Comparison of Treated Mean Intraocular Pressure in Stable Glaucoma with Different Severity in Vietnam

ABSTRACT Purpose: To compare stable glaucoma with different severity in a Vietnamese population in regard to mean intraocular pressure (IOP) and number of medications used. Materials and methods: A total of 116 eyes from 68 patients with medically treated glaucoma were prospectively enrolled at a single center and subjected to automated perimetry every 3 months for at least 9 months. Glaucoma progression was identifed according to early manifest glaucoma trial criterion using glaucoma progression analysis software. Eyes in which no progression was identifed were staged for glaucoma severity using field criteria (mild MD ≥ 6 dB, moderate MD –6 to –12 dB, advanced MD ≥ 12 dB, end-stage central island only). Groups were compared in terms of mean IOP and number of medications used. Statistical analysis was performed using SPSS v16.0. Results: A total of 109 eyes displayed no evidence of pro gres-sion during the study period. Pretreatment mean IOP for mild, moderate, severe and end-stage glaucoma was 28.2 ± 1.4, 28.8 ± 1.6, 29.1 ± 1.8, and 28.6 ± 0.8 mm Hg. The mean IOP of all 109 eyes during follow-up was 16.8 ± 1.4 mm Hg (95% conf dence interval = 15.4 ± 18.2 mm Hg). Mild, moderate, advan ced, and end-stage glaucoma had mean IOP of 17.5 ± 1.2, 16.9 ± 1.3, 15.8 ± 0.9 and 15.5 ± 1.1 mm Hg. The mean IOP of mild stage was significantly higher than advanced and end-stage (t-test, p < 0.001). Also, the mean IOP of moderate glaucoma was significantly higher than advanced and end-stage glaucoma (t-test, p < 0.05). Number of medications had no signi ficant difference among these glaucoma stages (chi-square test, p > 0.05). Conclusion: Reached IOP lowering contributes to glaucoma stabilization especially in late stages. To maintain stable glaucoma, there was no difference in medical procedure of glaucoma stages. How to cite this article: Thanh NTH. Comparison of Treated Mean Intraocular Pressure in Stable Glaucoma with Different Severity in Vietnam. J Current Glau Prac 2014;8(1):7-9.


INTRODUCTION
Elevated intraocular pressure (IOP) is an important risk factor for the development or progression of glaucomatous optic neuropathy. As such, IOP reduction is an important strategy to slow or halt glaucoma progression and irreversible visual impairment. 1,2 First-line medical treatment for lowering IOP is monotherapy with either a topical prostaglandin analog or a β-adre nergicantagonist(β-blocker).However,manypatients eventually require adjunctive therapy to achieve their target IOP and maintain stable glaucoma. 3 Although, many studies have reported on IOP in stable glaucoma and how this was achieved, no studies have examined this in a Vietnamese population. Therefore, the aim of this study was to compare stable glaucoma with different severity in regard to mean IOP and number of medications used.

MATERIALS AND METHODS
This prospective study was conducted within the glaucoma department at the Vietnam National Institute of Ophthalmology (VNIO) from August, 2011 to August, 2013 and approved by the VNIO research ethics committee.

Participants
Participants were included in the study if they were aged between 18 and 70 years and had established primary open angle glaucoma (POAG) on one or more topical medical therapies. Exclusion criteria included secondary open angle or angle closure glaucoma, a history of previous laser trabeculoplastyorglaucomafiltrationsurgery,iftheywere not able to give informed consent, if they could not perform automatedperimetryreliably(>3fixationlosses,>20%false positive,and>20%falsenegative),orifcoexistingocular conditions including previous trauma, significant cataract, corneal disease, or retinopathy. Participants on systemic medi ca tionsthatmayinfluenceIOP(e.g.oralβ-blocker)were also excluded.
Primaryopenangleglaucomawasdefinedbythepresence of characteristic optic nerve damage with a correspondingvisualfielddefectinthepresenceofanopen normal appearing iridocorneal angle and the absence of known secondary causes of elevated IOP.

Follow-up Protocol
First-line IOP lowering treatment consisted of either topical prostaglandinanalogorβ-blockermonotherapy.IfIOPwas increased above target, adjunctive therapy was added in a stepwise sequential manner until target IOP was reached.

Visual Fields
Automated perimetry was performed at baseline and at 3 monthly follow-up intervals for a minimum 9 months using theHumphreyperimeter.Baselineperimetryconsistedof two tests performed 1 week apart. Perimetry was performed inadarkroomunderthesupervisionofvisualfieldspecialist. Reliability indices were monitored and were considered high if>3fixationlosses,>20%falsepositives,or>20%false negatives were detected. In this situation, the testing was cancelled, participants reinstructed then testing commenced again.

RESULTS
A total of 116 eyes of 68 POAG patients were initially enrolled. Of these, 109 eyes displayed, no evidence of glaucoma progression using EMGT criteria and were included in the analysis. The mean and range of age was 46.2 ± 22.3 years with most patients aged 40 years or older ( Table 1). The mean and range of follow-up was 16.3 ± 5.7 months. Themeannumberofvisualfieldtestsperformedwas7.2± 2.1. The majority of eyes had mild POAG (Graph 1).

DISCUSSION
This study assessed the mean treated IOP of 109 eyes with noglaucomaprogressionusingEMGTvisualfieldcriteria in a Vietnamese population. The study found that mean IOPwassignificantlylowerinstableadvancedorend-stage glaucoma compared to stable moderate glaucoma or stable mild glaucoma.
Thefindingsofthisstudyareconsistentwiththerecommendation of the world glaucoma association (WGA) suggesting that target IOP should be progressively lower for increasing disease severity (safe IOP of mild stage is ≤ 21mmHg,ofmoderateis≤18mmHg,ofadvancedis≤15 mmHg,ofendis≤12mmHg), 7 although it is interesting to note that the mean IOP reported in this study does not exactly match the recommended levels by the WGA.
ToachievetargetIOP,thefirstchoicemonotherapyis usuallyaprostaglandinanalogorβ-blockerdependingon availability, patient suitability, and cost. In this study, almost 60%ofalleyeswithstableglaucomaachievedthiswithmono-therapyandupto75%ofmildtosevereglaucomaremained stable on a single agent. This fell dramatically to 27.8%for end-stageglaucomawhichlikelyreflectsadesiretoachieve a much lower IOP in this stage of disease.
When target IOP is not achieved, switching or adding an agentisthelogicalnextstep.Ineyesthatrespondinsufficientlytoinitialβ-blockeroraprostaglandinanalog,afixed combination therapy that consists brimonidine/timolol, or prostaglandin analog/timolol can be considered because of ease of use and cost advantages. In our population, this treatmentstrategywasseenin21.6%ofeyes.

CONCLUSION
It is essential to detect and monitor glaucoma progression to ensure that the treated IOP is safe for patients. IOP reducing is important to maintain stable glaucoma, with lower IOP required as the glaucoma becomes more advanced.