July 2018
Volume 59, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2018
Quantifying the proportion of normal eyes deviating from the “ISNT” rule using OCT measurement of peripapillary retinal nerve fibre layer thickness in a healthy cohort
Author Affiliations & Notes
  • Zakariya Jarrar
    Ophthalmology, King’s College London, St Thomas’ Hospital Campus, London, United Kingdom
  • Khadijah Basheer
    Moorfields Eye Hospital and the UCL Institute of Ophthalmology, London, United Kingdom
  • Anurag Garg
    Moorfields Eye Hospital and the UCL Institute of Ophthalmology, London, United Kingdom
  • Christopher J Hammond
    Ophthalmology, King’s College London, St Thomas’ Hospital Campus, London, United Kingdom
    Twin Research and Genetic Epidemiology, King’s College London, London, United Kingdom
  • Omar Abdul Rahman Mahroo
    Moorfields Eye Hospital and the UCL Institute of Ophthalmology, London, United Kingdom
    Twin Research and Genetic Epidemiology, King’s College London, London, United Kingdom
  • Footnotes
    Commercial Relationships   Zakariya Jarrar, None; Khadijah Basheer, None; Anurag Garg, None; Christopher Hammond, None; Omar Mahroo, None
  • Footnotes
    Support  Fight for Sight UK, Wellcome Trust, NIHR
Investigative Ophthalmology & Visual Science July 2018, Vol.59, 4073. doi:
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      Zakariya Jarrar, Khadijah Basheer, Anurag Garg, Christopher J Hammond, Omar Abdul Rahman Mahroo; Quantifying the proportion of normal eyes deviating from the “ISNT” rule using OCT measurement of peripapillary retinal nerve fibre layer thickness in a healthy cohort. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4073.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : The ISNT rule states that the neuroretinal rim in healthy optic nerve heads (ONH) is thickest inferiorly, followed by superiorly, then nasally, and thinnest temporally. Patients with ONHs that disobey the ISNT rule may be monitored more closely for glaucoma. A recent study has suggested that significant numbers of healthy individuals may deviate from the ISNT rule. We aimed to quantify, in a large healthy cohort, the proportion of individuals whose retinal nerve fibre layer (RNFL) measurements by optical coherence tomography (OCT) deviated from the ISNT rule.

Methods : ONH-centred spectral domain OCT volume scans (3D OCT, Topcon Corporation) were obtained from participants from the TwinsUK cohort over a nine-month period. RNFL thickness measurements from each quadrant were recorded. Poor quality, or inadequately centred, scans were excluded. When checking compliance with the ISNT rule, scans in which two or more quadrants had equal RNFL thicknesses were excluded. Participants with a diagnosis of glaucoma or suspected glaucoma were excluded. Right and left eyes were analysed separately.

Results : Scans were taken from 186 participants: mean (SD) age was 61.3 (12.1) years; 93.5% were female. 163 right and 160 left eyes were included. Mean (SD) inferior, superior, nasal and temporal thicknesses were 120 (16), 111 (15), 83 (15) and 74 (12) microns respectively for right eyes, and 121 (15), 110 (16), 79 (16) and 72 (11) microns respectively for left eyes. Proportions of eyes deviating from the ISNT rule were 43.4% (95% CI, 35.9-51.1%) and 48.4% (95% CI, 40.6-56.2%) for right and left eyes respectively.

Conclusions : Although mean peripapillary RNFL thicknesses for the cohort as a whole, as determined by OCT, followed the ISNT rule, over 40% of individual eyes deviated from the rule. Thus a significant proportion of healthy eyes may be erroneously classified as suspicious for glaucoma if the ISNT rule were to be applied to peripapillary RNFL thickness measurements.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

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