Hello OATAcer,
Are you referring to the Essay for OptomCAS? Honestly, those are very Personal. Everyone will have their own STYLE and VOICE to the essay. I would suggest going to a workshop at your local school or visit
http://www.unm.edu/~pre/law/archuleta.htm
On the site I gave you, focus on the "Questions." Maybe from that, you'll have two or three points that you're able to elaborate on (having the ability to write 1-2 paragraph for each point). Please, do focus on an "overall theme" for your essay though (ex: Growth, Leadership, etc) and stick with that. I know it'll be tempting to talk about ALL your experiences during your undergrad (ie: accomplishment, extra-curricular) ;however, you must stick to one theme so that the essay goes to a great direction (correlated to optometry).
Personally, that essay was a process. Ideally, it takes a month or two to do (rough drafts, MULTIPLE peer reviews, and a final). Come on, I know you've taken English Composition 1 and 2. Right? Those classes really prepare you for such task. Best wishes to you!