Low IOP, but glaucoma progressing?

Consider patient needs, adherence and other possible diagnoses

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Karl Mercieca MD, PGCME, FRCOpth, FEBOS-GL
The patient’s intraocular pressure (IOP) is seemingly low, but glaucoma continues to progress. What can be done? Karl Mercieca MD, PGCME, FRCOpth, FEBOS-GL, consultant ophthalmologist and glaucoma surgeon at Manchester Royal Eye Hospital, Manchester, UK, outlined several steps at the ESCRS Glaucoma Day 2019 in Paris, France. VISUAL DISABILITY THRESHOLD First, put the problem in perspective, and that requires specific patient information, Mr Mercieca said. “We are dealing with patients, not eyes. We are not dealing with pressure, we are dealing with a person who needs a certain quality of life.” Therefore, the goal of treatment should not be to reach an arbitrary IOP, but to prevent disabling visual loss over a patient’s expected lifespan. For example, an aggressive but potentially risky treatment such as trabeculectomy may be appropriate to achieve a very low IOP for a 54-year-old patient with pseudoexfoliation who is progressing significantly at an IOP of 15mmHg, but not for an 84-year-old with similar functional loss due to primary open-angle disease progressing more slowly at 20mmHg, Mr Mercieca suggested. Referencing European Glaucoma Society (EGS) 014 guidelines, Mr Mercieca discussed several factors to consider in setting a target IOP for glaucoma treatment. Early glaucomatous damage, short life expectancy, high untreated IOP, few additional risk factors and slow progression all gravitate toward a higher IOP target. Conversely, advanced glaucomatous damage, longer life expectancy, low untreated IOP, additional risk factors such as family history of glaucoma and pseudoexfoliation, and fast progression suggest a lower IOP target. The rate of progression is critical, Mr Mercieca said. While the median speed of loss is about -0.1dB/year, about 3% of patients progress more than -1.5dB/year (Saunders LJ et al. IOVS 2014;55:102-109). For a patient diagnosed at a 65% visual field index progressing at 5% annually, lowering IOP from 20mmHg to 16mmHg could mean just five years before reaching the visual disability threshold, compared with 26 years if 12mmHg is achieved. However, it’s important to make sure progression is actually occurring, Mr Mercieca emphasised. “You don’t want to condemn the patient to an invasive procedure with the possibility of hypotony if the progression isn’t real.” Additional testing, such as day phasing to detect IOP fluctuations, and ensuring patients are adhering to medication treatment, can help confirm possible reasons for progression. Non-IOP medical factors such as cerebrospinal fluid pressure factors, variable ocular blood flow, brain lesions, 24-hour blood pressure variation and the influence of vitamin B12, folate levels and drugs should also be investigated and treated as indicated, Mr Mercieca said. Karl Mercieca: doctormercieca@yahoo.com