24 Hour Ophthalmic Emergencies Part 4 – Flashes, Floaters and Double Vision

Author: William Spackman, Adam Booth / Editor: Liz Herrievan / Codes: OptC2, OptC6, OptP1, SLO1, SLO4 / Published: 20/05/2025

Editor’s intro: This fab four-part blog has been written for us by an ophthalmology registrar. The aim is to highlight the eye conditions we ED folk should be aware of, particularly those we need to refer asap. Some of the slit-lamp examination findings described might elude some of us (me, at least) in many cases, but don’t let that put you off! I’ve also Googled some of the more unfamiliar terms so you don’t have to….

Part 1 – Acute Red Eye

Part 2 – Swollen Lids and Ocular Trauma

Part 3 – Sudden Vision Loss

Introduction

There are a limited number of true ophthalmic emergencies, but it is important for emergency clinicians to be aware of ophthalmic conditions where immediate action needs to be taken. In many of the conditions discussed in this blog, prompt recognition and management can be sight-preserving and, in certain cases, life-preserving. This blog aims to guide emergency clinicians in the assessment and management of some of the most important emergency ophthalmic presentations.

Flashes and Floaters

Another common presentation to the emergency department is patients describing flashes and floaters in their vision. These symptoms can represent anything from a benign physiological process called posterior vitreous detachment to sight-threatening problems such as vitreous haemorrhage, retinal tears and detachment.

Patients may describe floaters as black, grey, red or brown spots, lines, cobwebs, veils or flies in their vision. They drift with eye movements and are typically seen easier against lighter backgrounds. These floaters represent opacities in the vitreous cavity such as collagen aggregates or blood that cast a shadow on the retina.

Flashes or ‘photopsia’ is a visual phenomenon whereby streaks of light are perceived, usually in the temporal periphery and are vertically orientated.¹

Posterior Vitreous Detachment

Posterior vitreous detachment is a physiological process whereby the vitreous detaches from the retina. This typically occurs in patients from around the age of 50 and is a normal process. It can occur earlier in patients who are short-sighted (myopic) and may also occur following trauma.¹

Posterior vitreous detachment (PVD) may present with new flashes and floaters in one eye. It is important to enquire about a shadow or curtain in the vision and any reduction in vision as this would not typically be expected in PVD alone. Visual acuity and confrontation fields should be assessed and are usually normal.

Patients with suspected PVD should be referred urgently for detailed fundal examination. An ophthalmologist will examine the vitreous for a Weiss ring or crinkled posterior hyaloid face indicative of PVD.¹ The vitreous is examined for pigment (Shafer’s sign) that is strongly correlated with retinal tear or detachment.¹ Detailed fundal examination is important in order to exclude retinal tears or detachment, as this occurs in around 15% of eyes presenting with symptomatic PVD.¹

If there is a straightforward PVD with no retinal tears or detachment seen, then no further action is required. It is important to warn patients to re-present should they develop any change in their symptoms.

Retinal Tear

A retinal tear occurs most commonly at the time of posterior vitreous detachment. As the posterior hyaloid face detaches from the retina, it may tug on the retina causing holes or tears to form. Patients with retinal tear may present with identical symptoms to that of PVD; hence the importance of careful examination of all patients presenting with acute flashes or floaters.

A retinal tear is seen on dilated fundus examination at the slit lamp or with an indirect ophthalmoscope. Retinal tears require urgent laser retinopexy to prevent retinal detachment.

Retinal Detachment

Retinal detachment occurs most commonly in the setting of PVD and subsequent retinal tear. Liquified vitreous passes through the retinal tear causing rhegmatogenous retinal detachment.² There are other causes for retinal detachment including serous retinal detachment and tractional retinal detachments that occur in diabetic patients.³

Risk factors for retinal detachment include trauma, high myopia, previous retinal detachment, family history of retinal detachment, intraocular surgery and lattice retinal degeneration.²

In addition to flashes and floaters, patients with retinal detachment may describe a shadow or curtain in their vision. They may also have a reduction in their central visual acuity if the macula has detached. These patients may have a demonstrable visual field defect in the area corresponding with the retinal detachment. Patients with symptoms suggestive of retinal detachment should be referred immediately.

Rhegmatogenous retinal detachment (the commonest type, due to a break or tear in the retina) generally requires surgical intervention. This may be with a scleral buckle, pneumatic retinopexy or most commonly, pars plana vitrectomy (PPV) with laser and insertion of gas/silicone oil.²

Vitreous Haemorrhage

Vitreous haemorrhage occurs when blood collects within the vitreous gel or sub-hyaloid space. This can occur for a number of reasons but is most commonly due to proliferative diabetic retinopathy, retinal tear, detachment or trauma.³

Patient typically present with new onset floaters. The degree of visual impairment is dependent on the amount of blood and where it is sitting within the vitreous space.

Patients should be referred urgently and examined by an ophthalmologist to identify the cause of the vitreous haemorrhage. B-Scan ultrasound may be required to visualise the fundus. Vitreous haemorrhage should be assumed to be caused by retinal tear or detachment unless there is evidence of an alternative cause such as proliferative diabetic retinopathy.

Management of vitreous haemorrhage primarily involves treating the underlying cause. In patients with proliferative diabetic retinopathy for example, one may opt to allow a vitreous haemorrhage to settle spontaneously and then perform PRP laser when there is adequate view.³ Where a retinal tear or detachment is suspected or the underlying cause is not known, the patient may have an emergency PPV to clear the blood and facilitate examination and treatment of any retinal pathology causing the bleed.

Other Causes

Other causes of floaters include:

• Intermediate Uveitis
• Lymphoma
• Asteroid Hyalosis
• Synchisis Scintillans
• Vitreous Syneresis

Double Vision

Double vision can be a challenging presentation to decipher. To the emergency clinician, it is important to be able to identify the life and sight threatening causes of double vision.

This section focuses on binocular diplopia as a result of cranial nerves 3,4 and 6 palsies as the differential diagnosis for binocular diplopia is vast. Other causes of acute binocular diplopia to consider include myasthenia gravis, thyroid eye disease, trauma and giant cell arteritis.

3^rd Cranial Nerve Palsy (Oculomotor Nerve)

A 3^rd nerve palsy is probably the most significant cause of binocular diplopia as it may be caused by a life-threatening posterior communicating artery aneurysm.³ A 3^rd nerve palsy presents with either vertical or horizontal diplopia, ptosis and anisocoria (unequal pupils) with a mydriatic (dilated) pupil on the affected side.³ Some or all of these features may be present, dependant on whether the palsy is partial or full.

Examination may reveal an eye that is abducted and depressed on the affected side. There may be a partial or complete ptosis and anisocoria. Examination of ocular motility may reveal limitation of elevation, depression and adduction.

All patients with a 3^rd nerve palsy, regardless of whether it is partial or full, should undergo urgent neuroimaging with angiography to exclude a posterior communicating artery aneurysm.³ Other compressive causes affecting the course of the 3^rd cranial nerve may also be seen.

Most commonly a 3^rd nerve palsy is due to microvascular causes secondary to cardiovascular risk factors and so optimisation of these is important in such cases. Involvement of the orthoptic team is important to manage the diplopia with occlusion or prisms and monitor.³

4^th Cranial Nerve Palsy (Trochlear Nerve)

A 4^th nerve palsy presents with vertical binocular diplopia, worse on downgaze and there may be a head tilt away from the side of the palsy. Examination would reveal a hypertropia (a type of strabismus, or misalignment of the eyes, where one eye turns upward) of the affected eye that is worse when looking to the contralateral side and worse when the head is tilted to the ipsilateral side.³

The most common causes of a 4^th nerve palsy are congenital, trauma and microvascular causes.³ Other causes include compressive lesions along the course of the 4^th nerve, cavernous sinus lesions, demyelination and vasculitis.³

It may be useful to ask to look at an old photograph of a patient to see if there was evidence of a historic head tilt that may suggest a congenital cause. If it is thought to be an acute palsy, then cardiovascular risk factors should be assessed and optimised. Generally, neuroimaging is not required at presentation if there are significant cardiovascular risk factors, and a microvascular cause is likely. If there is diagnostic uncertainty then this should be considered. With a microvascular nerve palsy, one would expect improvement by 3 months and if not, neuroimaging should be performed.³

Management is generally orthoptic-led to manage the diplopia and monitor recovery.

6^th Nerve Palsy (Abducens Nerve)

A 6^th nerve palsy will usually present with horizontal, binocular diplopia, worse in the distance and worse looking to the ipsilateral side. Examination may reveal an esotropia (eye is turned inwards) and there will be limitation of abduction in the affected eye.³

The causes of a 6^th nerve palsy include microvascular causes, trauma, vasculitis, cavernous sinus pathology, demyelination and raised intracranial pressure (ICP). A bilateral sixth nerve palsy should raise particular concern about raised ICP.³

Older patients presenting with an isolated, acute 6^th nerve palsy should have their cardiovascular risk factors assessed and optimised as a microvascular cause is most likely. If there is concern about an alternative cause, then neuroimaging should be considered at presentation but otherwise may only be necessary should there be no improvement by 3 months.³

Other Causes

Other causes of binocular diplopia:

• Myasthenia Gravis
• Thyroid Eye Disease
• Convergence insufficiency
• Trauma
• Decompensating phoria
• Orbital Apex Syndrome

Conclusions 

The role of the emergency clinician is to be able to recognise and distinguish serious ophthalmic pathology, initiate immediate investigation and management if appropriate and make a timely referral to ophthalmology. As discussed, prompt recognition of certain ophthalmic conditions is of great importance. Having a structured history and examination pattern will help narrow the differential considerably and ease discussion and referral to the ophthalmic team. Hopefully, this article will act as an aide to recall the key considerations of varying presentations and give clinicians confidence in assessing patients with emergency ophthalmic presentations.

References

1. American Academy of Ophthalmology. Posterior vitreous detachment – EyeWiki. Eyewiki.org. 2024 Oct 19 [accessed 2024 Nov 19].
2. American Academy of Ophthalmology. Retinal detachment – EyeWiki. Eyewiki.org. 2024 May 1 [accessed 2024 Nov 19].
3. Denniston AKO, Murray PI, editors. Oxford handbook of ophthalmology. 4th ed. Oxford University Press; 2018.