Visual acuity changes in cone and cone-rod dystrophies.

PURPOSE The purpose of the study was to evaluate longitudinal visual acuity (VA) changes in cone (CD) and cone-rod dystrophies (CRD) in order to develop recommendations for follow-up strategies and to define an optimal time for potential therapeutic intervention. METHODS Patients with clinically defined CD and CRD, who had at least three clinical examinations within a follow-up period of a minimum of 2 years, were included in the study. The observation period was divided into segments: between 1-2 visits and 2-3 visits in intervals of 2 years, and between 3-4 visits in 3-year intervals. Disease history was collected during the baseline examination. Median age of onset, age at first examination, and period between disease onset and 1st visit (latency) were estimated. Medians with 25th and 75th quantile of VA decrease in logMAR for each segment of observation were calculated. The median percentage of VA decrease was also calculated. RESULTS Initial results of the Tuebingen longitudinal study of VA changes in CRD and CD are presented as medians with 25th and 75th quintiles. Twenty-nine patients (14 men and 15 women) were studied. Nineteen of them had CRD and 10 CD. Median age at the baseline visit was 18 (11, 31) years for CRD and 26 (8, 41.5) years for CD. Median age of disease onset was 9 (8, 25) years for CRD and 7.5 (5, 15) years for CD. The median latency was 6.5 (3; 8.25) years in CD and 4 (2, 10) years in CRD patients. VA in CD and CRD patients was significantly different only during the first visit (p < 0.03). VA decrease was highest in the period between 2-3 visits with a median VA decrease of 36%, for CDR and between 3-4 visits for CD with a median VA decrease of 80%. In the CRD group the rate of VA decline was fairly even over the four visits, whereas in the CD group the decline appeared to progressively increase towards the end of the follow-up. CONCLUSION CRD patients were younger than those with CD at a baseline visit and had a longer period of follow-up. A statistically significant difference in VA in CRD and CD was observed at the first ophthalmological examination only. VA decrease was most prominent in the second decade of life in CRD and in third decade in CD patients. CRD was characterized by a more progressive VA decrease than CD. CRD had a high decline of VA over the second and the third examination, whereas VA decline in CD progressed towards the end of follow-up period (fourth examination). These results should be considered when advising and following up such patients on a long-term basis.