title: Age, stability of the precorneal tear film and the refractive index of tears.
abstract: OBJECTIVE
  To investigate the relationship between age, stability of the precorneal tear film and refractive index of tear samples drawn from a normal population.
  
  
  METHODS
  The stability of the precorneal tear film was estimated by measuring the Tear Thinning Time MT) using the Bausch and Lomb keratometer. Microlitre tear samples were obtained from the lower tear meniscus using glass capillary tubes. The refractive index (RI) was measured using a digital electronic Abbe refractometer with an accuracy of +/- 0.00005 units. Measurements were obtained from the right eyes of 110 subjects (55 male and 55 female) ranging in age from 18 to 89 years. They were all healthy, non-contact lens wearing individuals with no history of ocular disease or dry eye symptoms.
  
  
  RESULTS
  A significant relationship was found between age (x) and tear stability (TTT) in both genders. Females, TTT = 32.89-0.33x, (Spearman correlation coefficient, r = -0.537, P = 0.0001). Males, TTT = 29.25-0.29x (Spearman correlation coefficient, r = -0.353, P = 0.008). A significant correlation was found between age (x) and refractive index (RI) in females only RI = 1.33815-0.000023x, (Spearman correlation coefficient, r = -0.299, P = 0.027).
  
  
  CONCLUSIONS
  Tear stability is lower in the aged eye regardless of gender. Tear refractive index is lower in the older female eye.
authors.affiliation: West Coast Eye Research, 11/12 Argyll Square, Oban, Argyll, PA34 4AZ, Scotland.
authors.forename: S
authors.initials: S
authors.lastname: Patel
authors.forename: K E
authors.initials: KE
authors.lastname: Boyd
authors.forename: J
authors.initials: J
authors.lastname: Burns