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Long‐term endurance of adaptive shifts in tonic accommodation
Author(s) -
Ebenholtz Sheldon M.
Publication year - 1988
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.1988.tb01180.x
Subject(s) - tonic (physiology) , accommodation , darkness , psychology , chemistry , neuroscience , optics , physics
After an 8 min inducing period of sustained focusing on a target at the near point (NP) of accommodation, tonic accommodation was monitored at 8 min intervals over a 48 min period in darkness. A laser optometer provided evidence for asymptotically increasing tonic levels. Accordingly, eyes closed in darkness (EC) was not a condition for the relaxation or dissipation of enhanced tonic levels. Furthermore, refixating the NP target for 6 min, 24 min, after the initial focusing period, provided no significant enhancement of tonic accommodation over EC. On the other hand, focusing at far point (FP) or walking within a lighted hallway (WH) significantly reduced the tonic after‐effect to pre‐adaptative levels, but only transiently. Tonic after‐effect induced by NP focusing thus appear to be remarkably resistant either to long‐term attenuation or enhancement. A model based on the decay of accumulated sympathetic and parasympathetic neurotransmitters was developed to account for the contrasting fact that focusing at near targets for periods up to about 2–3 min as well as sustained focusing at far targets tends to yield complete decay to tonic after‐effects.