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摘自 “Clinical Refraction”第二版 800頁
關(guān)于主覺驗光過程調(diào)節(jié)控制和是否睫狀肌麻痹驗光
Control of Accommodation
Part of the emphasis on controlof accommodative activity may have resulted from the traditional concept thatophthalmic asthenopia was caused, to a large extent, by overactive ciliarymuscle contraction. Relief from chronic ciliary contraction was considered essentialto attainment of ocular comfort, although more recent indications are thattotal relaxation of accommodation may neither be required nor possible,nor evendesirable. The forcing of plus power into the refractive correction, beyondthat which is advisable, may result in new sources of asthenopia not previouslyimplicated.
Refractive status is representedby the focal position of the eye relative to the outer limiting membrane of theretina, with accommodation at rest in a normal tonic state. Techniques fordetermination of refractive error should each keep accommodation passive duringthe examination procedure. Two classic means of doing so are commonly used:cycloplegia and fogging.
Cycloplegic Refraction
Thechief advantage of cycloplegia is that inhibition of accommodation is usuallyensured when accommodative spasm or latent hyperopia is present. In the extreme,overaccommodation may cause a convergent strabismus, asituation in which a normal binocular refraction is obviously not possible.These conditions tend to resist routine techniques for accommodative relaxation,so that cycloplegia may be essential to even a monocular refraction. However,because cycloplegia may reduce or eliminate the normal tonic accommodation whileproducing simultaneous pupillary mydriasis,the refraction is significantlyaffected by the competitive effects produced by accommodative paresis orparalysis versus the spherical aberration through the peripheral pupil.For manyyears, cycloplegia was a confirmed technique among refracting ophthalmologistsfor all refractive situations,but in more recent times, it has been recommendedessentially for situations such as those noted or when persistent symptomsremain after spectacle correction based on noncycloplegic refractions. A numberof studies have compared the results attained by cycloplegia with those attainedby noncycloplegic methods. These were summarized in detail by Borishl> andindicate that generally: (a) more plus is accepted under cycloplegia by youngpersons as compared with adults, presumably because the younger accommodativesystem is more active; (b) myopes often reveal more minus with cycloplegia, presumablybecause of pupil dilation and subsequent expression of spherical aberrations;and (c) little clinically significant difference is found for a proportion ofthe population, including presbyopes. Among the objections to the habitual useof cycloplegia is the fact that the cycloplegic results often tended toindicate an increased amount of hyperopia in the amount of +0.50 to +1.50 OS,correction of which merely blurred vision when the normal accommodative statuswas resumed. This was ascribed to the notion that aggressive ciliary inhibitionoften included a portion of the ordinary ciliary muscular tonus. Paradoxically,in some hyperopic cases, cycloplegia appeared to reduce the inhibition ofaccommodation. Sometimes the spectacle prescription was calculated according toan arbitrary modification of the results of the cycloplegic refraction. Inoffices or clinics where cycloplegia was used as a routine refractingprocedure, the final correction often required a second (noncycloplegic)refraction. Itwasfound that fewer repeat refractions were required, and that a greater number ofpatients were satisfied with their initial prescriptions, if cycloplegia refractionswere notperformedroutinely. Cycloplegia is useful for certain situations, such as thosedescribed, and is sometimes used initially prior to retinoscopy orautorefraction preceding the subjective refraction. It should be kept in mindthat fairly large discrepancies need to be found between cycloplegic and noncycloplegicrefractions to indicate genuine tonic spasm of accommodation or latency ofhyperopia.
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