31 Degenerative Retinoschisis
31.1 Definitions and Histology
Degenerative (also called acquired or senile) retinoschisis is an acquired splitting of the retinal layers of unknown etiology. It has two subtypes, the typical form and the reticular form. In the typical form, the histological split is within the outer plexiform layer, and in the reticular form the split is within the nerve fiber layer (Fig. 31-1). 1 A gradual accumulation of viscous fluid, rich in mucopolysaccharide, occurs within the schisis cavity. As the neural pathways of the retina become damaged due to the retinoschisis, patients develop an absolute scotoma in the affected area.
Retinal breaks can occur in the inner layer, the outer layer, or both, and do not necessarily cause a rhegmatogenous retinal detachment (RRD). 2 In fact, inner layer breaks by themselves cannot lead to a retinal detachment, since there is no path for fluid to enter the subretinal space.
Two types of retinal detachment are associated with retinoschisis:
Schisis detachment: This term describes a situation where there are outer layer holes without inner layer holes, and intraschisis fluid has migrated into the subretinal space. 2
Progressive RRD associated with retinoschisis: This entity occurs when there are breaks in both the inner and outer layers, allowing liquefied vitreous to enter the subretinal space.
31.2 Clinical Features and Diagnosis
Degenerative retinoschisis can be seen in patients as young as 19 years, and the prevalence increases sharply after age 40 years. 3 It is associated with hyperopia, and occurs equally among males and females. Although it may appear in any quadrant, by far the most frequent location is the inferotemporal quadrant, followed by the superotemporal quadrant. Often, there are separate areas of involvement within the same eye that are not connected, because the disease is multicentric in origin. Bilateral involvement is present in more than 80% of cases. 2
Retinoschisis with and without breaks is almost invariably asymptomatic, even when the extent of the retinoschisis is posterior to the equator. 2 Since the subretinal fluid of schisis detachments usually does not extend beyond the borders of the retinoschisis, schisis detachments are also usually asymptomatic. Cases of schisis detachment with posterior extension of subretinal fluid may be symptomatic, but this phenomenon is rare. In contrast, progressive RRD is usually symptomatic.
Retinoschisis typically is characterized by a smooth, uniform, inward convexity of the retina (Fig. 31-2a,b). It is important to differentiate retinoschisis and peripheral subclinical retinal detachment secondary to small atrophic holes.
Retinoschisis is usually detected because of one of two findings: white lines in a vascular pattern in the inner layer, or the presence of tiny yellow-white flecks on the inner surface of the inner layer, colloquially called “snowflakes.” These “snowflakes” are thought to be remnants of Müller cell footplates and neuronal connections between the inner and outer layers. The use of indirect ophthalmoscopy combined with scleral depression is essential in making the diagnosis of retinoschisis. By this method, it should be possible to demonstrate the presence of a fluid-filled layer between the outer and inner retinal layers. A characteristic feature of retinoschisis is that, upon scleral depression, the area of schisis tends to be displaced inward as a unitary enclosed structure. This helps to differentiate it from an RRD in which scleral depression tends to decrease, and flatten, the area of elevation, as some of the subretinal fluid may escape through retinal breaks into the vitreous space. In some patients, scleral depression produces the phenomenon of “white with pressure” arising from only the outer layer, and this is a confirmatory sign of the presence of retinoschisis. Optical coherence tomography can also be a useful means of distinguishing between retinoschisis and retinal detachment (Fig. 31-3). Further, the outer layer in areas of retinoschisis will blanch with laser application, in contrast to areas of retinal detachment. 4 Table 31-1 compares the features of retinoschisis and retinal detachment.
Inner layer breaks are usually small, round, and difficult to detect (Fig. 31-4). The prevalence of outer layer breaks in eyes with retinoschisis is between 11 and 24%. 2 , 5 , 6 Outer layer breaks tend to be much larger, more posterior, and often have rolled white edges (Fig. 31-5).
Four clues pointing to a schisis detachment (Fig. 31-6) include the following:
The presence of an outer layer break.
The appearance of the schisis is not uniform in height, texture, or transparency.
There may be a curved yellowish line deep to the inner layer corresponding to the outer layer.
There may be a pigmented demarcation line in chronic cases.
Progressive RRD associated with retinoschisis is uncommon. Examination reveals opacified, corrugated retina typical of acute retinal detachment, but outer layer breaks are evident (Fig. 31-7). Inner layer breaks may be difficult to detect. 7