What Is Retinal Ischaemia?
Retinal ischaemia refers to a chronic or subacute reduction in blood flow to the retina, resulting in progressive hypoxia and degeneration of the retinal layers.
Unlike acute arterial or venous occlusions, retinal ischaemia develops silently. A patient may lose a substantial degree of visual function before becoming aware of the problem.
It may occur as a complication of several vascular conditions, including diabetic retinopathy, hypertensive retinopathy, carotid artery disease with reduced cerebral blood flow affecting the ophthalmic circulation, vasculitis and haematological disorders that increase blood viscosity.
Symptoms such as gradual visual field loss, reduced visual acuity and impaired color perception develop slowly, but the cumulative injury may be as destructive as an acute event.
Characteristics of Retinal Ischaemia
A central feature of chronic retinal ischaemia is the self-perpetuating cycle it creates. Hypoxia stimulates pathological neovascularisation through vascular endothelial growth factor (VEGF). The newly formed vessels are dysfunctional and prone to leakage, causing oedema and haemorrhage that further aggravate the ischaemia.
At the same time, photoreceptor cells, particularly the rods responsible for vision in low-light conditions, have exceptionally high oxygen requirements and are among the first cells to be affected by hypoxia.
In diabetic retinopathy, ischaemia is one of the principal drivers of disease progression. Progressive capillary occlusion creates areas of non-perfused retina that stimulate ischaemia-driven neovascularisation. Addressing the underlying ischaemia, rather than only its clinical manifestations, is therefore an important therapeutic objective.
Scientific Studies
Studies in animal models of ischaemic retinopathy have shown that hyperbaric oxygen therapy may suppress pathological neovascularisation by reducing VEGF expression, protect photoreceptors from hypoxic injury and slow neuronal degeneration.
Clinical studies involving patients with diabetic retinal ischaemia have reported stabilization or modest improvement in visual function and reductions in the extent of retinal ischaemia.
The effects of hyperbaric oxygen therapy are twofold. It supplies oxygen to the hypoxic retina through diffusion from the vitreous humour and reduces the ischaemic stimulus for VEGF, thereby addressing one of the principal drivers of the pathological neovascularisation that worsens the condition.
The Role of Hyperbaric Oxygen Therapy
In retinal ischaemia, hyperbaric oxygen therapy may be used as an adjunctive intervention aimed at compensating for chronic hypoxia and slowing the degenerative process. It does not replace laser photocoagulation, intravitreal injections or management of the underlying cause. Instead, it acts at a level these treatments cannot directly address by supplying oxygen to ischaemic retinal tissue.
Each session substantially increases oxygen tension within the vitreous humour, allowing oxygen to diffuse into the ischaemic retina independently of obstructed capillaries.
Reducing local ischaemia may decrease VEGF signalling and slow pathological neovascularisation. At the same time, antioxidant effects may protect photoreceptors from the oxidative stress associated with chronic hypoxia.
The treatment course is individualised according to the underlying cause and severity of the condition. It typically consists of 20 to 30 sessions, planned in collaboration with the ophthalmologist, with progress assessed through optical coherence tomography (OCT) and visual field testing.