Updates on Retinal Disease

By Dr Chan Choi Mun, Associate Consultant, Vitreo-Retinal Service, Singapore National Eye Centre

In Ophthalmology, the subspecialty managing vitreo-retinal diseases has classically been divided into Surgical Retina and Medical Retina. Surgical retinal cases include retinal detachments, trauma and intraocular foreign bodies. The field of Medical Retina is increasingly gaining importance as it encompasses several significant eye diseases, all of which can have a devastating impact on one’s vision. Age-related macular degeneration, which includes choroidal neovascularisation and polypoidal choroidal vasculopathy, is one of these conditions. Also falling within the purview of Medical Retina are the conditions of diabetic retinopathy, retinal vein occlusions, central serous retinopathy and hereditary retinal diseases.

Age-related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in the industrialised world. With Singapore’s ageing population, we are already noticing an increase in age related macular degeneration. As its name implies, it is a condition of older adults which affects the macula - the centre of the retina, and the area responsible for clear central vision. In the wet, or exudative, form of AMD, pathological choroidal neovascular membranes (CNV) develop under the macula, leading to leakage and accumulation of fluid and blood over the macula. Ultimately, a central disciform scar develops over the macula if AMD is left untreated. As such, a patient with AMD notices blurred central vision, disturbances of colour vision or metamorphopsia (where straight lines appear wavy). This translates to problems with recognising faces, reading, driving and all activities requiring good central vision.

Investigations

Before treatment can be instituted, specialised investigations need to be carried out. These tests are employed not just for AMD, but also for all retinal pathologies. Colour fundus photography, optical coherence tomography (OCT), rapid sequence fundal fluorescein angiography (FFA) and indocyanine green angriography (ICG) are essential.

Latest Developments

SNEC now has the latest 3D OCT, which provides a highly detailed three-dimensional view of the macula. There is also the Heidelberg Reina Angiograph (HRA) confocal laser scanning system which delivers crisp, minutely detailed, high-speed realtime digial angiographic images of the retinal vasculature. These greatly contribute to accurate and precise diagnoses.

Management of AMD

The traditional treatment of AMD has been to employ thermal laser to destroy the CNV. However, laser photocoagulation of juxta or subfoveal CNV, that is CNV which lies within 200 micrometers of the fovea, induces an immediate iatrogenic central scotoma. It was only recently that antiangiogenic agents, injected directly into the vitreous humour of the eye, were employed in the arsenal to treat AMD. The rationale for this is that animal and clinical studies have establied vasular endothelial growth factor or VEGF as a key mediator in ocular angiogenesis.

Anti-VEGF agents can cause regression of the abnormal blood vessels and improvement of vision when injected directly into the vitreous humor of the eye. Examples of these anti-VEGF agents include Ranibizumab (Lucentis, Genentech) and Bevacizumab (Avastin, Genentech), and they are usually injected on a monthly basis for the initial 3 months after diagnosis. Studies have demonstrated that treatment with these agents improves or stabilises vision.

In some situations, photodynamic therapy (PDT) is used in tandem with anti-VEGF agents. Also available at SNEC, PDT first involves the intravenous injection of verteporfin before directing a “cold laser”, which activates the verteporfin, at the affected area. Verteporfin is a photosensitizing dye, which reacts with water to create oxygen and hydroxyl free radicals. These radicals induce occlusion of the pathologic vasculature by means of massive platelet activation and thrombosis while preserving the normal choroidal vasculature and nonvascular tissue. The advantage conferred by PDT is that it avoids creating a central blinding scotoma when treating subfoveal CNV.

Diabetic Retinopathy

This is a condition very familiar to us. The hallmark of treatment for severe non-proliferative of proliferative diabetic retinopathy is panretinal photocoagulation laser treatment. That is unchanged. However, there is now the additional option of employing intravitreal injections of antiVEGF agents, similar to that employed in the management of AMD, for the treatment of vitreous haemorrhage secondary to proliferative diabetic retinopathy or for persistent macula oedema which is resistant to focal laser treatment.

Central Retinal Vein Occlusion

Akin to a stroke in the eye, the ischaemic form or central retinal vein occlusion (CRVO) can lead to a severe loss of vision. While panretinal photocoagulation laser can prevent neovascularisation within the eye, and its associated complication of painful neovascular glaucoma, it does not help reduce any incident macula oedema. Focal laser is the mainstay of treatment. However in cases with persistent unresolving macula oedema, anti-VEGF treatments are now being used at SNEC with some success.

Hereditary Retinal Diseases

Although rare, when they do strike, these conditions can be visually debilitating. They include retinitis pigmentosa, conerod dystrophies, retinal pigment epithelial dystrophies and the hereditary vitreoretinal degenerations.

SNEC has both the diagnostic and therapeutic capabilities to manage these patients well. These patients would require specialised electrophysiological testing, which includes the electroretinogram (ERG) and visual evoked potentials (VEP), to clinch the diagnosis. They would also need Goldmann visual fields to monitor their condition over the long term. These diagnostic tests are all available at SNEC in a special laboratory. These patients need to be followed up long term to exclude associated conditions such as cataracts and glaucoma. We are also performing ongoing research, in collaboration with the Singapore Eye Research Institute, looking at genetic testing for these patients.

Low Vision Clinic

Sometimes, in spite of the best treatment, or due to the inherent nature of the eye disease, some patients end up with permanent poor vision. These patients can be reviewed at the Low Vision Clinic at SNEC. This is a special service where patients are counseled on how to optimise their vision; are given certain optical aids, such as magnifiers, to facilitate their reading vision; and are refracted by an optometrist familiar with dealing with low vision patients. Hope and optimism, which is so important for patients with low vision, is upheld.