Abubakar Bosso Usman MD
Optical coherence tomography angiography (OCTA) with the RTVue100 (Optovue) can distinguish between healthy eyes and those with early glaucoma. Moreover, perifoveal macular thickness is more informative than peripapillary RNFL thickness, said Abubakar Bosso Usman MD at the XXXV Congress of the ESCRS in Lisbon, Portugal.
“Although the results of some researchers have shown limitations of the macular thickness parameters in the early diagnosis of glaucoma, this may be related to the technology, as OCT continues to evolve,” said Dr Usman, Department of Ophthalmology, 3rd Minsk City Hospital, Belarusian State Medical University, Republic of Belarus.
The prospective cross-sectional hospital-based study was conducted between January and June 2016. It included 40 eyes of 23 patients with early-stage primary open-angle glaucoma (POAG), 30 eyes of 17 glaucoma suspects and 20 eyes of 10 healthy patients. All of the patients were aged 40 years and older, had a best corrected visual acuity of 0.6 and better; spherical and cylindrical correction of plus or -2.5D and an open anterior chamber angle with no pigmentation and/or exfoliative material.
All eyes underwent OCTA scanning of the retina using the RTVue100 Optovue. The ‘ONH scan’ and ‘Retina Thickness Map program’ were respectively used to scan the 3.45mm peripapillary and a 5mm x 5mm region of the perifoveal macular regions. The parameters analysed included the retinal nerve fibre layer (RNFL) and perifoveal inner macular average total, superior, inferior, temporal and nasal thickness.
“Optical coherence tomography angiography is a new high-speed non-invasive imaging device with a high resolution and demonstrably better intraretinal layer separation. It also offers the ability of getting more sampling points of the macula, including determination of the full, inner and outer macular thickness, the fovea, and the perifoveal areas of the macula separately, at the same time maintaining a good scan quality,” Dr Usman said.
GREATER CHANGES IN PERIFOVEAL THAN PERIPAPILLARY THICKNESS
Statistical analysis found that patients in the stage I POAG group had significant decreases in all parameters of the peripapillary RNFL and perifoveal macular thickness compared to the control group. However, inter-group analysis using Mann-Whitney criteria revealed statistically significant differences only between the main and control groups in superior (139μm vs 163μm, p<0.05) and inferior (12μm vs 136.5μm, p<0.05) RNFL thickness. Peripapillary RNFL thickness did not differ significantly between the early glaucoma and the glaucoma suspect groups, or between the control and the glaucoma suspect.
However, perifoveal inner macular thickness was significantly different between the glaucoma and the control groups in the average total (275μm vs 289μm), in the temporal (271μm vs 290μm) and nasal (289μm vs 303μm) regions. In addition, there were significant differences in perifoveal inner macular thickness between the glaucoma and glaucoma suspect groups in terms of average total macular thickness (275μm vs 285μm), in the temporal (271μm vs 287μm) and nasal (289μm vs 298μm) regions. The study showed no significant differences between the control and glaucoma suspect groups in terms of perifoveal inner macular thickness.
Dr Usman noted that structural changes precede functional changes in glaucomatous chronic optic neuropathy, and it is the death and damage in retinal ganglion cells that underlies the pathology. Optical coherence tomography detects the atrophy of the RGC axons as a thinning of the retinal nerve fibre layer.
“Using angiographic OCT in our study we were able to identify the thinning of peripapillary RNFL and perifoveal inner macular thickness in the early stages. However, the macular parameters demonstrated higher areas under the curve,” he concluded.
Abubakar Bosso Usman: drbossoau@gmail.com
