While this sounds like an interesting idea in principle, I can't see a world like this surviving for long. You're basically capping the birthrate at 2 per couple, which in turn means the average birthrate would be lower than 2, thus below replacement level.

I think it's more likely the world would adapt itself to everyone being blind, and the practice of giving eyes to newborns would become some mythical thing that no one does anymore.

In such a world, the implications of this eye-giving practice would be profound and multifaceted:

Family Planning

• The number of children a couple chooses to have would be heavily influenced by the parents' willingness to sacrifice their own vision. Two-child families would likely be the norm, as a third child would have to be born without vision.
• Single parents would face significant ethical and logistical dilemmas. A single-eyed parent could only have one child and would be completely blind afterward.

Social Stigma & Inequality

• Children born with two eyes could be viewed as more privileged, potentially leading to social hierarchies based on the number of eyes one has.
• Third children born without vision could face significant discrimination and fewer opportunities in life.

Medical Advances

• Research into eye regeneration or artificial eyes would likely be a significant area of medical focus. Wealthy families might turn to these technologies as a way to circumvent the natural limitations of this world.

Legal Ramifications

• Laws might be put in place to prevent parents from having a third child unless they can secure an eye through other means (artificial, donation, etc.).

Technology

• Assistive technologies for the vision-impaired would be highly advanced. Even day-to-day gadgets like smartphones and vehicles would be designed with monocular or no vision in mind.

Economy

• An industry could emerge around "eye banks," similar to sperm or egg banks in our world, where individuals or couples who opt not to have children could donate their eyes.
• The cost of eye surgeries, along with any associated technologies, could be a significant economic burden on families, thereby exacerbating existing social inequalities.

Emotional and Psychological Impact

• The bond between parents and children could be stronger due to the tangible sacrifice made, but it could also lead to a sense of guilt or obligation in the child.
• Relationships between siblings could be strained, especially if one sibling has vision while another does not.

Cultural Shifts

• New forms of art and storytelling could emerge that focus on the experience of vision or the lack thereof.
• Spiritual and religious practices might evolve to incorporate this eye-giving ritual, attributing divine or cosmic significance to the act.

In summary, this hypothetical world would be characterized by complex social structures, technological innovations, and moral quandaries, all shaped by the unique requirements of eye-giving.

Do babies born with eyes to be replaced by parents, or do they born eyeless and a given set of eyes pass from one generation to the other?

If born with no eyes, a baby get an eye from each parent, thus having two to later give one to their own. In this situation one child is the preferred option. This imply that some babies get no eyes and must spend their life as blind.

If you're passing the same eyes on generation after generation basically, don't they degrade over time and start to fail?