Content area
Full Text
Intraocular light scatter is light that has reflected, refracted, diffracted or experienced multiple combinations of all three from particles along the optical path of travel. 1 There are five major sources that contribute to the total amount of ocular straylight: cornea, iris, sclera, retina and lens. 2 It is assumed that for young healthy eyes, the total amount of straylight is 1/3 by the cornea, 1/3 by the lens and 1/3 by the iris, sclera and retina. Obviously, these ratios change with age, pigmentation and specific pathologies. Corneal light scatter is constant with age 3 4 and it may change with corneal defects or after corneal refractive surgery. 5 - 7 The iris and the sclera scatter light depend on the patient's pigmentation 8 (for example, brown eyes absorb more light and consequently produce less scatter than light eyes). Lens scatter increases with age, being greater in patients with cataracts. 9 Finally, the retina produces light scatter to different locations being pigmentation-dependent. 8
A clinical application of straylight measurement is to diagnose patients with complaints caused by a high degree of light scattering in the eyes such as lens opacities or corneal turbidity after laser corneal surgery. Considering that scatter light causes contrast loss in the final retinal image, the estimation of this parameter becomes very important in cataract and refractive surgery procedures. Several clinical devices have been developed to evaluate straylight and glare (ie, nyktotest, mesotest and the straylight meter). 10 A recent computer version of the straylight meter has been designed to improve the clinical measurement of the ocular straylight. 11
The C-Quant is a newly developed instrument to measure the retinal straylight using the "compensation comparison" method. In essence, this method presents exactly the same stimuli to the subject as the direct compensation method described in previous reports, 12 and implemented in previous versions of the instrument. 13 In contrast, in the compensation comparison method, two stimuli of the direct compensation method are presented to and compared by the subject simultaneously. 11
The aim of the present study is to assess the effect that repeated measurement of retinal straylight has in the final values, which would be the optimum number of measurements needed to obtain an optimum reliability, and also the...