Vision can be defective to a variable degree. It may be easy to detect gross decrease in vision but it may be more difficult to detect subtle degree of loss of vision. It is very easy to miss gross loss of vision in one eye when the other eye is healthy unless one consciously tests each eye separately. It is a good practice to test each eye separately at regular intervals using any fine reading material such as newspaper.
Normally the image formed by the two eyes is coordinated into a single image by the brain. Two distinct images are seen once this coordination is disturbed due to various diseases involving the muscles of the eye and the nerves that control the same. Multiple images often are an early symptom of cataract.
Visible redness of the one or both eyes is a common symptom pertaining to several varieties of diseases. One should not mistake every red eye as having viral conjunctivitis (So called Madras eye). Hence do not self-medicate and delay seeking medical advice if you have a red eye. It could be something serious.
A common symptom of infection in the eye is stickiness of the eyelids due to discharge. This infection could be purely external or could be more serious. Persistent stickiness of the eye lashes needs early evaluation.
Watering could be the result of mal alignment of the eyelids or eyelashes or a blockade of tear ducts that normally drain the tear fluid into the nose. Presence of tearing in newborn babies can indicate lack of patency of the tear ducts and may need attention.
Normally the center of the eye gives a black reflex due to the pupil. A white reflex can be due to opacification of the normally transparent cornea, the lens (cataract) or due to an abnormal growth of tissue behind the lens. A white reflex in a child can potentially be dangerous and should not be ignored.
Abnormal look of the eye could be due to prominence of the eye, or could be the result of defects involving the eyelids. Prominence of the eye could be due to large eyeballs or due to protrusion of normal sized eye by abnormal growth behind the eye. Any change in appearance of the eye should be investigated. Previous photographs could be useful in comparing especially when one is not certain about the time of onset of the abnormal look of the eye.
Drooping of the upper eyelid could be present at birth or could occur later. If the defect has occurred later in life one should note the frequency of the occurrence and in what part of the day it is more prominent. These observations can help the doctor make important decisions.
Squinting indicates the misalignment of the eyes. In children, this can potentially lead to reduction of vision in the squinting eye due to disuse (lazy eye). When in doubt, taking photographs with flash can help identify the squint in the photographs. This is especially useful to the doctor, in case of children who refuse to cooperate with the doctor for adequate examination.