Persistent subfoveal fluid following successful macular hole surgery

In short: The presence of subretinal fluid following successful macular hole surgery appears to be common, and may be associated with delayed visual recovery, although not with the final result. Smaller holes and vitreofoveal traction are significant risk factors associated with increased rates of postoperative foveal detachment.

By Paris Tranos PhD, ICO, FRCS; Evangelos Lokovitis, PhD, Anastasios G.P. Konstas, PhD

Advances in vitreoretinal surgery and modifications in the techniques of macular hole repair have resulted in almost 100% anatomical success rates.^1,2 However, functional outcomes have not kept pace with anatomical developments. The introduction of spectral domain optical coherence tomography has facilitated detailed investigation of macular morphologic features, providing information on prognosticators of the outcome of macular hole surgery.^3,4

Delayed functional recovery after successful pars plana vitrectomy for full thickness macular hole (FTMH) correlates with postoperative disruption of the external limiting membrane and photoreceptor ellipsoid zone as well as persistence of subretinal fluid (SRF). The latter, also referred as outer retinal defect (ORD),^5–10 is a relatively common complication that results from the underlying healing process following macular hole surgery.

Subretinal fluid

There is controversy about the precise impact of postoperative SRF in terms of final visual outcome. Herbert et al.¹¹ found ORDs with SRF in 7 out of 16 eyes that underwent successful macular surgery and the defects were not associated with worse outcome or longer duration of symptoms. On the contrary, Takahashi et al.8 observed that those of their successfully closed macular holes that had SRF (44%) were associated with delayed visual recovery. Further, Christensen et al.⁷ reported that 36% of cases had postoperative SRF after 3 months, which disappeared at 12 months in the majority of cases (93%).

Recently published, Tranos et al.¹² have investigated the characteristics of postoperative foveal detachment following successful macular hole surgery. The frequency and natural course of this finding were assessed and its relevance to early visual recovery was examined. Moreover, for the first time, preoperative risk factors associated with a higher rate of subfoveal fluid despite restoration of the inner retina contour after successful macular hole repair were identified.

The authors reported that 48% of the successfully closed macular holes exhibited SRF during the early postoperative period, which was gradually absorbed in most cases (73%) during a follow-up period of 7 months. The rate of SRF absorption is likely to be underestimated because it has been documented that foveal morphology continues to improve for up to 12 months following surgery.⁷ The majority of foveal detachments resolved 3 to 5 months after surgery, in contrast to previous reports demonstrating more rapid absorption of SRF.¹⁰

The clinical significance of ORDs following successful macular hole surgery has also been addressed. ORDs are associated with reduced visual acuity and consequently there is an improvement of visual acuity upon their resolution. However, the development of postoperative SRF does not lead to a different final visual outcome compared with eyes without this complication.^5,6,7 Therefore, although ORDs may temporarily compromise vision and result in delayed visual recovery, they do not appear to have a lasting or meaningful effect upon final visual outcome.

The nature of the fluid within the ORDs has not been identified. One study, based on analysis of SRF aspirated in vivo during vitrectomy for macular hole, revealed the presence of macrophages and photoreceptors and concluded that the loss of photoreceptors may correlate with reduced retinal function.11 It was also postulated that the occurrence of viscous fluid may delay the flattening of the hole; however, no controlled evidence was offered to support this suggestion.

Preoperative risk factors

Recently, research has focused on the identification of preoperative risk factors for SRF following successful macular hole surgery.¹² Published reports have demonstrated that postoperative foveal detachment is independent of patients’ demographics or intraoperative parameters including the size of sclerotomy, application of retinopexy, peeling of coexisting epiretinal membrane and type of endotamponade. In contrast, stage 2 macular holes and posterior vitreous attachment at the edge of the macular hole (Figures 1 and 2) were significant risk factors for development of postoperative ORD. Both seem to represent an early stage in the natural history of a macular hole, implying that newer holes may be more prone to developing ORDs in the early postoperative period.

The third prognostic factor identified in the same study was the diameter of the macular hole. The smaller the hole, the more prone the eyes were to develop postoperative SRF. Previous studies have suggested that bridging of the inner neurosensorial tissue mimicking a foveal detachment is the initial step in macular hole closure, followed by proliferation of glial cells causing re-approximation of the normal photoreceptors to the central fovea.^3,6,14 The fact that foveal detachment was noticed more frequently in smaller holes of shorter duration may indicate that the morphological features of macular hole closure, which traditionally have been thought to depend mainly on macular hole stage and size, may involve other, as yet unidentified, healing parameters.

Considering the predisposing factors described above, with the introduction of ocriplasmin in the management of FTMHs measuring less than 400 mm,¹⁵ ORDs may be encountered more often than before because the treated FTMHs will be of an earlier stage. This might be a point of interest in the near future with the advancing use of pharmacologic vitreolysis for the treatment of idiopathic FTMH.

Conclusion

In conclusion, the presence of SRF following successful macular hole surgery appears to be common, and may be associated with delayed visual recovery. Smaller holes and vitreofoveal traction are significant risk factors associated with increased rates of postoperative foveal detachment. Although the latter is characterized by a relatively benign course, future controlled studies are required to clarify the impact of ORDs on photoreceptor realignment, considering that they occur more frequently in FTMHs of earlier stage with potentially better visual recovery.

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Dr Paris Tranos PhD, ICO, FRCS

OPHTHALMICA Eye Institute, Thessaloniki, Greece.

Dr Evangelos Lokovitis, PhD

OPHTHALMICA Eye Institute, Thessaloniki, Greece.

Dr Anastasios G.P. Konstas, PhD

OPHTHALMICA Eye Institute, Thessaloniki, Greece. Aristotle University of Thessaloniki, Greece.