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EYE ADVICE: Professional Papers


(ii) 2° PMA and Eye Preference

In the case of partially corrected or uncorrected presbyopes who have a high demand at near, the eye which is least hyperopic is usually the preferred eye. If hyperopia with prebyopia remain uncorrected for a long time (i.e. months or years), the preferred eye tends to increase in hyperopia at a slower rate, and depending on the amount of close work, may even become less hyperopic is some cases. This would lead to a mild refractive anisometropia, and can be explained by Fick's refinement on Hering's Law. (see above).

One might expect an equal innervation in the case of 2° PMA as it is stimulated reflexly, in for example uncorrected presbyopia. However, apart form better maintaining its spherical error, the preferred eye tends to develop less refractive and corneal ATR astigmatism, than the eye which is more hyperopic.

The explanation for this may well relate to the action of sympathetic meridional accommodation (SMA) in the preferred eye. Provided that the level of stimulation of PSA gives clear vision in the preferred eye, reflex or 2° PMA in this case would reduce the clarity of vision. SMA may be used to counteract the effect of 2° PMA, mainly in the preferred eye, thus enabling it to have less astigmatism. This would imply that Hering's Law does not strictly apply to purposeful SMA just as in the case of 1° PMA. If the PSA is not even near enough to give clear vision in any eye, SMA intervention would not improve vision and 2° PMA with its ATR effects on the lens and cornea, appears to persist equally in both eyes.

It is worth noting that the strong tendency for the preferred eye to have less total astigmatism in both situations where 1° or 2° PMA may be exerted, can give the refractionist a good clue in daily practice as to the equalisation or balance of spherical accommodation. For example, although there are exceptions to the rule, I have found that in uncorrected presbyopes the eye with least ATR astigmatism is usually the least hyperopic.






Paper 1 - Meridional (Astigmatic) Accommodation  Abstract

Physiology of Meridional Accommodation (A) Ciliary Muscle Action and Innervations
(B) Corneal Changes due to Ciliary Muscle Action
(C) Theory of Initiation of Meridional Accommodation

Clinical Implications of Meridional Accommodation


(A) Astigmatic Changes Related to WTR Corneal Toricity (i) Latent Astigmatism
(ii) Primary Accommodative Astigmatism (PAA)       (B) Reflex or 2°PMA and Induced ATR Astigmatic Changes
(C) Eye Preference and Meridional Accommodation (i) 1° PMA and Eye Preference
(ii) 2° PMA and Eye Preference (D) Proactive Prescribing for Presbyopia (i) Phakic Presbyopes
(ii) Pseudophakes and ATR Corneal Changes (E) Refractive Techniques and MA (i) Balancing Meridional Accommodation
(ii) Binocular Test of Cylinder Power (F) Further Clinical Subject Areas and Meridional Accommodation (i) Preventing Induced Oblique Astigmatism in Children
(ii) Low Vision
(iii) Keratoconus
(iv) Hard Contact Lenses
(v) PRK and PARK (Photorefractive Astigmatic Keratectomy)



Paper 2 - Common Chronic (Infective) Conjunctivitis and Nasal Rinsing

Paper 3 - Primary Open-Angle Glaucoma

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