This study found that a substantial proportion of patients (65 %) did not adhere to their scheduled review visits, and an overall low full adherence rate of less than 10 %. This confirms the well-known finding that a significant number of patients fail to fully comply with their review visits and glaucoma medication precisely as prescribed. Moreover, it is likely that the non-adherence rate might even be higher than estimated, if all cases of POAG had been included. By proportion, the slightly more female than male found in the sample may not directly be related to the diagnosed glaucoma, as sex did not influence the estimated cost. Some studies have suggested that sex is not linked to POAG, while others found an association [5, 19–21]. In this study, the slightly higher number of female than male in this study may be due to the higher proportion of female in the Ghana population and not an associated with POAG cases [22].
Glaucoma medications were found to be the major cost drivers to treatment as there were only few patients who had had surgery. The estimated average cost of GH¢ 967 ($484) per POAG patient per year is high considering that majority 61.9 % of the patients were less economically active and were not involved in any income generating activities. In 2012, the minimum monthly wage was 120.96 ($60) and with only 28.4 % of the Ghana population who were below the international poverty line of US$1.25 per day (2007–2011), the cost to the individual could be considered high [23]. There are recently reported financial challenges facing the Ghana NHIS therefore the projected TC of GH¢861,597 ($430,799) per year (assumed full adherence rate for all 891 patients) can be seen as additional burden for a country with Gross National Income (GNI) per capita (2012) of $1550 [22, 23]. On the other hand, the estimated TC could even be higher considering that costs related to eye care facilities use, equipment use, consultations and public health programs which were not part the cost evaluation. Additionally, other intangible costs such as stress, loss of leisure time, failure to participate in societal activities, modification of social and economic decisions were not factored in the calculation.
The indefinite management of glaucoma might have influenced the high proportion of NHIS registration among the patients. The national registration rate for the NHIS is reported to be around 70 % according to Government figures, but a study have suggested the number could be far lower [22]. The study revealed that, as many as twice high income earners are registered unto the scheme compared to the poor because of their ability to pay an annual renewable premium [22]. In this study, patients who were found not be registered with the NHIS could be attributed to their inability to afford the cost of registration or renewal fee, and this can possibly be cited to partly account for the gap in adherence rate. Indeed, all individuals who were aged 70 years and above were on the scheme because they were granted free registration by law.
The study showed a significant relationship between age and total estimated cost. Glaucoma is a chronic and progressive condition that is asymptomatic in its early stages, resulting in delayed case reporting. In Ghana, access to eye care is also a challenge to many and therefore patients might seek care at the advanced stages when visual defects become manifest [10]. At more advanced stages of the condition, there is likely to be an increase in reporting time, more resource consumption, and shift to more expensive medications to slow progression [12, 13]. The increase in reporting time could also be attributed to certain factors such as the elderly having access to some welfare packages such the free NHIS registration that enabled them increase the number of hospital visits. The association of cost with income may also reflect the unequal socio-economic status in Ghana, and the link between the purchasing power (ability to afford) and income.
The pattern of prescription found in the study may also underline cost implications and prescriber preferences. The predominance reliance on monotherapy and particularly the use of Timolol is uncommon in similar studies [12, 24]. In this study, this can be attributed to a preference for low-priced medication, its availability on the NHIS medication list, and prescriber preference which perhaps is due to the uncomplicated nature of administering it alone or in combination with other class of glaucoma medications [14, 25–28]. Though Acetazolamide has some reported systemic side effects mainly because of its oral route of administration [24], it was relatively prescribed for short-term use in this study, probably motivated by the desire to reduce IOP since the patients could not afford more expensive medications which has IOP-lowering potency. It is also the least expensive medication on the NHIS list and may underline the higher prescription rate. Other studies have reported it to be one of the least prescribed [29]. On the contrary, though Latanoprost is known for its potency for reducing IOP [13, 15], it was less frequently prescribed because of its high acquisition cost.
While the findings from this retrospective study are consistent with results from similar glaucoma cost estimation studies, a number of methodological limitations may limit the extrapolation of the data to a national scale. First, the low rate of adherence among the study population affected the sample size, and for that matter the total cost estimation. The costing evaluation method employed may also have led to underestimation of the TC because it did not include indirect cost associated POAG treatment such as facility use, diagnostic, personnel as well as indirect cost related to transportation for the patients and escorts. It is also possible some information may have been lost due to tracking, since the study involved case audit analysis to extract the relevant information from the patient folders.