DHA is taken up by the brain in preference to other fatty acids and its turnover is very fast. This makes it crucial to supplement adequate amounts of DHA for the optimal health and normal functioning of the brain in all ages. It is critical for the growth and development of the growing brain in infants. It is equally important for maintaining normal cognitive functioning when young and as people transition into old age.
1. DHA Improves Neurotransmission
DHA is a major structural component of the cerebral cortex. This is the part of the brain that handles language, memory, emotions, creativity, and attention. It also has a part to play in cellular communication within the brain. 
Neurotransmitters are brain chemicals that carry out the signaling and messaging involved. In this regard, DHA supports ideal levels of important neurotransmitters such as serotonin, dopamine, acetylcholine, and GABA. At the same time, it also boosts the number of neurotransmitter receptors, which allow the brain to use these brain chemicals in an optimal way.
2. DHA Promotes Neuroplasticity
Neuroplasticity is the term used to define the brain’s ability to change the structure. This can include the internal structure of the neurons as well as an increase in the number of synapses between them. Such neuroplasticity helps the brain build new neural pathways which can help optimize neural signaling and cognition.
DHA seems to encourage such neuroplasticity by assisting in developing new pathways.
3. DHA Offers Neuroprotection
Cerebrovascular diseases sometimes involve blood vessels supplying the brain. When these pathways become narrowed or blocked, they can severely restrict blood flow to the brain, raising the risk for a stroke.
The effects of phospholipids on membrane fluidity, cell signaling, and gene transcription can modulate the development and progression of a stroke.  Some, though not all studies indicate that frequent fish consumption may alleviate the risk of ischemic stroke. Omega 3s may also reduce other stroke-related risk factors like high blood pressure, abnormal lipid profile, arrhythmias, and atherosclerotic processes.
DHA, in particular, seems to have a lot to do with recovery after stroke by helping re-establish blood flow to the affected area. Animal studies have shown that at 24 hours mice treated with DHA have a significant reduction in brain injury. The injected mice also presented increased concentrations of DHA in their mitochondria. Findings suggest that injecting DHA after stroke-like events hold the potential to protect brain mitochondria against free radical damage.
Clinical studies are needed to determine if administering DHA after a stroke-like injury will offer the same neuroprotective effects for humans. 
4. DHA Activates BDNF
Brain-derived neurotrophic factor (BDNF) is the brain’s growth hormone. It’s a protein responsible for producing new brain cells and strengthening existing ones. Some of its other benefits also include easing depression, boosting weight loss and protecting against neurodegenerative diseases.
As a person gets older, their BDNF levels start to decline naturally. In terms of dietary options, DHA has the ability to turn on the brain’s BDNF. And when you pair DHA supplementation with exercise the effects seem to multiply manifold. 
The link between BDNF and exercise has been known for some time now and when you add in foods that supplement the diet with DHA, it becomes easier to up your BDNF levels as well.
The other area where DHA seems very important is in supporting eye health. DHA accounts for more than one-third of the fatty acids found in the retina.
5. Developing Vision
The fetus absorbs significant amounts of DHA in the final trimester of pregnancy as well as in the initial months of infancy. As such, it is absolutely essential for retinal development.
For growing infants, breastmilk is a natural source of DHA. Some infant formulas also come fortified with DHA to support healthy vision. An analysis of different studies showed that healthy pre-term infants fed DHA supplemented formula exhibited better visual clarity than others who were fed formula without the omega 3 supplements.
6. DHA Promotes Visual Acuity
Supplementing with DHA preserves healthy retinal function and lowers inflammation. Visual acuity refers to how well a person sees or the clarity of their vision. The first study investigating the impact of DHA on vision in normal healthy adults reported a 4% improvement in visual acuity after 90 days of supplementing with DHA.
The study worked with 74 healthy participants who were tested for visual acuity among other outcomes. Findings that 90-day DHA supplementation can improve visual acuity in people with corrected vision and those free of age-related macular degeneration and cataracts is promising. It also warrants further investigation in this area. 
7. DHA Helps With Dry Eye Syndrome
To maintain good vision and eye comfort, the front surface of the eye must be covered with an even layer of tears containing the right balance of oils and water. Dry eye syndrome (DES) is a chronic and progressive condition where there are insufficient lubrication and moisture on the surface of the eye. The results felt can range from subtle but constant eye irritation to significant inflammation.
Research looking into the benefits of DHA has seen fewer dry eye symptoms in individuals who take a supplement. This indicates that supplementation can improve the eyes’ oil film and reduce symptoms. Also, based on animal data and preliminary human studies, DHA and its derivatives seem to be a safe and effective topical treatment for dry eye patients. 
8. DHA Prevents Age-related Macular Degeneration
Age-related macular degeneration (AMD) is a major cause of irreversible vision loss in adults and treatment options are fairly limited. However, several observational studies indicate that consuming oily fish that increase DHA intake is associated with a reduced risk of developing AMD.
Chronic inflammation contributes to the development of AMD. DHA-dense foods can counter this given their anti-inflammatory potential. Plus, its anti-angiogenic properties can also help.
Anti-angiogenic is a substance’s ability to inhibit the growth of new blood vessels (angiogenesis). The course of abnormal angiogenesis contributes to the developing wet macular degeneration and diabetic retinopathy.