title: Changes in water content of high plus hydrogel lenses worn on an extended wear basis in a geriatric aphakic population.
abstract: OBJECTIVE
  To investigate the water content of hydrogel lenses of relatively high plus power hydrogel lenses after 3 months extended wear and compare values with unused lenses.
  
  
  METHODS
  Geriatric aphakic extended wear soft lens patients were fitted with one of four different brands of hydrogel lenses (A) Incanto 78 (Cantor and Nissel, UK), (B) PSL72 (Prospect lenses, UK), (C) ES70 (Ocular Sciences), (D) Proclear (Coopervision). After 3 months continuous wear the lens was removed and water content (WC) was determined at both lens surfaces using an Abbé refractometer. The water content was also measured for 40 unused lenses (+10 to +20D, 10 lenses per brand).
  
  
  RESULTS
  One hundred and thirty-two lenses were checked after 3 months extended wear. Mean (+/-S.D.) WC values for front (f) and back (b) surfaces of worn and unworn lenses were, respectively, (A) Worn (n=45): f 73.2(4.13) b 73.8(4.33); unworn f 80.5(0.68) b 81.1 (0.80). (B) Worn (n=37); f 70.5(4.49) b 70.9 (3.89); unworn f 72.5(0.94) b 72.3 (0.89). (C) Worn (n=34); f 68.3(3.18) b 68.4(3.63); unworn f 70.6 (0.48) b 71.1 (0.55). (D) Worn (n=16); f 63.4(3.68) b 63.3(3.19); unworn f 60.9 (1.56) b 61.5 (1.92). There was a significant correlation between WC measured from front and back surfaces (p < 0.01). In worn A-C lenses, front surface WC tended to be lower than back surface WC. For lenses A and C at both surfaces the WC of worn lenses was significantly lower than unworn lenses (p < 0.05). For lens D, mean WC of worn lenses was significantly higher than unworn lenses (p < 0.05). In 80% of B lenses, surface WC of worn lenses were significantly lower than WC of unworn lenses (p < 0.05). There was no relationship between WC and lens power.
  
  
  CONCLUSIONS
  On average, A and C lenses tended to desiccate but D lenses tended to swell as did 20% of B lenses. The front surface of worn lenses measured lower water content than the back surface suggesting the front surface is drier than the back. This apparent difference in water content between the surfaces could be an artefact emanating from differential rates of surface deposition.
authors.affiliation: Vissum/Instituto Oftalmológico de Alicante, Avda de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. sudhir.patel@psd.csa.scot.nhs.uk
authors.forename: Sudi
authors.initials: S
authors.lastname: Patel
authors.forename: Waheeda
authors.initials: W
authors.lastname: Illahi
authors.forename: Arthur
authors.initials: A
authors.lastname: Davies
mesh_terms: D000368:Aged; D001036:Aphakia, Postcataract / Q000534:rehabilitation*; D003262:Contact Lenses, Extended-Wear; D005500:Follow-Up Studies; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D012029:Refraction, Ocular; D012031:Refractometry; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate