Final answer:
The right eye's visual acuity is preserved because the axons from its lateral retina do not cross at the optic chiasm and the visual information is processed by the same side of the brain. Damage at the optic chiasm typically affects peripheral vision but spares direct visual acuity processed by the untouched pathways of the lateral retina.
Step-by-step explanation:
The visual acuity is preserved in the right eye because axons projecting from the lateral portion of the retina do not cross at the optic chiasm and continue to the same side of the brain. Therefore, the right eye's visual information is processed by the right side of the brain, ensuring the visual acuity remains intact despite any damage or lesion affecting the optic chiasm or pathways carrying visual information from the other eye or field.
The optic nerve connections are complex, segregating visual information between the left and right visual fields, and crossing over at the optic chiasm for the medial retinal fibers but not for the lateral ones. If a growth of the pituitary gland presses against the optic chiasm, it interferes with the transmission of signals from the medial retina, which affects peripheral vision but spares the direct visual acuity processed by the lateral retina. Thus, despite the presence of bilateral hemianopia, the direct visual acuity in each eye may be preserved.