J Korean Ophthalmol Soc.  2014 Jan;55(1):93-101.

Discriminating Between Normal and Glaucomatous Eyes Using the Modified ISNT Rule

• Lee MW
• Shin JH
• Kee CW

Abstract

PURPOSE
To evaluate the diagnostic ability of the modified ISNT rule (disc rim thickness of the smaller of inferior and superior > the larger of nasal and temporal) for normal and glaucomatous eyes compared to the classic ISNT rule (disc rim thickness of inferior > superior > nasal > temporal).
METHODS
Color stereo optic disc photographs of 113 normal subjects and 108 open angle glaucoma patients with early and moderate stage were morphometrically evaluated. The classic ISNT rule and the modified ISNT rule were assessed by masked evaluation of disc photographs at the 3, 6, 9 and 12 o'clock positions.
RESULTS
Among normal subjects, 58 of 113 eyes (51.3%) were normal and in open angle glaucoma patients, 104 of 108 eyes (96.3%) were abnormal with the classic ISNT rule. Among normal subjects, 98 of 113 eyes (94.2%) were normal and in open angle glaucoma patients, 102 of 108 eyes (94.4%) were abnormal with the modified ISNT rule. The modified ISNT rule was more accurate than the classic ISNT rule in terms of Cohen's Kappa analysis used for discriminating between normal and glaucomatous eyes.
CONCLUSIONS
The modified ISNT rule is useful for differentiating between normal and glaucomatous optic nerves and easily applied in clinical practice.

Keyword

ISNT rule; Neuroretinal rim; Optic cup; Optic disc; Stereoscopic disc photography

MeSH Terms

Glaucoma, Open-Angle
Humans
Masks
Optic Nerve

Figure

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  Figure 1. Clinical assessment of the ISNT rule for a normal optic nerve. The classic ISNT rule is that the neuroretinal rim width is greatest in the order, inferior > superior > nasal > temporal. The modified ISNT rule is that the neuroretinal rim width shows the smaller of inferior and superior is greater than the larger of nasal and temporal.

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  Figure 2. (A) Optic disc having a cup with temporal flat slope, (B) Optic nerve head with steep, punched-out optic cup.

Reference

References

1. Bowd C, Weinreb RN, Zangwill LM.Evaluating the optic disc and retinal nerve fiber layer in glaucoma. I: Clinical examination and photographic methods. Semin Ophthalmol. 2000; 15:194–205.

2. Caprioli J.Clinical evaluation of the optic nerve in glaucoma. Trans Am Ophthalmol Soc. 1994; 92:589–641.

3. Jonas JB, Gusek GC, Naumann GO.Optic disc, cup and neuro-retinal rim size, configuration and correlations in normal eyes. Invest Ophthalmol Vis Sci. 1988; 29:1151–8.

4. Morgan JE, Bourtsoukli I, Rajkumar KN. . The accuracy of the inferior>superior>nasal>temporal neuroretinal rim area rule for diagnosing glaucomatous optic disc damage. Ophthalmology. 2012; 119:723–30.

5. Per OL, Goran BS, Paal AN. . Use of the ISNT rule for optic disc evaluation in 40 to 79 year old. SJOVS. 2010; 3:16–22.

6. Vongphanit J, Mitchell P, Wang JJ.Population prevalence of tilted optic disks and the relationship of this sign to refractive error. Am J Ophthalmol. 2002; 133:679–85.

7. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ.The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol. 2002; 86:238–42.

8. Vijaya L, George R, Baskaran M. . Prevalence of primary open-angle glaucoma in an urban south Indian population and comparison with a rural population. The Chennai Glaucoma Study. Ophthalmology. 2008; 115:648–54.e1.

9. Anderson DR, Patella VM.Automated static perimetry. 2nd ed.Mosby: St. Louis;1999. p. 152–3.

10. Budde WM, Jonas JB, Martus P, Gründler AE.Influence of optic disc size on neuroretinal rim shape in healthy eyes. J Glaucoma. 2000; 9:357–62.

11. Harizman N, Oliveira C, Chiang A. . The ISNT rule and differ-entiation of normal from glaucomatous eyes. Arch Ophthalmol. 2006; 124:1579–83.

12. Arvind H, George R, Raju P. . Neural rim characteristics of healthy South Indians: the Chennai Glaucoma Study. Invest Ophthalmol Vis Sci. 2008; 49:3457–64.

13. Sihota R, Srinivasan G, Dada T. . Is the ISNT rule violated in early primary open-angle glaucoma–a scanning laser tomography study. Eye (Lond). 2008; 22:819–24.

14. Jonas JB, Mardin CY, Gründler AE.Comparison of measurements of neuroretinal rim area between confocal laser scanning tomog-raphy and planimetry of photographs. Br J Ophthalmol. 1998; 82:362–6.

15. Pogrebniak AE, Wehrung B, Pogrebniak KL. . Violation of the ISNT rule in Nonglaucomatous pediatric optic disc cupping. Invest Ophthalmol Vis Sci. 2010; 51:890–5.

16. Quigley HA, Brown AE, Morrison JD, Drance SM.The size and shape of the optic disc in normal human eyes. Arch Ophthalmol. 1990; 108:51–7.

17. Sekhar GC, Prasad K, Dandona R. . Planimetric optic disc pa-rameters in normal eyes: a population-based study in South India. Indian J Ophthalmol. 2001; 49:19–23.

18. Kee C, Koo H, Ji Y, Kim S.Effect of optic disc size or age on evalu-ation of optic disc variables. Br J Ophthalmol. 1997; 81:1046–9.

19. Garway-Heath DF, Ruben ST, Viswanathan A, Hitchings RA.Vertical cup/disc ratio in relation to optic disc size: its value in the assessment of the glaucoma suspect. Br J Ophthalmol. 1998; 82:1118–24.