A clinic in London is to genetically screen embryos for a couple to ensure their baby is not born with a squint.
Embryos can be screened for defective genes
The father-to-be, and his father, have severe squints which cause their eyes to look only downwards or sideways.
The London Bridge fertility centre has been granted permission to select an embryo free from the genes which cause the condition.
Critics said it was inappropriate because the condition was not life-threatening.
The licence to screen the embryos using a technique called Preimplanation Genetic Diagnosis (PGD) was granted by the Human Fertilisation and Embryology Authority (HFEA).
PGD involves removing a cell from an embryo at the eight-cell stage of development - when it is around three-days old.
If tests show that the cell does not contain faulty genes, then this clears the way for the embryo to be implanted into the mother's womb.
Professor Gedis Grudzinskas, director of the fertility clinic, said the squint was not just a cosmetic problem.
He told the BBC: "The particular condition is called congenital fibrosis of the extra-occular muscles.
"Whereas we all know somebody who's got a squint, in this particular condition the muscles that control the gaze of direction of the eye (are) grossly abnormal, so the gaze of the eye might be 90 degrees different from the direction which one might be looking, so to speak, the direction of one's face."
The father has undergone six operations to try to improve his condition, but they have resulted in only a marginal improvement.
Dr David King, a molecular biologist, and director of Human Genetics Alert, is opposed to screening for the condition.
He said: "I really do think that this has gone a good deal too far because this condition, despite being, admittedly, perhaps somewhat disabling doesn't shorten life in any way.
"The HFEA has ignored public opinion and has ignored its own rules which say that PGD should only be allowed for serious medical conditions."
The HFEA said each application to use PGD was considered on its own merits.
The UK fertility watchdog approved the extension of embryo gene screening to cover a wider range of diseases last May.
Previously, it had only permitted screening for severe inherited diseases such as cystic fibrosis.