Drusen and 'choroidal filling defects': a cross-sectional survey

Bruch's Membrane and the Choroid in Age-Related Macular Degeneration

A healthy choroidal vasculature is necessary to support the retinal pigment epithelium (RPE) and photoreceptors, because there is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex. This relationship is compromised in age-related macular degeneration (AMD) by the dysfunction or death of the choroidal vasculature. This chapter will provide a basic description of the human Bruch's membrane and choroidal anatomy and physiology and how they change in AMD.The choriocapillaris is the lobular, fenestrated capillary system of choroid. It lies immediately posterior to the pentalaminar Bruch's membrane (BrMb). The blood supply for this system is the intermediate blood vessels of Sattler's layer and the large blood vessels in Haller's layer.In geographic atrophy (GA), an advanced form of dry AMD, large confluent drusen form on BrMb, and hyperpigmentation (presumably dysfunction in RPE) appears to be the initial insult. The resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of GA. The death and dysfunction of CC and photoreceptors appear to be secondary events to loss in RPE. The loss of choroidal vasculature may be the initial insult in neovascular AMD (nAMD). We have observed a loss of CC with an intact RPE monolayer in nAMD, by making RPE hypoxic. These hypoxic cells then produce angiogenic substances like vascular endothelial growth factor (VEGF), which stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). Reduction in blood supply to the CC, often stenosis of intermediate and large blood vessels, is associated with CC loss.The polymorphisms in the complement system components are associated with AMD. In addition, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of proinflammatory molecules like CRP and complement components during AMD. In this toxic milieu, CC die or become dysfunctional even early in AMD. The loss of CC might be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation.Therefore, the mutualistic symbiotic relationship of the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Understanding age-related macular degeneration (AMD): relationships between the photoreceptor/retinal pigment epithelium/Bruch's membrane/choriocapillaris complex

There is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex that is lost in AMD. Which component in the photoreceptor/RPE/BrMb/CC complex is affected first appears to depend on the type of AMD. In atrophic AMD (~85-90% of cases), it appears that large confluent drusen formation and hyperpigmentation (presumably dysfunction in RPE) are the initial insult and the resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of geographic atrophy (GA). The death and dysfunction of photoreceptors and CC appear to be secondary events to loss in RPE. In neovascular AMD (~10-15% of cases), the loss of choroidal vasculature may be the initial insult to the complex. Loss of CC with an intact RPE monolayer in wet AMD has been observed. This may be due to reduction in blood supply because of large vessel stenosis. Furthermore, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of complement components as well as proinflammatory molecules like CRP during AMD. In this toxic milieu, CC die or become dysfunction making adjacent RPE hypoxic. These hypoxic cells then produce angiogenic substances like VEGF that stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). The loss of CC might also be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation. Therefore, the mutualistic symbiotic relationship within the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Foveal electroretinograms and choroidal perfusion characteristics in fellow eyes of patients with unilateral neovascular age-related macular degeneration

AIMS/BACKGROUND

A prolonged choroidal filling phase on fluorescein angiography has been reported to be a common finding and associated with visual function abnormalities in patients with age-related macular degeneration (AMD). This investigation was carried out to determine whether this perfusion defect was related to the slowing of foveal cone electroretinogram (ERG) implicit time seen in patients with AMD.

METHODS

Fluorescein angiograms and foveal cone ERGs were evaluated in the fellow eyes of 67 patients with unilateral neovascular AMD.

RESULTS

Twenty eight (42%) of the eyes had a choroidal perfusion defect. ERG implicit times averaged 1 ms slower (p = 0.0167) and were more likely to be delayed (p = 0.0078) in eyes with abnormal choroidal perfusion than in eyes with normal choroidal filling; significant relations were found also after controlling for age. ERG implicit time was also inversely related to ETDRS visual acuity and positively related to the extent of macular drusen; and the latter showed a borderline significant tendency to be more prevalent in eyes with prolonged choroidal perfusion. However, an association of a delayed ERG implicit time with prolonged choroidal filling remained after controlling for age, acuity, and the extent of drusen.

CONCLUSION

These findings further establish prolonged choroidal perfusion as a common finding in AMD and link it to retinal malfunction.

A new method of image analysis of fluorescein angiography applied to age-related macular degeneration

Quantitative analysis of retinal and choroidal abnormalities using current photographic techniques is complex and laborious. Digital image analysis techniques using the scanning laser ophthalmoscope overcome many of the problems with present techniques and allow reliable quantitation. A prerequisite of quantitation is accurate image acquisition and registration. The authors describe a reliable method of image analysis and apply it to the quantitation of hyperfluorescence in scanning laser fluorescein angiograms of different forms of age-related macular degeneration. Retrospective analysis of scanning laser fluorescein angiograms obtained using a standardised technique was undertaken. Eighty-six angiograms from patients with age-related macular degeneration were analysed and categorised as dry maculopathy, geographic atrophy of the retinal pigment epithelium, retinal pigment epithelial detachment (PED) or subretinal neovascularisation (SRNV). Fluorescein characteristics of both SRNV and PED showed a characteristic pattern of fluorescence. The advantages and disadvantages of the technique are discussed.