A Comparison of Optic Disc Grading Using Clinical Examination and Stereoscopic Photography in the Tema Eye Survey

Abstract

 

Purpose:

 

To compare assessment of optic disc cup-to-disc ratio performed by ophthalmologists at the slit lamp to stereoscopic photographs read by a reading center

 

Methods:

 

Subjects were evaluated as part of the Tema Eye Survey, a population-based study of blindness and eye disease in Ghana, West Africa. The optic disc was evaluated by an ophthalmologist using a 90 D lens at the slit lamp. The subjects had stereoscopic optic disc photography of the fundus by the NIDEK 3Dx camera the same day. Digital fundus images were read on a computer monitor by the reading center at Moorfields Eye Hospital, London, UK. Bland/Altman analysis was used to compare the difference of the two measurements stratified by the average of the two measurements.

 

Results:

 

2200 eyes of 1203 subjects were analyzed. Table 1 shows the disagreement between clinical examination and reading center assessments of cup-to-disc ratio. Thirty one percent of cup-to-disc ratio measurements differed by ≥ 0.2. The reading center classified 188 discs as having a vertical cup-to-disc ratio of 0.2. The average cup-to-disc ratio of these same subjects read by the clinical examiner was found to be 0.36 (SD=0.11, p<0.001). For the 177 subjects who were classified as having cup-to-disc ratios of 0.8 by the reading center, the average cup-to-disc ratio determined in the clinic for these subjects was 0.66 (SD=0.09, p<0.001).

 

Conclusions:

 

Stereoscopic optic disc photographs read by a reading center tend to overestimate the degree of cupping in discs with large cup-to-disc ratio and underestimate the degree of cupping in discs with small cup-to-disc ratio compared to clinical examination. Clinically, when following a patient for glaucoma progression using prior stereoscopic optic disc photographs, it may be better to compare prior photographs of the optic disc to current photographs rather than comparing prior stereoscopic photos with the current clinical examination.  

 

Keywords: optic disc • imaging/image analysis: clinical