Is the ISNT rule violated in early primary open-angle glaucoma--a scanning laser tomography study

Area of Science:

• Ophthalmology
• Optic Nerve Head Imaging
• Glaucoma Research

Background:

• The ISNT rule (Inferior-Superior-Nasal-Temporal) describes optic nerve head morphology.
• Assessing neuroretinal rim (NRR) area is crucial for diagnosing glaucomatous optic neuropathy.

Purpose of the Study:

• To evaluate the ISNT rule's relevance in differentiating normal and early glaucoma.
• To assess NRR area ratios as indicators of glaucomatous optic neuropathy using Heidelberg Retina Tomography II (HRT II).

Main Methods:

• Compared 136 control eyes with 63 early primary open-angle glaucoma eyes.
• Utilized HRT II for optic nerve head topography and Humphrey visual field testing.
• Analyzed disc area and rim area parameters using Student's t-test.

Main Results:

• The ISNT rule was applicable in 71% of normal and 68% of glaucoma eyes.
• Superior to inferior NRR area ratio was lower in glaucoma (0.90) vs. normal (0.96) eyes.
• Significant NRR loss occurred in inferotemporal and superotemporal quadrants in glaucoma eyes.

Conclusions:

• The typical optic disc configuration, with wider inferior NRR, is often preserved even in early glaucoma.
• The ISNT rule's clinical applicability is limited, despite a trend in NRR width variations.
• NRR area ratios and quadrant-specific loss are valuable indicators in early glaucoma detection.