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Retinal vein occlusion.

This article presents the classification, risk factors and management of retinal vein occlusion, outlining the implications for patients.

Optometrists

Therapeutic optometrists

Dispensing opticians

Introduction

Retinal vein occlusion (RVO) is a vascular disorder of the retina where there is a sudden obstruction in the flow of blood usually by what is thought to be a clot, in the venous outflow of blood from the retina back to the heart. (1) This article will consider the classification, risk factors, clinical presentation and investigation of the condition.

Classification

RVO can clinically be classified into the following types:

* Central retinal vein occlusion (CRVO) is usually due to a fibrin and platelet thrombin before or at the level of lamina cribrosa. The haemorrhages appear all over the retina (see Figure 1) (2,3)

* Hemi-retinal vein occlusion (HRVO): the pathogenesis is thought to be the same as for CRVO. In this condition the retinal haemorrhages involve only one half the retina, either superiorly or inferiorly; this is much less common than the CRVO (1)

* Branch retinal vein occlusion (BRVO) is due to blockage of flow by an atherosclerotic artery at the crossover of a retinal vein and retinal artery (see Figure 2, page 74) (4)

* Macular vein occlusion is the blockage of a small branch retinal vein in the macular area, which can cause a decrease in visual acuity but may be clinically difficult to see and diagnose.

RVO may be sub-classified further:

* Ischaemic RVOs are much more likely to cause profound, irreversible loss of visual acuity. This is diagnosed by a visual acuity of less than 6/60, the presence of a relative afferent pupillary defect (RAPD), and extensive deep retinal haemorrhages. An absence of a b-wave on electroretinogram (ERG) also confirms that the RVO is ischaemic5

* Non-ischaemic RVOs are diagnosed by a visual acuity of better than 6/ 60, absence of a RAPD and lack of extensive deep retinal haemorrhages. Macular vein occlusions are usually non-ischaemic.

Risk factors

Systemic

Hypertension is the commonest underlying risk factor for RVO. (6) It may be undiagnosed and difficult to isolate as it may be due to 'spiking' of blood pressure. The best way of identifying these spikes is to undertake 24-hour continuous monitoring of blood pressure. (1-3) RVO is also more common in diabetes especially when the diabetic retinopathy is severe. (1-3) Hypercholesterolaemia is a risk factor for atherosclerosis, which is indirectly a risk factor for RVO. (6) It is important to note that smoking increases the risk of developing a CRVO significantly. (6)

If there is a history of other thrombotic episodes or that of spontaneous abortions and the patient with the CRVO is relatively young (less than 50 years old), then it would be important to investigate the patient for rare inherited systemic thrombotic disorders. (7) These disorders can be sub-classified into:

* Disorders with decreased antithrombotic proteins: anti-thrombin deficiency; protein C deficiency; and protein S deficiency (8)

* Disorders with increased prothrombotic proteins: factor V Leiden (activated protein C deficiency); prothrombin Gene mutation G20210A; and increased levels of factor VII, VIII, IX, XI and Von Willebrand Factor.

Ocular

High intraocular pressure (IOP) is a known risk factor in development of RVOs and hence the association between glaucoma and RVO. (6) One of the ways of reducing the risk for recurrent RVO is to reduce IOP with anti-glaucoma medication.

[FIGURE 1 OMITTED]

Clinical examination

Clinical examination allows the practitioner to define the type of RVO and establish whether it is ischaemic or non-ischaemic. Assessment should take into account the patient's previous and current refractive error, visual acuities with and without correction as well as any improvement noted with pinhole. The presence or absence of a relative afferent pupillary defect (RAPD) and examining for signs of rubeotic vessels on the iris are essential when assessing these patients. After measurement of intraocular pressures, gonioscopy is performed to determine if there are any rubeotic vessels in the angle. The lens is assessed for presence of cataract, as this may also be another confounding cause of reduced vision. The vitreous is assessed for signs of red blood cells as well as posterior vitreous detachment. Finally the retina should be carefully examined to assess the extent, distribution and depth of the retinal haemorrhages, associated macular oedema and/or thickening, the presence or absence of new vessels on the disc (NVD) or new vessels elsewhere (NVE). It is also important to assess the presence or absence of an epiretinal membrane (ERM), as there is an increased chance of formation of this in patients with a history of RVO. (9)

Investigations

Patients with RVO are likely to undergo the following investigations in addition to assessment of potential underlying risk factors:

* Optical coherence tomography (OCT) is the most common and most helpful investigation performed after a RVO. It gives essential information about the presence or absence of sub-clinical macular oedema and/or retinal thickening. It also allows one to perform baseline assessment of the retina before treatment is initiated

* Prior to the days of OCT, fundus fluorescein angiography (FFA) was the most common investigation performed after a RVO. However, since the advent of OCT it is much less commonly used as it is an invasive investigation and has a small but significant rate of morbidity and mortality if the patient has an anaphylactic reaction to the fluorescein dye injection. Nowadays it is only performed if there is a good clinical reason for it and the patient understands and accepts the associated risks. These reasons may include the following: to confirm diagnosis in cases where there is a clinical suspicion of a vein occlusion, but clinically there is not enough evidence or the retinal changes may have resolved prior to the clinical examination; to assess the extent of retinal ischaemia as patients with a significant amount are more likely to develop neovascularisation and rubeosis iridis and may benefit from prophylactic pan-retinal photocoagulation (PRP); and if there is a question about whether abnormal vessels around the disc are collaterals or NVD. NVD classically leak on FFA but collaterals do not. NVD would need treatment with PRP, as there is a risk of vitreous haemorrhage with these; FFA can also confirm the presence of NVE, which would also need treatment with PRP as there is a risk of vitreous haemorrhage if left untreated. FFA was used to confirm the presence or absence of associated cystoid macular oedema (CMO). This can now be assessed much easier and quicker and without any associated risk to patients by OCT scan (10,11)

[FIGURE 2 OMITTED]

* An electroretinogram (ERG) can be used to assess whether a RVO is ischaemic or non-ischaemic. A flat b-wave on the ERG is suggestive of ischaemia. However, as ERG's are difficult to perform and not many centres have access to these facilities, it is unusual for it to be performed in the setting of a RVO. (12-14)

Treatment

In RVO the treatment objectives are as follows:

* Reduction of underlying risk factors

* Treatment of reduced vision

* Treatment of secondary complications

* Prophylactic treatment to reduce the risk of future complications of RVO.

Each of these will now considered in turn.

Reduction of underlying risk factors

Starting patients on IOP reducing treatment reduces the local risk factor; this is usually a prostaglandin analogue such as Latanoprost unless there is a contraindication to use of these drops. Any other group of medicines to reduce IOP is also effective.

Treatment of reduced vision

* The mainstay of treatment is use of intravitreal injections, either anti-VEGF or steroids. Other approaches involve laser or surgical intervention.

Anti-VEGF treatments include:

* Ranibizumab (Lucentis), is a monoclonal antibody fragment or the antibody binding segment ([F.sub.ab]) against vascular endothelial growth factor A (VEGF-A), and thus stops growth of new blood vessels. The injections are typically administered once per month for the first three months followed by monthly injections as necessary (15)

* Aflibercept (Eylea) is a recombinant fusion protein that is made from VEGF binding portions from the extracellular domains of the VEGF receptors 1 and 2 that are fused to the Fc portion of the human IgGl immunoglobulin. Like Ranibizumab injections these are given once a month for three months as a loading dose. After this it is given bimonthly as necessary (16)

* Bevacizumab (Avastin) is the full monoclonal antibody against VEGF. It is not licensed for use in the eye, but it has been proven by various trials that Bevacizumab injections are as effective as Ranibizumab injections and that they do not have any statistically significantly increased amount of side effects. As Bevacizumab is significantly cheaper than Ranibizumab, a lot of patients who pay for their own treatment prefer this option. (17)

It must be said that the three anti-VEGF antibodies are not exactly identical in their effects; even though the majority of patients respond to all three anti-VEGF antibodies, it has been noted that there are patients who respond only to one or the other. Steroids treatments include:

* Intravitreal injections of triamcinolone were traditionally used in the treatment of CMO post-RVO. It was found that in certain cases, where the drop in vision was due to associated CMO, it did improve visual acuity by improving the CMO. However, due to the short half-life of triamcinolone in the eye, its effect was limited, and in many people the CMO would recur. It also could cause a spike in intraocular pressure and even though in most cases this would settle as the triamcinolone washed out of the eye, there were cases that developed long-term pressure rises causing glaucoma (18,19)

* Ozurdex is a relatively new way of delivering a slow release dexamethasone from an implant injected into the vitreous cavity. The implant releases dexamethasone continuously for up to six months from the date of injection. Intravitreal injections of Ozurdex have been shown to significantly improve vision after RVO by improving CMO but some patients need sustained treatments every four to six months in order to stop their vision from deteriorating again. (20-24)

Retinal grid laser treatment was used before the advent of anti-VEGF antibodies. It was shown to be of benefit only in CMO secondary to BRVO if the visual acuity after six months had not improved to better than 6/12. The same studies showed that macular grid laser treatment was not effective in improving vision in those who had CMO secondary to CRVO or HRVO. With the advent of newer anti-VEGF treatment and intravitreal slow release steroid treatment, the use of laser in treating CMO secondary to RVO has seen a sharp decrease over the past decade. (25) Surgical treatments for RVO include:

* Vitrectomy ILM peel; this seems to help aerate the fundus and allow an improvement in vision in a limited number of patients who have a vitrectomy

* Vitrectomy and radial optic neurotomy for CRVO; this surgical approach was developed before the advent of anti-VEGF antibodies and slow-release intravitreal devices. The idea was to allow an expansion of blood vessels on their exit from the lamina cribrosa of the optic disc by cutting the elastic rim of the optic disc

* Vitrectomy and arterio-venous sheathotomy for BRVO: this surgical approach was described as some branch retinal vein occlusions occur at the crossing of the branch retinal vein over a branch retinal artery. As both vessels share the same sheath, surgical decompression by dissecting the retinal vein from the underlying retinal artery can establish normal venous flow and lead to an improvement in vision (26)

* Laser retino-choroidal anastomosis establishes an anastomosis between the retinal circulation and choroidal circulation and in some cases leads to improvement in vision in patients with CRVO.

Treatment of secondary conditions

All neovascularisation, whether NVD or NVE, are treated with double-frequency Nd:YAG laser PRR Rubeosis iridis and rubeotic glaucoma are also still treated with this approach.

Prophylactic treatment

Prophylactic treatment in ischaemic RVO is to reduce the risk of future neovascularisation, and that of rubeosis iridis and rubeotic glaucoma. The treatment is again with double-frequency Nd:YAG laser PRP.

Complications

The complications of RVO can be divided into early and late. Early complications include development of CMO and macular haemorrhages both of which can affect visual acuity. Late complications include various type of neovascularisation, including NVD, NVE and rubeosis iridis.

NVD and NVE can lead to vitreous haemorrhage if not treated appropriately and rubeosis iridis can lead to rubeotic glaucoma if not treated early enough to prevent a rise in intraocular pressure because of aqueous outflow obstruction by the new vessels in the angle.

As mentioned before, ERM formation secondary to the RVO can lead to further gradual loss of vision and increase in distortion after the RVO has occurred.

* Optometric considerations

For optometrists it is most important to know that the refraction can be unstable in patients with RVO as the presence of CMO and ERM can cause a significant hyperopic shift; this is because both of these conditions lift the fovea forward and reverses when the condition resolves with treatment. Thus, refraction in patients with RVO who are undergoing treatment for various complications can change significantly and hence why it can be challenging to prescribe spectacles for these patients.

In the setting of a RVO, refinoscopy reflexes may be feint or even absent due to epithelial corneal oedema resulting from raised intraocular pressure secondary to rubeosis iridis, or vitreous haemorrhage.

Prognosis

The prognosis for RVO varies by type. In general, macular branch RVO tends to have the best prognosis, followed by BRVO, HRVO and then CRVO. Patients with an ischaemic CRVO tend to do worse than those with non-ischaemic presentation; (1) however, this is a general rule and cannot be applied to every case. Even though some RVOs resolve spontaneously, the prognosis for visual improvement tends to be better the earlier treatment is initiated. The prognosis for dealing with complications of RVO is often more favourable the earlier treatment is commenced.

Conclusion

Optometrists plays a key role in identifying patients presenting with RVO and referring appropriately for both ophthalmological and systemic management to deliver the best outcome for the patient.

Exam questions

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 13 May, 2016. You will be unable to submit exams after this date. CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.

References

Visitwww.optometry.co.uk, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.

Kaykhosrov Manuchehri is a consultant ophthalmic and vitreoretinal surgeon working at BMI The Chiltern and Shelburne and Spire Harpenden and Thames Valley Hospitals. He has completed fellowships in vitreoretinal surgery at Birmingham and Midland Eye Hospital and Oxford Eye Hospital and medical retina at Moorfields Eye Hospital.

Course code: C-50139 Deadline: 13 May 2016

Learning objectives

General Optical Council

Approved CET for Optometrist

* Be able to explain to patients about the implications of retinal vein occlusion (Group 1.2.4)

* Be able to explain to patients about the implications of retinal vein occlusion appropriate to their level of understanding (Group 2.2.1)

* Understand the risk factors for retinal vein occlusion (Group 6.1.1)

General Optical Council

Approved CET for Therapeutic Optometrist

* Understand the natural progress of retinal vein occlusion (Group 1.1.1)

General Optical Council

Approved CET for Dispensing Opticians

* Be able to explain to patients about the implications of retinal vein occlusion (Group 1.2.4)

* Understand the management of retinal vein occlusion (Group 8.1.3)

Kaykhosrov Manuchehri MB BCh (Hon) BAO FRCOphth
Causes of reduced vision in retinal vein occlusion

Cystoid macular oedema    Elevated intraocular pressure
Retinal haemorrhages      Rubeotic glaucoma
Vitreous haemorrhage      Optic atrophy
Epiretinal membrane       Ischaemic damage to photoreceptors


Peter Campbell

Which aspect of your current role inspires you?

The increasing role that optometrists play in shared-cared clinics is very exciting. Optometrists working alongside nurse practitioners, orthoptists and ophthalmologists demonstrates how well the different professions can complement each other.

Where do you think optometry is heading?

I think as more optometrists become independent prescribers, their role will become increasingly essential in the management of patients with chronic eye disease such as glaucoma,

What has been influential in steering your career path?

Completing the professional doctorate programme at the Institute of Optometry and London South Bank.
Competency tracker

In this edition of OT, practitioners can
test a range of competencies:

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Optometrists     COMMUNICATION  OCULAR           STANDARD OF   [??]
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Therapeutic      KNOWLEDGE      OPTIONS
optometrists

Dispensing       COMMUNICATION   OCULAR          STANDARDS
opticians                        ABNORMALITIES   OF PRACTICE

Contact lens     [??]
opticians

Clinical editor: Dr Ian Beasley
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Author:Manuchehri, Kaykhosrov
Publication:Optometry Today
Geographic Code:1USA
Date:Apr 1, 2016
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