Q & A

A) Why do our eyes make tears and cry?

The eyes make tears to act as 1) lubricant for the eye surface from mechanical frictional damage induced by eyelid movements, eye rubbing etc..., 2) to wet and maintain integrity of the cornea surface which relies heavily on its smooth surface to refract the incident object lights for forming images on the retina.

We cry to pour out huge amount of tears as means of rinsing, diluting intruding objects and to flush them out of the eye territory.

B) Why do some people have blue, or green, or brown eye colors?

As the cornea is transparent, the color of the eye refers to the color of the iris which in term is determined by the amount of melanin pigment (brownish-black) in the pigment epithelium of the iris. Brown eye has more melanin pigment than Blue eye which has more melanin pigment than Green eye.

C) Which animal in the world has the best sight?

The animal with best sight is the bird which also detect ultraviolet light on top of the visible spectrum

D) Is it 100% safe to wear contact lenses? Which type is best, daily, monthly？ What is the worst short-sighted my eyes can be and still use contact lenses?

Nothing in the world is 100% safe. For better long-term eye health, Rigid gas permeable lens is better than soft contact lens. For soft contact lenses, daily wear is more safe than extended monthly wear. However, sometimes the refractive error, say large or odd astigmatism cannot be fitted with daily wear lens, then extended wear is needed. There is not well defined boundary beyond which short-sighted eyes cannot wear contact lens. Nevertheless, if short-sightness is high, say more than -10 dioptres, then the daily putting in and taking out of contact lenses may mechanically induce enough eyeball shape transformation that the risk of retinal break and detachment is increased. One safety precaution is to have the retina checked and having retinal conditions fixed before prescribing contact lenses.

E) Is laser eye surgery 100% safe?

I think you are referring to the laser surgery to correct short-sightness as there are many other types of laser treatment for other eye conditions.

Laser eye surgery for refractive errors needs to be conducted by experienced surgeons on the basis that there are no contraindicating eye conditions. My teachers invented the machine and procedure and they typically spend a lot of time during first visit to make sure that there are no contraindications. In my experience, as much as 80 % of candidates are indeed unfit for the procedure after screening. Common contraindications include dry eyes, allergic eye conditions, refractive error more than -8 dioptres equivalent etc.....