A 42-year-old woman from Delhi presents with progressive night blindness over 3 months, followed by progressive loss of peripheral vision while central vision remains intact. On examination, visual acuity is 6/6 but confrontation testing reveals a concentric visual field defect. Fundoscopy shows bone spicule-like pigmentation in the peripheral retina with optic disc pallor. Which photoreceptor type is primarily affected in this condition?