Adults should ideally undergo a comprehensive eye examination every 2-3 years, especially those aged 20-39. However, some factors may necessitate an exam every 1-2 years, such as being African American and people who wear glasses or contacts. Annual exams are also recommended for all adults regardless of age, for those with risk factors such as family history of eye diseases like glaucoma, high blood pressure, diabetes, etc. Adults aged 65 and above require an examination every year because they are likely to develop vision-threatening diseases such as cataracts.