Peripheral retinal degenerations: referral refinement part 10: C-16864 O.
Peripheral retinal degenerations and retinal detachment
The increasing adoption of indirect ophthalmoscopy techniques means that optometrists are routinely looking further into the retinal periphery. Imaging instruments, such as the Optomap, have also increased access to this area. Optometrists, therefore, need to be aware of the significance of the conditions that are increasingly likely to be found.
In order to decide if a given peripheral retinal degeneration is a risk factor for RD, we must first consider how a detachment arises. Rhegmatogenous retinal detachments (RRD) are the most common and occur when fluid in the vitreous cavity passes through tears or holes in the neurosensory retina and separates it from the underlying retinal pigment epithelium (RPE). Detachment becomes more likely if the break in the neurosensory retina is held open by ongoing vitreoretinal traction, encouraging liquid vitreous that has been mobilised by saccadic eye movements to pass through the open break. (1) Therefore, if a peripheral retinal degeneration is to be considered a risk factor for RRD then it must predispose the formation of breaks, either through enhanced attachment between the vitreous cortex and the neurosensory retina and/or a weakness of the neurosensory retina itself. Furthermore it is only those conditions that affect the inner retina and its interface with the vitreous, that are likely to be rhegmatogenous. Conditions that affect the outer retina are unlikely to be a risk factor for RD.
Conditions that affect the outer retina
Also known as cobblestone degeneration, this condition is present in about 25% of the population and appears as well defined yellow white patches between the equator and the ora serrata. It is characterised by the absence of the outer layers of the retina, in particular the choroid, which permits an uninterrupted view of the sclera. Sometimes large blood vessels can also be seen through this window giving the impression of a well-defined red stripe over the white background of the sclera (Figure 1). It is possible that Pavingstone defects are present from birth and should not be considered a degeneration at all. Although these lesions have a striking hole-like appearance, the defect is in the outer retina, leaving the inner layers intact with no predisposition to break formation.
[FIGURE 1 OMITTED]
Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE) is a common benign lesion. It is present at birth and is not a degenerative condition. It is a flat round or oval lesion, which is dark grey or black in colour and up to three disc diameters in size. It is darker and more well-defined than a choroidal naevus because it is more superficial and therefore there is less retinal tissue to dull the appearance and soften the edges. It is an outer retina change and does not affect the vitreo-retinal interface; therefore it does not predispose to retinal detachment. When CHRPE lesions occur in groups, known as bear tracks (Figure 2a), it is worth asking the patient if there is a family history of gastrointestinal problems, in case they are a sign of rare inherited condition of the bowel known as Familial Adenomatous Polyposis. Individual CHRPE lesions can lose pigment over time, altering the uniform appearance and making recognition more difficult. Some lesions may become almost totally de-pigmented with only a thin rim of residual pigment remaining at the edge, giving the false impression of a hole (Figure 2b).
Reticular pigmentary degeneration (also known as honeycomb degeneration) is a relatively common finding in the peripheral fundi of older patients. It is characterised by a fine network of pigmentation and has no clinical significance.
Optometrists are familiar with drusen that form at the posterior pole in those affected by age-related macular degeneration (AMD). Similar clusters of pale yellow lesions can be found near the equator of the eye in elderly patients (Figure 3). They are not a risk factor for detachment and do not require referral.
Conditions that affect the inner retina
White without pressure
White without pressure refers to geographic areas of whiteness in the peripheral retina that are not caused by scleral indentation. It is an optical phenomenon probably related to increased density of collagen fibrils at the interface with the retina. It occurs in 30% of normal eyes and is usually bilateral. There are reports that traction-induced giant retinal tears will follow the posterior border of an area of white without pressure. This does not mean that white without pressure caused the tear, but it may have determined the route that the tear took. It is now believed that white without pressure it is not a risk factor for RRD and there is no need for referral. However, optometrists should be aware that white without pressure can sometimes give the false impression of a retinal break. A true defect in the neurosensory retina will allow the red choroidal reflex to appear brighter in the area of the defect as compared to the adjacent fundus. A similar, but misleading appearance, can occur when an area of seemingly white retina entirely encloses the retina with the normal orange red colouration.
[FIGURE 2 OMITTED]
Microcystoid degeneration consists of small vesicles set in an area of greyish white retina near the ora serrata. It is present in all eyes and, although it increases in extent with age, it is not directly responsible for break formation. However, the cysts may give rise to the formation of splits between the layers of the neurosensory retina, producing retinoschisis.
In the age-related form of retinoschisis, cystoid spaces coalesce to form mucopolysaccharide-filled cavities that cause the inner retina to separate from the outer retina (Figure 4). This splitting of the neurosensory retina is present in 7% of the population over 40 years of age and occurs almost exclusively in hypermetropes, most commonly in the inferior temporal quadrant and often in both eyes. There is total loss of function in the affected area, resulting in an absolute scotoma, but there is no threat to sight because, unlike a retinal detachment, a retinoschisis does not progress from the periphery towards the macula. With retinoschisis, it is rare to see RPE changes, whereas in retinal detachments these changes are relatively common. There is generally no flow of liquid from the vitreous into the schisis cavity, which means that it appears as a smooth bulge that does not change shape or position with eye movements.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
It is possible for breaks to occur, which could then trigger a retinal detachment (detachment of the neurosensory retina from the RPE), but this only happens in 0.05% of cases; (2) there is no need for prophylactic treatment of retinoschisis.
Optometrists who suspect a retinoschisis in an asymptomatic patient should refer on a routine basis and then monitor annually if the diagnosis is confirmed. The contrasting characteristics of retinoschisis and RRD are shown in Table 1. In particular it is wise to keep to the advice "never diagnose retinoschisis in a myope".
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
Atrophic round holes
Atrophic round holes (Figure 5) are not caused by posterior vitreous detachment (PVD) or by blunt trauma. It is most likely that they are caused by chronic atrophy related to vascular changes. They are generally round or oval in shape and are referred to as atrophic round holes to distinguish them from the U shape tears caused by vitreous traction. Any break in the attached retina appears redder than the surrounding tissue because of the unobstructed view of the choriocapillaris. Note that a peripheral retinal haemorrhage will have irregular margins as it diffuses into the surrounding tissue, whereas a hole has perfectly smooth borders.
The incidence is not related to age and atrophic holes are seen in the young. Many holes are associated with myopia or lattice degeneration (see later). Some atrophic holes are surrounded by a small area of subretinal fluid (SRF). These have not progressed to a full clinical detachment because there is no vitreous traction to encourage flow through the break. In this situation the RPE is able to pump all the liquefied vitreous into the choroid, with the exception of the immediate zone around the break. A ring of reactive hyperpigmentation at the border of the SRF indicates chronicity and stability. Very rarely an asymptomatic (no flashes or floaters) atrophic hole can slowly progress to a clinical detachment. Where there is a detachment in a young myope with no PVD, the most likely cause is an atrophic hole. Although atrophic round holes can potentially lead to a detachment this is extremely rare (3,4,5) and they do not require treatment and there is no need for referral. It is therefore important to be able to distinguish atrophic round holes from retinal tears, which do require urgent referral (see Table 2). It is useful to refer to a break that results from focal loss of tissue due to atrophy as a "hole", while a break induced by vitreous traction is described as a "tear". Unfortunately this convention is frequently ignored and the two terms are used interchangeably. In an operuclated tear (Figure 6), the traction separates a small plug of neurosensory retina from the surrounding retina. This is known as the operculum and it can be seen as a grey disc-shape floater lying over the area of the tear. It remains stuck to the vitreous cortex and moves with it on eye movements. Shrinkage means that it appears slightly smaller than the break that it previously occupied. Operculated tears are also round and the best way of distinguishing them from atrophic round holes is the presence of the disc-shaped floater. Flap tears (Figure 7) produce U or V shape breaks with the apex of the flap pulled into the vitreous cavity but still attached at the anterior border of the tear. Thus the apex of the flap always points towards the posterior pole.
[FIGURE 7 OMITTED]
Lattice retinal degeneration is a common peripheral condition that is present in 8% of eyes, but is more common in myopes. It develops in early adulthood rather than in old age. It has several different ophthalmoscopic presentations, which have previously been described as separate conditions. The classic appearance is a crusty, circumferentially oriented oval patch that appears layered on the surface of the retina. Sometimes there is excess pigment and sometimes fine white lines (sclerosed vessels) criss-cross the patch of degeneration giving rise to the lattice appearance. One variant is characterised by tightly packed "snowflakes" that produce a glistening appearance, which has been described as "snailtrack degeneration". Histopathology reveals retinal thinning and sometimes small atrophic holes will be evident, which can lead to asymptomatic localised retinal detachment as described above. (6)
The vitreous overlying the area of lattice is liquefied, but there is exaggerated vitreoretinal attachment along its margin. It is this combination (thin retina, strong vitreous attachment and a reservoir of liquefied vitreous) that makes lattice degeneration a risk factor for tractional tears following PVD. However, this does not mean that all areas of lattice should receive prophylactic laser treatment. Although lattice degeneration is a risk factor for RRD, the majority of these patients do not develop a detachment. Only 1% of eyes with lattice changes suffered RRD in a 10-year follow up period (7) and it was concluded that prophylactic treatment should be discontinued. Furthermore, treatment may not always prevent detachment because new breaks can occur in areas not visibly affected by lattice. Referral for lattice, even in the presence of atrophic round holes, is therefore not required.
It may seem to be a contradiction that lesions such as atrophic round holes and lattice degeneration can be risk factors for RRD, yet they do not warrant referral. Laser retinopexy is routinely applied to retinal tears or detachments and is very effective at preventing visual loss. Why is it not used on those peripheral retinal degenerations that can theoretically lead to a detachment? It is important to understand that it is not always appropriate, or even feasible, to attempt to reduce a disease risk by prophylactic treatment. There are two reasons why this is not done for peripheral degenerations. Firstly, the incidence of RRD secondary to lattice or atrophic holes is extremely low. Secondly, when prophylactic treatment of peripheral degenerations was undertaken in the past, the results did not show overall that it was effective in preventing detachment. This was confirmed by a Cochrane review, (9) which is now widely accepted by ophthalmologists. Laser retinopexy is, therefore, not applied prophylactically to peripheral retinal degenerations. One possible exception is when there is a history of detachment, associated with lattice degeneration, in the fellow eye.
What should optometrists tell the patient when they identify a risk factor for retinal detachment? They should tell the patient that retinal detachment is a rare condition and that even though features in their eyes have been identified that make this slightly more likely, the risk is still not high. The symptoms of a retinal break or detachment should be described and the patient told to seek advice immediately if they should occur. Emphasise that only sudden changes in floaters are significant. Nervous myopes should be discouraged from trying to constantly monitor their floaters for a small increase in numbers. It is also important to stress that there is no need to modify lifestyle, pastimes or sport. The myth that women can suffer RD as a result of the strains of child birth is totally without foundation.
It can be seen from Table 3 that the only peripheral retinal degeneration that requires referral is retinoschisis. Where there is doubt about the correct differential diagnoses then it is always wise to refer on the basis that it is the most serious condition. Thus, if an area of elevated retina has some features of retinoschisis but some that would suggest detachment then referral would have to be urgent. Treatment is required for retinal tears and detachment and referral refinement for these conditions will be considered in more detail in the next article in this series.
About the authors
Graham Macalister is a specialist optometrist at Moorfields Eye Hospital. Paul Sullivan is a vitreo retinal consultant at Moorfields Eye Hospital, where he is the director of education.
See http://www.optometryco.uk clinical/index. Click on the article title and then download "references".
Table 1 Comparison between the characteristics of retinoschisis and rhegmatogenous retinal detachment Retinoschisis Rhegmatogenous Retinal detachment Split within the neurosensory Neurosensory retina separates from RPE retina Smooth, shiny Rippled, irregular Stationary on eye movement Drifts or undulates with eye movements No flashes or floaters Flashes, floaters, cobwebs Bilateral usually Rarely bilateral simultaneously 7% of population >40 years 0.1% of population 70% hypermetropes Myopes over-represented Stable absolute scotoma Progressive relative scotoma No breaks Break present (may be difficult to locate) No tobacco dust Tobacco dust Infero-temporal commonest Superior-temporal commonest No pigment disturbance Pigment disturbance possible if chronic No spread, innocuous Sub-retinal fluid spreads, can threaten macula Routine referral to confirm Urgent referral for treatment diagnosis Table 2 The features of atrophic round holes are contrasted with those of operculated tears and flap tears Operculated Feature Atrophic hole tear Shape Round or oval Round with disc shape operculum floating above the break Vitreous None Traction formed the traction break but is absent after the operculum has separated Location Far periphery Far to mid periphery Retinal or Never Rarely vitreous haemorrhages Symptoms Never (unless Possible in traction (flashes, clinically significant phase (or if clinically floaters) RD occurs) significant RD occurs) Incidence of RD Rare 1/68 (much less if asymptomatic) Prophylactic Never (for exceptions Rarely treatment of see lattice) break Referral No Routine (unless significant sub-retinal fluid) Feature Flap tear Shape U shape with central flap Vitreous Usually continuous traction traction Location Far to mid periphery Retinal or Often vitreous haemorrhages Symptoms Frequent in traction (flashes, phase (or if clinically floaters) significant RD occurs) Incidence of RD 1/38 Prophylactic Always treatment of break Referral Immediate to A&E Table 3 Summary of peripheral retinal lesions and actions required Peripheral Risk factor degeneration for RRD? Action Pavingstone No None required CHRPE No None required Reticular No None required Peripheral drusen No None required WWP No None required Microcystoid No None required Retinoschisis Very rare Refer routinely for progression confirmation of diagnosis. Then monitor annually Atrophic round Very rare Retinal detachment holes warning. Monitor annually Lattice Very rare Retinal detachment warning. Monitor annually
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|Title Annotation:||CET: CONTINUING EDUCATION & TRAINING|
|Author:||Macalister, Graham; Sullivan, Paul|
|Article Type:||Disease/Disorder overview|
|Date:||Sep 30, 2011|
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