Do you see ghostly halos around lights when you look at street lamps or vehicle headlights at night?
This halo effect is due to the irregular scattering of light rays, said Dr Ho.
Three parts of the eye come into play - the pupil, cornea and lens.
This phenomenon is partly related to large pupil size in dim light, said Dr Ho. The pupil controls the amount of light entering the eye and it enlarges when it is dark at night to allow more light in. This causes light to appear diffused.
The cornea helps to focus light that enters the eye. Hence, cornea-related problems like astigmatism result in poor focusing of light.
In some people whose pupils tend to dilate more, laser refractive surgery (Lasik) may cause an increased scattering of light when light goes through the operated part of the cornea.
Lens-related factors include cataract, which is the clouding of the lens - a structure that focuses light rays onto the retina. Artificial lenses that replace the clouded ones in cataract surgery may also cause glare in minority of people.
The condition is not serious unless there is severe pain, headache or nausea - these symptoms indicate the possibility of glaucoma, which can lead to blindness, said Dr Ho.
See an ophthalmologist if the halos hinder safe driving or seeing objects at night, she added.
7: Tearing when cutting onions
Unlike emotional crying, tearing up when one cuts onions has a practical, mechanical purpose. It washes away irritants in the eye.
'When an onion is cut, a volatile vapour that contains sulphur is released,' said Dr Ho. 'As the vapour wafts towards your eyes, it reacts with the water on the eye surface to form sulphuric acid.'
The acid burns and irritates the eye, so tears are released to flush it out, she said.
She advises against prolonged exposure, as it causes superficial erosion of the eye surface. Instead, try running a fan and wearing goggles when cutting onions or submerging them in water while cutting them, she said.
8: Side stitch
When you do sports like running and swimming, you may experience discomforting pain in your abdomen that ranges from a dull ache to an intense, stabbing pain. This is what we commonly call a side stitch.
Doctors call it an Exercise-Related Transient Abdominal Pain (ETAP), said Dr Ng Chung Sien, a sports medicine specialist at Changi General Hospital.
'ETAP is defined as a localised pain that may occur in any region of the abdomen during exercise,' he said. 'It is most commonly located just below the rib cage on the right side of the abdomen.'
What causes a side stitch is unclear. It could be due to the stretching of ligaments during exercise or an irritation of the abdominal wall lining due to friction caused by movement, said Dr Ng.
There is little to worry about if the pain subsides after exercise. However, if the pain persists, one should consult a doctor.
Otherwise, some useful tips to note are to increase exercise intensity gradually and to avoid eating large amounts of carbohydrate-rich foods an hour or two before activity, he advised.
That is because these foods can expand the stomach and irritate the inner abdominal wall, hence increasing the likelihood of stitches, he said.
9: Cold sweat
This condition is usually associated with anxious moments. When a person breaks out in cold sweat, he is perspiring but feels cold - which is strange because one sweats in warm temperatures. The perspiration is not actually cooler than normal though.
It is all due to perception, said DrNg. 'When we are anxious, there is a sudden release of adrenaline, which causes sweating,' he said. 'Adrenaline also causes blood vessels to shut down slightly, causing a person to feel cold.'
Other than anxiety, cold sweats can be caused by viral infections, malaria, tuberculosis and some types of blood cancer, said Dr Ng.
Cold sweats may also occur during emergencies such as a heart attack.
To be on the safe side, see a doctor if you get a cold sweat that is not related to a moment of anxiety. Causes are many and some are serious - like heart problems and immune disorders.
10: Funny bone
When you hit the back of your elbow, you may get a sharp, tingly shock. It is commonly called hitting your funny bone.
In fact, this is not a bone at all but a nerve that lies in the bony groove of the elbow joint.
'The sensation is the result of direct compression of the ulnar nerve at the elbow,' said Dr Peng Yeong Pin, head of the department of hand and reconstructive microsurgery at the National University Hospital. 'This type of nerve compression is known as the cubital tunnel syndrome.'
So why do we not feel such shocks when other parts of the body are hit?
'The ulnar nerve is not protected by muscles,' explained Dr Peng. 'When this part gets knocked accidentally, there will be a direct impact on the nerve, resulting in the tingly and painful response.'
Here is something that is not so funny: You should not keep hitting the nerve just for the thrill of it. Chronic tension or repeated irritation of the nerve will result in nerve damage that can be irreversible, he warned.
