Certified Ophthalmic Medical Technologist (COMT) Practice Exam

Which of the following is a primary visual field defect associated with diseases affecting the optic nerve head?

1. Nasal step

2. Color blindness

3. Night blindness

4. Floaters

The correct answer is: Nasal step

A nasal step is a significant visual field defect typically observed in cases of optic nerve impairment, such as glaucoma or other diseases affecting the optic nerve head. This defect involves a clear demarcation in the visual field where vision is reduced or absent in the nasal (inner) field, while the temporal (outer) field remains intact. This specific type of field loss arises due to the pattern of nerve fiber damage as it relates to the distribution of visual input from the retina to the brain, showcasing a focal area of dysfunction associated with optic nerve pathology. In contrast, color blindness primarily pertains to deficiencies in the cones of the retina responsible for color perception and is not directly linked to visual field defects; rather, it affects color discrimination abilities. Night blindness is associated with difficulties seeing in low-light conditions and is more related to retinal function than to the optic nerve. Floaters are visual disturbances caused by changes in the vitreous humor or the eye's internal structure and do not represent a defect in the visual field itself. Thus, the nasal step stands out as the correct identification of a visual field defect associated specifically with optic nerve head diseases.