Corneal reflex is a test done as a part of cranial nerves assessment.
The test is done by touching the peripheral margin of cornea at the cornea scleral junction by a whisk of cotton.
It’s wise to avoid thick cloth to perform this test, since it can cause injury to the cornea. The cotton thread should be sterile, so that the test doesn’t be a source of infection.
A scratch in cornea can cause opacity of cornea, infections etc.
Another safe alternative method of doing this test is by blowing a puff of air in the eye. Since this is a non touch method, it don’t posses risk of injuring the cornea or introducing infection.