Buckingham Palace is being tight-lipped about how the Queen came to suffer an extremely bloodshot eye.
The red left eye was clearly visible in photographs taken as she watched polo players take to the field at the Cartier Queen's Cup Final, in Surrey.
A Buckingham Palace spokesman declined to comment on how the Queen suffered the red eye but said "nothing untoward" had happened and the monarch was in "fine fettle".
The final, at Guards Polo Club, in Windsor Great Park, Egham, is rated as one of the world's top five polo events, attracting some of the best international players.
It also drew a number of celebrities to the crowd, including recently knighted actor Sir Kenneth Branagh, singer Katie Melua, burlesque star Dita Von Teese and former royal correspondent Jenny Bond.
The Queen was accompanied to the event by Prince Philip, who has returned to royal duties after leaving hospital following treatment for a bladder infection.