Br J Ophthalmol 83:378 doi:10.1136/bjo.83.3.378
  • Correspondence

Red-free light in applanation tonometry

  1. M H SHAIKH,
  2. J S MARS
  1. Eye Department, Royal Albert Edward Infirmary, Wigan WN1 2NN
  1. Mr M H Shaikh.

    Editor,—Goldmann’s applanation tonometry is generally performed using cobalt blue filter and fluorescein in order to obtain accurate localisation of the apex of the tear meniscus.1 2 The peak transmission value of the cobalt blue filter BG12 on the Haag–Streit slit lamp 900 BM is 0.80 at 400 nm, whereas that of the red-free filter BG39 is 0.965 at 490 nm. The peak absorption value …