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Acquired Macular Diseases: Pathophysiology, Diagnosis and Management

Lorne B. Yudcovitch, OD, MS, FAAO

College of Optometry, Pacific University

2043 College Way

Forest Grove, OR 97116

 

Contents

Introduction

 

The optometrist is often faced with clinical challenges concerning macular disorders, both in terms of proper diagnosis as well as recommendations and treatment for the patient. Fortunately, current techniques such as scanning laser ophthalmoscopy and photodynamic therapy have helped assist with solving these challenges. Yet aside from recent technological advances, much of the diagnosis of macular conditions still relies on a thorough case history and careful examination by the practitioner.

This course will only discuss the acquired macular diseases - those macular diseases that may arise typically later in a person's life, rather than congenital hereditary macular disorders. As such, this course will not be discussing the hereditary macular disorders, examples of which are noted in Table 1 below:

 

Table 1.
Some Hereditary Macular Disorders
Fundus Flavimaculatus/Stargardt's Dystrophy
Best's disease (Vitelliform Dystrophy)
Dominant Drusen (Doyne's Honeycomb Dystrophy)
Pattern Anomalies of Retinal Pigment Epithelium
Central Areolar Choroidal Dystrophy
Rod Monochromatism (Achromatopsia)
Progressive Cone Dystrophies
Ocular Albinism/Oculocutaneous Albinism
Certain Forms of Retinitis Pigmentosa (i.e. inverse)
Mucopolysaccharidosis (MPS) Syndromes

 

The classic forms of age-related macular degeneration (i.e. exudative or "wet" macular degeneration and non-exudative or "dry" macular degeneration) will also not be discussed in this course, as these macular diseases are fairly well known by the optometrist and highlighted in numerous other papers in more detail.

 

Basic Macular Anatomy

The macula comprises approximately a 1.5 mm diameter area 15 degrees temporal, and very slightly inferior to, the optic nerve. The retinal layers consist of (from innermost layer to outermost layer):

  1. Internal limiting membrane (ILM)
  2. Nerve fiber layer (NFL)
  3. Ganglion cell layer
  4. Inner plexiform layer
  5. Inner nuclear layer
  6. Outer plexiform layer
  7. Outer nuclear layer
  8. External limiting membrane
  9. Photorecptors
  10. Retinal pigmented epithelium (RPE)

The layers interior to the rods and cones are angled more towards the foveola (center) of the macula, creating the foveal depression. The nerve fiber tissue in this area is called Henle's fiber layer. Bruch's membrane, a collagenous tissue, lies below the retinal pigment epithelium, bordering the choroid. Figure 1 below shows the general macula anatomy, while Figure 2 shows ocular coherence tomography (OCT) and histological cross-section of the macula.


Figure 1
Figure 1. Left - Normal macular anatomy. Right – normal macular fundus appearance.
(Source Left : http://www.gene.com/gene/products/education/vascular/amd.jsp)


Figure 2
Figure 2. Above - Normal macula cross section as seen with ocular coherence tomography (Source: http://www.nyee.edu/macular-holes.html). Below – histological cross-section of the macula and underlying choroid. (Source: http://www.bu.edu/ histology/p/07901loa.htm)

 

Categories of Acquired Macular Disease

As stated above, acquired macular diseases are typically due to 'later-life'-based changes or etiologies. These etiologies are usually:

The rest of the course will examine various acquired macular diseases. The author has attempted to present these conditions from the "most common" to the "least common" condition seen in practice.

 

Epiretinal Membrane

Epiretinal Membranes (ERMs) are relatively common macular disorders that go by several other names (premacular gliosis, cellophane maculopathy, surface-wrinkling retinopathy, preretinal fibrosis, and macular pucker). They are caused by retinal glial cell proliferation, where the internal limiting membrane (ILM) develops wrinkling and breaks that ultimately allow glial cells access to surface (Figure 4). It is postulated that these breaks may be created when posterior vitreous detaches from macula. ERMs usually affect otherwise healthy people, and are bilateral in 5 percent of cases. Their clinical appearance is dependent on density of the membrane and distortion of retinal vasculature near the membrane.


Figure 4
Figure 4. OCT of epiretinal membrane.
(Source: http://www.nyee.edu/macular-holes.html)

 

Cellophane maculopathy is a specific type of ERM. It typically appears as a translucent membrane with irregular light reflex or sheen, that is best detected with 'red free' light (Figure 5). Fine surface striae may form as it thickens and contracts, with tortuous supero- and inferotemporal vessels. The posterior vitreous is usually detached from the macula. Most patients are asymptomatic, or have slight metamorphopsia. Visual acuities are usually normal or slightly reduced.



Figure 5
Figure 5. Cellophane maculopthy (specific type of epiretinal membrane).

Source: http://www.uams.edu/jei/patients/retina_services/macularpucker.asp

 

Macular pucker is a more severe form of ERM, with retinal wrinkling centered around the fovea and more severe blood vessel distortion (Figure 6). Some vessels may actually be obscured by the wrinkled ILM. Metamorphopsia and reduced visual acuities (20/40 to 20/60) are common with macular pucker. A pseudohole or cystoid macular edema (CME) may form from partial posterior vitreal detachment (PVD) with persistent adhesions to the macula.

 

Figure 6
Figure 6. Macular pucker. Note the extensive retinal wrinkling pulling the vasculature.

 

Secondary ERMs may be caused by:

Treatment of ERMs usually involve vitrectomy and membrane peeling (Figure 7). This is a very delicate procedure that removes the membrane. Ironically, it may cause a worse epiretinal membrane to form as an outcome. Membrane peeling is indicated only if significantly reduced visual acuities (i.e. worse than at least 20/40, with significant visual complaints) from the ERM are present.

 

Figure 7
Figure 7. Simple schematic diagram of membrane peeling procedure.
(Source: http://www.eyemdlink.com/EyeProcedure.asp?EyeProcedureID=50)