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Summary
A major cause of infant blindness is retinopathy of prematurity, where abnormal retinal blood vessel development results in damage to the eyes. Fetuses in the womb receive the most DHA during the last trimester of pregnancy, premature born infants thus receive less DHA through the uterus. Research points towards a positive role for DHA in the reducing the risk and severity of retinopathy of prematurity.
 
Introduction
Retinopathy of prematurity (ROP) is a leading cause of infant blindness worldwide. It is characterized by abnormal development of blood vessels of the retina in prematurely born infants, leading to visual impairments and even blindness.
During normal development in the womb, the retina of the fetus are surrounded by an embryonic vascular network that is replaced by a mature vascular network post-birth. Hypoxia (i.e. insufficient oxygen levels) is an important regulator of vascular development: as tissues grow and require more oxygen, growth factors are recruited to hypoxic regions to stimulate the development of new blood vessels.

The ROP process knows two post-natal stages; delayed vascular development and subsequent overcompensation of vascularization. First, as premature babies are exposed to more oxygen post-birth than in the womb, the hypoxic conditions needed for the development of new vasculature are not met. As a consequence, no new vasculature is developed and some existing blood vessels are even degenerated. During the second phase, as the retina continues to develop and grow post-birth, the existing vasculature is not able to supply enough oxygen to the retina and a hypoxic environment arises. The eye tries to compensate for this by excessive formation of vasculature to the retina. This leads to uncontrolled overcompensation: too many new (fragile) blood vessels are formed, which can lead to bleeding and even retinal detachment with visual impairments as a result.

Importantly, DHA is involved in the regulation of vascular development, and the retina of the eye have one of the highest DHA contents of all tissue types. Transfer of DHA to the developing fetus  (through the placenta) increases dramatically during the last trimester of pregnancy to support growth and development. As a consequence, prematurely born babies receive less (placental) DHA than babies born at or after 40 weeks of gestation.  Research has found that omega-3 fatty acids, DHA in particular, have beneficial properties in the context of ROP, as can be seen below.
 
Research findings
A study by the David Geffen School of Medicine assessed the red blood cell membrane levels of omega-3 fatty acid DHA and omega-6 fatty acid AA (arachidonic acid) in 56 premature infants (Gillespie et al., 2022). They found that higher red blood cell membrane levels of AA and DHA in premature infants was associated with a reduced risk of ROP development and severity.

Yang and colleagues reported ROP severity reducing  properties of DHA-containing fish oil in their 2022 study (Yang et al., 2022). In their study, 89 infants born 6 or more weeks prematurely were given either a fish oil (DHA containing) emulsion or soy oil (without DHA) by means of injection. The authors reported that DHA content in red blood cells increased in the fish oil group compared to the soy oil group. Crucially, the fish oil group had a lower incidence of severe ROP than the soy oil group, though the authors found no group difference in ROP prevalence.

In their 2021 study, Hellström and colleagues tested the effect of DHA and AA on the development and severity of ROP in infants born 12 or more weeks prematurely (Hellström et al., 2021). Hundred-and one prematurely born infants were orally given oil droplets containing 100mg/kg bodyweight AA and 50mg/kg bodyweight DHA for the amount of weeks these babies were premature. The control group of 105 premature infants received no supplements. The authors reported that the AA/DHA receiving group had higher serum levels of AA and DHA. As a result, this reduced the risk of developing severe ROP by 50% compared to the control group.
 
Conclusion
Other than the preventative role of DHA in premature births (Add hyperlink to page on DHA & birthweight), studies show an effect of omega-3 fatty acids, in particular DHA, in reducing the risk and severity of ROP. Publications discussed above report that higher red blood cell membrane DHA content reduces ROP risk and especially severity. The proposed mechanism behind this positive effect is likely active during phase 2 of ROP. This phase is characterized by overcompensation of vascular development as a result of poor retinal blood flow; DHA likely reduces this overcompensation. As a result, proper vascularization of the retina is promoted, which in turn reduces ROP severity.
 
References
Gillespie, T. C., Kim, E. S., Grogan, T., Tsui, I., Chu, A., & Calkins, K. L. (2022). Decreased Levels of Erythrocyte Membrane Arachidonic and Docosahexaenoic Acids Are Associated With Retinopathy of Prematurity. Investigative Ophthalmology & Visual Science, 63(12), 23. https://doi.org/10.1167/iovs.63.12.23

Hellström, A., Nilsson, A. K., Wackernagel, D., Pivodic, A., Vanpee, M., Sjöbom, U., Hellgren, G., Hallberg, B., Domellöf, M., Klevebro, S., Hellström, W., Andersson, M., Lund, A.-M., Löfqvist, C., Elfvin, A., Sävman, K., Hansen-Pupp, I., Hård, A.-L., Smith, L. E. H., & Ley, D. (2021). Effect of Enteral Lipid Supplement on Severe Retinopathy of Prematurity. JAMA Pediatrics, 175(4), 1–9. https://doi.org/10.1001/jamapediatrics.2020.5653

Yang, R., Ding, H., Shan, J., Li, X., Zhang, J., Liu, G., Zheng, H., Su, Y., Yao, H., & Qi, K. (2022). Association of fish oil containing lipid emulsions with retinopathy of prematurity: A retrospective observational study. BMC Pediatrics, 22(1), 113. https://doi.org/10.1186/s12887-022-03174-9

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