pupil of eye vs apple of eye

Some examples from the web:

• I was referring to the pupil of your eye, young lady.
• Less commonly, weight loss/ loss of condition, dilation of the pupils of the eye and, rarely, seizures were also observed.
• Right pupil... of an eye.
• "Pupils of Rock's eyes exhibited slow reaction to strong light."
• - Uncommon adverse events: weight loss/ loss of condition; dilation of the pupils of the eye
• A tight-fitting, brilliantly black school-uniform, the aroma of raw milk, mesmerizing eyes, pupils of jet, and eyebrows of pure asphalt.
• Poems prepared by pupils of classes 4A and B.
• He is the head pupil of Kong Qiu, and a proven commander.
• Now imagine the odds of that, especially when the shooter was a former pupil of mine who could always be counted upon for accuracy.
• Kalman interviewed the pupils of this third category.
• Another recommendation is for schools to work towards improving pupil-teacher ratios, particularly when it comes to pupils of a lower educational ability.
• Liu Yu-de's a pupil of that school
• I was a pupil of his.
• He wrote love letters to the pupil of senior high school.
• There is the rumour that the pupil of Master Shibahara... are attacking other schools and taking away the roofs over their heads.
• This policy implies that no pupils of non-EU staff (Category III) can be accepted in Brussels - except siblings to currently enrolled pupils.
• In recent years the province of Pistoia and its municipalities have noted an increase in social unease due to the difficulty in providing assistance to disabled pupils of all school levels.
• He supported Saddam Hussein's invasion and annexation of Kuwait in 1990 and considers himself a pupil of Iran's Ayatollah Khomeini.
• It shall be unlawful for pupils of one race
• ...when those golden pupils of yours, grow wide...

Some examples from the web:

• She was the apple of his eye.
• You were the apple of my eye.
• David was the apple of his eye.
• Harriet was the apple of my eye.
• Apples of my eye, my granddaughters.
• You're the apple of my eye.
• Carrie Rivai, apple of my eye.
• She's the apple of your eye.
• These little things are the apples of my eye.
• I'll watch him like the apple of my eye.
• Naturally, they began to guard the Zone like the apple of their eye.
• My daughter, because she's the apple of my eye.
• I shall guard you... like the apple of my eye.
• Your father was the apple of my eye.
• You Are the Apple of My Eye.
• This is the apple of their eye and is protected accordingly.
• Now he's got our daughter in jail, the so-called apple of his eye.
• I'll cherish you like the apple of my eye.
• I guard him like the apple of my eye, Sveto...
• David was the apple of Virgil's eye for a reason.