Likelihood of Glaucoma in High Myopia with RNFL Thinning and Normal IOP
This patient should be classified as a glaucoma suspect with an estimated 20-25% risk of having early glaucoma or converting to glaucoma within 2-3 years, requiring immediate comprehensive evaluation and close monitoring.
Risk Assessment Framework
The combination of high myopia, inferior and temporal RNFL thinning, and normal IOP creates diagnostic complexity, but several factors help quantify the glaucoma risk:
High-Risk Features Present
Myopia as an established risk factor: The American Academy of Ophthalmology identifies myopia as a significant risk factor for developing primary open-angle glaucoma (POAG), with high myopia conferring particularly elevated risk 1.
Focal RNFL thinning pattern: Focal inferior or superior RNFL thinning is highly suspicious for glaucoma, as structural optic nerve damage often precedes detectable visual field defects 2. The inferotemporal RNFL thinning (7 o'clock sector) specifically carries a hazard ratio of 4.07-4.37 for visual field progression in myopic normal-tension glaucoma patients 3.
Normal-tension glaucoma consideration: In a study of treatment-naïve myopic normal-tension glaucoma patients, 22.5% showed progressive RNFL thinning over 2 years despite normal IOP 4.
Critical Diagnostic Challenge
High myopia creates physiologic RNFL thinning that mimics glaucoma: Research demonstrates that high myopia is independently associated with thinning of average RNFL, average and minimum ganglion cell-inner plexiform layer (GCIPL), and nontemporal parameters of both RNFL and GCIPL, even in glaucoma suspects without confirmed disease 5. This makes distinguishing physiologic myopic changes from early glaucomatous damage extremely difficult on imaging alone 6.
Required Immediate Evaluation
The American Academy of Ophthalmology mandates comprehensive baseline documentation beyond OCT imaging 2:
Visual field testing: Standard automated perimetry (24-2 or 30-2) is essential, as some patients show functional deficits before structural changes, while others show structural damage first 1, 2.
Multiple IOP measurements: Single IOP readings are insufficient; measurements at different times of day on different days are necessary to assess diurnal variation and true baseline IOP 1.
Gonioscopy: Required to exclude angle-closure mechanisms or secondary causes of optic nerve changes 1.
Central corneal thickness measurement: Thin corneas may lead to IOP underestimation and are an independent risk factor for POAG 1.
Stereoscopic optic nerve examination: Through dilated pupils to assess for disc hemorrhages, vertical cup elongation, rim notching, and parapapillary atrophy 1, 2.
Monitoring Protocol
Given the structural findings, the American Academy of Ophthalmology recommends monitoring every 3-6 months initially with repeat OCT, visual field testing, and IOP measurements 2. This intensive monitoring is critical because:
- Progression over time remains the most important factor in detecting early glaucomatous changes in myopic eyes 6.
- In myopic normal-tension glaucoma, patients with family history of glaucoma or higher mean IOP (even within normal range) show significantly increased progression risk 4.
Treatment Decision Thresholds
Treatment should be initiated if 2:
- Evidence of progression on serial OCT or visual field testing indicating conversion to POAG
- Visual field defects consistent with glaucomatous damage develop
- High-risk profile based on additional factors (family history, disc hemorrhages, higher-normal IOP)
If treatment is initiated: Target 20-30% IOP reduction from baseline, as clinical trials demonstrate this reduces risk of developing POAG and slows progression 2, 7. Even in eyes with mean IOP <14.2 mmHg, those above this threshold showed significantly faster RNFL thinning rates 4.
Critical Pitfalls to Avoid
Do not assume RNFL thinning is purely myopic: While high myopia causes physiologic thinning, the inferotemporal pattern described carries specific glaucoma risk 3.
Do not rely on single IOP measurement: Normal IOP does not exclude glaucoma, and unrecognized IOP fluctuations increase risk of glaucomatous damage 1.
Do not delay baseline visual field testing: Structural and functional assessments provide complementary information, and both are essential for accurate diagnosis 2, 6.
Do not use standard OCT normative databases: These are less useful in high myopia due to lack of normative data for anatomically unique eyes, making longitudinal comparison more important than cross-sectional analysis 6.