To draw a crying eye, the artist draws a normal eye with more reflective spots to show wetness. If desired, the artist can add a collection of water at the inside of the bottom lid and a drop descending down the cheek. The artist also take into account the change of expression in the eye to express whatever emotion he wishes the character to convey.
The artist represents the reflectivity of a crying eye by adding more reflective spots. A reflective spot is represented by a white or light gray spot, and it's usually seen on top of the iris and pupil or around the outer rim of the eye sphere. However, this may change according to the image's light source.
If the artist adds tears, he should draw the falling water where it would rightly be falling according to gravity.
To realistically represent the sad expression one usually sees in a crying eye, the artist should draw the eye as being more rounded, taking a higher shape in the middle. The iris becomes smaller within the eye due to this shift of muscles, and often the pupil shrinks. Also, the outer arch of their eyebrow goes down, while the inner arch goes up.