The purpose is to compare the treatment frequency of preterm infants who developed severe Retinopathy of Prematurity (ROP) during the years 2015-2018 with 2020-2021 in the country, using the statistical method 'difference in differences' to investigate the potential for scientific evidence regarding the introduction of dexamethasone eye drops' effect on the development of severe treatment-requiring ROP. During these years, the investigatots assess that the recommended oxygen saturation levels for preterm infants have remained stable at each clinic, which will serve as its own reference.

Retinopathy of Prematurity (ROP) can develop in premature infants and involves abnormal growth of blood vessels in the retina. It can lead to severe visual impairment or blindness if not treated in time. In Sweden, approximately 40-50 children require treatment for severe ROP each year. Children at the highest risk are screened to detect ROP at an early stage, and, if necessary, laser treatment of the retina is performed or an injection of an anti-vascular endothelial growth factor (anti-VEGF) agent is administered. However, laser treatment burns away the outermost part of the retina, and anti-VEGF carries a significant risk of recurring treatment needs, resulting in increased anesthesia and examination sessions for the child, risk of eye infection, lens damage, and uncertainty about the drug's broader effects on the child's brain or body.

Dexamethasone is a corticosteroid commonly used in eye drop form to treat inflammatory and angiogenic eye diseases. Dexamethasone is also administered systemically in neonatal care to treat lung disease and wean premature infants off ventilator support, often in relatively high doses early in the infant's life.

Increased inflammation in the eyes has been reported in ROP. According to both national and several international guidelines, dexamethasone eye drops are administered in tapering doses after laser treatment for severe ROP, often staring with 1 drop 3 times daily. When a child begins developing severe ROP, it is classified as Type-1 ROP and Type-2 ROP. Type-1 ROP requires treatment within 72 hours, while Type-2 ROP is considered a precursor to Type-1 ROP.

In the Southern Healthcare Region of Sweden, the investigators have initiated earlier use of low dose dexamethasone eye drops, specifically when it appears that the child is transitioning from Type-2 ROP to Type-1 ROP. Usually 1 drop daily. In a pilot study published in September 2021, the investigators observed that only 24% of children who received dexamethasone eye drops at Type-2 ROP progressed to Type-1 ROP, compared to 74% of children who did not receive dexamethasone eye drops for the same type of ROP.

In Sweden, there is a national quality registry for ROP care, SWEDROP, with approximately 98% coverage. The investigators now aim to conduct a study based on this quality registry and compare the results from the Southern Healthcare Region with other regions in Sweden that have not used dexamethasone for Type-2 ROP. The goal is to determine whether the "difference-in-differences" method can provide stronger scientific evidence supporting this treatment approach. The plan is to compare the number of children who progressed to laser treatment in the years before the introduction of dexamethasone for Type-2 ROP with data from 2020-2021, when almost all children in the Southern Healthcare Region, received dexamethasone for Type-2 ROP. Specifically, the investigators will compare the years 2015-2018 with 2020-2021. The year 2019 served as a transitional period in the Southern Healthcare Region, where children were treated with varying doses, and therefore it will not be included in the primary comparison. The treatment frequency will be analyzed both for all screened children and specifically for those who developed severe ROP. Severe ROP is defined as type 1 and type 2 ROP.

Age at treatment will also be analyzed.

Inclusion Criteria:

- During 2015-2018 and 2020-2021, all children born before week 30 in the Southern Health Region and three regions where dexamethasone eye drops were not used to prevent severe treatment-requiring ROP were included

Exclusion Criteria:

If a child has not completed the screening examinations for ROP-

Between 2015-2018 and 2020-2021, all children born before week 30 in the Southern Healthcare Region and three other regions where dexamethasone eye drops were not used to prevent severe treatment-requiring ROP were included in the study population. A specific analysis was conducted on the children who developed severe ROP, Type 1 and Type 2 ROP.