Incidence and treatment outcomes of retinopathy of prematurity in preterm infants assessed through wide-field fundus imaging: a retrospective cohort study

Introduction

Retinopathy of prematurity (ROP) remains a major cause of childhood blindness globally. The premature birth of an infant, combined with incomplete retinal vascularization, contributes to the development of aberrant neovascularization and proliferative vitreoretinopathy, which can progress to retinal detachment—a hallmark of advanced and vision-threatening ROP. During the 1940s and 1950s, a substantial number of ROP cases were reported in Europe and North America, largely attributed to the absence of oxygen concentration monitoring during supplemental oxygen therapy in preterm neonates (1,2). Elevated oxygen levels are a well-established risk factor for ROP pathogenesis (3,4). Despite the introduction of standardized oxygen administration protocols, including concentration monitoring and time regulation, the global incidence of ROP remains approximately 10% (5).

Advancements in perinatal medicine and neonatal intensive care have significantly improved over the past few decades. However, clinical priorities have often focused on enhancing the survival of extremely low birth weight infants, with comparatively less emphasis on reducing the associated morbidities. As a result, the incidence of complications such as neurodevelopmental impairment, bronchopulmonary dysplasia, sepsis, and ROP has not demonstrated a corresponding decline (6,7).

Wide-field fundus imaging technology was introduced in China around 2004 and has since been progressively adopted for the screening of pediatric ocular conditions. In the same year, China released its initial edition of the “Guidelines for the Screening of ROP”. Further emphasizing national commitment to ROP prevention, the 2016 “13th Five-Year National Eye Health Plan” highlighted the need for widespread training in ROP prevention and treatment, with the aim of lowering the incidence and disability rates among preterm infants.

Research in China has indicated that approximately 20,000 newborns experience blindness or severe visual impairment due to this condition each year (5). Despite the increased awareness of the need for strict oxygen control and proactive measures to prevent and treat ROP, the incidence of ROP remains at a high level. Current treatment options for ROP include laser therapy, vitrectomy, anti-vascular endothelial growth factor (anti-VEGF) drug therapy, and direct ablation of abnormal blood vessels (8). With existing criteria, only about 5–10% of screened infants will equire treatment (9). Therefore, efforts to safely reduce the number of stressful and costly creening examinations would be beneficial.

Almeida et al. have primarily examined the incidence of ROP and its associated risk factors, establishing a direct correlation between the occurrence of ROP and both gestational age and birth weight (4). Most ROP cases are self-limiting and do not require therapeutic intervention; during follow-up, spontaneous regression of the ridge and demarcation line is commonly observed. This study aims to further examine the occurrence of ROP and evaluate clinical outcomes following intravitreal administration of anti-VEGF agents. We present this article in accordance with the STROBE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-224/rc).

Methods

General data

A total of 300 preterm or low birth weight infants, with a gestational age of less than 32 weeks or a birth weight below 2,000 g, admitted to the neonatal department of Baoding Maternal and Child Health Hospital between November 2022 and March 2024, were consecutively enrolled and underwent fundus screening using the RetCam wide-field imaging system. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of the Baoding Maternal and Child Health Hospital (No. 2023-01-K0022) and informed consent was taken from all the patients’ parents or legal guardians.

ROP screening method

Screening criteria: Infants with a birth weight of <2,000 g or a gestational age of <32 weeks, and who survived for 28 days or longer, were eligible for screening. For infants with a history of resuscitation or oxygen therapy, the decision to initiate screening was made at the discretion of a neonatologist.

Screening procedure: fundus screening was conducted by an ophthalmologist experienced in pediatric ocular disorders, including vitreoretinal diseases. Mydriasis was achieved by instilling one drop of compound tropicamide into each eye every five minutes, for a total of three applications. Fundus examination was conducted one hour after the final instillation. Once adequate pupillary dilation was observed, one drop of proparacaine hydrochloride was instilled into each eye, followed by a one-minute waiting period before imaging. The 130° pediatric probe was disinfected twice using alcohol swabs and air-dried prior to use. The infants were wrapped in a blanket and secured, with assistance provided to stabilize the head. A pediatric eyelid speculum was used to gently open the eyelids, and initial images of the iris and pupil were captured. The RetCam probe was placed vertically on the corneal surface after application of gatifloxacin gel, ensuring slight contact with the cornea. Image clarity was adjusted on the display monitor, and fundus images were captured and saved from five standard fields: posterior pole, superior, inferior, nasal, and temporal.

The initial examination was scheduled between 28 and 42 days after birth or at a corrected gestational age of 32 weeks (corrected gestational age = gestational weeks at birth + postnatal weeks). Follow-up examinations were conducted within two weeks of the previous screening. In cases of rapidly progressing lesions, the interval between examinations was shortened accordingly.

Classification standards: the International Classification of Retinopathy of Prematurity, as defined during the 1984 International ROP Conference and revised in 2005, was adopted (10,11). Retinal lesions were categorized anatomically into three zones:

• Zone I: a circular area centered on the optic disc with a radius equal to twice the distance from the disc to the macula, encompassing approximately 60° of the posterior retina.
• Zone II: a ring-shaped area extending from the edge of Zone I to the nasal ora serrata.
• Zone III: the residual crescent-shaped temporal retina outside Zone II.

The extent of retinal involvement was quantified in clock hours. The severity of ROP was staged as follows:

• Stage 1: presence of a white demarcation line at the junction between vascularized and avascular retina.
• Stage 2: formation of a ridge at the demarcation line.
• Stage 3: extraretinal fibrovascular proliferation extending into the vitreous.
• Stage 4: partial retinal detachment due to fibrovascular traction, subdivided into Stage 4A (macula not involved) and Stage 4B (macula involved).
• Stage 5: total retinal detachment, often exhibiting a funnel-shaped configuration.

Additional signs such as vascular dilation and tortuosity at the posterior pole, along with iris vascular engorgement, were classified as “Plus” disease, indicating increased severity. Pre-threshold disease included any lesion in Zone I, Stage 2 with “Plus” disease in Zone II, or Stage 3 and 3+ in Zone II. Threshold disease was defined as Stage 3 with “Plus” disease in Zones I or II, involving at least 5 contiguous or 8 cumulative clock hours of retinal involvement.

Exclusion criteria: Infants with life-threatening comorbidities, congenital ocular malformations, or those for whom retinal screening was not feasible due to conditions such as intraocular hemorrhage were excluded from the examination protocol.

Statistical analysis

All statistical analyses were conducted using SPSS version 22.0. Quantitative data conforming to a normal distribution were presented as mean ± standard deviation (x¯±s), while non-normally distributed data were expressed as interquartile ranges. The Kruskal-Wallis test was applied for the comparison of quantitative data across groups. Rank correlation tests were employed for the analysis of ordinal variables. Spearman correlation analysis was used to assess associations between ROP incidence and potential risk factors. A value of P<0.05 was considered statistically significant.

Results

ROP incidence

As depicted in Table 1, a total of 300 preterm infants underwent ROP screening. The mean gestational age was 32.66±2.87 weeks, and the mean birth weight was 1,549.76 g. Of these infants, 177 were male and 123 were female. ROP was diagnosed in 37 cases, yielding an incidence rate of 12.33%. Among the affected infants, two cases were located in Zone I, 17 in Zone II, and 18 in Zone III. In terms of disease severity, 15 cases were classified as Stage 1, 16 as Stage 2, and 5 as Stage 3.

As presented in Table 2, “Plus” disease was observed in nine cases. These infants had gestational ages ranging from 26 to 28 weeks, and corrected gestational ages between 32 and 37 weeks at the time of Stage 1 disease onset, typically occurring after six weeks of age. Anti-VEGF therapy was administered between 34 and 39 weeks of corrected gestational age, corresponding to 8 to 13 weeks postnatally.

Factors related to ROP

Relationship between birth weight, gestational age, and ROP. The findings of this study indicated that all infants diagnosed with ROP had a gestational age of less than 32 weeks and birth weight below 2,000 g. Among those who progressed to threshold ROP, gestational age was ≤28 weeks and birth weight was less than 1,100 g. Statistically significant differences in gestational age and birth weight were observed between the ROP and non-ROP groups (Z=−8.500 and −8.610, P<0.001). A negative correlation was identified between the occurrence of ROP and both gestational age (R=−0.499) and birth weight (R=−0.490), with both associations reaching statistical significance (P<0.001).

Similarly, when comparing the threshold ROP group with the non-threshold ROP group, statistically significant differences were found in gestational age and birth weight (Z=−5.002 and −4.990, P<0.001). The development of threshold ROP was negatively correlated with gestational age (R=−0.338) and birth weight (R=−0.341), with both correlations demonstrating statistical significance (P=0.020 and 0.019, respectively). These findings are summarized in Table 3.

Outcomes after anti-VEGF drug therapy

Following anti-VEGF treatment, regression of ROP lesions was observed in 8 infants after a single intravitreal injection of ranibizumab. One infant exhibited disease reactivation one month after the initial injection and subsequently achieved lesion regression following a second administration of anti-VEGF therapy (Figures 1,2).

Figure 1 Case 2 before and after treatment. (A) Before treatment, the temporal blood vessels only developed to zone I, and the blood vessels were “Plus”. (B) After treatment, the temporal blood vessels continued to develop to the periphery. (C) Before the treatment, the nasal blood vessels were significantly tortuous, the ridges widened, and turned to red. (D) After the treatment, the blood vessels became thinner and the retinal blood vessels continued to grow to the periphery.

Figure 2 Case 8 before and after treatment. (A) Before treatment, the nasal blood vessels of the patient only developed to zone I, the blood vessels were “Plus”, the ridges were widened and red, and there was “popcorn” sign. (B) After treatment, the Plus sign subsided, the nasal blood vessels continued to grow to the periphery, and the “popcorn” sign subsided. (C) Before treatment, the blood vessels were obviously tortuous, and the temporal blood vessels only developed to zone I. (D) The patient’s blood vessels become thinner after treatment, and retinal blood vessels continue to grow periphery.

Discussion

As the most populous developing country, China reports approximately 16 million live births annually, with preterm infants accounting for 7% to 10% of this population. The incidence of ROP among these infants ranges from 15% to 20%. In April 2004, the Chinese Medical Association released the Guidelines for the Prevention and Treatment of Oxygen and Retinopathy in Premature Infants, which established standardized criteria for ROP screening (11). According to these guidelines, all preterm or low birth weight infants with a birth weight of <2,000 g should undergo fundus screening and be monitored until peripheral retinal vascularization is complete. The screening scope may be appropriately extended for preterm infants with severe medical conditions. The initial examination is recommended at 4–6 weeks postnatally or at a corrected gestational age of 32 weeks. These guidelines provide a foundational reference for standardized ROP screening and have facilitated the implementation of structured screening protocols nationwide. The introduction of wide-field fundus imaging systems and intravitreal anti-VEGF therapy has significantly advanced the diagnostic and therapeutic capabilities in the management of ROP.

Choice of screening method

Wide-field fundus imaging systems have been adopted in numerous hospitals across China, with general ophthalmology or neonatal healthcare personnel trained to perform routine screening for neonatal ocular diseases.

The wide-field fundus imaging system represents a specialized and relatively recent advancement in ophthalmic diagnostics. Numerous studies have validated its use in ROP screening. This modality offers several advantages:

• It is user-friendly and can be mastered with minimal training, enabling pediatricians, neonatologists, and other medical personnel to perform image acquisition. The resulting images can subsequently be interpreted by pediatric ophthalmologists, thereby alleviating the screening workload traditionally borne by ophthalmology specialists.
• The high-resolution images are intuitive and can be archived for longitudinal comparison, aiding in disease monitoring and treatment evaluation. With a 130° lens, the system captures fundus images extending to the retinal equator, thereby minimizing the risk of overlooking peripheral lesions. However, given that the system produces two-dimensional images, raised retinal lesions may require supplementary assessment using an indirect ophthalmoscope to determine their extent.
• The technique does not necessitate scleral indentation, thereby reducing discomfort and the potential for ocular reflexes during the examination.
• A notable limitation is the high cost of the equipment, necessitating substantial institutional investment and support for widespread implementation (10,12).

Key parameters in the operation of wide-field fundus imaging systems include imaging angle, focal length, and brightness settings (10,12). In cases where the neonate is uncooperative, such as when crying or agitated, the examination should be paused temporarily. Efforts should be made to gently soothe and stabilize the emotional state of the infant prior to resuming the procedure, in order to ensure optimal image quality and examination accuracy.

Timing of screening and follow-up frequency

Neonatal ocular screening is commonly conducted within 1 to 7 days after birth, which is clinically valuable for the early identification and intervention of congenital or early-onset ocular disorders. However, this timeframe may be premature for effective screening of ROP, as the onset and progression of ROP typically occur over a period of 4 to 6 weeks. In the present study, Stage 1 ROP lesions were observed in preterm infants around the sixth week postnatally. Screening conducted too early may increase the frequency of examinations and cause unnecessary discomfort to the infant, as retinal vasculature remains underdeveloped during this period. Therefore, the initial ROP screening is generally recommended between 4 and 6 weeks of age (10).

Clinical experience has revealed that only a small proportion of infants diagnosed with ROP ultimately require treatment. While the overall incidence of ROP ranges from 15% to 20%, not all cases necessitate therapeutic intervention (13). Understanding the staging and progression of ROP is essential for guiding appropriate management strategies. In this study, 37 infants were diagnosed with ROP, representing an incidence rate of 12.33%; among them, only nine cases met the criteria for treatment.

In 2014, the Fundus Disease Group of the Ophthalmology Branch of the Chinese Medical Association issued updated guidelines for ROP screening, which introduced detailed definitions for the threshold and pre-threshold periods (14). Type 1 ROP, which qualifies as an indication for treatment, includes the following: (I) Zone I Stage 1 with “Plus” disease (Zone I 1+), Stage 2 with “Plus” disease (Zone I 2+), Stage 3 with or without “Plus” disease (Zone I 3+/3); (II) Zone II Stage 2 or Stage 3 with “Plus” disease (Zone II 2+/3+); and (III) aggressive ROP. Type 2 ROP includes Zone I Stage 1 or Stage 2, and Zone II Stage 3 without “Plus” disease, and typically requires ongoing clinical observation.

The updated classification introduced the concept of anterior segment involvement (“anterior empathy”) (14). Treatment indications were established for Type 1 ROP, while Type 2 cases were recommended for close monitoring. At the time, treatment modalities primarily included retinal laser photocoagulation and cryotherapy.

Additional lesions, indicative of disease progression, may include iris vascular engorgement, pupil dilation, peripheral vascular hyperemia, and vitreous haze. However, the presence of these signs is not mandatory for the diagnosis of “Plus” disease (15).

Recent clinical judgment in the assessment of ROP has shifted from a primary focus on staging to a greater emphasis on retinal zoning (16). For instance, lesions classified as Stage 1 in Zone I are now considered more severe than Stage 3 lesions located in Zone III, due to the anatomical and functional significance of the posterior pole.

In cases of aggressive posterior ROP (APROP), lesions are typically localized to the posterior retinal arteries and veins. These lesions are characterized by pronounced vascular tortuosity and dilation, absence of peripheral vascular development, and poorly defined retinal borders. Due to the rapid progression of APROP, the disease often does not follow the typical sequential stages observed in classical ROP, making timely diagnosis and intervention particularly challenging.

Choice of treatment

Intravitreal administration of anti-VEGF agents has introduced a novel therapeutic approach for the management of ROP (17). Similar to other neovascular ocular conditions, ROP is characterized by excessive expression of VEGF in the vitreous, leading to pathological neovascularization in neonates (18). The intravitreal injection of anti-VEGF agents reduces intraocular VEGF levels, thereby suppressing abnormal vascular proliferation.

However, VEGF plays a key role in the normal development of intraocular structures, including the retina and optic nerve. Emerging evidence indicates that intravitreal anti-VEGF agents may enter the systemic circulation and potentially interfere with the development of vital organs such as the brain, heart, lungs, liver, and kidneys in preterm infants. Given that the technical requirements and equipment for intravitreal injection are less demanding compared to binocular indirect ophthalmoscope-guided laser photocoagulation, anti-VEGF therapy has been adopted by many institutions and clinicians as a first-line treatment modality for ROP (19).

However, anti-VEGF therapy remains a double-edged sword. Studies have indicated that following intravitreal anti-VEGF administration, retinal cells may upregulate fibrogenic cytokines such as transforming growth factor-β2 and connective tissue growth factor, promoting the formation of fibrovascular membranes. This process may contribute to the progression of tractional retinal detachment. Cases have been reported in which annular fibrous membranes developed following anti-VEGF therapy, with rapid disease advancement to Stage 4b or even Stage 5 ROP (20,21).

Therefore, the use of intravitreal anti-VEGF therapy for ROP requires strict adherence to established indications and must be accompanied by vigilant post-treatment follow-up. Prophylactic administration of anti-VEGF agents in the absence of threshold disease is strongly contraindicated.

Fibrovascular proliferation, extensive retinal hemorrhage, and rapid-onset tractional retinal detachment may occur within a short period following anti-VEGF treatment. Prompt intervention during this crucial window is essential to prevent progression to advanced-stage ROP.

Conclusions

In summary, wide-field fundus imaging has proven to be an effective tool for ROP screening in preterm infants. Screening is best initiated at approximately six weeks postnatally, with particular attention to those with lower birth weight or gestational age. Anti-VEGF therapy remains an effective treatment option for threshold ROP, provided that it is used with caution and within appropriate clinical guidelines.

Acknowledgments

We are particularly grateful to all the people who have given us help on our article.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-224/rc

Data Sharing Statement: https://tp.amegroups.com/article/view/10.21037/tp-2025-224/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-224/prf

Funding: This study was supported by the Baoding Science and Technology Plan Project (No. 2341ZF301).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-224/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of the Baoding Maternal and Child Health Hospital (No. 2023-01-K0022) and informed consent was taken from all the patients’ parents or legal guardians.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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