Age-Related Macular Degeneration

Age-related macular degeneration is a general term for any type of acquired maculopahy that affects people over 50-years-old.  The most common type of age-related macular degeneration (AMD) is an atrophic form of the disease known as dry age-related macular degeneration.

Dry age-related macular degeneration (ARMD) is characterized by the following clinical features:

• Gradual breakdown of retinal pigment epithelial cells in the macula
• Gradual blurring of central vision
• Appearance, enlargement or coalescense of retinal drusen in the macula
• In advanced stages, development or progression of geographic atrophy

Case Report

• A 72-year-old white woman presented with a chief complaint of decreased vision
• Case history described a subjective decrease in vision over the past year
• The patient had not been examined in two years and wanted to know if new eyeglasses would help to improve her vision

Conclusion

Gradual atrophy of retinal pigment epithelial cells with resultant accumulation of metabolic debris and loss of photoreceptor function is the main cause of vision loss in dry age-related macular degeneration.  Progression of atrophy like that seen in this patient is the culmination of prolonged, progressive changes in the retina.  The most advanced presentation of this progressive atrophy can result in total loss of central vision known as geographic atrophy.

History of Present Illness

• Associated signs and symptoms:  none
• Location:  vision is worse in the left eye
• Duration:  past one year
• Quality:  n/a
• Context:  decreased vision is more noticeable when reading
• Severity:  mild decrease in vision
• Timing:  vision seems to be getting worse over time
• Modifiers:  none

Review of Systems

The patient reported that she was in good health and taking no medications.

Past, Family and Social History

Non-contributory

Uncorrected Distance Visual Acuity

• 20/20 in the right eye
• 20/40 in the left eye

Normal Examination Findings

• Mental status
• General medical observation
• Pupils
• Gross visual fields
• Basic sensorimotor examination
• External examination
• Adnexal examination
• External ocular examination with biomicroscopy

Intraocular Pressure Measurements

• 15 mm Hg in the right eye
• 16 mm Hg in the left eye

Ophthalmoscopy

• Normal fundus appearance in the right eye
• Focal geographic atrophy in the left macula

Clinical Diagnosis

The clinical diagnosis is a determination based on the knowledge obtained from the patient’s medical history and from the results of the eye examination alone, without the benefit of diagnostic tests or procedures.

The patient’s clinical diagnosis is dry age-related macular degeneration based on the following clinical findings:

• Focal atrophy of retinal pigment cells in the left macula
• Decreased visual acuity in the left eye

Treatment Plan

To gather the information required to treat macular degeneration, a diagnostic and treatment program is initiated.

• Determination of different types of diagnoses
• Selection of one or more treatment options

Several macular diseases have clinical signs that mimic the appearance of dry, age-related macular degeneration.

Differential Diagnoses

Familial Drusen

• Drusen usually outside macular region
• Drusen usually form circular pattern around inner posterior pole
• Rarely affects vision

Myopic Degeneration

• Only in high axial myopia
• Drusen rarely present
• Usually has associated peripheral retinal changes

Inflammatory Maculopathies

• Variable presentation of chorioretinal atrophy that may involve macula
• Associated inflammatory signs (vitreous cells)

Most patients with dry macular degeneration do not experience significant vision loss (90% less than 20/50).  ARMD typically has an asymmetric presentation with the fellow eye showing clinical changes about one-third of the time within two years of the intial presentation in the first eye.  There are multiple risk factors for ARMD but the most important are age, history of smoking, family history, poor vascular health, obesity, and nutritional factors.  While the risk of progression to the most severe form of the disease (wet or exudative macular degeneration) is very low, monitoring for potential conversion to the wet form is the highest clinical concern.

Ordering Diagnostic Tests

The following diagnostic tests can help determine the severity of dry age-related macular degeneration and help monitor progression.

• Refraction
• 10-2 threshold visual field examination
• Retinal laser scan with spectral-domain OCT
• Extended color vision examination
• Electroretinogram
• Dark adaptation testing

Some authorities also recommend additional testing including genetic testing and macular pigment density testing, both discussed later.

Refraction

• Measuring visual acuity is a method of evaluating functional vision loss
• Age-related macular degeneration can produce central visual field defects which result in a loss of visual acuity
• There was no improvement in the left eye’s visual acuity after a subjective refraction was performed or by pinhole testing

Retinal Laser Scan — Macula

• Measuring the thickness of the macula along with a detailed analysis of retinal structure provides an overall assessment of retinal health
• The procedure can be accomplished by using the Cirrus OCT manufactured by Carl Zeiss Meditec

Visual Field Examination

Automated threshold perimeters measure the visual field by plotting the threshold luminance value of the patient in various locations in the visual field.  The luminance of the light stimulus is represented by non-specific units of measurement called decibels (dB).

Clinically significant macular degeneration can produce a central scotoma in the visual field — even subtle macular degeneration can cause a decrease in the threshold values in the central points that loosely correlate to an expected degree of Snellen acuity.

• 32+dB — expect normal Snellen acuity
• High teens to low thirties — one or two lines loss
• Mid to high teens — three to four lines loss
• Low to mid teens — five to eight lines loss

Automated threshold perimeters characterize specific parameters of the overall visual field status by the use of numbers called Global Indices.  Two of the indices, Mean Deviation (MD) and Pattern Standard Deviation (PSD) express the raw data generated by the instrument.  The Pattern Standard Deviation is a measure of focal loss of visual field taking into account any generalized depression in the hill of vision.

A visual field defect can be classified as mild, moderate, or advanced based upon an abnormal Mean Deviation.

• Mild visual field defect = 0 through -5.99 dB
• Moderate visual field defect = -6.00 dB through -11.99 dB
• Advanced visual field defect = anything above -12.00 dB

Right Eye

• No loss of retinal sensitivity

Left Eye

• Mild loss of retinal sensitivity
• Central scotoma at the point of fixation superiorly
• Paracentral scotomas temporally

Both Eyes

• Clinically significant asymmetry
• Visual field test results correlate with OCT tests, visual acuity and the clinical examination

The results of the examination revealed central and paracentral scotomas in the left eye.  These visual field defects are seen in macular degeneration and other retinal lesions.  Mid-to-high threshold values would correspond to the acuity loss in the 20/40 Snellen range.  

Physical Diagnosis

Because the central scotoma in the left eye agrees with measurable, observable structural damage to the left eye’s macula, the clinical diagnosis of age-related macular degeneration is confirmed.

Genetic Testing

While there is little doubt that genetics play a significant role in the pathogenesis of ARMD, current testing is still suspect for clinically significant sensitivity and specificity.  At best, they may help indicate which patients who already have the disease may progress more rapidly.  No currently available test can accurately predict who might develop ARMD.

Macular Pigment Density Tests  

Once again, there is little doubt of the importance carotenoids play in maintaining macular health.  Exactly how they relate to ARMD is still the subject of debate.  

Of more concern is the lack of standards in evaluating macular pigment density, lack of knowledge regarding what is normal or abnormal in the individual patient presentation and how the measurement can or does relate the rate of vision decline.  As explained in the summary on MPOD tests in Archives of Clinical and Experimental Ophthalmology 2011, clinicians should exercise caution in considering MPOD tests as an accurate predictor of ARMD onset or progression.

All of the diagnostic test results confirmed the initial diagnosis of subclinical macular degeneration in the right eye and mild-to-moderate macular degeneration in the left eye. 

According to Current Procedural Terminology, when eye doctors perform ophthalmological examinations, the complexity of medical decision-making is not separated from the examining techniques used.  As a guideline to assist eye doctors in enhancing their medical decision-making skills, consider that the complexity of medical decision-making involves three components. 

The first component concerns the number of possible diagnoses and treatment options that must be considered. Determination of the diagnosis of macular degeneration involves the determination of structural damage to the retina with associated functional loss of vision.

The second component concerns the amount and complexity of medical records and diagnostic tests that have to be obtained, reviewed and analyzed.  In addition to an eye examination, this visit required the review and analysis of a subjective refraction, a retinal laser scan, and a threshold visual field examination.

Third, the complexity of medical decision-making is affected by the risk of significant complications and/or morbidity associated with macular degeneration and the risks involved in any treatment options.  This patient’s retinal condition was classified as a significant problem where the risk of significant central vision loss without treatment was possible.  In addition, the treatment plan will involve continued monitoring of her retinal condition.

Treatment Guidelines

Dry macular degeneration is generally considered to be an irreversible process, even if detected early.  Multiple studies, starting with the 1991 AREDS study, have shown variable benefit in the role of antioxidant therapy through macro-nutrient support.  All the studies have random, somewhat arbitrary, and differing analysis of available nutrient supplements with highly variable claims of benefit in slowing progression of the disease.  While the results could be considered somewhat less than exciting, nutritional support can still be considered the frontline therapy for at risk or confirmed ARMD patients.  At this time, the most positive results support the use of the carotenoids lutein and zeazanthine as well as omega-3 fatty acids.

Patients with almost any stage of ARMD should be counseled regarding home monitoring of their disease.  At a minimum, this should include paying close attention to the quality of their detailed vision.  Amsler grids have been advocated for years.  While very insensitive in detecting change, to the point of many authorities doubting their clinical value, they may help a small percentage of patients better detect qualitative changes in their vision.

There is no local (retinal) treatment for early, dry age-related macular degeneration so no referral to a retinal specialist is warranted.  

Most importantly, those at risk or diagnosed with ARMD should be counseled regarding the deleterious effects of smoking and obesity.

Treatment Program

The patient was counseled regarding the nature of her disease and given an Amsler grid for home monitoring.  It was recommended she begin nutritional supplementation in the the form of lutein 30mg/day, zeazanthine 30mg/day, and omega-3 supplements containing at least 2000mg/day of EPA/DHA.

Next visit scheduled for 6 months.

Discussion

This case demonstrates several key aspects of monitoring the current knowledge base in ocular disease.  It is important to accurately follow patients with ARMD with the greatest concern in watching for conversion to the more serious wet or exudative form of the disease.  While accurate detection of ARMD is possible with normal ophthalmoscopic examination, additional diagnostic testing can be very beneficial in confirming the diagnosis and monitoring for disease progression.  As the changes with advancing disease are often suble, progression is best monitored by SD OCT technology with RPE change analysis and or autofluorescence capability.  Although sometimes beneficial, visual field testing and Amsler grid monitoring are subject to extremely poor sensitivity in detecting change.  Treatment of dry ARMD is at this time limited to lifestyle changes and supplementation with antioxidants.