Farsighted parents had a child with normal vision, the second child was farsighted.

Farsighted parents had a child with normal vision, the second child was farsighted. Is hyperopia determined by a dominant or recessive gene?

Since we have a marriage of two parents with the same phenotype – farsightedness, and in the first generation we get both a normally seeing child and a farsighted one, it turns out that farsightedness is dominant (A). Moreover, both parents are heterozygous for it (Aa), that is, they carry genes for farsightedness and normal vision.
If both parents or one of them were homozygous, then the entire first generation of children would be born farsighted.