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Continuing advances contribute to understanding, treatment of vitreomacular interface diseases
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Diseases of the vitreomacular interface are very common in the comprehensive ophthalmologist’s and retina specialist’s practice, and they are increasing in incidence and prevalence as the population ages.
The most common occurrence at the vitreomacular interface is a posterior vitreous detachment (PVD), which, like cataract, is a natural aging change, but it also has the ability to negatively affect visual function. A PVD is present at autopsy in 75% of patients at age 65 years and 86% of patients at age 90 years. It is more common in the myope.
An epiretinal membrane (ERM), first described by Iwanoff in 1865, is a common lesion. It has also been described as a macular pucker, preretinal membrane, cellophane maculopathy, surface wrinkling retinopathy and premacular fibrosis. An ERM is associated with inflammation and proliferation of glial cells at the vitreomacular interface. It is nearly always associated with a vitreomacular adhesion (VMA) and may be associated with vitreomacular traction (VMT).
In a VMA, the vitreous adheres to the macula in an abnormally strong way. VMT is a VMA with further proliferation of fibroglial tissue and myofibroblasts, resulting in active traction on the internal limiting membrane (ILM) of the macula. VMA with VMT is associated with 84% of macular holes, which can be visually devastating. VMA with VMT can also result in macular edema or retinoschisis.
Macular holes were originally described by Knapp in 1869. Macular holes were classically described as idiopathic in 80% of cases and secondary to trauma, inflammation and the like in 20%. Newer thinking suggests that the 80% of cases once described as idiopathic are really secondary to VMA combined with VMT. Macular holes are classically staged according the work of Gass. Stage 1 is basically VMA with VMT but still an intact macular ILM, stage 2 a partial-thickness hole, stage 3 a full-thickness hole, and stage 4 a full-thickness hole with a PVD and Weiss ring. Macular hole size is now included in many classification schemes, and optical coherence tomography has resulted in an extraordinary advance in our understanding of what is happening anatomically at the vitreomacular interface. It is, however, worth an additional moment of review to look at this critical area at the histological level, which I found significantly enhanced my understanding of these entities.
The ILM is the boundary between the retina and vitreous body. It is formed by astrocytes and the endfeet of the Müller cells, which are both glial cells and capable of undergoing fibrous metaplasia into fibroblasts or myofibroblasts, which helps explain the development of VMA and VMT. The ILM is also separated from the vitreous by a thin basal lamina in the normal young eye. The vitreous is 98% to 99% water, as compared to 70% to 74% in the cornea, resulting in a transparent, colorless space for the transmission of light. It is embryologically produced by nonpigmented ciliary epithelium. Vitreous contains hyaluronic acid and a network of collagen type 2 fibers, a wide array of proteins and hyalocytes. It is a gel when young and healthy, and its viscosity is two to four times that of water. The collagen fibers when young are held apart by electrical charges. With age, these charges are reduced, and the fibers tend to clump together as the gel liquefies in a process called vitreous syneresis. Inflammatory cells, as well as wandering glial cells, retinal pigment epithelial cells, macrophages, fibrocytes and laminocytes, can also be found in the vitreous and may congregate at the vitreomacular interface. Cellular proliferation is exaggerated in many disease states associated with inflammation and after trauma.
The junction between the macular ILM and the vitreous is fertile ground for the development of a more strongly adherent VMA, which can progress to VMT and a plethora of pathology. If the VMA is not too strong, it spontaneously resolves through formation of a PVD, but if too strong, a macular hole or hemorrhage can result. Amazing to me is that so much can be going on in these few microns at the vitreomacular interface, with potential for serious impact on our patients’ visual function and quality of life.
Advances in diagnostics such as OCT, advances in therapy such as ocriplasmin and ever more precise surgical interventions are improving the prognosis every year for our patients with pathology at the vitreomacular interface. Ophthalmology practice is not without its daily challenges and moments of frustration, but our increasing ability to understand, diagnose and treat once-blinding diseases such as macular hole is something special and worthy of praise.