This service has merely been provided in the past and has not been questioned. Ask your Civilian Personnel Office exactly what your legal requirements are for these individuals if they are using significant resources. You may be able to increase your manning in a variety of different ways. Student externship programs with a school of optometry are an excellent option. Although this will take some time for supervision and evaluation, students are a ready source of optometric skill that should be utilized if at all possible.
Most schools are only too happy to establish agreements with military clinics.
Reserve and National Guard optometrists are another source of temporary manning. Often these individuals are prior military or are at least familiar with the military healthcare setting. Manning assistance may also be possible. If effectively justified, an optometrist from another base would be tasked to assist your clinic temporarily. Again, this offers the added benefit of working with an individual who is already familiar with processes or programs unique to the Air Force.