Final answer:
The question discusses RLR paresis and secondary deviation in internuclear ophthalmoplegia, which is due to a defect in the abducens nerve or MLF, leading to conjugate gaze problems and double vision. A secondary deviation is larger than a primary deviation and occurs when the paretic eye is the fixating eye. Eye exams test for this through specific movements and reflexes.
Step-by-step explanation:
The question refers to RLR paresis, which is related to the condition of internuclear ophthalmoplegia. This condition arises from damage to the abducens nerve or the medial longitudinal fasciculus (MLF) and is characterized by a deficit of conjugate lateral gaze. This means that the lateral rectus muscle of one eye does not contract appropriately, resulting in problems with both eyes moving together, commonly leading to diplopia, or double vision. The secondary deviation in this context refers to the increased effort needed by the non-paretic eye to maintain fixation when the paretic eye is the one fixating, and it is 'larger' than the primary deviation which is when the non-paretic eye is fixating and the paretic eye is following.
During an eye examination, the pen light test is used to identify anomalies in eye movement and to check for proper functioning of extraocular muscles and the related neuronal circuits, including the MLF. Convergence, accommodation, and the vestibuolo-ocular reflex (VOR) are also assessed to determine the integrity and coordination of the extraocular muscles, such as the medial and lateral recti, and the central nervous system pathways that control eye movements.