2.4

The Myopic Retina

Shu-Yen Lee*,†

A crescent of peripapillary atrophy, chorioretinal degeneration and atrophy, lattice degeneration and posterior staphyloma are very common findings in the posterior segment of the elongated myopic eye. With higher levels of myopia, particularly if the myopia is greater than –6.00 DS or the axial length greater than 26 mm, the retina may be more severely affected. In the presence of myopic macular degeneration and atrophy, the macula is at risk of lacquer cracks and choroidal neovascularization, potentially causing the loss of central vision. The lattice degeneration is prone to retinal breaks, and thus predisposes the eye to retinal detachment. Abnormal vitreoretinal relationships are not uncommon, and can result in macular holes and detachment, myopic foveoschisis and vitreomacular traction.

Posterior Staphyloma

The posterior staphyloma is a pathognomonic feature of eyes with pathologic myopia. It is a localized ectasia of the sclera, choroids, and retinal pigment epithelium that can be of variable size and involve different aspects of the posterior fundus. The morphological classification of posterior staphylomatous findings were described by Curtin1 to nasal, maculacentered, disc-centered and tiered staphylomas. These staphylomas are best observed with indirect binocular ophthalmoscopy and B-scan ultrasonography. The posterior staphylomas are usually present from a young age and may progress with age, particularly with high myopias and long axial lengths. Vision progressively deteriorates in eyes with staphylomas that are

*Singapore National Eye Centre, Singapore. E-mail: lee.shu.yen@snec.com.sg

†Duke-National University of Singapore, Graduate Medical School, Singapore.

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macula-centered because of the progressive thinning of the choroids and retinal pigment epithelium in the macula.2

Myopic Chorioretinal Atrophy

The terms “tessellated” and “tigroid” fundus appearances have been commonly used to describe the myopic retina. As a consequence of the elongation of the globe and the internal structures within, peripapillary crescent formation and chorioretinal atrophy are common features seen in highly myopic eyes3,4 (Fig. 1).

The areas of atrophy may be focal or diffused, defined or irregularly shaped, isolated or composed of multiple pale white areas in the posterior pole. There may be clumps of pigment within these areas. The choroidal vessels are usually easily seen beneath the thinned out retina. Fundus fluorescein angiography would show staining of these atrophic areas while they are hypofluorescent with indocyanine green angiography.

The natural history of these areas of atrophy is gradual enlargement and coalescence. As the fovea becomes more extensively involved, central vision becomes progressively affected.

Figure 1. Myopic fundus with peripapillary atrophy and a large area of chorioretinal atrophy within the macula.

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Lacquer Cracks

With the thinning of the retinal pigment epithelium and choroid, ruptures of Bruch’s membrane occurs in up to 4.2%.5 These typically occur with a streak of retinal hemorrhage that is not associated with any underlying choroidal neovascularization. Upon resolution of the blood, pale linear or stellate lines are revealed across the macula (Fig. 2), without disruption of the adjacent retina. The lacquer cracks are best defined as linear hyperfluorescence in the early phase of fluorescein angiography and late hypofluorescence on indocyanine angiography. Over time, the cracks may widen and join with areas of atrophy. Central vision may be affected depending on the course of the lacquer crack, especially if there is foveal involvement. It should be noted that the presence of lacquer cracks does put the eye at risk of choroidal neovascularization. Hence, lacquer cracks are not innocuous findings and central visual prognosis may be guarded.

In our series of 28 Asian eyes with myopia of greater than –6.0 DS, six eyes (21.4%) were found to have lacquer cracks as the underlying cause. The mean initial visual acuity was 6/36 and progressively improved to 6/21 at 3 months, 6/15 at 6 months and 6/18 at 12 months. In general, the

Figure 2. Myopic macula chorioretinal degeneration with lacquer crack across the fovea.

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prognosis for central vision is good once the hemorrhage has cleared, unless there is foveal involvement. A lacquer crack that courses the fovea will result in persistent metamorphopsia and deterioration of central acuity.

Myopic Choroidal Neovascularization

Myopic choroidal neovascularization (mCNV) has been reported to occur in up to 10% in those with myopia6 and up to 40.7% in high myopia.7 The patient would report metamorphopsia or central blurring of vision that occurs acutely. The mCNV typically occurs at the edge of a lacquer crack or an area of atrophy within the macula. The area of hemorrhage is usually small with minimal serous exudation compared to the age-related type of choroidal neovascularization. A welldefined grey subretinal membrane can often be seen adjacent to the hemorrhage (Fig. 3a).

The typical term that has been used to describe a pigmented lesion in the myopic macula is a Foerster–Fuchs’ spot.8,9 This represents subretinal or intraretinal migration of RPE accompanying the CNV.

Figure 3a. A myopic CNV which is seen as a greyish subfoveal membrane with surrounding subretinal blood.