The Ability of Disc-to-Fovea Distance to Disc-Diameter Ratio to Estimate Optic Disc Size

Hyun Gyu Yoo; Jae Hong Ahn; Mar Vin Lee

doi:10.3341/jkos.2013.54.6.913

Journal List > J Korean Ophthalmol Soc > v.54(6) > 1009703

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Yoo, Ahn, and Lee: The Ability of Disc-to-Fovea Distance to Disc-Diameter Ratio to Estimate Optic Disc Size

Original Article

J Korean Ophthalmol Soc 2013;54(6):913-918.

Published online: 7 September 2013

DOI: https://doi.org/10.3341/jkos.2013.54.6.913

The Ability of Disc-to-Fovea Distance to Disc-Diameter Ratio to Estimate Optic Disc Size

Hyun Gyu Yoo, MD, Jae Hong Ahn, MD, PhD, Mar Vin Lee, MD

Department of Ophthalmology, Ajou University School of Medicine, Suwon, Korea

Address reprint requests to Mar Vin Lee, MD Department of Ophthalmology, Ajou University Hospital #164 Worldcup-ro, Yeongtong-gu, Suwon 443-380, Korea Tel: 82-31-219-5260, Fax: 82-31-219-5259, E-mail: mvdevil@daum.net

Received 10 November 201214 December 2012 Accepted 6 April 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To investigate the usefulness of the measurement of disc-to-fovea distance to disc-diameter ratio (DF/DD ratio) in detecting large and small discs.

Methods

A total of 300 randomly selected subjects were included in the present study. All patients underwent stereo-scopic disc photography and DF/DD ratio, which is the shortest distance between disc margin and fovea divided by mean disc diameter was determined by planimetry. The diagnostic accuracy of DF/DD ratio was evaluated using areas under the receiver operating characteristics curves (AUCs), sensitivity, and specificity.

Results

No significant differences in disc-to-fovea distance were observed among small and large disc groups. The DF/DD ratio was significantly lower in subjects with large discs (1.74 ± 0.27) compared with subjects with small discs (2.70 ± 0.15). AUCs of the DF/DD ratio were 0.942 and 0.947 in detecting large and small discs, respectively. In detecting disc size by a fixed DF/DD ratio of 2.0, sensitivity was 100% for both large and small discs, and specificity was 70.1% and 40.9% for the large and small discs, respectively.

Conclusions

The DF/DD ratio may be a simple and useful clinical aid in detecting large and small discs. The 2.0 fixed DF/DD ratio, showed 100% sensitivity in detecting both large and small discs, although medium discs may be mis-diagnosed as small discs more often than as large discs.

Keywords: Disc diameter, Disc-to-fovea distance, Optic disc size, Stereoscopic disc photography

References

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Figure 1.

Receiver operating characteristic (ROC) curve of the DF/DD ratio and R-DF/DD ratio for detection of small disc (A) and large disc (B). DF/DD ratio = disc-to-fovea distance to disc-diameter ratio; R-DF/DD ratio = round up scale of disc-to-fovea distance to disc-diameter ratio.

Table 1.

Distribution of patients

Disc size	Round up scale of disc-to-fovea distance to disc-diameter ratio
Disc size	1.50 Group^*	2.00 Group^†	2.50 Group^‡	3.00 Group^§	Total
Small disc^∏	0	1	16	11	28
Medium disc^#	9	138	81	1	229
Large disc^**	20	23	0	0	43
Total	29	162	97	12	300

^* DF/DD ratio less than 1.75;

^† DF/DD ratio equal to or greater than 1.75, and less than 2.25;

^‡ DF/DD ratio equal to or greater than 2.25, and less than 2.75;

^§ DF/DD ratio equal to or greater than 2.75;

^∏ Mean disc diameter shorter than 1.5 mm;

^# Mean disc diameter between 1.5 and 2.0 mm;

^** Mean disc diameter longer than 2.0 mm.

Table 2.

Sensitivity and specificity of the DF/DD ratio and R-DF/DD ratio scales for diagnosing small and large disc

Parameter	Scale	Small disc^*		Large disc^†
Parameter	Scale	Sensitivity (%)	Specificity (%)	Sensitivity (%)	Specificity (%)
DF/DD ratio	2.0	100	40.9	100	70.2
R‐ DF/DD ratio	1.5	100	0.0	71.4	96.7
	2.0	100	10.9	100	39.7
	2.5	97.7	73.9	100	4.4
	3.0	4.3	99.6	100	0.0

DF/DD ratio = disc-to-fovea distance to disc-diameter ratio; R-DF/DD ratio = round up scale of disc-to-fovea distance to disc-diameter ratio.

^* Mean disc diameter shorter than 1.5 mm;

^† Mean disc diameter longer than 2.0 mm.

Table 3.

Comparison of disc diameter and disc area between R-DF/DD ratio groups

	1.50 Group^* (n = 29)	2.00 Group^† (n = 162)	2.50 Group^‡ (n = 97)	3.00 Group^§ (n = 12)
VDD (mm)	2.18 ± 0.27	1.94 ± 0.19	1.69 ± 0.14	1.58 ± 0.07
HDD (mm)	2.03 ± 0.14	1.73 ± 0.14	1.48 ± 0.11	1.21 ± 0.12
DD (mm)	2.10 ± 0.18	1.84 ± 0.15	1.58 ± 0.09	1.39 ± 0.07
DA (mm²)	3.39 ± 0.52	2.66 ± 0.44	1.98 ± 0.24	1.47 ± 0.16

Value are presented as mean ± SD.

R-DF/DD ratio = round up scale of disc-to-fovea distance to disc-diameter ratio; VDD = vertical disc diameter; HDD = horizontal disc diameter; DD = disc diameter; DA = disc area.

^* DF/DD ratio less than 1.75;

^† DF/DD ratio equal to or greater than 1.75, and less than 2.25;

^‡ DF/DD ratio equal to or greater than 2.25, and less than 2.75;

^§ DF/DD ratio equal to or greater than 2.75.

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