Knowledge of chronology of optic disc stereophotographs influences the determination of glaucomatous change

Abstract

To determine the influence of knowledge of the chronology with which stereoscopic photographs of the optic disc were obtained on how the photographs are interpreted. Case series. Disc photographs of patients enrolled in the Advanced Glaucoma Intervention Study and Collaborative Initial Glaucoma Treatment Study studies from Wills Eye Hospital. Two sets of interpretable optic disc stereo slides were included for evaluation. All patients had a follow-up of at least 5 years with baseline and follow-up photographs. Three observers (1 glaucoma attending physician and 2 glaucoma fellows) evaluated the stereophotographs in chronological order to identify the clinical impression of glaucomatous change (glaucomatous deterioration or improvement) based on information such as neuroretinal rim width, nerve fiber layer defects, rim color, peripapillary atrophy, disc hemorrhages, and blood vessel alterations. Three months later, the slide pairs were shuffled so the observers were masked to the chronological sequence. The photographs were reevaluated to determine if there was glaucomatous change. Agreement between the 2 readings was measured for each observer individually and for the 3 observers collectively. The difference between the number of photographic pairs identified as worse when chronological order was known versus unknown was evaluated using a chi-square test. Intraobserver and interobserver agreement were assessed in terms of kappa values. Intraobserver agreement between chronologically masked and unmasked readings was 61%, 64%, and 71% for the 3 observers, respectively. Average intraobserver agreement between masked and unmasked readings was 65% (kappa, 0.35). Agreement in identifying change (either deterioration or improvement) was 59%, 70%, and 68%, respectively, for each observer. Agreement in identifying stability was 63%, 62%, and 73%, respectively. The number of cases identified as having deteriorated was significantly higher (101 vs. 54) when the observer knew the chronological order with which the photographs were taken (P=0.007). Interobserver agreement was higher when the chronology of photographs was known (kappa, 0.68+/-0.05 for unmasked evaluation; kappa, 0.30+/-0.05 for masked evaluation). When disc photographs are read with knowledge of the chronology with which they were obtained, the observations differ considerably from when the readings are made without this knowledge.