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Is it normal? Peripheral retinal findings--Part 2.

INTRODUCTION

In part 1 of this series (Optometry Today, April 4, 2015, p52-56) that the peripheral retina is the area extending from the equator anteriorly to the ora serrata. The peripheral retina is best viewed on a dilated patient using binocular indirect ophthalmoscopy (potentially also with scleral depression), contact fundus lens using the trapezoid mirror, and/ or wide-field photography. Often employing more than one of these techniques will give the clinician the most complete picture of the patient's peripheral retina.

Continuing the march through various peripheral retinal degenerations, this section will cover congenital hypertrophy of the retinal pigment epithelium (CHRPE), intraretinal degenerations and frank retinal detachments.

CONGENITAL HYPERTROPHY OF THE RETINAL PIGMENT EPITHELIUM (CHRPE)

CHRPE, also known as a halo naevus, occurs in 1.2-4% of the general population. (1,2) It is almost always unilateral and is most often located temporally and close to the equator. (1,3) As it is congenital, CHRPE is not age-dependent although they may enlarge or develop additional lacunae with time; there is no correlation with refractive error. (3)

CHRPEs appear as single, flat, round lesions with sharply demarcated smooth or scalloped margins (see Figure 1). (1,4) In about half of cases there is a ring of hypopigmentation found just inside the margin of the lesion giving it the alternative name of halo naevus. (1,5) CHRPEs are usually light brown to grey-black in colour. Many have white areas of lacunae, which are atrophied window-like defects. (1) The average size of the lesion is 4.5mm with a range from 1.6mm to 20.1mm. (2,3)

The pathophysiology involves a thickening of the retinal pigment epithelium (RPE) with overlying photoreceptor loss but with preservation of the inner retina. (6) Technologies such as autofluorescence, OCT, and B-scan ultrasonography are helpful in differential diagnoses, viewing clefts, and uncovering the integrity of the surrounding retinal structures. On autofluorescence, CHRPEs will hypofluoresce and can be differentiated from choroidal naevi by the lack of fluorescent lipofuscin. (7) Additionally on fundus photography, and viewing with indirect ophthalmoscopy, the use of the red-free filter will cause the CHRPE to remain similar in appearance but will cause the deeper retinal structures, including choroidal naevi, to lighten or disappear (remember the mnemonic: 'retina remains with red-free'). (1,2) CHRPEs are also commonly mistaken for choroidal melanomas; however, melanomas are elevated, less uniformly pigmented, less sharply demarcated, and may exhibit growth in all three dimensions. (8)

CHRPEs were originally considered benign and stationary. Current research, however, has shown that in 70-80% of cases, CHRPEs have a very slow, flat enlargement. This seems to be related to number and relative size of the lacunae. (3) The enlargement itself is not cause for concern, but is important to monitor as CHRPEs may have a corresponding relative scotoma on threshold visual field testing that may become more absolute with time. (8) Perhaps more importantly, in rare instances, CHRPEs may have an associated small nodule found to be primary malignant adenocarcinoma. (3) These adenocarcinomas are usually present at the initial exam so the clinician should pay close attention particularly at the first diagnosis. (1) The adenocarcinoma develops from the RPE and does not metastasize but can cause retinal detachment (RD) and potential blindness. (3)

CHRPEs are associated with systemic diseases: familial adenomatous polyposis (FAP) and with Gardner and Turcot syndromes, which are variations of FAP. The lesions in these diseases, however, can be distinguished from traditional CHRPEs in their characteristic pisciform shape, bilaterality, and multiplicity of lesions. (8) Patients with FAP often have 'bear tracks' of CHRPEs in both eyes. Because 90% of patients with FAP have these CHRPE-like lesions, screening high-risk children with ophthalmoscopy is an excellent tool to catch FAP early as the autosomal dominant condition gives rise to multiple colon polyps, which invariably transform to becoming malignant by the fourth decade. (10)

[FIGURE 1 OMITTED]

Upon discovering a single, unilateral CHRPE on examination, the clinician should photograph and document the location, size, colour, and number of lacunae associated with the CHRPE. (4) No referral is needed but close observation for growth or an associated nodule of adenocarcinoma is required. (3)

INTRARETINAL DEGENERATIONS

Senile degenerative retinoschisis

Senile degenerative retinoschisis is an idiopathic splitting between the inner nuclear and outer plexiform layers of the peripheral retina. The incidence is between 2-7% of the population above the age of 40 years old, (4) and specifically 3.9% between 60-80 years old. (11) It appears as a bullous or dome-shaped elevation that does not shift with movement of the eyeball and appears more transparent and with less wrinkling than RD. Vitreoretinal 'glitter' or 'snowflakes' and whitish sclerotic vessels may be visualised on the surface (see Figure 2). (4) It is located inferior-temporally in 45% of cases and is bilateral in 57% of cases. (11) There is no sex predilection. (11) Either or both outer layer and inner layer breaks may be present. (11)

Most patients with retinoschisis are asymptomatic and discovered on routine examination. A retinoschisis may be differentiated from RD by appearance, visual field testing, ultrasound B-scan, (12) and more definitively with OCT imaging. (13,14) Table 1 highlights several important differences between retinoschisis and RD.

[FIGURE 2 OMITTED]

The prognosis is excellent with the vast majority following a natural non-progressive and stationary course and with up to 8% spontaneously involuting. The incidence of frank RD has been reported between 0.05 and 2% with the high end related to post cataract surgery complications. (11,15)

Treatment should only be performed in exceptional cases such as enlargement into the foveal area, posterior layer retinal breaks, schisis-detachment and progressive, frank, symptomatic RD. (15)

JUVENILE X-LINKED RETINOSCHISIS

Juvenile X-linked retinoschisis is an inherited disorder transmitted as an X-linked recessive trait and thus affecting males almost exclusively. (8) The incidence is between 1:5,000 to 1:20,000. (16) The onset is by the first decade but is probably present as early as birth. (4) The disease has been mapped to the RS1 (retinoschisin) gene on chromosome Xp22.1 which is responsible for coding retinal proteins necessary for cell-cell adhesion. (4) More specifically, the retina-specific retinoschisin is thought to function in maintaining cellular organisation of the retina and structural integrity of the photoreceptor-bipolar synapse and also to regulate intra- and extracellular fluid balance. (16) There have been 191 mutations identified on the RS1 gene with new ones identified regularly. (17)

Clinically, presenting symptoms may include reduced vision, strabismus, or nystagmus. (4) All cases are bilateral and associated with retinal foveal schisis at the macula, sometimes called 'spoke phenomenon'.18 The foveal schisis usually first appears as a stellate striation in the macula that may also show fine, radiating folds, cysts, or pigment mottling. (8) With time atrophic changes occur in the foveal schisis altering the appearance. Schisis also occurs in the peripheral retina in about half of patients, (4,18) and is usually bilateral in the inferior-temporal quadrants. Other characteristics include vitreous haemorrhage, vitreous veils, and retinal vessels bridging inner and outer layers. (4) In the case of vitreous haemorrhage, 5% of patients experience these and usually in the first decade of life, but most clear spontaneously. (16)

Progression is usually rapid in the first five years of life and then slows to stationary by about 20-years-old. (8) Progression is marked by increased height of schisis cavity and atrophic changes. Most patients maintain vision of about 6/18 until their fourth or fifth decades when macular atrophy eventually leads to further reduction of vision. (8) Overall, progression and severity are highly variable, even within families. (16)

Juvenile retinoschisis may be differentiated from degenerative retinoschisis based on the younger age of onset and the schisis occurring in the nerve fibre layer rather than in the outer plexiform layer as in degenerative retinoschisis. (18) Further assessment is essential, and includes electroretinogram (ERG) testing, which shows a classic pattern of reduced scotopic amplitudes and initial selective b-wave reduction consistent with inner retina damage. The ERG patterns, however, are widely varied and are related to the wide variety of genotype mutations. (19) Fundus autofluorescence also shows a widely variable resultant pattern. (19) Thus the most definitive diagnostic tool is OCT imaging which is further useful in detecting the exact location of the splitting defect. (20)

Children with suspected juvenile X-linked retinoschisis should be referred for advanced testing and for genetic counselling. Due to the slowly progressive nature of the disease after the first five years of life, prophylactic treatment is not recommended as it is associated with numerous complications, namely RD. Treatment is recommended when there is a RD, vitreous haemorrhage, or when the macula is obscured by the schisis cavity. (8) In such cases, treatment may be beneficial in restoring vision. (21) From a lifestyle perspective, these children should be advised to avoid high contact physical activity since minor trauma can lead to vitreous haemorrhage and/or RD. (4)

As it is an area with continued research interest, there is hope for patients with juvenile X-linked retinoschisis. Recently, delivery of normal RS1 genes to knockout mice resulted in significant restoration of retinal structure and function. (16) Novel topical and systemic administration of carbonic anhydrase inhibitors (specifically dorzolamide) has been moderately successful in a few cases. (22) Along with typical low vision aids and management, a patient benefits from learning about the latest research and knowing that advances are being made.

Microcystoid or peripheral cystoid degeneration

Along a continuum with degenerative retinoschisis, cystoid degeneration refers to clusters of small intraretinal cysts just posterior to the ora serrata. The cysts form within the outer plexiform layer and extend circumferentially. (12) They can coalesce and progress to retinoschisis but do not themselves lead to RD. No treatment is required and referral is not indicated. (4)

Pars plana cysts

Pars plana cysts are elevated cysts of the non-pigmented ciliary epithelium of the pars plana. They are usually bilateral and occur in up to 16% of the population. (12) They are filled with clear hyaluronic acid and usually present in one of three ways: isolated, confluent, or clustered. (12) They may be associated with microcystoid areas and can progress to retinoschisis although the possibility is controversial. Again, no treatment is required and referral is unnecessary but as always patients should be monitored carefully for new symptoms, signs, changes or breaks.

RETINAL DETACHMENT

Several peripheral retinal findings discussed in this series have a risk of frank retinal detachment. Retinal detachment is a separation of the neurosensory retina from the underlying RPE. There are three main types of retinal detachments: rhegmatogenous, tractional, and serous (exudative).

[FIGURE 3 OMITTED]

Rhegmatogenous retinal detachment (RRD) occurs when a retinal break allows vitreous fluid to access subretinal space and thus separates the retina from the RPE. Tractional retinal detachments are non-rhegmatogenous, not arising secondary to a retinal break but result from traction between the vitreous and retina. Fibrotic proliferation strands that grow into the vitreous in diseases such as proliferative diabetic retinopathy, sickle cell retinopathy, retinopathy of prematurity, and others, contract causing tensile forces to detach the retina. Serous or exudative retinal detachments are also classified as non-rhegmatogenous and occur secondary to fluid accumulation between the neurosensory retina and the RPE. The fluid may be blood, lipids, or serous fluid from disease processes such as Coat's disease, central serous retinopathy, choroidal tumours, optic pits, and uveal effusion syndrome. (4,5,8)

The peripheral retinal findings discussed in this two-part series are more commonly associated with RRD and thus we will focus briefly on this type.

The incidence of RRD is low at 1 in every 10,000 people in the UK, (23) and globally. (24) A patient may experience symptoms of photopsia, floaters, a dark curtain in the visual field, or a loss of visual acuity.

Some patients, however, may be asymptomatic. An RRD appears as an undulating, mobile, convex area of retina with corrugated folds (see Figure 3). The retinal break appears as a darker-red area. There may be tobacco-dust pigmented cells in the vitreous (Shafer's sign), vitreous haemorrhage, or operculum. The affected eye may have reduced intraocular pressure or a relative afferent pupillary defect. Chronic RRDs often present with demarcated pigment lines, intraretinal cysts, fixed folds or subretinal precipitates. On B-scan ultrasonography the detached retina appears as a highly reflective echo in the vitreous cavity that has remaining attachment to the optic nerve head and ora serrata.4,5,8

[FIGURE 4 OMITTED]

A recent review proposed the pathophysiology of RRD as involving several steps: initial vitreous syneresis that allows gel movement followed by vitreoretinal adhesion dynamics that may be sufficient to cause a retinal tear making subretinal space accessible for the vitreous fluid to enter and thus separating the retina from the RPE. (24,25)

All RDs should be referred to a vitreoretinal specialist. The treatment urgency for RRD depends on patient symptoms and the status of the macula. A macula-on symptomatic retinal detachment demands treatment within two days. (4) If the macula is already off then urgent treatment is recommended within four days, (4) however, visual outcomes are similar as long as the patient is treated within 10 days. (5) Chronic RRDs should ideally be treated within one week. (5) For asymptomatic RRD that does not threaten the macula, intervention may be delayed but the general consensus is that the detachment should still be treated. (4) The goal of treatment is to eliminate traction and to create chorioretinal adhesions around the tear. Scleral buckling, pneumatic retinopexy and pars plana vitrectomy are effective at reducing tractional forces and are often combined with cryopexy or laser photocoagulation to create a fluid barrier and seal the retina (see Figure 4). (24,25)

The prognosis is variable depending on the underlying aetiology. Careful observation must be made for redetachment in the same eye and detachment in the fellow eye. (4) A patient should be further educated about potential symptoms of RD and instructed to return immediately if experiencing any of these symptoms.

PUTTING IT TOGETHER

This series of articles should emphasise the importance of thorough investigation of the retinal periphery in all of your patients, even asymptomatic ones with proper understanding and classification of retinal lesions. Appropriate monitoring for the development of potential complications is also of paramount importance. As outlined in the first article the old adage, 'if in doubt, send it out' remains true and practitioners should recognise their limitations, referring patients with appropriate urgency if they are unsure of their findings.

1 CET PCINT

Continuing with the exploration of retinal degenerations, the second part in the series considers the clinical presentation of additional findings that may be discovered lurking in the periphery.

// REFLECTIVE LEARNING

Having completed this CET exam, consider whether you feel more confident in your clinical skills--how will you change the way you practice? How will you use this information to improve your work for patient benefit?

Dr Kate Lanier OD, FAAO

ABOUT THE AUTHOR

Dr Kate Lanier is a clinical instructor at Anglia Ruskin University and author for KMK Continuing Education. She completed a primary care/ ocular disease residency at the W.G. (Bill) Hefner VA Medical Center hospital in the US and worked in a medical-model private practice in North Carolina.
Table 1

Retinoschisis versus retinal detachment

               Retinoschisis              Retinal detachment

Visual field   Absolute defect and        Relative defect that may
               usually stable             be progressive

State of the   Usually normal             May have tobacco
vitreous                                  dust and/or vitreous
                                          haemorrhage

Appearance     Smooth surface, dome-      Corrugated, irregular
               shaped                     surface

With eye       Stationary                 Undulating
movement

Symptoms       Usually none               May have flashes,
                                          floaters, darkening
                                          curtain across vision

Most common    Often inferior-            Unilateral (if bilateral
location       temporal, bilateral, and   then not usually
               simultaneous               simultaneous)

Incidence in   2-7% over 40 years old     Less than 1%
population                                of population

With scleral   Height remains             Subretinal fluid may
depression     unchanged                  be displaced

Ultrasound     No after-movement, thin    May have after-
B-scan         and dome shaped            movement, thicker, and
                                          maintains attachment to
                                          ONH and ora serrata

OCT            Splitting of               Detachment of retina
               retinal layers             from RPE
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Title Annotation:CET//PERIPHERAL RETINA
Author:Lanier, Kate
Publication:Optometry Today
Geographic Code:4EUUK
Date:Apr 18, 2015
Words:2657
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