Discussion

OCT has become the standard of care for diagnosing a variety of ocular pathologies, but is generally not available at most institutions after-hours, when many patients present with acute complaints. This study demonstrated the several advantages of having an OCT for diagnosis and management of acute complaints and of ocular emergencies.

In the after-hours or acute-care setting, the most important goal of care is the timely diagnosis and treatment of vision threatening pathology while efficiently using ancillary testing and consultants. For example, timely diagnosis of central retinal artery occlusion (CRAO) is critical for proper ophthalmic and medical management. However, fundus examination alone may fail to reveal a cherry red spot or retinal opacification in up to 10% or 42% cases of CRAO, respectively. OCT provides much higher sensitivity for detection of ischaemia in acute CRAOs.5 6 Our study included six patients with CRAO, and OCT successfully confirmed the diagnosis in five of those patients. In one patient, poor visual acuity prevented adequate fixation to obtain a useful image. As shown in figure 1, the OCT demonstrated characteristic hyper-reflectivity and obscuration of internal retinal layers in a case of CRAO. In the emergency setting, where fluorescein angiography is usually unavailable, OCT helps provide early objective confirmation of this diagnosis. OCT may be particularly helpful in subtle cases without characteristic fundus findings in the absence of severe visual loss. For example, a 60-year-old woman presented with decreased vision for 1 week in her left eye. Her visual acuity in the left eye was 20/640, pinhole to 20/50. Funduscopy revealed mild thickening in the nasal macula. OCT of the macula showed inner retinal hyper-reflectivity with loss of definition of individual retinal layers, which suggested a diagnosis of recent CRAO (figure 1); the patient was transferred to the emergency room for cardiovascular workup. We have also found it helpful to have OCT documentation of CRAO at the time of urgent care visit as clinical picture may be different by time of follow-up visit; for instance, the retina may reperfuse by the time the patient is seen by a retina attending during normal business hours. While there is no treatment with proven efficacy in reperfusion of the retina, many institutions, including ours, offer intervention to patients such as ocular massage, intraocular pressure lowering, carbogen inhalation with varying degrees of success.7 8 All CRAO patients require transfer to a hospital for systemic workup. Additionally, for patients presenting within the safe therapeutic window, our institution offers intra-arterial thrombolytic therapy with tissue plasminogen activator through interventional neuroradiology. Immediate OCT allows us to confirm the diagnosis for rapid triage in appropriate cases.

OCT was also helpful in identifying other retinal pathology necessitating prompt evaluation and treatment by retina specialists with urgent retina clinic referral. For example, a 64-year-old woman who complained of distorted vision was found to have a small haemorrhage in the nasal macula on funduscopic examination. OCT of the macula revealed subretinal haemorrhage and exudate consistent with a choroidal neovascular membrane (figure 2). The patient was referred to retina clinic where fluorescein angiogram revealed leakage consistent with choroidal neovascularisation, for which prompt anti-vascular endothelial growth factor (VEGF) therapy was initiated. Four other cases of new choroidal-neovascularisation were identified with OCT. The OCT proved invaluable in our after-hours clinic following the solar eclipse of 2017. The OCT ruled out solar retinopathy in most patients (n=9), reassuring the patients and precluding the need for retina clinic referral. The OCT also confirmed solar retinopathy in two patients (figure 3). Another example of the OCT’s utility is the case of a man who presented with metamorphopsia and was referred for neurological workup after OCT confirmed lack of macular pathology; he was found to have optic neuritis and brain lesions consistent with multiple sclerosis.

As macular/foveal involvement is a critical factor for planning timing of surgical intervention and predicting visual prognosis following RD, OCT was a valuable adjunct to clinical examination.9–11 OCT was used to differentiate macular-involving versus macular-sparing RD in 39 (19%) patients. figure 4 demonstrates a narrowly fovea-sparing RD, a level of detail often not determinable on clinical examination; the patient was taken for urgent retinal detachment repair. In another case, despite the patient’s best corrected visual acuity of 20/40, OCT showed a partial foveal involving retinal detachment, aiding in surgical planning and patient counselling regarding the prognosis (figure 5). In cases of macula-off retinal detachments, the OCT provides objective documentation. As most ophthalmic lawsuits in the USA relate to RD, such documentation substantiates the appropriateness of care in the after-hours setting.12 This documentation may be relevant to several diagnoses, including CRAO or choroidal neovascularisation as discussed above.

The OCT is also helpful in ruling-out emergent pathology, thus helping refine triage of patients to subspecialty clinics in our hospital and reducing need for after-hours subspecialty consults. For example, patients with suspected CSR were generally given follow-up appointments in the retina clinic within a week of presentation prior to the availability of OCT. Our study included 14 patients with CSR (7%), as shown in figure 6. With OCT verification, follow-up appointments could be extended to 3 weeks without fear of occult choroidal neovascular membranes. Furthermore, OCT has been shown to be more sensitive for detecting CSR than slit-lamp examination, and likely aids in detecting cases that would otherwise be temporised.13 In our study, the majority of patients had normal findings (56, 28%), demonstrating its utility in ruling out pathology. For example, a patient who reported a history of contralateral CSR complained of visual disturbance; without OCT verification of flat maculae, the patient would have likely been referred to retina clinic rather than neuro-ophthalmology. In three patients with a history of anterior uveitis, including a child, and a complaint of blurry vision or metamorphopsia, OCT was used to rule out cystoid macular edema (CME); without OCT availably, these patients would have been brought back for urgent imaging. The OCT was also used to document absence of pathology in patients referred from outside ophthalmologists and optometrists for neuro-ophthalmic diagnoses such as optic nerve head oedema.

The OCT may also improve patient satisfaction. Bed-side ultrasonography has been shown to improve patient satisfaction, likely due to expedited care and diagnosis.14 As discussed above, OCT allowed residents to show patients OCT images, explain the course and prognosis of CSR, reassuring the patient while offering a practical follow-up appointment. In the many cases where pathology was ruled out by the OCT, the patient left our institution having undergone state of the art imaging to assuage their concerns rather than with continued anxiety until such imaging could be obtained. While this study did not survey patients, almost all practitioners perceived enhanced patient satisfaction in connection to the OCT.

OCT in our after-hours clinic also benefited our clinicians in training. Most residents and fellows felt that the OCT reduced their stress levels. Uncertainty has been correlated with physician stress.15 Having an instrument as sensitive as OCT accessible to rule out subtle pathology removes a significant degree of uncertainty. For instance, when a resident calls a retina fellow describing a macula sparing retinal detachment, the OCT substantiates that the macula is not involved. Additionally, the OCT was felt to reduce medical errors by most residents. Medical errors cause both short-term and long-term emotional stress in residents.16–20 The benefit of reducing stress and medical errors is more likely to be found in residents early in their training; this was corroborated by the survey results as a larger proportion of first year residents found stress reduction in connection to the OCT than did second year residents or fellows. We believe that as clinical examination skills improve, the scope of pathology necessitating ancillary imaging narrows.

While we analysed utilisation of OCT in an eye-only emergency setting, OCT can be expanded to the general emergency department setting. Bruce et al demonstrated the benefit of non-mydriatic fundus photos to augment the poor ophthalmoscopy by emergency physicians.2–4 Similarly, Baker et al demonstrated that ocular ultrasounds performed by emergency physicians can aid in accurate diagnoses of RD by non-ophthalmology medical professionals.1 Our findings suggest that OCT can augment fundus photography in the emergency setting. Furthermore, these imaging modalities can be used in underserved areas to address ophthalmic emergencies in areas where ophthalmologists are unavailable. In fact, technology to remotely control OCT is under development.21 We believe that the automated OCT used in this study, which has voice direction for patient fixation in multiple language options, would be operable by emergency department staff after minimal training. Although trauma cases were not well represented in our sample, OCT has been shown to aid in the identification of globe perforation and may aid in ruling out such injuries in the emergency setting.22

One limitation of this device is the minimum vision requirement necessary for patients to find fixation cues without operator redirection. A small number of attempted scans had insufficient signal strength, all in patients with visual acuity 20/400 or worse. As the automated OCT required some fixation ability on the target, severely decreased visual acuity prevented adequate alignment. While this OCT allows for manual adjustment, this can be time consuming and may require an operator with greater skill and experience. Most manual OCT devices such as Zeiss Cirrus or Spectralis can obtain quality OCT images in patients without optimal fixation, but require more training, skill or experience for successful imaging. By comparison, technical training required to use this device was very brief making it more easily available to residents with limited imaging experience. W The option to use the fellow eye for fixation limitation could be helpful in cases requiring manual override.

In conclusion, OCT accessibility in the after-hours setting improved the diagnosis and disposition of patients. Residents and fellows reported that the availability of the OCT changed clinical management, improved patient satisfaction and reduced practitioner stress. Additional studies will be helpful to further appreciate the benefits of including OCT alongside clinical examination in both eye-only and general emergency settings.