Peripheral myopic degenerations and myopic choroidal neovascularisation

Patients with myopic CNV report sudden scotoma in central or paracentral visual fields and consequent drop in vision. Likewise, patients often report symptoms of distorted vision (metamorphopsia).

Retinal peripheral degenerations do not cause visual disturbances. However, as some of them bring an increased risk of retinal detachment, patients with peripheral retinal degeneration may report symptoms related to retinal tear/retinal detachment development (new onset of floaters and flashing lights).

The myopic CNV is almost always a type 2 or “classic” type of CNV membrane. It is relatively small (compared to CNV in age-related macular degeneration (AMD) cases) and usually smaller than 1000 microns. The presence of intraretinal fluid is uncommon. A subretinal haemorrhage often is present along with the membrane.(13) Bear in mind that subretinal haemorrhages in myopic patients may be secondary to lacquer cracks.(14) Those changes represent ruptures of the Bruch’s membrane and may be precursors of the CNV. In any case, subretinal haemorrhage needs to be reviewed by an experienced clinician. The inactive or old CNV becomes pigmented and is noted as a pigmented spot in the posterior pole (called Fuchs spot). The resolution of untreated CNV can end up with the atrophy of the respective retinal tissue.

Lattice degenerations represent localised retinal lesions with thinning of the neurosensory retina and adherent vitreous at the edge of the lesions. Typically, they look like white crossing lines. However, they may be present in radial patterns adjacent to retinal vessels. The lattice degenerations may have pigment, yellow deposits, and small oval atrophic holes. It is important to remember that retinal tears can be near the lattice degenerations and that retinal detachment is found in 14-35% of cases.(10,11)

Snail-track degeneration represents glistening white dots. Some experts consider them the early stage of lattice degeneration. The snail tracks as lattice degeneration represent thinning of the neurosensory retina with adherent vitreous and traction at the edges of the lesion. It is most common in myopic eyes, and retinal tears may be seen in 54% of patients with this type of peripheral degeneration.(10,11)

Peripheral retinal tufts are small, peripheral, focal areas of elevated glial hyperplasia associated with vitreous or zonular attachment and traction. They can be cystic (5% of adults), non-cystic (72% of adults), and zonular (15% of adults). Both cystic and zonular tufts increase the risk of retinal tears.(15)

Senile or degenerative retinoschisis represents the splitting of retinal layers, while retinal detachment is the complete detachment of the neurosensory retina from the retinal pigment epithelium (RPE). It is present in 2-7% of the population, mainly in people who are older than 40 years and hyperopic. It is almost always present in temporal quadrants, and it is asymptomatic. It causes absolute visual field scotoma, while retinal detachment causes relative scotoma. Furthermore, the retinoschisis is not mobile, while the retinal detachment is.(16) Bear in mind that retinoschisis may cause retinal detachment in 0.05-2.5% of cases. In addition, peripheral cystoid degeneration, which represents peripheral microcysts, may lead to retinoschisis.

White-without-pressure and dark-without-pressure are peripheral retinal changes that are benign. They give a white or brown appearance to the peripheral retina. Dark-without-pressure lesions are more posterior than white-without-pressure lesions.

Slit lamp examination – you can easily recognise the myopic CNV son a slit lamp. In most cases, it is represented by central or paracentral subretinal haemorrhage. The peripheral retinal lesions are also easily seen on a slit lamp. For examination of the peripheral retina, you should use a 90D non-contact lens or cornea-contact lens with a wide field.

Colour fundus photography is a great tool to catch most peripheral retinal changes, including the macula. Keep in mind that some cameras have limitations, and when you check the peripheral retina in myopic patients, ask for montage imaging or use ultra-widefield cameras.

Table 1. The table displays how to recognise rhegmatogenous retinal detachment (RRD) from retinoschisis.

Optical coherence tomography is crucial in diagnosing myopic CNV. The active membrane represents a “fluffy” subretinal hyperreflective material with no fluid. Likewise, this imaging modality becomes more helpful in identifying peripheral lesions (i.e., differentiating retinoschisis from retinal detachment).

Patients with active myopic CNV need to be treated urgently. The golden treatment standard is intravitreal injections of anti-VEGF. Several studies (RADIANCE, REPAIR, and MYRROR) have proven the benefits and safety of intravitreal ranibizumab and aflibercept in the treatment of myopic CNV.(3,17,18)

There is controversy in the prophylactic treatment of lattice degenerations or other peripheral lesions that increase the risk of retinal detachment. According to some reports that suggest laser treatment, there is no strong evidence of efficacy in preventing retinal tear formation or developing retinal detachment.(19)

It is important to familiarise yourself with the differentiation between retinal detachment and retinoschisis. Retinoschisis does not require any surgical procedure. Yet, you should regularly monitor it, as it has a risk of developing retinal detachment.