Medical Definition of ophthalmology. plural. ophthalmologies. : a branch of medical science dealing with the structure, functions, and diseases of the eye.
It will be just fine! Most cake mixes only use 1 or 2 eggs anyway. Replace the water with milk if you have it and then either add an extra dash of oil or just go ahead and replace the oil with melted butter. You'll never miss that egg.
A yolk from a large egg weighs about 2/3 ounce. One way to balance the eggs with the fat and to get a smoother cake is to add extra yolks. You could use one egg plus three yolks for a total of about 3-3/4 ounces. The liquid (including the eggs) should weigh the same as, or more than, the sugar.