Original Article Published on 26 May, 2023

The Relationship between Intraocular Pressure and Estimated Intracranial Pressure in Patients with Normal Tension Glaucoma

Intraocular & Intracranial Pressures in NTG
Vol. 18 No. 1 : 2023 (46-58)

Syamil MS Syamil MS
Rona AN Rona AN
JEMAIMA CH JEMAIMA CH

Abstract
This study aims to determine the relationship between intracranial pressure (ICP) and intraocular pressure (IOP) in patients with normal-tension glaucoma (NTG) who were already on anti-glaucoma treatment using an estimated ICP (estICP) and translaminar pressure difference (estTPD) formula. A cross-sectional comparative study consisted of 66 subjects (66 eyes) who were divided into NTG (n=33) and normal (n=33) group was conducted from 1st November 2017 until 31st May 2020 at a tertiary hospital in Malaysia. After obtaining consent from subjects, ocular and systemic data including IOP, visual field testing, axial length, central corneal thickness (CCT), peripapillary and macular retinal nerve fibre layer evaluation as well as blood pressure (BP) and body mass index (BMI) were collected. The estICP (mm Hg) was calculated as 0.44 x BMI (kg/m2) + 0.16 x diastolic blood pressure (mmHg) – 0.18 x age (years) – 1.91. The estTPD was derived from this calculated value, where estTPD (mm Hg) = IOP – estICP. Analysis showed there was no significant difference in estimated ICP between NTG and normal subjects [mean difference (95% CI): 0.37 (-1.39, 2.12), p=0.679]. The difference in estTPD between NTG and normal subjects were found to be statistically insignificant too [mean difference (95% CI): -1.24 (-2.95, 0.47), p=0.149]. The variables significant in multivariate model included best corrected visual acuity (p=0.028), retinal nerve fiber layer (RNFL) (p=0.003), average macular (p=0.002) and estTPD (p=0.008). The EstTPD was found to be protective towards NTG, which the unit increased in estTPD will decreased the odds of having NTG by 26.5% [Adj. OR (95% CI): 0.735 (0.586, 0.922), p=0.008]. In conclusion, ICP was correlated in increased in IOP. A higher TPD may be associated with a lower chance of developing NTG.
Keywords : Glaucoma, intracranial pressure, intraocular pressure,
Abstrak
Kajian ini adalah bertujuan untuk menentukan hubungkait antara tekanan intrakranium (ICP) dan tekanan dalam mata (IOP) pada pesakit tekanan glaukoma normal (NTG) yang sedang menerima rawatan anti-glaukoma melalui formulasi teranggar ICP (estICP) dan perbezaan tekanan translaminar (estTCP). Kajian keratan rentas ini terdiri daripada 66 subjek yang dibahagikan kepada dua kumpulan iaitu kumpulan NTG (33 subjek) serta kumpulan normal (33 subjek) dan telah dijalankan sepanjang 1 November 2017 sehingga 31 Mei 2020 di sebuah hospital tertier di Malaysia. Setelah mendapatkan persetujuan, subjek diperiksa dan seterusnya data yang direkodkan termasuklah tahap tekanan dalam mata, tekanan darah, serta indeks jisim badan (BMI). Ujian lain yang turut dijalankan termasuklah ujian medan penglihatan Humphrey, panjang bola mata, ketebalan sentral kornea (CCT), serta evaluasi terhadap lapisan kepala saraf optik dan makula menggunakan mesin 'Optical Coherence Tomography' (OCT). Anggaran tekanan intrakranium (estICP) dihitung melalui formula; estICP (mmHg) = 0.44 x BMI (kg/m2) + 0.16 x tekanan darah diastolik (mmHg) – 0.18 x umur (tahun) – 1.91. Seterusnya, anggaran kecerunan tekanan translamina (estTPD) dihitung dengan IOP - estICP. Keputusan analisa menunjukkan tiada perbezaan signifikan pada estICP antara kumpulan NTG serta normal [perbezaan min (95% CI): 0.37 (-1.39, 2.12), p=0.679]. Perbezaan estTPD antara kumpulan NTG dan normal juga didapati tidak signifikan [perbezaan min (95% CI): -1.24 (-2.95, 0.47), p=0.149]. Pembolehubah yang didapati menjadi signifikan pada model multivariat termasuklah tahap ketajaman penglihatan terbaik setelah dikoreksi (BCVA) (p=0.028), lapisan urat saraf retina (RNFL) (p=0.002), purata ketebalan lapisan makula (p=0.002), serta estTPD (p=0.008). EstTPD juga didapati bersifat mencegah pesakit daripada penyakit NTG, di mana peningkatan satu unit estTPD dapat mencegah penyakit NTG sebanyak 26.5% [Adj. OR (95% CI): 0.735 (0.586, 0.922), p=0.008]. Kesimpulannya, tekanan dalam kepala didapati berhubungkait dalam peningkatan tekanan dalam mata. Perbezaaan Tekanan Rentas Lamina  (TPD) yang lebih tinggi juga didapati mengurangkan kemungkinan mendapat penyakit NTG.
Kata Kunci : glaukoma, tekanan dalam mata, tekanan intrakranium,

Correspondance Address
Associate Professor Dr. Jemaima Che Hamzah. Department of Ophthalmology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Jalan Yaacob Latif, Bandar Tun Razak, 56000, Kuala Lumpur, Malaysia. Tel: +603-9145 5555 ext 5981/5982 Email: jemaima@ppukm.ukm.edu.my


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