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EYE ADVICE: Professional Papers


E. Refractive Techniques and MA

(i)     Balancing Meridional Accommodation

MA requires balancing just as it is required for spherical accommodation. For MA this is quite time-consuming, as we have the added difficulty of fluctuations in axis as well as power. As it is not ordinarily possible to measure refractive astigmatism under binocular viewing conditions, I usually try to relax the focussing as much as possible in both eyes to get the best possible MA balance.

We normally wish to measure the astigmatic error (power and axis) when the visual system (and thus MA) is most at rest. As with spherical errors, we should not prescribe re-actively by correcting for any over-action of accommodation (in this case PMA). This will only serve to stimulate more 1° PMA and create asthenopic symptoms.

Several aids can be employed to achieve a more relaxed visual system thus facilitating measurement of cylinder power, axis and MA balance at both distance and near:

-  Advising patients to avoid prolonged near work close to examination time.

-  Resting the accommodation by having the patient close his/her eyes intermittently for a few seconds before important measurements are taken.

-  Using a trial frame instead of refractor head, would generally relax the patient and thus reduce neuromuscular unrest.

Laurence and Marquez have suggested ways of relaxing PMA. Laurence (1920): who is quoted by Fletcher, advocated the fogging method of refracting for astigmatism. This would minimise 1° and to a lesser extent 2° PMA due to reduction in meridional blur stimulus and reduction in PSA.

Marquez (1942) applied a trial lens to neutralise the corneal cylinder. He then performed an over-refraction with separate lenses and calculated the resulting cylinder and total sphere power. It appears that this method would prevent PMA stimulation in WRT astigmats when the trial WRT cylinder is removed.


Keratometry readings can serve as a check for MA balance. Hofstetter and Baldwin (1957) have found that the RA between the two eyes is most often equal. As there are a few exceptions to this rule, one cannot use the inter-ocular corneal cylinder difference (IOC) as a definitive measure of the inter-ocular difference in refractive astigmatism (IOR). However, I believe that in most cases, any difference between IOC and IOR would be related to overreaction or underaction of PMA.

Near retinoscopy could be used to check cylinder power and MA balance for near prescriptions.

(ii)    Binocular Test of Cylinder Power.

A binocular test of best cylinder power can be attempted after testing for monocular cylinder power/axes and MA balance at both distance and near. The final power used would depend on the individual's needs. E.g. for prescriptions that are mainly for near work one should aim for full WRT or minimum ATR cylinder correction to prevent fatigue.







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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