This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glaucoma, Subject name: Ophthalmology
Earliest sign in visual field suggestive of glaucoma: 
Select and explain. 
A. Isopter contraction, B. Baring of blind spot, C. Seidels scotoma, D. Arcuate scotoma
A: Isopter contraction
Answer: A: Isopter contraction 
Explanation: Isopter contraction is earliest sign of glaucoma though it is not very specific. High Yield points regarding visual fields Isopters : degrees of visual field. A normal visual field extends approximately 100deg temporally (laterally), 60deg (nasally), 60deg (superiorly), and 70deg (inferiorly). A physiologic scotoma (a blind spot) exists at 15deg temporally where the optic nerve leaves the eye.. Earliest field defect in glaucoma is isopter contraction f/b baring of blind spot. Earliest specific defect is paracentral scotoma > Seidel scotoma. NOTE- in PAOG there is no expansion of blind spot. other conditions where blind spot expansion is seen are - Papilledema Optic nerve hypoplasia.