Discussion

The photoreceptors have enormous metabolic needs that are met only by their close apposition to the retinal pigment epithelium (RPE) and the choroidal circulation. During RD, the outer retina is separated from the RPE and choroid leading to major metabolic derangements at least in part due to hypoxia.6 7 In experimental models of RD, these metabolic derangements result in photoreceptor apoptosis, particularly among cones, that begins during the first day and peaks by day 3.8–11 Within just a week after the detachment, the outer segment layer is reduced to approximately 10% of its normal width with complete loss of cone-specific cellular markers.12

Given the progressive photoreceptor damage that occurs in animals during the first week of a RD, it is surprising that clinical studies have not demonstrated a strong relationship between detachment duration and VA outcomes for detachments of up to 5–7 days in duration. In 1982, Burton4 reported on a series of patients who had undergone scleral bucking for repair of RD, and showed better VA outcomes resulted when surgery was performed within the first 5 days. In 1998, Ross and Kozy published a prospective study of patients undergoing scleral buckling for macula-off RD and concluded that delay of repair for up to 7 days does not negatively affect visual outcome.13 Subsequently, several other groups have reported similar findings that delays in repair of macula-off RD with scleral buckle up to 6–10 days provided similar VA outcomes.14–16 However, in 2009, Henrich et al published results with scleral buckling in macula-off detachments and suggested a much shorter interval of 3 days should be used for the optimal timing of repair.17 One reason why it may be hard to find a difference in the first 5–7 days with scleral buckling alone is because at the end of a scleral buckle, the macula is rarely attached, even with drainage. This adds a source of variability if the DMD is the primary driver of eventual vision outcomes. For this reason, we excluded patients from our study who underwent scleral buckling alone.

In 2013, Kim et al reported optimal results of vitrectomy for macula-off RD occur within the first 6 days, and a similar study by Kikushima et al in vitrectomy patients suggested repair within the first 10 days.18 19 Interestingly, in Kikushima et al’s study, the number of patients who achieved 20/40 or better vision after 2 days significantly decreased, although no significant decrease in visual prognosis was found with delay of surgery up to 10 days.18

One universal finding among these studies is the large variation in final VA that is observed after repair of macula-off detachments, which cannot be solely attributed to preoperative characteristics, surgical timing or the choice of surgery. This large variation in final VA may in part be explained by histopathological findings of non-uniform photoreceptor damage that occurs after RD.12 20 When focal areas of damage occur subfoveally, VA can be severely compromised, but if the subfoveal region is spared, VA can be preserved.21–23 Such variation may make it difficult to identify clear effects of detachment duration on final visual outcomes without large numbers of patients undergoing similar types of interventions. Overbinning patients during statistical analysis can further mask clinically significant effects by reducing the number of patients in each group.

Our study sought to directly address the issues encountered in these other studies. We restricted our inclusion criteria to only include patients who underwent primary vitrectomy or combined vitrectomy scleral buckle in which subretinal fluid was drained leaving the macula effectively attached at the end of the case. To determine appropriate bin size, we used the meta-analysis performed by van Bussel et al,⁵which we consider the most extensive analysis of timing of repair for macula-off RD. In this study, macula-off detachments of 3 days or less in duration had better VA outcomes than detachments of 4–7 days in duration. To date, there have been no studies that have found that surgical intervention within the first 3 days of a macula-off detachment affects final VA. To avoid overbinning, while still addressing the question of whether surgical timing is important during the first 3 days, we a priori separated eyes into two groups, those that were repaired within 3 days and those that were repaired within 4–7 days. The expected result based on existing literature of this binning strategy was that DMD would not affect VA outcomes in either the group of 3 days or less or the group of 4–7 days.

We found that even for detachments repaired within 3 days, the DMD was correlated with the final VA, independent of preoperative VA, lens status, age and surgeon. Consistent with previous reports, we also found that better preoperative VA and pseudophakia at final follow-up were associated with better final VA.

There are several potential confounding factors that may have affected our results. First, our study was retrospective and we did not have information on the height of RD at the time of presentation. This is a major weakness since detachment height has been linked to final VA outcomes, independent of detachment duration.3 It is possible that the distribution of detachment heights across patients having detachments of 3 days or less was asymmetric and may have compromised our findings.

A second factor that could have affected our results is the accuracy of dating DMD. We used the patient’s reported loss of central vision as a marker for foveal detachment; however, non-retinal causes of central acuity reduction, such as a Weiss ring or vitreous haemorrhage may have caused the decrease in VA. While none of the patients in our study had vitreous haemorrhages obscuring the macula, significant floaters may not have been documented and the distinction between visual loss from vitreous debris versus macular involvement may not have been properly assessed. We also cannot rule out the possibility that some patients had detachments for durations longer than their perceived reductions in central acuity. Of note, accurate dating of macular detachment is a limitation faced by all prior studies on surgical timing of macula-off detachments.4 5

Finally, due to the retrospective nature of the study, there was a wide range in the follow-up duration. Although follow-up was added to our generalised linear model and showed no statistically relationship with VA outcomes, longer follow-up for some patients would have been preferred given the slow recovery that can be observed after RD.

Despite these weaknesses, our study does indicate that shorter DMD is associated with better final VA even among patients whose detachment is ≤3 days. These findings are consistent with our current understanding of progressive photoreceptor damage that begins within 24 hours of RD and can be halted with retinal reattachment.8 Based on these results, interventions that shorten the duration of the macula-off RD, including those occurring within the first 3 days, may result in improved long-term VA outcomes.