Discussion
Here, we presented our findings from a systematic review and meta-analysis on estimates of sensitivity and specificity of teleretinal screening for detection of DR and AMD when compared with face-to-face clinical examination as the real-world reference standard.17 18 We found that teleretinal screening achieved a high accuracy for detection of any DR with a sensitivity of 0.91 (95% CI: 0.82 to 0.96) and specificity of 0.88 (95% CI: 0.74 to 0.95) and referrable DR with a sensitivity of 0.88 (95% CI: 0.81 to 0.93) and specificity of 0.86 (95% CI: 0.79 to 0.90).
Our results are in keeping with a recent review, which showed that teleretinal screening can achieve very high accuracy with a sensitivity of 0.84 (95% CI: 0.79 to 0.88) and specificity of 0.95 (95% CI: 0.94 to 0.96) for detection of any level of DR.7 27 Based on our findings, data on AMD are limited but the diagnostic accuracy was calculated to be lower with a sensitivity of 0.71 (95% CI: 0.49 to 0.86) and specificity of 0.88 (95% CI: 0.85 to 0.90). The diagnostic accuracy teleretinal screening has been previously characterised at specific levels of DR severity; however, data on the overall accuracy for detection of referrable cases have not been consistently reported. Another review estimated a sensitivity of 0.76 (0.69 to 0.82) and specificity of 0.95 (0.93 to 0.96) for detection of DMO.8 In our study, we also noted a lower level of accuracy for detection of DMO and referrable DR in comparison to any DR.
Given that the previous reviews to date on this topic have typically excluded ungradable images from their analysis, our sensitivity analysis with the exclusion of ungradable images showcases a cautionary message for future investigators. In fact, the specificity of fundus imaging for identification of referral-warranted DR improved by nearly 10% after ungradable images were removed from analysis. This observation is expected and can be explained by spectrum effect, whereby systematic removal of a patient subgroup, such as difficult to diagnose cases with media or corneal opacity, leads to an easier diagnosis and detection of referrable and non-referrable cases.28
Based on our findings, evidence in support of implementation of teleretinal screening for detection of AMD was limited in comparison to DR. Only three studies provided diagnostic accuracy data for detection of any AMD.17 19 29 Although these results are encouraging, with an overall sensitivity of 0.71, more research is required to establish a role for fundus imaging for diagnosis and treatment of patients with AMD. One strategy to generate more diagnostic accuracy data for AMD detection is to implement AMD detection into the already existing teleretinal screening infrastructure for DR. If teleretinal screening proves to be a highly accurate tool within the structure of the pre-existing teleophthalmology programmes, further emphasis may be placed on detection of AMD.
The role of OCT for diagnosis and monitoring of retinal disorders is well established.30 However, whether its incorporation into teleophthalmology screening programmes is beneficial remains controversial.17 Only one study in this systematic review provided a direct comparison in the diagnostic accuracy of fundus photography combined with OCT and fundus photography alone.17 In the paper by Maa et al, despite the detailed cross-sectional analysis of the macula, optic nerve head and retinal nerve fibre layer that is provided in OCT scans, the authors did not detect any improvement in sensitivity or specificity of fundus photography for the detection of glaucoma and retinal disorders with the addition of OCT.17 In contrast to these results, other groups have clearly demonstrated a role for OCT in addition to fundus photographs, especially for the detection of diabetic macula oedema which requires a stereoscopic view.31–35 In the current meta-analysis, only a fraction of the studies used OCT alone or as an adjunct modality in addition to fundus photographs and we were unable to perform a formal meta-regression. Due to widespread use of OCT as well as recent advances in OCT technology such as swept-source OCT and OCT angiography, it is inevitable that more data will become available in the near future.36
Meta-regression based on pupil status showed a sizeable improvement in diagnostic accuracy when eyes were dilated prior to capturing of the image which approached statistical significance. Although we are unable to identify the exact reason behind this observation, it can be hypothesised that a larger pupil diameter allows for increased capture of light by the camera and therefore generates a higher quality image.7 This finding should be verified in different ethnic groups as well as in individuals with difference in iris colour which could elicit different levels of response to pharmacological dilation.37
Limitations and future directions
It is important to note that there is a large degree of heterogeneity in the diagnostic criteria for referrable DR and AMD. Additionally, there is also a large degree of heterogeneity in the sample including patients with type I and II diabetes of differing durations. Similar to all review papers, publication bias may be present whereby studies that achieve high diagnostic accuracy are preferentially published in comparison to studies where the accuracy is lower which could lead to an overestimation of sensitivity and specificity. Our study results are only applicable to teleretinal programmes using human graders. Recent diagnostic test accuracy meta-analyses have provided very promising accuracy estimates for machine-learning-based teleretinal screening programmes for DR.38 39 Future studies should assess the diagnostic accuracy of automated systems using artificial intelligence and deep-learning algorithms in teleophthalmology screening programmes for ocular diseases.40 Lastly, the focus of this review was on teleretinal screening for the most common retinal pathologies. As more data become available, future investigations should assess the utility of teleglaucoma screening programmes.41