This industry comprises establishments of health practitioners having the degree of O.D. (Doctor of optometry) primarily engaged in the independent practice of optometry. These practitioners provide eye examinations to determine visual acuity or the presence of vision problems and to prescribe eyeglasses, contact lenses, and eye exercises. They operate private or group practices in their own offices (e.g., centers, clinics) or in the facilities of others, such as hospitals or HMO medical centers, and may also provide the same service as opticians, such as selling and fitting prescription eyeglasses and contact lenses.