. We present indirect evidence suggesting that HBO in newborn rats induces a persistent cerebral vasoconstriction concurrently with a severe and maintained reduction in ventilation. It is speculated that the outcome of these physiologic responses to hyperoxic exposures may be: (a) extension of tolerance to both CNS and pulmonary oxygen poisoning; (b) creation of a profound hypoxic-ischemic condition in vulnerable neural structures; and (c) impairment of the circulatory and ventilatory responses to hypoxic stimuli on return to air with consequent development of a secondary hypoxic-ischemic condition. These hypothetical pre- and post-HBO events may set the stage for the development of some delayed neurological disorders, including the retinopathy of prematurity and the retardation of brain development in fetuses or prematurely-born infants subjected to oxygen therapy.

Ocular findings in prematurely born children at 5 years of age

Fifty-eight prematurely born children (gestational age < or = 32 weeks) were studied at the age of 5 years. The ophthalmological examination was part of an extensive neurodevelopmental evaluation. The eye study revealed significant hyperopia (> or = + 2.0) in 22.4%, myopia (> or = -1.0 D) in 8.6%, astigmatism (> or = 1.0 D) in 12.1%, and anisometropia (> or = 1.0 D) in 12.1%. The myopic refractive error was high in all of the cases: from -6.0 to -14.0 D. Manifest strabismus was found in 24.2% and significant visual impairment or blindness in 6.9%. Optic atrophy and cicatricial retinopathy of prematurity were the main causes for severe visual defects. In the randomly selected full-term children of the same age, significant hyperopia was seen in 14.3%, astigmatism in 5.4% and strabismus in 1.8%. The pattern of the eye findings was different in the preterm children compared with those born at term.

Analysis of experimental antiangiogenic therapy

Angiogenesis is a fundamental process by which new blood vessels are formed. Progressive tumor growth necessitates the continuous induction of new capillary blood vessels which converge upon the tumor. Suppression of tumor growth can be accomplished with the use of antiangiogenesis agents. AGM-1470 is a potent angiogenesis inhibitor in vitro and in vivo. In mouse studies, AGM-1470 has suppressed the growth and neovascularization induced by four murine tumors resulting in a 55% to 77% decrease in tumor growth. In these mice significant toxicity did not result from AGM-1470 therapy. AGM-1470 administered systemically to C57BI/6 male mice for 20 to 28 days inhibited the growth of: (1) Lewis lung carcinoma resulting in a T/C (treatment/control = mean tumor volume of treated/mean tumor volume of control) of 0.38 +/- 0.03 (P < .001); (2) colon adenocarcinoma 38 resulting in a T/C of 0.23 +/- 0.02 (P < .001); and (3) fibrosarcoma 105 resulting in a T/C of 0.31 +/- 0.05 (P < .001). To determine if antiangiogenic therapy was equally effective in mice of both sexes and in immunodeficient animals, we tested AGM-1470 in the treatment of fibrosarcoma 105 in both female mice and nude mice. For female mice T/C was 0.24 +/- 0.06 (P < .001). For nude mice T/C was 0.27 +/- 0.06 (P < .001). These results demonstrate that AGM-1470 suppresses the growth of a variety of different tumors. Furthermore, the antitumor effect of AGM-1470 therapy is independent of the immune system and sex.

Prognostic factors in the natural course of retinopathy of prematurity. The Cryotherapy for Retinopathy of Prematurity Cooperative Group

BACKGROUND

There exists no reliable information that allows the ophthalmologist to predict with any degree of certainty a particular infant's chances of requiring surgical treatment for retinopathy of prematurity (ROP) or of reaching an unfavorable outcome on the basis of the retinal findings at the time of the nursery examination.

METHODS

In the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity (CRYO-ROP), 4099 infants weighing less than 1251 g at birth underwent eye examinations that began at 4 to 6 weeks after birth and subsequently continued at 2-week intervals. Independent variables in the population were studied using multiple logistic regressions.

RESULTS

An increased risk of reaching threshold ROP was found associated with lower birth weights, younger gestational age, white race, multiple birth, and being born outside a study center nursery. For infants who developed ROP (66%), corresponding probabilities are presented for developing severe ("threshold") ROP or of having an unfavorable macular outcome. The risk of an unfavorable macular outcome was increased with zone 1 ROP, "plus" disease, the severity of the stage, and the amount of circumferential involvement. A higher risk also was associated with a rapid rate of progression of ROP to prethreshold disease but not with the postconceptional age at which ROP was first noted.

CONCLUSION

The findings indicate that the ocular characteristics of ROP, along with some easily identifiable and available basic systemic and demographic information about an infant, can assist the ophthalmologist in understanding variations in an individual baby's chance for a good or poor macular outcome.

Properties and function of the ocular melanin--a photobiophysical view

This paper reviews the biosynthesis and physicochemical properties of the ocular melanin. Age-related changes of melanin granules and the corresponding formation of lipofuscin pigments in the retinal pigment epithelium (RPE) are also described. Adverse photoreactions of the eye and, in particular, light-induced damage to the RPE-retina are reviewed in relation to the ocular pigmentation. A hypothesis on the photoprotective role of the RPE melanin is presented that is based on the ability of the cellular melanin to bind redoxactive metal ions. Since bound-to-melanin metal ions are expected to be less damaging to the pigment cells, it is proposed that sequestration of heavy metal ions by the RPE melanin is an efficient detoxifying mechanism. It is postulated that oxidative degradation of RPE melanin may lower its metal-binding capability and decrease its anti-oxidant efficiency. Cellular and environmental factors that may contribute to possible oxidative damage of the RPE melanin are discussed in connection with the etiology of age-related macular degeneration.

Retinopathy of prematurity: risk factors in a prospective population-based study

A prospective study of risk factors for retinopathy of prematurity (ROP) in all very low birthweight (less than 1500 g) infants born in New Zealand in 1986 is reported. Of 413 liveborn infants admitted to neonatal units, 338 (81.2%) survived to be discharged home. Of surviving infants, 313 (93%) were examined by indirect ophthalmoscopy, as were eight infants who died before discharge. Sixty-nine infants (21.5% of 321) had acute retinopathy. On multiple logistic regression analysis, three variables made statistically significant independent contributions to the risk of any acute retinopathy; gestational age (P less than 0.0001), principal hospital caring for the infant (P less than 0.01) and treatment with indomethacin (P less than 0.01). Only two variables, gestational age (P less than 0.0001) and hospital (P less than 0.01), made significant contributions to the risk of stage 2 or more ROP. For both categories of ROP, timing of the examination also had a statistically significant effect (P less than 0.001). After adjustment for other significant predictor variables, it was estimated that approximately 70% of infants of less than 26 weeks' gestation were at risk of ROP and nearly 50% of stage 2 or more ROP, in comparison with less than 2% of infants of 32 weeks' gestation or more; infants treated with indomethacin were over 1.5 times more likely to have ROP than infants not so treated. Failure to enforce uniform timing of examination was the most serious defect in the study; only 205 (64%) of the 321 infants were examined at the recommended time. However, reanalysis of the model with information limited to these 205 infants yielded similar risk factors. The incidence of ROP, both observed (P less than 0.05) and adjusted for other significant variables in the regression model (P less than 0.01) was lowest in the two largest level III hospitals. These hospitals also had the best survival rates after adjustment for birthweight, gestation and gender (P less than 0.01). We speculate that the larger level III units obtained better results because their size and experience enabled them to provide a better overall quality of care.

Evaluation of bilirubin as possible protective factor in the prevention of retinopathy of prematurity

Retinopathy of prematurity (ROP) appears to be a multifactorial disease, the prevention of which is probably impossible even with the most accurate methods of blood-gas monitoring and oxygen restrictions. The oxidative processes and consequent formation of free radicals are probably influenced by the availability of various antioxidants in the immature retina. Bilirubin, the end product of haem catabolism, has recently been regarded as a potential physiological antioxidant. In order to test the suggestion as to the possible effect of bilirubin in reducing the incidence of ROP a retrospective study was undertaken of the medical records of 151 neonates born between 1984 to 1988 who weighed less than 1500 g. Of these, 78 had various degrees of ROP, whereas 73 had no ROP and served as a control group. The daily mean bilirubin values were analysed in accordance with gestational age and birth weight as well as the severity of ROP, and the results were compared with those obtained for the control group. The results showed no correlation between bilirubin levels and severity of ROP in all subgroups of gestational age and birth weight. These findings indicate that there is no apparent protective effect of bilirubin on the development of ROP.

Effect of partial cryoablation on retinopathy of prematurity

Cryotherapy has been shown to be an effective treatment for retinopathy of prematurity stage 3. It is said to reduce the unfavourable outcome of the disease by 50%. The accepted method of therapy includes ablation of the whole avascular retina from the ridge to the ora serrata. This is achieved by two to three rows of cryoapplications. When 360 degrees cryo treatment is performed, it requires 52 cryo applications. We present our method of cryotherapy which involves only one row of cryoapplications in the avascular retina anterior to the fibrovascular ridge. An average of 25-30 cryoapplications was required for a 360 degrees treatment. The anatomical results in 23 babies are presented. Complete regression of active retinopathy was found in all.

Eleven years' experience with retinopathy of prematurity: visual results and contribution of cryoablation

We report our 11 years' experience of cryotherapy for retinopathy of prematurity (ROP). Charts of 624 infants weighing under 1250 g who were admitted to our Neonatal Intensive Care Unit during 1977-87 were reviewed. Three hundred and eighty nine babies survived, and the total ROP prevalence was 57.5%. Cryotherapy was applied to 35%. Only one case (0.25%) of blindness was detected, and four babies (1%) had a final visual acuity of less than 20/200 in one eye. The complication rate following cryoablation was very low.

Blindness and partial sight due to retinopathy of prematurity in The Netherlands: 1975-1987

In 1975-1987 at least 84 children developed blindness or impaired vision due to retinopathy of prematurity (ROP) in the Netherlands. Neonatal data were obtained on 74 (86%). Unexpectedly most children (40 i.e. 54%) had been in level I and II hospitals after birth. Screening for ROP had been either insufficient or not timed according to present recommendations in 33 out of 40 children in level I and II hospitals and 25 out of 34 in level III hospitals. As the number of children with ROP has not changed appreciably over the last 40 years, while birth rates in the Netherlands have steadily decreased, the incidence of blindness/impaired vision due to ROP has probably increased. In the current population at risk of ROP which differs considerably from the one during the first epidemic, the disease may not be completely preventable. We conclude that improvements in screening procedures and timely treatment are crucial in order to improve the present situation.

Ocular examination in nine-month-old infants with very low birthweights

In the period 1980-1987 ocular examinations were performed on 185 infants with a very low birthweight (less than 1500 g) at the age of nine months corrected for the duration of pregnancy. The mean gestational age of the infants was 30 weeks, while the mean birthweight was 1160 g. The mean spherical refraction was 0.9 D (S.D. 1.3 D), the mean astigmatism was C-0.6 D (S.D. 1.0 D), while convergent strabismus was found in 10% of the patients. The purpose of the investigation was to see if there was a relation between spherical equivalent of refraction, astigmatism and strabismus on the one hand and 11 perinatal parameters and cerebral palsy diagnosed at the age of nine months on the other hand. Statistical analysis was performed with the Student t-test. No significant correlation between the findings of ocular examination and the perinatal parameters could be detected.

Retinopathy of prematurity. Clinical findings in a Danish County 1982-87

The study includes all infants in a Danish county born 1982-87 considered at risk of acquiring retinopathy of prematurity (n = 411; 178 girls, 233 boys). 325 had birthweight (BW) less than or equal to 1750 g and/or gestational age (GA) less than or equal to 34 weeks. The remaining referrals were on account of functional immaturity/significant oxygen treatment (n = 86). With a median onset age of 6.5 weeks (range 5-9 weeks) ROP was recorded in 63 infants. A negative correlation (r = -0.34) between GA and ROP onset age suggested a later onset in the very immature infant. ROP appeared in 60% of those born at GA less than or equal to 28 weeks (n = 30) and in 50% of survivals with BW less than or equal to 1000 g (n = 20). With BW and GA beyond the limits of 32 weeks and 1750 g only 5 cases of ROP were observed. Out of the 14 infants with at least stage 3 ROP 6 became blind in both eyes after few months (GA at delivery 25-31 weeks/BW 920-1595 g). All considered, 57 of the 63 with ROP showed spontaneous regression, however, leaving myopia of prematurity in 8 subjects.

Retinopathy of prematurity (ROP): optimal timing of clinical evaluation and standard procedures

The authors present the protocol currently used in their institution for initial and follow-up evaluation of infants at high risk for developing retinopathy of prematurity (ROP). After topical anesthesia and lid speculum insertion, the examination is carried out using an indirect binocular ophthalmoscope with a +20 or +28-diopter lens. Mydriasis is achieved by instilling one drop of 1% tropicamide, followed by one drop of 0.5% tropicamide + 2.5% phenylephrine 15 minutes later and after an additional 15 minute interval, another drop of 1% tropicamide. If mydriasis is insufficient after one hour, one drop of a 0.5% tropicamide-5.0% phenylephrine solution may be instilled. The initial examination is performed between the third and fourth weeks of life. If any areas of retinal immaturity are found, the examination is repeated every other week and, later, every three to four weeks, until vascularization has reached the ora serrata. Should any sign of ROP be present during the first examination, the patient is examined weekly or every other week depending on the severity of clinical findings.