Age-Related Macular Degeneration Tổng quan về bệnh

Giới thiệu

Macular degeneration is a chronic, progressive degenerative disease that occurs in the pigment, neural, and vascular layers of the macula that causes central vision loss. 

Age-Related Macular Degeneration_Disease Background

Dịch tễ học

Macular degeneration is the leading cause of irreversible vision loss, especially in the elderly. Global estimates for age-related macular degeneration (AMD) by the United Nation (UN) and World Health Organization (WHO) are at 20-25 million people with 8 million people having severe blindness. In 2004 in the US, there is as many as 1.75 million people aged 40 years old and above who had advanced age-related macular degeneration in at least one eye, while as much as 7.3 million people had high-risk features in one or both eyes. Additionally, a population-based survey in the US also noted that the macular degeneration is more prevalent in non-Hispanic whites than in Mexican Americans or blacks. It is also estimated that as much as 288 million people may suffer from age-related macular degeneration by 2040.

Sinh lý bệnh

The macular disorder may have one or more of the following: Formation of drusen which are localized deposits of extracellular material usually concentrated in the macula, abnormalities in the retinal pigment epithelium (eg hypopigmentation or hyperpigmentation), retinal pigment epithelium (RPE) and choriocapillaris geographic atrophy, neovascular (exudative) maculopathy, and choroidal neovascularization (CNV), polypoidal vasculopathy (PCV), reticular pseudodrusen, or retinal angiomatous proliferation.  

Yếu tố nguy cơ

The following are important risk factors for AMD:

• Increasing age (>50 years old)
• Genetic factors (eg complement factor H genes)
• Family history of AMD
• Cigarette smoking history of >20 years
  • Current smokers have 2- to 3-fold risk and there is a dose-relationship with pack years of smoking
• Hypertension
• Diet (eg low intake of antioxidants and zinc, high total fat and trans-fat)
• Obesity
• Presence of AMD in the other eye
• Race
  • While Caucasians are at increased risk compared to African or Hispanic descent, studies fail to show consistent differences in risk between Caucasians and Asians

• Gender

  • Studies have consistently shown women to be at increased risk

Phân loại

Classification of Age-Related Macular Degeneration by Age Related Eye Disease Study (AREDS)¹

This classification system is used in predicting the risk of progression from early to late AMD and visual loss.  

No Age-Related Macular Degeneration (AREDS category 1)  

No AMD or AREDS category 1 is characterized by having no drusen or presence of few small drusen (<63 microns in diameter).  

Early Age-Related Macular Degeneration (AREDS category 2)  

Early AMD or AREDS category 2 is characterized by the presence of any or all of the following: 

• Multiple small drusen
• Few intermediate drusen (63-124 microns in diameter) or
• Mild abnormalities in the RPE

At this stage, there is a low risk of progression to advanced AMD after 5 years.

Intermediate Age-Related Macular Degeneration (AREDS category 3)  

Intermediate AMD or AREDS category 3 is characterized by the presence of any or all of the following:

• Extensive intermediate drusen
• At least one large drusen (≥125 microns in diameter) or
• Geographic atrophy not involving the center of the fovea

Advanced Age-Related Macular Degeneration (AREDS category 4)  

Advanced AMD or AREDS category 4 is characterized by geographic atrophy that involves the center of the fovea and/or any of the manifestations of neovascular AMD.  

Neovascular Age-Related Macular Degeneration Classification by Angiographic Patterns of Fluorescence¹  

Classifying AMD via angiographic patterns of fluorescence helps in identifying specific treatment to give the patient.  

Classic CNV  

Classic CNV is characterized by well-demarcated, uniform hyperfluorescence in the early phase of fundus fluorescein angiography (FFA) and then at the late phase of the angiogram, it shows leakage that obscures the boundaries.  

Occult CNV  

Occult CNV is characterized by either an area of irregular elevation of RPE (fibrovascular pigment epithelial detachment) that appears as stippled hyperfluorescence present in the midphase of the angiogram or leakage from an undetermined source that appears as speckled hyperfluorescence with dye pooled in the subretinal space.  

¹Modified from: Flaxel CJ, Adelman RA, Bailey ST, et al. Age-related macular degeneration Preferred Practice Pattern ®. Ophthalmology. Jan 2020