Fundus Autofluorescence in Lamellar Macular Holes and Pseudoholes



Fundus Autofluorescence in Lamellar Macular Holes and Pseudoholes


Ferdinando Bottoni



DEFINITION OF PSEUDOHOLE AND LAMELLAR MACULAR HOLE

The definitions of macular pseudohole (MPH) and lamellar macular hole (LMH) have been a matter of great debate in the past. Today there is a general consensus to define an MPH as a macular lesion that has the appearance of a full-thickness macular hole (FTMH) but does not have a loss of foveal tissue. By contrast, a loss of foveal tissue is mandatory for a diagnosis of LMH (1,2). However, and in contrast to FTMH, in LMH only part of the foveal tissue is lost (there is no full-thickness defect).

Before optical coherence tomography (OCT) was available, the definitions of MPH and LMH were based on certain characteristic history and examination findings, which were shown to be not sensitive enough for a clear differential diagnosis. Clinically, both MPH and LMH have a similar appearance, with a round and well-circumscribed reddish lesion at the center of the fovea (1,3, 4, 5, 6, 7, 8, 9, 10). Functional tests, such as the Watzke-Allen test (11) and microperimetry (12), in which no scotoma is detected in either MPH and LMH are not useful for differentiating between these conditions, and both clinical entities can lead to similarly impaired vision (median 20/40) (1, 2, 3).

OCT evaluation has proved valuable in the diagnosis of macular holes, as it is able to visualize retinal anatomy with near microscopic resolution (≈10 μm for STRATUS OCTTM [Carl Zeiss Meditec]; ≈5-7 μm for spectral domain OCT). However, although OCT studies have added valuable information regarding the definition, pathogenesis, and progression of macular holes (6, 7, 8, 9, 10), it is not always possible to differentiate between MPH and LMH. In particular, when there is residual tissue at the bottom of the foveal defect, as occurs with macular holes in stage 2 (according to the OCT classification of Azzolini et al. [9]), OCT imaging may not be able to indicate with certainty whether there is loss of retinal tissue. In such cases, the diagnosis of MPH or LMH is often a matter of speculation.


PATHOGENESIS

The pathogenesis of MPH and LMH is not fully understood, but they have always been considered to be quite different processes. It has been hypothesized that MPH is attributable to the centripetal contraction of an epiretinal membrane (3). In contrast, LMH is thought to be the result of an abortive process in the formation of an FTMH. Posterior vitreous detachment is the main initiating process of the latter, but epiretinal membrane contraction has been suggested as a likely secondary factor (2). This mechanism is supported by two findings: (i) 62% to 89% of LMHs may present with
an epiretinal membrane (1,2); and (ii) pseudo-opercula, suggestive of an aborted macular hole, have been reported in only 24% of patients with LMH (1), Therefore, it seems that the pathogenesis of LMH cannot simply be attributed to an abortive process in FTMH formation.


FUNDUS AUTOFLUORESCENCE

It is believed that fundus autofluorescence (AF) derives mainly from the lipofuscin-laden retinal pigment epithelium (RPE; see Chapter 3) (13). It is generally accepted that lipofuscin represents the product of degradation of photoreceptor outer segments. In a normal fundus, the distribution of AF is diffuse, with decreased intensity at the optic nerve head, the retinal blood vessels, and the macula (13,14). Macular AF is attenuated by the presence of luteal pigment, which has a higher concentration along the outer plexiform layer at the fovea (Fig. 14B.1) (15). Any foveal defect, including an LMH that spares the photoreceptors (2), may alter the degree of foveal AF by decreasing the amount of masking luteal pigment and thus increasing the foveal AF.


IMAGING TECHNIQUES


Slit-Lamp Biomicroscopy

Slit-lamp biomicroscopy in patients with MPH and LMH may simply show the common feature of a round, reddish lesion at the center of the macula, but it is not sensitive enough to detect a small loss of foveal tissue, which is present in LMH with preserved visual acuity. Additionally, the presence of an epiretinal membrane is not definitive in the differential diagnosis of LMH and MPH; as mentioned above, 62% to 89% of patients with LMH may have an associated epiretinal membrane (1,2), which will always be present in MPH (3).

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Aug 29, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Fundus Autofluorescence in Lamellar Macular Holes and Pseudoholes
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