Ординатура / Офтальмология / Английские материалы / Optical Coherence Tomography in Age-Related Macular Degeneration_Coscas_2009

Over recent years, OCT has become an essential part of the examination in routine follow-up for AMD to guide clinical practice and analyze the response to treatment. OCT examinations can clearly demonstrate the efficacy of treatment by showing regression or persistence of leakage. Moreover, alterations of the outer retinal layers can also be analyzed.

Therefore, OCT has rapidly acquired an indispensable place in diagnosing, treating, and following patients with AMD.

Fluorescein angiography (for classic CNV) and SLO-ICG angiography (for the more frequent occult CNV) remain the “gold-standard” to diagnose the various clinical forms of CNV as precisely as possible.

A combination of these various imaging modalities probably remains the best way to assess how choroidal neovascularization responds to treatment, to identify good and poor responders, and to define indications for combined treatment modalities.

New OCT Techniques

New Spectral-Domain OCT techniques now provide more than mere quantification of macular thickness and intraretinal or subretinal fluid accumulation by allowing clear visualization of the effect on photoreceptors of CNV proliferation.

CNV can occur posterior to the RPE (occult CNV), or more rarely, anterior to the RPE (classic CNV).

The outer layers of the retina comprise the photoreceptors as well as structures on either side of the photoreceptors (external limiting membrane and the IS/OS interface). Better analysis of the outer retinal layers will allow more accurate prognosis and will help identify either reversible or fibrotic late lesions.

All these data are important to guide patient care and specifically to decide whether to stop or continue treatment

Imaging Modalities

Despite its apparent simplicity and its noninvasive nature, OCT cannot replace all other ophthalmological investigations.

In fact, OCT cannot directly visualize choroidal neovascularization, its degree of perfusion, or its exact location, but OCT does provide valuable and suggestive indirect signs.

Correlations

Functional and morphological correlations are essential to guide the treatment strategy, taking into account not only measurements of central visual acuity, but also microperimetry to evaluate macular function.

Comprehensive evaluation of these different signs by the ophthalmologist guides not only the initial indication for treatment but also the imaging modalities during follow-up for AMD and the frequency and duration of intravitreal injections.

These imaging methods and treatment strategies mainly concerns wet AMD. They must also be applied in agerelated maculopathy, for the early detection of choroidal neovascularization.

Clinical Practice

This chapter covers the detailed analysis of OCT images by describing the natural history and the response to treatment of each of the main clinical forms of AMD.

Clinical cases will be used to illustrate the contribution of OCT compared to that of angiographies and functional investigations in order to guide first-line treatment (currently consisting of intravitreal anti-VEGF injections).

The modalities and duration of post-treatment follow-up and the decision to repeat injections are also based on the investigations discussed above.

In many cases, treatment must be continued for several months or even longer. This is a delicate treatment strategy that should be tailored to the individual patient.

Age-Related Maculopathy

Current classifications group all of the precursor signs of age-related macular degeneration under the term “agerelated maculopathy” (ARM) comprising:

▬The various clinical forms of drusen,

▬Alterations of the RPE, either hypo-pigmentation or hyper-pigmentation,

▬Deposits of autofluorescent lipofuscin material, which are possibly related to the above findings.

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These lesions are frequently observed in populations over the age of 50, and their frequency increases considerably with age. They can evolve over many years and sometimes throughout the subject’s lifetime without causing any complications.

In the majority of cases, the disease remains stable for many years, with no progression to the advanced or complicated stages of true AMD.

I. Different Types of Drusen

Diffuse Deposits

Diffuse deposits or basal laminar drusen are mainly composed of lipoproteins located between the RPE basement membrane and plasma membrane. These deposits are early markers of ARM.

However, even with SLO-ICG angiography or OCT examination, they cannot be identified on clinical examination.

Detection of the first drusen on biomicroscopy therefore constitutes the initial clinical stage of the disease.

Hard Drusen

Small, well-defined hard drusen are easily detected on biomicroscopy or angiography but are barely visible on OCT (Figures 1a and 2).

Hard drusen are usually stable and complications are relatively rare. They only occur fairly late in the course of the disease.

This distinguishes them from soft drusen, which are associated with an increasing risk of neovascular or atrophic complications over time (after 5 or 10 years).

Hard drusen could change gradually, starting with clusters then sero-granular drusen and can even give rise to complications (Figures 1b and 2).

Hard drusen can be transformed into typical soft drusen after many years. A few hard drusen frequently persist around the central part of the fovea where large, soft drusen accumulate (Figure 1b, c, and Figure 2).

Soft Drusen

Soft drusen are often still only characterized by their dimensions. They are considered to be a part of AMD. (Figure 1c and d; Figures 3, 4, and 5). They are fairly common, observed in 10% of patients between the ages of 50-60 years and 25-30% by the age of 80 years.

Typical, soft drusen are pale yellow, with irregular and poorly-demarcated contours.

On fluorescein angiography, they stain late and progressively but without leakage.

SLO-ICG angiography better visualizes soft drusen, which are dark and hypo-fluorescent throughout the angiographic sequence and well-defined in the late phase. The hypo-fluorescence of even small soft drusen on SLO-ICG angiography is a diagnostic characteristic (Figures 3, 4, and 5).

OCT

On OCT, soft drusen are clearly visible as an elevation of the RPE with a moderately reflective cavity, which partially reveals Bruch’s membrane with little or no posterior shadowing.

They have variable dimensions and are generally larger towards the center of the fovea. The most important contribution of SD-OCT in this scenario is to demonstrate associated alterations of the outer retinal layers (Figure 2).

The various stages of the natural history of drusen have been precisely classified to define risk factors for the appearance of complications of AMD. These risk factors are based on drusen number, size, confluence, and associated pigment migration.

Chapter 8 · Clinical Features and Natural History of AMD

HARD, SOFT AND MIXED DRUSEN

Small peripheral drusen

Mixt drusen

Soft drusen

Confluent Soft drusen

Mixt drusen

a

b

c

d

e

d

e