Intraocular Pressure and Cup-to-Disc Ratio Asymmetry in Diagnosing Iris Melanoma.

Purpose: Distinguishing an iris melanoma from an iris nevus can be challenging as few clinical features other than documented growth are helpful in making the diagnosis. In this study, we compared the presenting intraocular pressure (IOP) and cup-to-disc ratio (CDR) between affected and unaffected eyes in patients with iris melanoma and iris nevus.

Patients and methods: This was a single-institution retrospective case series of patients treated for iris melanoma and iris nevus from January 2013 to October 2022. Thirty-nine subjects with iris melanoma and forty age-matched patients with iris nevus were included. We analyzed the difference in IOP, CDR, and diagnosis of glaucoma between affected and unaffected eyes in patients with iris melanoma and control iris nevus cohort.

Results: The average IOP for eyes with iris melanoma and iris nevus was 18.8±6.1 mmHg and 14.6±3.5 mmHg (P<0.001), respectively. The average CDR was 0.36±0.27 and 0.24±0.14 (P=0.02), respectively. The average IOP of the contralateral unaffected eye in iris melanoma patients was 16.3±3.5 mmHg, significantly less than the affected eye (P=0.03). The average CDR of the contralateral unaffected eye in iris melanoma was 0.25±0.15, which was trending towards being less than the affected eye (P=0.05). There was no difference in the average IOP (P=0.89) or average CDR (P=0.49) between the affected and unaffected eye in patients with iris nevus.

Conclusion: We demonstrate that patients with iris melanoma are more likely to have greater IOP and CDR in the affected eye compared to the unaffected eye, and a diagnosis of unilateral glaucoma than eyes with iris nevus. Patients with iris melanoma had greater IOP asymmetry between the affected and unaffected eye. Therefore, IOP and CDR asymmetry may suggest a diagnosis of iris melanoma.