It may be common among the laymen in the community but spelling ophtho or ophthalmology without the "h" wrong is a sure ticket to a declined interview or a really bad experience during an interview. Believe it or not, not knowing how to properly spell the full name or even the abbreviated name may indicate to a lot of ophthalmology residents and attendings that you do not know the differences between optometry and ophthalmology. If you use the incorrect spellings and abbreviations in non-medical communication, that's probably ok because these days the average person on the internet can't spell to save their life. If you're talking to medical professionals, though, it makes it seem as if you're not quite sure what you're referring.
As another example, imagine if you were to refer to an internist, or an IM attending, as an intern. Likewise, how do you think a psychiatrist would respond if you referred to him or her as a psychologist. If you are applying to ophthalmology and can't even spell it properly, do you really think a PD would give you an interview?
