Continuous Wear Benefit for Plus Presbyopes

Narelle Hine MSc(Optom), Dip App Sc (Optom), DCLP, FAAO

The advent of silicone hydrogels has revitalised my presbyope contact lens practice, especially for hyperopes. The proven optimal oxygen transmissibility of silicone hydrogels at last allows hyperopes the opportunity to successfully and safely try 30 night continuous wear (CW)- a very popular option with presbyopes because they are so visually challenged at near they cannot easily see to insert or handle their contact lenses. Until the release of silicone hydrogels all published oxygen transmissibility research has contraindicated closed eye wear of all plus hydrogel lenses.

My clinical experience with presbyopic hyperopes has shown that corneal hypoxia as indicated by the presence of stromal striae and folds, commonly occurs with LWC and MWC lenses after only 4 - 8 hours of daily wear.

Endo Folds - click to enlarge

The higher the plus power of the lens, the less the average oxygen transmissibility of the lens and the greater the corneal hypoxia resulting in corneal oedema. This difference in striae response is classically demonstrated in comparative slit lamp examination of the stroma in a monovision wearer e.g. OD +3.00D vs OS +5.50D. Presbyopes may require even more consideration in choice of lenses than younger patient populations. The gradual changes to the integrity and function of the corneal endothelium with age affects the ability to efficiently control corneal hydration. The longterm effect on the endothelium of swelling and deswelling of the corneal stroma and epithelial fragility is as yet not well understood. Consequently to avoid hypoxia I have adopted the policy of fitting all my hyperopic patients with lens materials of at least 70% WC for daily wear.

Apart from slower recovery from hypoxia, many presbyopes also show the additional challenge to hydrogel lens wear of an unstable tear film leading to dry eye, more prevalent in post menopausal women.

Dry Eye - click to enlarge

Studies suggest that the major cause of their tear instability in normal aging presbyopes is less to do with reducing tear volume and the lipid layer and more related to the strength of the tear binding interface at the corneal epithelium and the efficiency of the blink action to reform the tear film. Compared to earlier generation lenses, the surface treated silicone hydrogels provide good wettability, good tear deposit resistance and a low WC demand of the polymer assists eyes with less than perfect tear film to maintain wear.

However adequate tear film stability and volume is still essential for success with CW. Persistent symptoms of dry eye affect 10 - 15% of CW candidates and cannot be usefully managed with lubricants. Dry eye remains the chief cause for discontinuation from CW for both young and presbyope patient groups in my practice.

Lipid Deposits - click to enlarge	Mucin Deposits - click to enlarge

For the past two years I have monitored at six monthly intervals a small group of eight 30 night CW hyperopic presbyopes (age range 56 to 70 years) whom I fitted with monovision silicone hydrogels (BVP range +1.25D to +6.00D). To date there has been no striae/fold or microcyst response in either eye which indicates the lenses are as safe for CW hyperopes as myopes. The patients love their lenses and are very grateful for the round the clock convenience.