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Vestibulo-Ocular Reflex to Transient Surge Translation: Complex Geometric Response Ablated by Normal Aging

¹Departments of Ophthalmology and ²Neurology, the ³Jules Stein Eye Institute, and the ⁴Neuroscience and ⁵Bioengineering Interdepartmental Programs, University of California, Los Angeles, California; and ⁶Department of Otolaryngology, Nippon Medical School, Nippon, Japan

Submitted 17 June 2005; accepted in final form 23 October 2005

The linear vestibulo-ocular reflex (LVOR) to surge (fore-aft) translation has complex kinematics varying with target eccentricity and distance. To determine normal responses and aging changes, 9 younger [age, 28 ± 2 (SE) yr] and 11 older subjects (age, 69 ± 2 yr) underwent 0.5g whole body surge transients while wearing binocular scleral search coils. Linear chair position and head acceleration were measured with a potentiometer and accelerometer. Subjects viewed centered and 10° horizontally and vertically eccentric targets 50, 25, or 15 cm distant before unpredictable onset of randomly directed surge in darkness (LVOR) and light (V-LVOR). Response directions were kinematically appropriate to eccentricity in all subjects, but there were significantly more measurable LVOR and V-LVOR responses (63–79%) in younger than older subjects (38–44%, P < 0.01). Minimal LVOR latency averaged 48 ± 4 ms for younger and significantly longer at 70 ± 6 ms for older subjects. In the interval 200–300 ms after surge onset, horizontal LVOR gain (relative to ideal velocity) of younger subjects averaged over all target distances was 0.55 ± 0.04 and was significantly reduced in older subjects to 0.33 ± 0.04. Horizontal V-LVOR gain was 0.58 ± 0.04 in younger and significantly lower at 0.35 ± 0.06 in older subjects. Vertical gains did not differ significantly between groups. Target visibility had no effect in either group during the initial 200 ms. The LVOR and V-LVOR were augmented by saccades in younger more than older subjects. Aging thus decreases LVOR velocity gain, response rate, and saccade augmentation, but prolongs latency.