EYE ADVICE: Professional Papers

(ii) Low Vision

Both cases described below have impaired visual acuities. The commentary under the case of Mr P.K. stresses the importance of an adequate near addition to prevent excessive demand on PSA leading to unnecessary 2° PMA and adverse ATR changes. The case of Mr S.H, is of congenital onset. This case emphasises the need to measure the corneal toricity and to prescribe the maximum WTR cylinder that is accepted to allow for a constantly clear image, without relying on 1° PMA for optical clarity. This would stabilise the vision and allow for improved visual acuity in cases of amblyopia. Keratometry is a very important clinical measurement in both cases. Experience will allow the practitioner to vary the prescribed cylinder appropriately.

Mr P.K.   Born 1930

Jan 1989, old gasses:   R) -1.75/-1.50*105    L) -1.50/-1.00*95.

May 1989    Sub:  R) -1.00/-1.75*105 (6/12=)    L) -0.75/-2.50*90 (6/18=).

Jul 1990      Sub:  R) pl/-2.25*95 (6/12=)    L) -0.75/-2.75*90 (6/18=).

Decided to give: +7.00 Near Additon in S.V. Near Spectacles.

Apr 1992     Sub:  R) +0.25/-0.50*120 (6/12=)    L) +0.50/-1.25*87.5 (6/18).

This persisted until last seen in May 1995.

 2° PMA can be activated when low vision patients who have insufficient PSA attempt to accommodate at a much reduced working distance without a correction. Mr P.K. suffered moderately reduced vision due to lens opacities and diabetic maculopathy. Before July 1990, he wore near additions of less than +3.50.  He was reading extensively and at an extremely short working distance due to the reduced vision. This led to the ATR lenticular changes due to 2° PMA. When the demand on PSA was reduced by the higher near addition, the lenticular astigmatism was also significantly reduced.

Master S.H. Born 1970

Condition:  Leber's optic atrophy. No glasses were previously worn as the patient was told that they would not improve vision.

Jun 1984   Unaided vision:  R) 6/30    L) 6/12-2.

Jun 1984   (other Optom.)  Sub  R) +1.75/-2.25*15 (6/18=)  L) +0.25/-0.50*170 (6/12-2).

Jul 1984 - Retinoscopy:   R) +3.00/-3.00*4    L) +1.25/-1.25*176.

Jul 1984 - Keratom.  R) 43.95*12==47.50*102 (3.55)   L) 44.70/169==46.75*79 (2.05).

Jul 1984 - Max subjective accepted R) +2.00/-2.75*10 (6/18)  L) +0.75/-1.25*170 / (6.12). 

Jan 1987 - Subjective   R) +2.00/-2.50*12.5 (6/18)   L) +0.75/-1.25*165 (6.9-).

From the keratometry readings, and the subjective result as obtained by another optometrist in June 1994, it is apparent that Mr S.H. must have been compensating for a significant amount of corneal toricity. By correcting the latent astigmatism up to the maximum amount possible, the patient's demand on PMA was reduced. This not only helped to prevent asthenopia but offered better vision, as less astigmatic focussing was required for clear vision. As can be seen, the patient's vision improved slightly by January 1997 - enough for him to pass the vision standard for driving a car. The patient remarked : "the glasses have made a difference".

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