When considering an aqueous drainage device or shunt for glaucoma, the product directions for use identify eligible patients based on the type of glaucoma, the stage of the disease, and the history of prior treatment. Because payor coverage policies typically mimic these indications, reimbursement depends on a close alignment of the chart documentation with the eligibility criteria.¹ For the Hydrus Microstent (Alcon), the directions for use say it is “indicated for use in conjunction with cataract surgery for the reduction of intraocular pressure (IOP) in adult patients with mild to moderate primary open-angle glaucoma (POAG).”² The iStent inject W Trabecular Micro-Bypass System Model G2-W is indicated for use in conjunction with cataract surgery for the reduction of IOP in adult patients with mild to moderate POAG.³ The Glaukos iStent infinite “is indicated for use in adult patients with primary open-angle glaucoma in whom previous medical and surgical treatment has failed.”⁴ Allergan’s Xen gel stent is “intended to reduce intraocular pressure in patients with primary open angle glaucoma where previous medical treatments have failed.”⁵ Alcon’s Ex-Press glaucoma filtration device is “intended to reduce intraocular pressure in glaucoma patients where medical and conventional surgical treatments have failed.”⁶ The US Food and Drug Administration (FDA) says an aqueous shunt “is intended to reduce intraocular pressure in neovascular glaucoma or glaucoma where medical and conventional surgical treatments have failed.”⁷ Significantly, where the stage of glaucoma is mentioned in the directions for use for the aqueous drainage device, it relies on prior visual field (VF) testing for gradation.

Glaucoma Stages

In 2006, Mills and colleagues described “a reliable, comprehensive staging system to assess glaucoma stage in the absence of a universally accepted glaucoma staging system (GSS) on the basis of visual field results.”⁸ They wrote, “the Bascom Palmer GSS was deemed most appropriate by the expert panel as it allowed for structured severity stage assignment based primarily on Humphrey visual field parameters in a relatively simplified manner.” This grading system is as follows:

• Stage 0: ocular hypertension; mean deviation (MD) >0.00
• Stage 1: early glaucoma; MD -0.01 to 5
• Stage 2: moderate glaucoma; MD -5.01 to 12
• Stage 3: advanced glaucoma; MD -12.01 to 20
• Stage 4: severe glaucoma; MD -20.01 or worse
• Stage 5: end-stage glaucoma; no Humphrey VF in worst eye

There are other considerations in this GSS that add more granularity, including probability plot, pattern deviation, and affected hemifield(s). The reader should review Mills’ 2006 article for details.

ICD-10 was introduced in 2015 and included a GSS that is coarser than Bascom Palmer’s system (Table 1).⁹ It mentions only mild, moderate, and severe stages, omitting advanced and end-stage. Physicians and staff are instructed to add a seventh character to the selected ICD-10 code for glaucoma that signifies the stage.

• 0: stage unspecified
• 1: mild stage
• 2: moderate stage
• 3: severe stage
• 4: indeterminate stage

For example, POAG in the right eye is H40.1113 — the terminal character 3 means “severe.” In ICD-10, the term unspecified means not annotated in the chart documentation. The term indeterminate means that the physician could not make a clinical determination.¹⁰ This might occur because the patient has not taken a VF test or could not complete it. Alternately, it may mean that the VF test was very unreliable. Peracha et al found that “a significantly higher number of Humphrey visual field tests were reliable in the mild to moderate glaucoma groups compared with the severe group within this population of patients. The majority of unreliable fields were due to fixation losses. Increased severity of glaucoma correlated with reduced reliability. Decreased visual acuity, higher numbers of glaucoma medications, and decreased pupil size were also associated with reduced reliability; however, IOP was not significantly associated with glaucoma severity.”¹¹ Reliability in VF testing is not black and white, but “a continuum of degrees and types of reliability and unreliability.”¹² Because patients need to learn how to take the VF test, a single test is not very useful. Research by Chauhan et al in Canada found that “the ideal frequency should be between two and three visual fields per year, depending on how great a rate of progression you feel a given patient can tolerate without risking visual disability over the course of his or her lifetime.”¹³

Visual field testing is done much less often than is recommended. Stagg et al reviewed medical records for more than 380,000 patients with open-angle glaucoma and found “more than 75% of enrollees with OAG received <1 visual field test per year and thus did not receive guideline-adherent glaucoma monitoring.”¹⁴ Coleman et al studied more than 13,000 Medicare beneficiaries and found 70% of patients had at least 1 VF test in the year prior to glaucoma surgery, and that VF testing before glaucoma surgery in glaucoma Medicare beneficiaries is suboptimal relative to the recommended standard of care.¹⁵ Fremont et al analyzed patterns of care for open-angle glaucoma in managed care.¹⁶ They observed that “patients with moderate to severe glaucomatous damage had visual field tests at shorter intervals than did patients with mild damage.” Using the data in their paper and a weighted average calculation, the mean time between VF tests was 15.8 months for mild stage glaucoma and 13.1 months for moderate/severe stage glaucoma. Both intervals are longer than 12 months, which is widely considered a lower bound for testing.

In our consulting practice, we also find that VF testing is significantly underutilized. For every 100 eye exams performed by ophthalmologists on Medicare beneficiaries in a year, there are just 11 VFs, and that number should be higher. Perhaps some of the new VF analyzers in development will help make this valuable test easier, faster, and more frequently used.

Conclusion

Where the indications for use in the FDA-approved labeling of an aqueous drainage device include the stage of glaucoma, the physician’s assessment of the stage primarily depends on VF testing. Payor coverage policies typically mimic the product’s FDA-approved labeling, so reliable VF testing is crucial for reimbursement. A single VF is insufficient to make this determination. A glaucoma diagnosis that is “unspecified” or “indeterminate” might not support your claim. A “severe stage” diagnosis might not support your claim if the device is only indicated for a “mild” or “moderate” stage. GP

Kevin J. Corcoran, COE, CPC, CPMA, FNAO, is president of Corcoran Consulting Group in San Bernardino, California.

References

1. South Carolina Blue Cross. Aqueous shunts and devices for glaucoma – CAM 90321. October 2022. Accessed June 19, 2023. https://www.southcarolinablues.com/web/public/brands/medicalpolicy/external-policies/aqueous-shunts-and-devices-for-glaucoma/ 
2. Hydrus Microstent instructions for use. Accessed July 10, 2023. https://www.ivantisinc.sg/wp-content/uploads/2021/10/C00268-Rev-D-Layout-for-CAN-and-Singapore.pdf 
3. iStent inject W important safety information. Accessed January 17, 2024. https://www.glaukos.com/important-safety-information/istent-inject-w/ 
4. iStent infinite instructions for use. Accessed July 10, 2023. https://www.glaukos.com/wp-content/uploads/2022/10/iStent-infinite-IFU.pdf 
5. Xen instructions for use. Accessed July 10, 2023. https://allergan-web-cdn-prod.azureedge.net/actavis/actavis/media/allergan-pdf-documents/labeling/xen/dfu_xen_glaucoma_treatment_system_us_feb2017.pdf 
6. Ex-press instructions for use. Accessed July 10, 2023. https://professional.myalcon.com/sites/g/files/rbvwei1041/files/2020-07/Alcon.EX-PRESS%20Billing%20and%20Coding%20Guide%207.20.pdf 
7. US Food and Drug Administration. Aqueous shunts – 510(k) submissions – guidance for industry and for FDA reviewers/staff. November 1998. Accessed June 19, 2023. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/aqueous-shunts-510k-submissions-guidance-industry-and-fda-reviewersstaff 
8. Mills RP, Budenz DL, Lee PP, et al. Categorizing the stage of glaucoma from pre-diagnosis to end-stage disease. Am J Ophthalmol. 2006;141(1):24-30. doi:10.1016/j.ajo.2005.07.044
9. Rhee, DJ, Lau, S, Sozeri, YG. Glaucoma staging and progression risk factors. Review of Ophthalmology. February 10, 2022. Accessed October 26, 2023. https://www.reviewofophthalmology.com/article/glaucoma-staging-and-progression-risk-factors 
10. Centers for Medicare and Medicaid Services. ICD-10 official guidelines for coding and reporting FY 2023. Accessed July 10, 2023. https://www.cms.gov/files/document/fy-2023-icd-10-cm-coding-guidelines-updated-01/11/2023.pdf 
11. Peracha M, Hughes B, Tannir J, et al. Assessing the reliability of Humphrey visual field testing in an urban population. Invest Ophthalmol Vis Sci. 2013;54(15):3920-3920.
12. Anderson DR. Visual field exam analysis: how reliable are the results? Ophthalmology Management. 2011(2). Accessed July 10, 2023. https://www.ophthalmologymanagement.com/issues/2011/february-2011/visual-field-exam-analysis-how-reliable-are-the-r 
13. Chauhan BC. How many visual fields are enough? Rev Ophthalmol. 2011. Accessed July 10, 2023. https://www.reviewofophthalmology.com/article/how-many-visual-fields-are-enough 
14. Stagg BC, Stein JD, Medeiros FA, et al. The frequency of visual field testing in a US nationwide cohort of individuals with open-angle glaucoma. Ophthalmol Glaucoma. 2022;5(6):587-593. doi:10.1016/j.ogla.2022.05.002
15. Coleman AL, Yu F, Rowe S. Visual field testing in glaucoma Medicare beneficiaries before surgery. Ophthalmology. 2005;112(3):401-406. doi:10.1016/j.ophtha.2004.09.034
16. Fremont AM, Lee PP, Mangione CM, et al. Patterns of care for open-angle glaucoma in managed care. Arch Ophthalmol. 2003;121(6):777-783. doi:10.1001/archopht.121.6.777