Starting a major series of CET articles looking at various aspects of macular disease, Louise Stainer explains macular holes. Module C35606 one distance-learning point for optometrists and dispensing opticians
This is the first in a series of articles which will highlight a number of macular conditions that may be encountered in community eye care practice. Adjunct tests such as ocular coherence tomography (OCT) are now sometimes available on the high street and may be performed in addition to the patient’s standard eye examination. This supplementary information may highlight subtle macular changes and aid both initial and differential diagnosis of various conditions that may previously not have been recognised until they had progressed further or not detected if early changes remained stable. Part 1 will concentrate on macular hole, lamellar macular hole and macular pseudohole.
Macular hole
The cause of the majority of macular holes is idiopathic (unknown). However, they have also been linked to a number of conditions including epiretinal membrane (Figure 1), cystoid macular oedema (Figure 2) and macular trauma. The incidence of macular hole is 1 in 5,000 patients.1 They are more common in women and the risk of their occurrence is greatest in females in their 50s and 60s. The exact pathogenesis is not completely certain. One theory is that their development is linked to the presence of vitreous traction. Age-related structural changes in the vitreous include liquefication and shrinkage. Usually these culminate in separation of vitreoretinal connections at various sites (complete posterior vitreous detachment). One of these is situated at the macula and if the vitreous and macula remain bound during these vitreous changes (vitreomacular adhesions) vitreous traction often results.
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Macular holes are classified depending on the extent of their progression and are subdivided into stages 1 to 4.
Stage 1 macular holes are characterised by the presence of vitreomacular traction due to the occurrence of an incomplete posterior vitreous detachment (PVD). This leads to the development of subtle intraretinal cystic changes or foveal pseudocysts in the macular region.3 Alternative opinions are that a small detachment of the retina from the retinal pigment epithelium (RPE) occurs first (foveolar detachment).4 A combination of a foveolar detachment and cystic changes may be seen on the macular OCT scan. The individual may be unaware of any changes to their vision unless they cover the other eye, particularly if it is normal. This stage may be further subdivided into stages 1a and 1b. In the former a yellow foveal spot may be seen.
This may self-resolve with disappearance of the spot, if a full PVD occurs, relieving vitreomacular traction.4 Otherwise the foveal spot progresses into a foveal ring over a period of weeks to months as the grade 1a becomes a grade 1b hole.5 This may be due to increased visibility of xanthophyll pigment situated on the RPE as the foveal detachment increases in size. This causes displacement of foveal photoreceptors outwards towards the edge of the hole.6 Persistent vitreal traction also causes elevation of the fovea to the surrounding perifoveal retina.7 Subtle striae may be visible on fundus examination, radiating from the foveal ring. These are best viewed with the slit lamp using retro-illumination.7 Fortunately studies have shown that stage 1 macular holes self-resolve in approximately 50 per cent of cases.1
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A stage 1 macular hole advances to stage 2 when the vitreous located immediately in front of the macula continues to shrink. Pseudocystic changes continue to progress, affecting all retinal layers until only a thin neural retinal tissue roof is present.3 Continuous traction causes this to open, resulting in a small full-thickness hole (less than 400µm in size).8 This hole may be a variety of shapes and situated centrally or eccentrically to the macula. The section of condensed vitreous may lie over the hole. This is incompletely detached and usually a pseudo-operculum (contains no photoreceptors). There is still vitreofoveal attachment at this stage.
The likelihood that a stage 2 hole progresses into stage 3 is high and the chance of self-resolution minimal. A stage 2 develops into a stage 3 hole when it increases in size to over 400µm due to continued vitreofoveal traction.1,8 The hole is now typically round with smooth borders that tend to be greyish in colour and elevated due to the rim of retinal detachment and underlying subretinal fluid surrounding the hole.9 Yellow deposits remain on the RPE situated at its base and the cystic changes are still present (Figure 3). A stage 3 hole is characterised by an absence of any vitreofoveal attachment (although the pseudo-operculum is usually still present).8
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A person with a stage 4 macular hole has had a complete PVD in that the vitreous is no longer attached to the optic disc or the fovea (Figure 4). The former may be accompanied by the presence of a Weiss ring in the vitreous that can be observed during slit-lamp examination.9
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Lamellar and pseudomacular holes
A lamellar macular hole is a partial thickness macular hole. It is thought to occur following a cessation in the cystic development of a full thickness macular hole (FTMH).11 The causative factor (vitreomacular traction) acting anteroposteriorly with respect to the retina is the same as for FTMH.11 Epiretinal membranes are commonly observed in individuals with lamellar macular hole. In these cases membrane contraction causes tangential traction that is thought to be either solely or partly responsible for hole formation.12
Epiretinal membranes are also found with the majority of macular pseudoholes.13 In these patients the contractile forces of a macular epiretinal membrane give the illusion of a macular hole when in reality none is present.3 Unless the epiretinal membrane is severe it may be difficult to distinguish a full thickness macular hole from lamellar and pseudoholes during slit-lamp examination as they all look very similar.
All have the appearance of a single red macular lesion with clearly defined edges. However, the visual acuity of individuals with pseudoholes tends to be almost normal in the absence of any co-existing ocular pathology, whereas the visual acuity associated with full thickness macular holes is generally between 6/24 and 6/60.14 The visual acuity associated with a lamellar macular hole has been found to vary from 6/12 to 6/24.14
OCT has made the differential diagnosis of lamellar macular holes, pseudoholes and full-thickness macular holes significantly easier. It has been stated that OCT scans of lamellar holes have a number of traits that help distinguish them from the other types and confirm diagnosis.12 In lamellar holes the foveal contour is irregular in nature compared to the smooth shape of a full thickness macular hole and the steepening contours of a pseudohole. There is no full-thickness foveal defect present and the photoreceptor layer is unaffected in both lamellar and pseudoholes in contrast to a full thickness macular hole.12
However, in a lamellar hole there is a break present in the inner fovea and separation of the inner foveal retina from the outer retina. This intraretinal schisis that occurs between the inner and outer retinal layers (outer plexiform and outer nuclear retinal layers) is situated near the base of the lamellar macular hole together with cystic spaces.15 This usually does not occur in a pseudohole – there is no loss of tissue or break in the fovea.3 Pseudohole treatment is not usually indicated, but an epiretinal membrane removal peel may be performed in conjunction with a vitrectomy in cases associated with severe symptoms and/or loss of visual acuity.
Symptoms and diagnosis
As the macular hole progresses, the patient’s vision is more likely to be affected. Symptoms include a progressive reduction in the clarity of their central vision. For example people’s faces may become progressively more blurred. People with a macular hole may also complain of visual distortion (metamorphopsia) that tends to be the pin-cushion pattern. Objects at the centre of the perceived image appear smaller (micropsia) than their actual size.
This is because the brain no longer receives as many signals from the macular centre as foveal photoreceptors have been displaced outwards from their usual position.16,17 Distortion areas can be confirmed by the patient during monocular examination of the Amsler grid using their reading prescription. However, visual distortion may be reported in a variety of macular conditions. Individuals with a grade 3 or grade 4 macular hole may also develop pericentral positive scotoma visual field defects as the hole increases in size and photoreceptors at the edge become unable to function.6
A macular OCT can provide significant information including the presence of vitreous traction, thickness and size of the macular hole. It can also be useful in determining indication of a macular hole developing in the individual’s other eye – the risk of occurrence having been estimated at between 10 and 15 per cent.1 If the macula appears normal and there is already a PVD present, a macular hole is unlikely to occur.17
The Watzke-Allen slit-beam test can also prove to be a useful tool in the diagnosis of macular hole, especially in those practices where an OCT is not available. During slit-lamp examination of the fundus with a Volk lens, a narrow slit beam of light is briefly positioned over the fovea. The patient is asked if the rectangular light looks regular or if there are any parts missing. If the fovea is intact the beam will look normal, but if a full-thickness macular hole is present the beam will appear distorted (thinned or kinked) or there may be a gap approximately halfway down.18 The beam will appear normal in individuals with a pseudohole as these changes in the beam correspond to the absence of retinal tissue.19
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Surgical treatment
Macular hole treatment usually incorporates internal limiting membrane (ILM) peeling and vitrectomy. Various dyes such as indocyanine green (ICG) that stain and highlight the membrane aid its removal, but there are concerns regarding retinal toxicity.20 This is minimised by reducing the concentration of ICG and retinal exposure time while maintaining improved visibility of the ILM.20 Injection of a heavy gas into the vitreal space adjacent to the macula (gas tamponade) is generally performed following the vitrectomy. Following surgery, posturing by the patient (keeping face down for approximately a week) is required to ensure that the gas bubble remains in the correction position temporarily sealing the hole. Vitrectomy and the presence of the gas are thought to reduce vitreous traction as well as stimulating the multiplication of glial cells that contribute to hole repair and closure.21
The gas bubble acts by pressing against the macula to enable and promote retinal adhesion.21 The ILM peel is also thought to help relieve traction by ensuring any posterior hyaloid as well as epiretinal membranes present are removed.22 Silicone oil can be used as an alternative to heavy gas and the advantage is that posturing post-surgery is not necessary. This approach is used in cases where posturing is not possible such as children and elderly patients who are unable to maintain the necessary position.7 However, removal of the oil needs to be performed post surgery (this is usually done at between six and 12 weeks postoperatively).7 There is a significant risk of cataract development (75 per cent) following macular hole surgery.21 Phacoemulsification and lens replacement are often performed during the same surgical episode as macular hole surgery. Other less common complications include reopening of the original hole, retinal detachment and endophthalmitis.21
As well as aiding the diagnosis of macular hole, OCT can also be useful in confirming macular hole closure following vitrectomy. Fortunately, the success rate is high; studies have shown that hole closure is achieved in between 90 and 100 per cent of cases, with an improvement in best corrected visual acuity (BCVA) in 79-95 per cent of patients.23 The majority of cases have a macular OCT scan showing an unremarkable macula with a normal foveal depression and no retinal defect present. However, the presence of various anomalies can affect results despite successful macular hole closure. These may include chronic subretinal fluid, disruption of retinal layers including the nerve fibre layer, RPE or photoreceptor layers or recurrence of epiretinal membranes.24 These can all be detected using OCT.
Recent clinical trials have involved a compound called ocriplasmin.25 Ocriplasmin is an enzyme that breaks down certain proteins and triggers enzymatic vitreolysis. It can alleviate vitreous traction that would otherwise promote macular hole progression in the absence of a full PVD. The study found that ocriplasmin treatment resulted in subsequent macular hole closure in some individuals even if vitreomacular adhesion was not completely resolved. However, the other patients (59.4 per cent of cases) still required vitrectomy to treat their macular hole.25
The drug is administered by intravitreal injection. Potential complications include intraoperative bleeding or postoperative intraocular pressure elevation. NICE guidelines are currently in development regarding treatment of vitreomacular adhesion (VMA) with ocriplasmin.26 This treatment is not as invasive as a vitrectomy so theoretically the risks are less. It could provide a useful first line treatment option for suitable patients and may rule out the need for vitrectomy in some.
This article illustrates the usefulness of OCT (and other diagnostic tests) in the assessment of macular hole and the postoperative success of any surgical treatment given.
References
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26 National Institute for Health and Clinical Excellence (NICE). Vitreomacular traction: ocriplasmin [ID544] [online]. Available from http://guidance.nice.org.uk/TA/WaveR/144. (accessed August 6 2013).
Acknowledgements
The author thanks Mr Salman Mirza for his advice regarding this article.
? Louise Stainer is a hospital optometrist at Optegra Eye Hospital, Birminghamar disease, Louise Stainer explains macular holes. Module C35606 one distance-learning point for optometrists and dispensing opticians