Relationship between mean follow-up intraocular pressure, rates of visual field progression and current target intraocular pressure guidelines.

AIMS: To investigate if eyes presenting intraocular pressure (IOP) within the limits of current guideline-driven target IOP indeed experience slow rates of glaucomatous visual field (VF) progression. METHODS: A total of 8598 24-2 VF tests from 603 eyes from the African Descent and Glaucoma Evaluation Study with manifest glaucoma were included. The sample was split into three groups based on baseline VF mean deviation (MD): G1 (better than -5.0 dB), G2 (-5.0 to -10 dB) and G3 (worse than -10 dB). We investigated the relationship between existing target IOP guidelines and rates of MD progression in these groups. RESULTS: For stable eyes, the medians and IQR of the mean follow-up IOP were G1=15.0 mmHg (IQR: 13.1 to 17.7), G2=13.2 mmHg (IQR: 11.6 to 14.3) and G3=11.9 mmHg (IQR: 10.1 to 13.8) (p<0.01). When considering the mean follow-up IOP within the limits proposed by current guidelines, the median MD slopes were: -0.20 dB/y (IQR: -0.43 to -0.02) for G1<21 mmHg, -0.19 dB/y (IQR: -0.51 to -0.01) for G2<18 mmHg and -0.15 dB/y (IQR: -0.47 to 0.05) for G3<15 mmHg (p=0.63). There were no significant differences between racial groups. CONCLUSION: In a sample of patients with manifest glaucoma, despite substantial variability between eyes, adherence to treatment guidelines helped slow the rates of global VF progression at various stages of disease. TRIAL REGISTRATION NUMBER: clinicaltrials.gov Identifier: NCT00221923.

Improved visualization of deep ocular structures in glaucoma using high penetration optical coherence tomography.

The introduction of optical coherence tomography (OCT) has revolutionized ophthalmology through the ability to non-invasively image the retina in vivo. Glaucoma is the leading cause of irreversible blindness worldwide. Despite major advances in imaging techniques, the pathogenesis of glaucoma remains poorly understood at present. The lamina cribrosa (LC) is the presumed site of axonal injury in glaucoma. Its thinning and deformation have been suggested to contribute to glaucoma development and progression by impeding axoplasmic flow within the optic nerve fibers, leading to apoptosis of retinal ganglion cells. To visualize the deep ocular structures such as the choroid and the LC, OCT imaging has been used, particularly the enhanced depth imaging (EDI)-OCT modality of spectral domain (SD)-OCT. However, the posterior laminar surface especially is not seen clearly using this method. A new generation of OCTs, swept-source (SS)-OCT, is able to image the LC and the choroid in vivo. SS-OCT employs a longer wavelength compared with the conventional OCT, generally set at 1050 nm (instead of 840 nm). We review current knowledge of the LC, findings from trials that use SD-OCT and EDI-OCT, and our experience with a prototype SS-OCT to quantify choroid changes and visualize the LC in its entirety.

Imaging of the Lamina Cribrosa using Swept-Source Optical Coherence Tomography.

The lamina cribrosa (LC) is the presumed site of axonal injury in glaucoma. Its deformation has been suggested to contribute to optic neuropathy by impeding axoplasmic flow within the optic nerve fibers, leading to apoptosis of retinal ganglion cells. To visualize the LC in vivo, optical coherence tomography (OCT) has been applied. Spectral domain (SD)-OCT, used in conjunction with recently introduced enhanced depth imaging (EDI)-OCT, has improved visualization of deeper ocular layers, but in many individuals it is still limited by inadequate resolution, poor image contrast and insufficient depth penetrance. The posterior laminar surface especially is not viewed clearly using these methods. New generation high-penetration (HP)-OCTs, also known as swept-source (SS)-OCT, are capable to evaluate the choroid in vivo to a remarkable level of detail. SS-OCTs use a longer wavelength (1,050 nm instead of 840 nm) compared to the conventional techniques. We review current knowledge of the LC, findings from trials that use SD-OCT and EDI-OCT, and our experience with a prototype SS-OCT to visualize the LC in its entirety. Key Points What is known? •     The LC is the presumed site of axonal injury in glaucoma •     Compared to spectral domain-OCT, enhanced depth imaging-OCT improves imaging of the LC •     Even so, currently used SD-OCT techniques are restricted by poor wavelength penetrance of the deeper ocular layers What our findings add? •    SS-OCT may be a superior imaging modality for deep ocular structures •    Prior studies used SS-OCT to evaluate choroidal thickness in both healthy and 'normal tension glaucoma' eyes •    SS-OCT enables good evaluation of three-dimension (3D) lamina cribrosa morphology. How to cite this article: Nuyen B, Mansouri K, Weinreb RN. Imaging of the Lamina Cribrosa using Swept-Source Optical Coherence Tomography. J Current Glau Prac 2012;6(3): 113-119.