Weakness of the accommodation is a frequent cause of asthenopia and should be tested for during refraction. There are various ways of doing this. I have devised a modification of the test for relative accommodation which I believe to be both rapid and reliable for clinical purposes.
CAUSES OF ACCOMMODATIVE IMPAIRMENT
Accommodation may be difficult for several reasons. Three factors largely govern its ease of performance: the plasticity of the lens, the integrity of the innervation and the contractile power of the ciliary muscle.Experience has shown that the full force of the ciliary muscle can be exerted for only a short interval without fatigue and resultant asthenopic symptoms. The increased contraction that is required in hypermetropia may be beyond the ability of the ciliary muscle to sustain for any length of time. In presbyopia the ciliary muscle does not seem to be lacking appreciably in actual contractile power, but
EGGERS H. RESERVE ACCOMMODATION. Arch Ophthalmol. 1949;41(6):701–703. doi:10.1001/archopht.1949.00900040720004
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