title: The effect of hypothyroidism on color contrast sensitivity: a prospective study.
abstract: BACKGROUND
  Thyroid hormone has been shown to control retinal cone opsin expression, the protein of color vision, in adult rodents.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the effect of hypothyroidism on color contrast sensitivity in adult overt hypothyroid patients.
  
  
  METHODS
  Thirty-eight overt hypothyroid (31 females, 7 males) subjects and 20 euthyroid (16 females, 4 males) controls were studied prospectively. Color vision examination was performed by Chromatest, a software program analyzing the tritan (blue-yellow) color contrast threshold (tritan CCT) and protan (red-green) color contrast threshold (protan CCT). Color contrast sensitivity analyses of hypothyroid subjects were performed on admission and after L-thyroxine treatment when biochemical euthyroidism was achieved.
  
  
  RESULTS
  After a median period of 90 (90-210) days, 24 (19 females, 5 males) patients were euthyroid and eligible for a second color vision examination. Baseline tritan CCT and protan CCT values were significantly higher in the hypothyroid group compared to euthyroid controls, which clinically translates into impaired color contrast sensitivity (p < 0.001 and p < 0.001, respectively). There was a significant decrease in tritan CCT (p = 0.002) and protan CCT (p < 0.001) values in the hypothyroid group after euthyroidism was achieved, which denotes improvement in color contrast sensitivity.
  
  
  CONCLUSIONS
  It is a novel finding of the current study that color contrast sensitivity is impaired in hypothyroidism and significantly improves after euthyroidism is achieved.
authors.affiliation: Division of Endocrinology and Metabolism, Konya Necmettin Erbakan University, Konya, Turkey.
authors.forename: Mehtap
authors.initials: M
authors.lastname: Cakir
authors.affiliation: Department of Ophthalmology, School of Medicine, Selcuk University, Konya, Turkey.
authors.forename: Banu
authors.initials: B
authors.lastname: Turgut Ozturk
authors.affiliation: Division of Endocrinology and Metabolism, Konya Necmettin Erbakan University, Konya, Turkey.
authors.forename: Elif
authors.initials: E
authors.lastname: Turan
authors.affiliation: Division of Endocrinology and Metabolism, Konya Necmettin Erbakan University, Konya, Turkey.
authors.forename: Gulsum
authors.initials: G
authors.lastname: Gonulalan
authors.affiliation: Departments of Internal Medicine, Konya Necmettin Erbakan University, Konya, Turkey.
authors.forename: Ilker
authors.initials: I
authors.lastname: Polat
authors.affiliation: Departments of Ophthalmology, Meram School of Medicine, Konya Necmettin Erbakan University, Konya, Turkey.
authors.forename: Kemal
authors.initials: K
authors.lastname: Gunduz
keywords: Color vision; Cone; Hypothyroidism; Opsin; Thyroid