Myopic Foveoschisis

Etiology

Myopic foveoschisis, as the name suggests, is almost always seen in eyes with high myopia and posterior staphyloma.[5] Antonio Scarpa, a skilled anatomist, was the first to describe "posterior staphyloma" as an abnormal outward protrusion of the eyeball owing to changes in the collagen of the scleral wall.[6] However, the ectasia in the choroid and the retina is not similar, and this differential retina stretching is primarily responsible for causing myopic traction maculopathy. The ectasia causes tractional forces on the retina in a plane parallel to its surface and perpendicular to it, which in turn causes the layers of the retina to split up.

This tractional force acting along the surface of the retina because of the increase in the size of the eyeball is also responsible for the formation of a macular hole.[7][8] Apart from posterior staphyloma and elongation of the eyeball, other factors contributing to etiology may be traction exerted by premacular cortical vitreous, stiff retinal vasculature, or internal limiting membrane rigidity. Multiple consequences of high myopia, such as lacquer cracks produced by breaks in the choroid due to ectasia, choroidal atrophy, and choroidal neovascularization, can coexist in eyes with myopic foveoschisis.[9][10]

Epidemiology

Pathologic myopia is defined as more than -6 D or if the axial length is more than 26 mm.[11] About 2% of the total world population is known to have pathologic myopia. Of these, 8% to 34% have myopic traction maculopathy. Women are more commonly affected than men (3:1). Myopic eyes are known to increase in size at varied rates for many years. Therefore, myopic foveoschisis may manifest from early adulthood to even later years. There is no known geographical predisposition. The progression of this disease is gradual, and the severity increases with time; however, there may be intermittent phases when the disease may become static.

Pathophysiology

The pathophysiology of myopic traction maculopathy is complex. In the eyes, pathologic myopia and ectasia of the posterior scleral wall lead to posterior staphyloma, also called scleroconus. This ectasia causes a stretch in the posterior scleral wall, choroid, and the retina. Due to different stretch responses of the retina and choroid, differential stretching causes the retina to split up into layers. The myopic eye's elongation occurs not only along the axial length but also in a plane tangential to the retina at the posterior pole.[12] This anteroposterior stretch causes a perpendicular tractional force on the retina's surface and leads to layers of the retina splitting up. The tractional force acting along the surface of the retina because of the increase in the size of the eyeball is responsible for the formation of a macular hole.[7][8]

Myopic traction maculopathy is a dynamic disease that gradually progresses over the years. The disease begins with schisis in the inner retinal layers, slowly progressing over the years, leading to schisis in the outer retinal layers. With the disease's progression, an inner or outer lamellar macular hole can develop in many cases.[13] A full-thickness macular hole is also reported in several advanced cases of myopic traction maculopathy.[14] Advanced stages of myopic foveoschisis usually involve macular detachment. In some instances, there may be a resolution of schisis, but this resolution is usually temporary.

Myopic foveoschisis is believed to be multifactorial in origin, and other causes of anteroposterior traction on the retina include internal limiting membrane (ILM) rigidity, vitreomacular traction, and the presence of epiretinal membranes. Based on this etiology, some people believe that a mere peel of ILM in the temporal part of the macula might resolve the foveoschisis. However, reports on such management are pretty limited.[15] Myopic foveoschisis is not a single entity but a broad spectrum of clinical pictures. To date, no single comprehensive classification is available that fits all scenarios. Based on the optical coherence tomography (OCT) picture, 4 retinal "types" of MTM are recognized:

1. Inner schisis or inner-outer schisis
2. Outer schisis
3. Schisis detachment
4. Detachment

OCT also delineates features of the fovea, and 3 foveal patterns are recognized:

1. Intact fovea
2. Inner lamellar macular hole
3. Full-thickness macular hole

There may be present associated epiretinal anomalies or outer lamellar macular holes.[16]

History and Physical

Patients with myopic traction maculopathy can present from early adulthood to the later years of life. Most commonly, they present in the fifth or sixth decade of life, but presentation in the third or even second decade of life is not unusual. The chief complaint is usually a unilateral or bilateral diminution of vision in a highly myopic patient. Rarely, the patients may be completely asymptomatic with no visual complaints.

The onset of symptoms is insidious, and the progression is gradual. Both eyes may be affected simultaneously or at a gap of a few months or years. Patients may also have a history of floaters, light flashes, metamorphopsia, or scotoma.

On examination, there may be visible areas of scleral thinning. The cornea may have tell-tale signs of prior refractive surgery if the patient has undergone surgery. Myopic eyes usually have a deep anterior chamber. The crystalline lens may have signs of cataractogenesis, especially in older patients. On indirect ophthalmoscopy examination of the fundus with a 20D lens, posterior vitreous detachment may be seen. There may be evidence of lattice degeneration in the retinal periphery, with or without holes.[2] 

The disc is generally large with a physiologically large cup. Background tesselations due to chorioretinal degeneration are noted. The macula may not show anything remarkable other than prominent tesselations on examination. Lacquer cracks, Forster-Fuch spots, myopic choroidal neovascular membrane, and posterior staphyloma may be noted to be coexistent in these eyes.[17] 

The clinician may note diffuse atrophic patches in the retina, which appear whitish-yellow. Peripapillary atrophy may also be noted, which appears as well-defined atrophic areas around the disc or at the posterior pole. Fundus examination with a 90D lens can make the clinician suspicious of myopic foveoschisis. Shallow macular retinal detachments and macular holes may be picked up on slit-lamp biomicroscopy.

Evaluation

A good fundus evaluation with a 20-D and a 90-D lens is indispensable. A detailed ophthalmoscopic examination elicits the various pathological lesions present in a myopic eye. Slit-lamp biomicroscopy with a 90D lens alerts the clinician to the possibility of myopic traction maculopathy and makes them probe thoroughly into the disease.

Spectral-domain OCT (SD-OCT) is essential for diagnosing myopic traction maculopathy; this delineates the retina layer by layer and provides detailed information about the pathology. The OCT shows the formation of cystic cavities within the retina, which causes a split in the layers of the retina, giving rise to a thicker inner layer and a thinner outer layer.[18][19] If the schitic cavities are present in the retina's inner and outer layers, it is called compound foveoschisis. A localized posterior detachment of the fovea is delineated. Other features noted on OCT are epiretinal membrane, lamellar or full-thickness macular hole, inner segment/outer segment (IS/OS) junction disruption, paravascular microholes, and retinal micro folds.[20] These scans must be interpreted carefully to determine the presence of lamellar or full-thickness macular holes.

Since myopic eyes are large, large OCT scans (12 mm) are preferred. Scanning the entire posterior pole is imperative. OCT scans should be performed along the horizontal and vertical axis. Myopic traction maculopathy cannot be judged solely based on OCT. Fundus photographs are essential for the evaluation of the eye. Conventional 30-degree photographs do not help properly evaluate the staphyloma; therefore, wide-field fundus photos are preferred. They give the full extent and the location of the staphyloma.

Treatment / Management

Myopic traction maculopathy can only be managed surgically. However, there is no consensus on the management plan. Owing to the rarity of the disease, there are very few studies in the literature quoting specific treatment principles. Surgeons in different parts of the world have been developing management protocols based on their clinical experience.

Pars plana vitrectomy and ILM peeling have shown promising results in eyes with myopic traction maculopathy. There is a hypothesis that peeling the ILM relieves traction on the macula and decreases recurrence by removing the scaffold for the proliferation of cells. However, due to the need for superior surgical skills and complications of an iatrogenic macular hole, it may not be a preferred entity for some surgeons. Scleral buckling is another modality that helps relieve traction on the macula by providing external compressive force; it has the advantage of being extraocular, decreasing the risk of cataract formation and iatrogenic holes. Scleral buckling might also help in early resolution compared to ILM peeling (see Image. Relieved Traction on the Internal Limiting Membrane After Surgery). 

Before deciding on the treatment plan, the surgeon must identify the tractional forces operating on the patient's retina. Both forces, tangential or perpendicular to the plane of the retina, need to be considered. Once the nature of force has been ascertained, a surgical modality that applies the force parallel to it but in the opposite direction must be chosen.

For eyes having a macular hole, due to tangential traction applied by the internal limiting membrane, the surgery of choice is pars plana vitrectomy with internal limiting membrane peeling.[21] Other eyes having the clinical picture of schisis and detachment should undergo a macular buckle to counter the perpendicular tractional force.[22][23] A macular buckle is a device created to cause shortening in the axial length of the eye at the posterior pole.[24][25] Different models of macular buckles have been put into use. Sometimes, myopic eyes may have a combination of perpendicular and tangential tractional forces, as in the case of macular detachment with a macular hole. The surgery of choice in such cases is a pars plana vitrectomy with internal limiting membrane peeling and macular buckling.[26][27](B3)

Suppose the force isn't correctly identified and countered, like providing counter perpendicular traction in an eye with tangential traction, or vice versa. In that case, the problem may not only persist, but it may also get aggravated, and the surgeon may end up doing more harm than providing benefit to the patient. Therefore, the MTM retinal pattern (schisis and detachment) should be treated with a buckle. In contrast, the MTM foveal pattern (macular hole) should be treated with a vitrectomy and ILM peeling, and the MTM retinal with foveal pattern (schisis and detachment combined with macular hole) should be given a combined treatment of vitrectomy with macular buckle.

Differential Diagnosis

Myopic foveoschisis is a cause of gradual progressive loss of vision in high myopic eyes. Other causes of such diminution of vision in myopic eyes need to be ruled out. Such causes include:

• Myopic choroidal neovascularization
• Retinal detachment
• Lamellar or full-thickness macular hole
• Forster-Fuch spots at the fovea

Elaborate history-taking, detailed clinical examination, and judicious use of investigative modalities usually help to make the correct diagnosis.

Staging

To date, there is no universally accepted classification system for myopic foveoschisis, but two systems are commonly used.

International Photographic Classification and Grading System for Myopic Maculopathy

In 2015, the meta-analysis for pathologic myopia study group published the International Photographic Classification and Grading System for Myopic Maculopathy based on the color view of the fundus. The classification system is as follows:

• Category 1: Tessellated fundus (well-defined choroidal vessels)
• Category 2: Diffuse atrophy (whitish-yellow appearance)
• Category 3: Patchy atrophy (well-defined atrophic areas around the disc or at the posterior pole)
• Category 4: Macular atrophy

MTM Staging System

Recently, Barabara Parolini and colleagues have presented the MTM staging system (MSS) based on the OCT features of the retina.[28] This classification system considers the tractional forces operating perpendicular and parallel to the retina's surface, as seen on the OCT. Based on the MTM staging system (MSS), the disease can be classified as follows:

• Stage1a: Inner-outer macular schisis with a normal foveal profile
• Stage1b: Inner-outer macular schisis with a lamellar macular hole
• Stage1c: Inner-outer macular schisis with a full-thickness macular hole
• Stage2a: Predominantly outer macular schisis with a normal foveal profile
• Stage2b: Predominantly outer macular schisis with a lamellar macular hole
• Stage2c: Predominantly outer macular schisis with a full-thickness macular hole
• Stage3a: Macular schisis detachment with a normal foveal profile
• Stage3b: Macular schisis detachment with a lamellar macular hole
• Stage3c: Macular schisis detachment with a full-thickness macular hole
• Stage4a: Macular detachment with a normal foveal profile
• Stage4b: Macular detachment with a lamellar macular hole
• Stage4c: Macular detachment with a full-thickness macular hole

Epiretinal abnormalities can occur at each stage, and a "+" sign can indicate their presence. This classification system standardizes the nomenclature, gives insight into the natural progression of the disease, and helps plan its management.

Prognosis

The prognosis of surgery depends on the patient's preoperative visual acuity. The lower the visual acuity, the poorer the surgical outcome. If the visual symptoms have been present for a long time, the likelihood of complete visual recovery is remote. The presence of foveal detachment and a full-thickness macular hole worsens the prognosis. High axial length, deep staphyloma, and the presence of choroidal thinning all make the surgical outcome less favorable, with poor recovery of visual acuity and incomplete anatomical resolution.[29]

Complications

Surgery for MTM is technically challenging. The visual contrast in high myopic eyes is poor, and ILM peeling becomes difficult. The thin ILM in such eyes is extremely fragile and difficult to grasp and peel. Therefore, an iatrogenic tear of ILM and the formation of a macular hole post-surgery is not uncommon. For fear of forming a macular hole, some surgeons advocate fovea-sparing ILM peeling. Cataract formation is quite common following pars plana vitrectomy and gas tamponade. Macular buckling is technically challenging and may have complications like an incomplete resolution or recurrence of MTM, choroidal detachment, subretinal hemorrhage, or extrusion of the buckle in the post-operative phase.