Purpose
To investigate the morphological changes including choroid and optic nerve head (ONH) parameters in patients with occludable angles before and after acute IOP elevation.
Methods
A dark room prone test for diagnosis angle closure was applied to angle closure suspects. Scanning by Spectralis OCT was applied. Images of the ONH and the subfovea choroid were compared before and after IOP elevation using follow-up mode. Choroidal thickness and ONH parameters were measured manually, including Bruch membrane opening (BMO) distance, the cup depth (distance from BMO reference to inner limiting membrane), and the laminar cribrosa depth (LCD, the vertical distance from midpoint of BMO to the anterior laminar surface).
Results
95 eyes out of 64 patients had an IOP elevation more than 4 mmHg. Among them, 56 (87.5%) were female, and the age was 60.2 ± 9.3 years (39 - 85 years). The IOP increased by 12.3±11.8 mmHg (4.0- 47.0 mmHg), from 16.1±4.1mmHg before test to 27.8 ± 12.5mmHg after test. Using the flicker comparison method, 82 eyes out of 88 (97.7%) showed ONH backward movement after IOP elevation, including RNFL, BMO, and lamina movement. Cup depth showed an increase (RNFL raise) in 45 eyes (48.9±5.2%) and a decrease (RNFL compression) in 47 eyes (51.1±5.2%). Cup depth increase participants had a significantly lower IOP increase (+8.3 ± 6.7mmHg) than the cup decrease participants (16.5 ±14.3mmHg) (P<0.001). The BMO distance remained constant after IOP elevation (P=0.996). The relative location of lamina cribrosa to BMO was also unchanged. Either anterior or posterior surface of lamina were clearly imaged in 50 eyes (52.6) and the LCD showed no difference before and after test (P=0.981). 77 eyes (82.8±4.0 %) showed choroid thinning, decreasing by 15.8±24.9 μm (from 280.3±86.7 μm to 264.0±76.4 μm, P<0.001). The decrease in choroid was more obvious in men (P=0.011), those with thicker choroid at baseline (P<0.001), and those with higher IOP elevation (P<0.001).
Conclusions
Acute IOP elevation lead to ONH, BM and lamina to backward movement before choroid thinning. The RNFL showed an elevation relative to BM in a lower IOP elevation condition and compression in a higher IOP elevation condition. The in-vivo morphological changes of different tissue reflect their stiffness and other physical properties and may have indications on glaucoma pathologic processes.
Keywords: 627 optic disc •
550 imaging/image analysis: clinical