Retinal displacement following rhegmatogenous retinal detachment repair is a phenomenon in which the retina shifts from its anatomical position relative to the retinal pigment epithelium (RPE) after surgery for rhegmatogenous retinal detachment.
It was first reported by Shiraga et al. in 2010. With the widespread use of fundus autofluorescence (FAF) imaging, awareness has increased, and it has become clear that retinal displacement relative to the RPE causes metamorphopsia and aniseikonia.
Even if the retina is anatomically reattached after surgery, if the correspondence between the photoreceptors in the macula and the RPE is shifted, metamorphopsia, distortion, and aniseikonia may persist. This displacement is visualized as hyperautofluorescent lines (retinal vessel prints; RVPs) on fundus autofluorescence. RVPs are “imprints” of pigment distribution left by retinal vessels on the RPE, and the positional shift from the current retinal vessels is used as an indicator of displacement.
QWhy does metamorphopsia persist even after successful surgery for rhegmatogenous retinal detachment?
A
Even if the retina is anatomically reattached, if the retina is displaced relative to the RPE, the correspondence between macular photoreceptors and the RPE is disrupted, leading to persistent metamorphopsia and aniseikonia. Fundus autofluorescence imaging can objectively assess this displacement by detecting RVPs (hyperautofluorescent lines).
The following symptoms may be observed when postoperative visual function improvement is insufficient.
Metamorphopsia: A condition in which straight lines appear wavy or objects appear distorted. If it appears or persists after surgery, involvement of retinal displacement should be suspected.
Aniseikonia: A condition in which the size or shape of objects appears different between the two eyes. It is one of the frequently reported complaints after rhegmatogenous retinal detachment repair.
Macropsia/Micropsia: Objects appear larger (macropsia) or smaller (micropsia) than they actually are. This occurs due to retinal stretching, contraction, or displacement.
Decreased visual acuity: Visual acuity may decrease due to macular displacement or associated lesions (e.g., epiretinal membrane).
High autofluorescence lines (RVPs): Fundus autofluorescence imaging reveals hyperautofluorescent lines corresponding to the previous retinal vessel locations. The discrepancy from the current retinal vessel positions indicates the degree of displacement. 2)
Detection principle of RVPs: Short-wavelength light (488 nm) excites lipofuscin in the RPE. Lipofuscin is normally shielded by retinal vessels, resulting in hypoautofluorescence, but when the retina is displaced, the previous vessel locations remain as relative hyperautofluorescence. 2)
Fundus and Morphological Findings
Retinal folds: Fine folds on the retinal surface may be observed postoperatively. This is one of the findings suggesting the presence of displacement.
Epiretinal membrane: It is frequently associated with displacement and can be an additional factor for decreased visual acuity and metamorphopsia.
Residual subretinal fluid (SRF): A small amount of SRF may remain in the early postoperative period. It can cause symptoms independent of displacement.
Quantitative Assessment
M-CHARTS: Used for quantitative assessment of metamorphopsia. The minimum separation distance of dot arrays (M-score) quantifies the degree of metamorphopsia.
PHP (Preferred Hyperacuity Perimeter): A device for automated quantitative assessment of metamorphopsia in the macular area.
VR (Visual Reality) technology: A latest evaluation method applied for quantitative assessment of aniseikonia.
QWhat is fundus autofluorescence (FAF) imaging?
A
Fundus autofluorescence imaging is a non-invasive test that uses the autofluorescence of lipofuscin in the retinal pigment epithelium (RPE). Short-wavelength light (488 nm) is used to excite and capture fluorescence emitted from the RPE. 2) In retinal displacement, characteristic hyperfluorescent lines (RVPs) corresponding to the course of old retinal vessels are observed.
Macula-off rhegmatogenous retinal detachment: Cases where the macula is involved in the detachment are prone to displacement. This is thought to be due to the disruption of the positional relationship between the photoreceptors and the RPE during detachment.
Retinal detachment extent of 1 quadrant or more: The larger the detachment area, the greater the tendency for postoperative displacement.
PPV (pars plana vitrectomy): Displacement is more common after PPV compared to scleral buckling. PPV often uses gas tamponade, and the buoyancy and interfacial tension of the tamponade are thought to be involved.
Gas tamponade: Expanding gases such as SF6 (sulfur hexafluoride) or C3F8 (perfluoropropane) are used. The buoyancy and interfacial tension of the tamponade may act to slide the retina against the RPE. 3)
Detection of hyperautofluorescent lines (RVPs) using fundus autofluorescence (with a green laser scanning laser ophthalmoscope) is central to diagnosis. 2)
Imaging is performed by exciting lipofuscin in the RPE with 488 nm short-wavelength light. Normally, vascular projections on the RPE appear hypoautofluorescent. When the retina is displaced, the old vascular projections (RVPs) remaining on the RPE and the current retinal vessel positions are imaged with a shift. The direction and amount of this shift correspond to the direction and degree of displacement. 2)
Epiretinal membrane: Confirmed by OCT as a preretinal membrane. One of the most common complications causing metamorphopsia. May also be associated with distortion.
Recurrent rhegmatogenous retinal detachment: Check for detachment using fundus examination and OCT.
Residual subretinal fluid: A small amount of SRF may remain in the early postoperative period. Distinguish by checking the displacement pattern on fundus autofluorescence.
PVR (proliferative vitreoretinopathy): Tractional changes due to epiretinal and subretinal proliferative membranes. Differentiate with OCT and fundus findings.
QHow to differentiate between epiretinal membrane and retinal displacement?
A
Both can cause metamorphopsia, but retinal displacement is characteristically visualized as a shift of RVPs (hyperautofluorescent lines) on fundus autofluorescence. Epiretinal membrane is seen as a hyperreflective membrane on the retinal surface on OCT. Since both may coexist, it is desirable to evaluate using a combination of fundus autofluorescence and OCT.
Currently, there is no established treatment for retinal displacement itself. The treatment strategy is determined by the degree of displacement and the presence of associated lesions.
If the displacement is mild and has little impact on visual function, observation is the basic approach. In some cases, spontaneous improvement may be expected over time after surgery.
If there are associated lesions due to displacement, treatment for each condition should be considered.
Cases with epiretinal membrane: If visual acuity loss and metamorphopsia are severe, consider vitrectomy to remove the epiretinal membrane. However, the invasiveness of the surgery itself must also be considered.
Residual subretinal fluid: Most cases resolve spontaneously, but if it persists, investigate the cause and consider additional treatment.
Cases with PVR: For retinal deformation due to traction from proliferative membranes, PPV with membrane peeling may be required.
Retinal displacement after PPV with gas tamponade is thought to be caused by the physical effects of the tamponade agent.
Two important mechanisms of gas tamponade are interfacial tension and buoyancy. 3) Intraocular gas presses against the retina at the posterior pole, while laterally and inferiorly, buoyancy forces lift the retina. This is theorized to cause slippage of the retina relative to the RPE.
As characteristics of expansive gases, SF6 (sulfur hexafluoride) expands to about twice its volume within 24 hours after injection and is absorbed over 2-3 weeks. C3F8 (perfluoropropane) expands to about four times its volume within 72 hours and persists for 6-8 weeks. Air persists for several days. 1) During the expansion and absorption process, the dynamics of the tamponade interface change, and retinal displacement is thought to occur during this period.
Silicone oil (SO) allows long-term tamponade, but some reports indicate poorer outcomes for retinal displacement compared to gas. 1) Differences in the physical properties (density, interfacial tension) of SO may affect the pattern of displacement.
Retinal displacement is thought to occur most commonly as inferior displacement. Postoperative positioning (face-down) and the location of gas within the eye are believed to influence the direction of displacement.
Computer simulation analyses have been used to study the relationship between the physical effects of tamponade and the direction of retinal displacement. Simulations contribute to understanding the mechanism of displacement and improving surgical techniques.
Retinal vessels leave subtle structural influences on the RPE related to oxygen and metabolic waste transport. When the retina is displaced, pigment changes corresponding to the former vessel positions (RVPs) remain on the RPE, appearing as hyperautofluorescent lines on fundus autofluorescence. 2) This phenomenon enables non-invasive detection of displacement after rhegmatogenous retinal detachment surgery.
7. Latest Research and Future Perspectives (Reports at Research Stage)
Research is ongoing on the possibility that maintaining a prone (face-down) position after PPV may reduce retinal displacement. While some reports indicate less displacement in groups that strictly adhered to prone positioning, the effect is not consistent. Establishing an optimal postoperative positioning protocol remains a challenge.
Studies are being conducted to compare the impact of tamponade material choice on the incidence and severity of retinal displacement. 1) The effects of different gas types (air, SF6, C3F8) and concentrations on displacement are also being investigated.
Development of quantitative evaluation methods for aniseikonia using Virtual Reality (VR) technology is progressing. It is expected to serve as an objective assessment tool to replace conventional M-CHARTS and PHP, with potential applications in monitoring retinal displacement and evaluating treatment outcomes.
Research is advancing to analyze the relationship between the physical effects of tamponade and retinal displacement using computer simulations. Numerical analysis combining variables such as eye shape, gas volume, and body position is expected to provide a quantitative understanding of the displacement mechanism and optimize surgical techniques.
