Bilateral Symmetry of Visual Function Loss in Cone-Rod Dystrophies

Invest Ophthalmol Vis Sci. 2016 Jul 1;57(8):3759-68. doi: 10.1167/iovs.15-18313.


Purpose: To investigate bilateral symmetry of visual impairment in cone-rod dystrophy (CRD) patients and understand the feasibility of clinical trial designs treating one eye and using the untreated eye as an internal control.

Methods: This was a retrospective study of visual function loss measures in 436 CRD patients followed at the Ophthalmology Department of the Catholic University in Rome. Clinical measures considered were best-corrected visual acuity, focal macular cone electroretinogram (fERG), and Ganzfeld cone-mediated and rod-mediated electroretinograms. Interocular agreement in each of these clinical indexes was assessed by t- and Wilcoxon tests for paired samples, structural (Deming) regression analysis, and intraclass correlation. Baseline and follow-up measures were analyzed. A separate analysis was performed on the subset of 61 CRD patients carrying likely disease-causing mutations in the ABCA4 gene.

Results: Statistical tests show a very high degree of bilateral symmetry in the extent and progression of visual impairment in the fellow eyes of CRD patients.

Conclusions: These data contribute to a better understanding of CRDs and support the feasibility of clinical trial designs involving unilateral eye treatment with the use of fellow eye as internal control.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Blindness / etiology*
  • Blindness / pathology
  • Blindness / physiopathology
  • Child
  • Child, Preschool
  • Clinical Trials as Topic
  • Cone-Rod Dystrophies / complications*
  • Cone-Rod Dystrophies / pathology
  • Cone-Rod Dystrophies / physiopathology
  • Disease Progression
  • Electroretinography
  • Feasibility Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mutation / genetics
  • Observer Variation
  • Retrospective Studies
  • Visual Acuity / physiology
  • Young Adult


  • ABCA4 protein, human
  • ATP-Binding Cassette Transporters