Morphological and hydrodynamic correlates in monkey eyes with laser induced glaucoma

Yuyan Zhang, Carol B Toris, Ye Liu, Wen Ye, Haiyan Gong

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

This study investigated the relationship between decreased outflow facility (C) and changes in hydrodynamic aqueous humor outflow patterns and morphology in cynomolgus monkey eyes with unilateral chronically elevated intraocular pressure (IOP). Argon laser photocoagulation burns to the trabecular meshwork (TM) were made in one eye of each monkey (N = 3), leaving the contralateral eye as a normotensive control. IOPs were followed by pneumatonometry for 16-70 months. C was measured by fluorophotometry before sacrifice. To label the hydrodynamic patterns of outflow, the eyes were enucleated and perfused with fluorescent microspheres (0.5 μm; 0.002%) at the last pressure measured before death minus 7 mmHg. The eyes were perfusion-fixed at the same pressure. Confocal images were taken along the inner wall (IW) of the Schlemm's canal (SC). The total length (TL) and the filtration length (FL) of the IW decorated by tracers were measured in frontal sections. The average percent effective filtration length (PEFL = FL/TL) was calculated for each eye. Sections exhibiting SC were processed and examined under light and electron microscopy. The average IOP was significantly higher in laser-treated eyes (mean ± SD = 61.33 ± 4.16 mmHg) than controls (22.67 ± 4.16 mmHg, P = 0.002). The average C was 13-fold lower in laser-treated eyes (0.03 ± 0.02 μl/min/mmHg) than controls (0.39 ± 0.17 μl/min/mmHg, P = 0.057). By confocal microscopy, in control eyes, SC was open and a segmental distribution of microspheres was found in the TM with a greater concentration near the collector channel (CC) ostia. Much less tracer labeling was seen along SC in laser-treated eyes than control eyes. The average PEFL in controls (47.47 ± 10.79%) was 6-fold larger than in laser-treated eyes (8.40 ± 4.81%, P = 0.048). The average distance between the inner and outer wall of SC was 5-fold greater in control eyes (18.99 ± 6.03 μm) than in laser-treated eyes (3.47 ± 0.33 μm, P = 0.048). By light microscopy, there was extensive pigmentation throughout the TM, denser extracellular matrix in the JCT region, and most of SC collapsed with focal herniations of the IW and JCT protruding into the CC ostia in laser-treated eyes. By electron microscopy, few or no microspheres were observed in laser-treated areas and the areas with SC collapse. More microspheres were observed near the CC ostia area in non-lasered areas. In conclusion, in the laser-induced glaucoma model, laser damage results in a reduction in the available area for outflow across the IW of SC which contributes to the decrease in C and thus elevation of the IOP. Constriction of SC, caused by the chronic elevation of IOP, further decreases the available area for outflow across the IW which decreases C even more in a vicious cycle. This study suggests that the available area for aqueous humor outflow across the IW of SC may play a role in regulating outflow resistance and maintaining IOP.

Original languageEnglish (US)
Pages (from-to)748-756
Number of pages9
JournalExperimental Eye Research
Volume89
Issue number5
DOIs
StatePublished - Nov 1 2009

Fingerprint

Hydrodynamics
Glaucoma
Haplorhini
Lasers
Intraocular Pressure
Microspheres
Trabecular Meshwork
Aqueous Humor
Electron Microscopy
Fluorophotometry
Light
Pressure
Macaca fascicularis
Light Coagulation
Argon
Pigmentation
Burns
Constriction
Confocal Microscopy
Extracellular Matrix

Keywords

  • aqueous outflow facility
  • confocal microscopy
  • electron microscopy
  • intraocular pressure
  • laser-induced glaucoma
  • light microscopy
  • monkey eye
  • trabecular meshwork

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

Cite this

Morphological and hydrodynamic correlates in monkey eyes with laser induced glaucoma. / Zhang, Yuyan; Toris, Carol B; Liu, Ye; Ye, Wen; Gong, Haiyan.

In: Experimental Eye Research, Vol. 89, No. 5, 01.11.2009, p. 748-756.

Research output: Contribution to journalArticle

Zhang, Yuyan ; Toris, Carol B ; Liu, Ye ; Ye, Wen ; Gong, Haiyan. / Morphological and hydrodynamic correlates in monkey eyes with laser induced glaucoma. In: Experimental Eye Research. 2009 ; Vol. 89, No. 5. pp. 748-756.
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AU - Zhang, Yuyan

AU - Toris, Carol B

AU - Liu, Ye

AU - Ye, Wen

AU - Gong, Haiyan

PY - 2009/11/1

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N2 - This study investigated the relationship between decreased outflow facility (C) and changes in hydrodynamic aqueous humor outflow patterns and morphology in cynomolgus monkey eyes with unilateral chronically elevated intraocular pressure (IOP). Argon laser photocoagulation burns to the trabecular meshwork (TM) were made in one eye of each monkey (N = 3), leaving the contralateral eye as a normotensive control. IOPs were followed by pneumatonometry for 16-70 months. C was measured by fluorophotometry before sacrifice. To label the hydrodynamic patterns of outflow, the eyes were enucleated and perfused with fluorescent microspheres (0.5 μm; 0.002%) at the last pressure measured before death minus 7 mmHg. The eyes were perfusion-fixed at the same pressure. Confocal images were taken along the inner wall (IW) of the Schlemm's canal (SC). The total length (TL) and the filtration length (FL) of the IW decorated by tracers were measured in frontal sections. The average percent effective filtration length (PEFL = FL/TL) was calculated for each eye. Sections exhibiting SC were processed and examined under light and electron microscopy. The average IOP was significantly higher in laser-treated eyes (mean ± SD = 61.33 ± 4.16 mmHg) than controls (22.67 ± 4.16 mmHg, P = 0.002). The average C was 13-fold lower in laser-treated eyes (0.03 ± 0.02 μl/min/mmHg) than controls (0.39 ± 0.17 μl/min/mmHg, P = 0.057). By confocal microscopy, in control eyes, SC was open and a segmental distribution of microspheres was found in the TM with a greater concentration near the collector channel (CC) ostia. Much less tracer labeling was seen along SC in laser-treated eyes than control eyes. The average PEFL in controls (47.47 ± 10.79%) was 6-fold larger than in laser-treated eyes (8.40 ± 4.81%, P = 0.048). The average distance between the inner and outer wall of SC was 5-fold greater in control eyes (18.99 ± 6.03 μm) than in laser-treated eyes (3.47 ± 0.33 μm, P = 0.048). By light microscopy, there was extensive pigmentation throughout the TM, denser extracellular matrix in the JCT region, and most of SC collapsed with focal herniations of the IW and JCT protruding into the CC ostia in laser-treated eyes. By electron microscopy, few or no microspheres were observed in laser-treated areas and the areas with SC collapse. More microspheres were observed near the CC ostia area in non-lasered areas. In conclusion, in the laser-induced glaucoma model, laser damage results in a reduction in the available area for outflow across the IW of SC which contributes to the decrease in C and thus elevation of the IOP. Constriction of SC, caused by the chronic elevation of IOP, further decreases the available area for outflow across the IW which decreases C even more in a vicious cycle. This study suggests that the available area for aqueous humor outflow across the IW of SC may play a role in regulating outflow resistance and maintaining IOP.

AB - This study investigated the relationship between decreased outflow facility (C) and changes in hydrodynamic aqueous humor outflow patterns and morphology in cynomolgus monkey eyes with unilateral chronically elevated intraocular pressure (IOP). Argon laser photocoagulation burns to the trabecular meshwork (TM) were made in one eye of each monkey (N = 3), leaving the contralateral eye as a normotensive control. IOPs were followed by pneumatonometry for 16-70 months. C was measured by fluorophotometry before sacrifice. To label the hydrodynamic patterns of outflow, the eyes were enucleated and perfused with fluorescent microspheres (0.5 μm; 0.002%) at the last pressure measured before death minus 7 mmHg. The eyes were perfusion-fixed at the same pressure. Confocal images were taken along the inner wall (IW) of the Schlemm's canal (SC). The total length (TL) and the filtration length (FL) of the IW decorated by tracers were measured in frontal sections. The average percent effective filtration length (PEFL = FL/TL) was calculated for each eye. Sections exhibiting SC were processed and examined under light and electron microscopy. The average IOP was significantly higher in laser-treated eyes (mean ± SD = 61.33 ± 4.16 mmHg) than controls (22.67 ± 4.16 mmHg, P = 0.002). The average C was 13-fold lower in laser-treated eyes (0.03 ± 0.02 μl/min/mmHg) than controls (0.39 ± 0.17 μl/min/mmHg, P = 0.057). By confocal microscopy, in control eyes, SC was open and a segmental distribution of microspheres was found in the TM with a greater concentration near the collector channel (CC) ostia. Much less tracer labeling was seen along SC in laser-treated eyes than control eyes. The average PEFL in controls (47.47 ± 10.79%) was 6-fold larger than in laser-treated eyes (8.40 ± 4.81%, P = 0.048). The average distance between the inner and outer wall of SC was 5-fold greater in control eyes (18.99 ± 6.03 μm) than in laser-treated eyes (3.47 ± 0.33 μm, P = 0.048). By light microscopy, there was extensive pigmentation throughout the TM, denser extracellular matrix in the JCT region, and most of SC collapsed with focal herniations of the IW and JCT protruding into the CC ostia in laser-treated eyes. By electron microscopy, few or no microspheres were observed in laser-treated areas and the areas with SC collapse. More microspheres were observed near the CC ostia area in non-lasered areas. In conclusion, in the laser-induced glaucoma model, laser damage results in a reduction in the available area for outflow across the IW of SC which contributes to the decrease in C and thus elevation of the IOP. Constriction of SC, caused by the chronic elevation of IOP, further decreases the available area for outflow across the IW which decreases C even more in a vicious cycle. This study suggests that the available area for aqueous humor outflow across the IW of SC may play a role in regulating outflow resistance and maintaining IOP.

KW - aqueous outflow facility

KW - confocal microscopy

KW - electron microscopy

KW - intraocular pressure

KW - laser-induced glaucoma

KW - light microscopy

KW - monkey eye

KW - trabecular meshwork

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