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Management & investigation of retinal conditions.

MODULE 13 PART 5: CLINICAL OPTOMETRY COURSE CODE: C-13747 O/D

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Anatomy

Retinal conditions may be classified as being either macular or those associated with the peripheral retina. The macula measures 5.5-6.0mm in diameter, which is approximately four disc diameters. It is has a circular shape. The centre of the macula is situated 4mm temporal and 0.8mm inferior to the centre of the optic disc. Within the macula region is a central pit called the fovea. It measures 1.5mm wide and can be seen during ophthalmoscopy by an oval light reflex. The floor of the foveal depression is called the foveola, measuring 0.33mm. It is the thinnest point of the retina and is without ganglion cells. The deepest point of the foveola is named the umbo. The umbo represents the precise centre of the macula, the area of retina that results in the highest visual acuity (VA); it has a very high concentration of cones. The foveal avascular zone (FAZ) measures approximately 0.35-0.50mm in diameter and is delineated using fluorescein angiography.

The peripheral retina can be divided into belts of near, middle, far, and extreme periphery. The belt of the near periphery is 1.5 mm wide, and the belt of the middle periphery, or equator, is 3mm wide. The far periphery extends from the equator to the ora serrata. The width of this circular area varies, depending on ocular size and refractive error. The average circumference of the eye is 72mm at the equator and 60mm at the ora serrata, and the average width of this strip is 6mm. One clock hour corresponds to 5-6mm of far peripheral circumference. Therefore, the far periphery of the retina may be divided into 12 segments that measure approximately 6mmx6mm. The ora serrata and pars plana are referred to as the extreme periphery.

Macular disease

Patients with macular disease may complain of a reduction in central VA or have difficulties with their colour vision. Red-green colour vision defects are often indicative of optic nerve disease whereas blue-yellow defects point to retinal abnormalities. This finding is termed Kollner's rule. Patients may complain of distortion of their vision (metamorphopsia). The Amsler grid is a useful tool for patients to use in order to detect early maculopathy. More specifically patients will complain of diminution of image size (micropsia) when their foveal cones are physically separated. This is a feature of central serous retinopathy (CSR--see later). When the patient with maculopathy notices a scotoma it is a positive phenomenon in that the patient is aware that something is blocking their vision. This contrasts with the negative scotomas that are produced by optic nerve lesions. Here the patient is aware of a gap in their vision. When patients have macular disease, they are often photosensitive and take a prolonged time to recover when tested using the photostress method. Contrast sensitivity may be reduced in patients with macular disease. Unless there is extensive maculopathy, in general there is no relative afferent pupillary defect (RAPD) in patients presenting with macular disease.

Low-vision aids should be considered in any individual who suffers from macular disease that affects his or her ability to perform activities of daily living. Various devices exist for different tasks including reading, writing, computer work, driving, and distance vision. Reading lamps and simple magnifiers may be of significant benefit. Closed-circuit television and scanning devices are also available to provide electronic magnification and contrast enhancement. Implantable intraocular telescopes are also in development.

Macular hole

A macular hole is defined as a full thickness depletion of the neural retinal tissue in the centre of the macula. The majority of macular holes are idiopathic, however there is a small association with a history of retinal detachment, previous trauma, and previous macular oedema.

Women are more commonly affected than men in an almost 2:1 ratio. The average age of onset is 65 years. Patients generally present with painless central visual loss or metamorphopsia. The risk of involvement to their fellow eye at five years is approximately 16%.

Macular holes can be classified into four stages. Stage la is an impending macular hole. It is characterised by a yellow foveolar spot with loss of the foveal depression. Stage lb is an occult macular hole and is characterised by a yellow ring with a bridging interface of vitreous cortex. About 50% of Stage 1 holes resolve following spontaneous vitreofoveolar separation.

Stage 2 is an early full thickness macular hole, which is characterised by a retinal defect. The VA is typically diminished and a pseudo-operculum may overlie the hole. The VA with a Stage 2 hole ranges between 6/15 and 6/120.

A Stage 3 macular hole is characterised by a round retinal defect greater than 400[micro]m in diameter. Stage 4 macular holes show enlargement of this round defect, which is then surrounded by a cuff of subretinal fluid with complete posterior vitreous separation from the posterior pole and optic disc.

The diagnosis of a macular hole can be made clinically. The Watske-Allen test is a useful clinical sign. The test is performed by projecting a narrow slit beam over the centre of the suspected macular hole. A patient with a macular hole will observe the projected beam to be broken or thinned. Optical Coherence Tomography (OCT) is also a very useful investigative tool for diagnosing and classifying macular holes (Figure 1).

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Stage 1 macular holes are initially monitered on a regular basis, as there is a 50% rate of spontaneous improvement. Surgery for macular holes necessitates a vitrectomy with strict post-operative posturing required for one week.

Solar maculopathy is included in the differential diagnosis for a macular hole. This injury occurs as a direct result of sungazing. It is acute in onset and its incidence increases around the time of eclipses. Although vision is initially reduced, a large percentage of cases subsequently improve and retain the standard of vision required for driving.

Epiretinal membrane

An epiretinal membrane is an avascular fibro-cellular membrane, which proliferates on the inner surface of the retina producing various degrees of macular dysfunction. They may be idiopathic. Secondary membranes occur in association with a history of retinal vascular disease, intraocular inflammation or ocular trauma. Secondary membranes may follow retinal detachment surgery, photocoagulation or cryotherapy.

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The symptoms of an epiretinal membrane are consequent on its thickness and its degree of contracture. Epiretinal membranes may be classified as either cellophane maculopathy or macular pucker. Cellophane maculopathy is caused by a thin layer of epiretinal cells. The membrane is transparent, produces no distortion of the inner retinal surface, and the patient is asymptomatic. Their VA may be normal or slightly reduced. The macula exhibits an irregular light reflex or sheen at the macula. The membrane is easiest to see under "red free" light. No surgical intervention is indicated. A macular pucker is caused by thickening and contraction of the epiretinal membrane. Patients will then experience metamorphopsia and associated blurring of vision. Their VA may be reduced to 6/12 or worse depending on the thickness of the membrane. Macular signs include distortion of the blood vessels with associated retinal wrinkling. There may be an associated macular pseudo-hole within the membrane and cystoid macular oedema (CMO) may complicate this condition.

OCT is very useful in distinguishing a macular pseudo-hole from a full thickness macular hole. Epiretinal membranes appear as a hyper-reflective band on the anterior retinal surface (Figure 2). Treatment of epiretinal membranes causing macular pucker is by surgical removal of the membrane.

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Central serous (chorio)-retinopathy

Central serous (chorio)-retinopathy (CSR) generally affects patients in the third or fourth decade of life. There has been an association with development of CSR and periods of high stress. Pregnancy, hypertension and the use of steroids can precipitate or exacerbate a CSR.

A CSR can be classified as either "typical" or the less commonly found "bullous". The patient will present with a sudden onset of unilateral blurred vision in association with a positive relative scotoma, micropsia or metamorphopsia. The VA is only marginally reduced and can be improved using a plus lens. Clinical examination reveals a circular elevated separation of the sensory retina at the macula (Figure 3). There may be small precipitates on the retinal surface. A bullous CSR is characterised by large, single or multiple, serous retinal and retinal pigment epithelium (RPE) detachments that are associated with a bullous inferior retinal detachment (Figure 4). This may be termed a "hanging teardrop" appearance.

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Fluorescein angiography shows leakage at the level of the RPE (Figure 5). In the majority of cases there is a spontaneous resolution of CSR. For those cases that do not resolve within four months, laser photocoagulation may be indicated. A complication of laser treatment is a paracentral scotoma. Photodynamic therapy is also used for the treatment of chronic CSR and anti-vascular endothelial growth factor (anti-VEGF) agents have also been employed. It is important that patients avoid taking steroids when possible, including oral, inhaled, intranasal, and topical dermatologic applications. In general the visual prognosis is good. The majority of patients have no significant permanent visual dysfunction.

Cystoid macular oedema

Cystoid macular oedema (CMO) occurs when there is a breakdown in the inner blood retinal barrier resulting in leakage and a subsequent thickening of the macula (Figure 6). The resulting oedema can be diffuse or cystic in nature. Cystic oedema of the macula can follow intraocular surgery, including cataract surgery. Other causes include vascular occlusive disease, retinal inflammatory disease, retinal photo toxicity, and diabetic retinopathy. CMO has also been reported where topical Latanoprost has been used for the treatment of glaucoma.

Patients with macular oedema will present with a reduction in central VA. Thickening of the macula can he clinically observed using stereoscopic fundus biomicroscopy. There is a loss of retinal transparency and a loss of choroidal detail in the macular area. Fluorescein angiography and OCT are useful in evaluating and monitoring macular oedema. There is a petalloid pattern of dye leakage from the perifoveal capillaries on fluorescein angiography (Figure 7).

The treatment of CMO depends on its underlying cause. If secondary to retinal vascular disease, including diabetic retinopathy and retinal vein occlusion, the standard care remains laser photocoagulation. However, the use of intravitreal injections of anti-VEGF and steroids are now not uncommon. Where the oedema is secondary to chronic intraocular inflammation, this improves with the use of steroids.

CMO was traditionally associated with intracapsular cataract surgery (Irvine-Gass syndrome). The technique of phacoemulsification has, however, reduced post-operative macular oedema. Post-operative CMO is seen where there is complicated surgery such as posterior capsular rupture and vitreous loss. Treatments include topical steroids or non-steroidal anti-inflammatory drugs (NSAIDs), periocular injections of steroids, or systemic carbonic anhydrase inhibitors. Surgical correction removes any element of vitreo-macular traction. Vitreo-macular traction occurs when there is an incomplete posterior vitreous separation with pre-retinal tissue, with proliferation and hence associated traction in the zone of the persistent vitreous attachment. In general there is a prominent vitreo-retinal attachment at the posterior pole in association with a peripheral vitreous detachment

Louise O'Toole MMedSci FRCSI(Ophth) MRCOphth FEBO

This article is the first of two that will discuss the investigation and management of retinal and vascular conditions. The article describes both macular and peripheral retinal diseases whilst a second article will discuss vascular abnormalities of the retina.

(PVD). There may be distortion of the internal limiting membrane with retinal striae and vascular tortuosity observable. This may then lead to macular oedema. There may also be a localised traction-related macular detachment. The patient experiences reduced central vision with some degree of metamorphopsia. If the VA is good, no treatment is indicated. However, if there is evidence of progressive traction and visual loss, surgical intervention is then required.

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Macular dystrophies

Stargardt's disease

Stargardt's disease and fundus flavimaculatus are thought of as being variants of the same disease process. The term fundus flavimaculatus is used when the characteristic flecks that accumulate at the level of the RPE are distributed throughout the fundus and onset is in adult life. The term Stargardt's disease is used when the flecks are confined predominantly to the posterior pole and are present early in life.

Stargardt's disease is the most common of the inherited macular dystrophies, accounting for approximately 7% of all retinal dystrophies. The inheritance pattern of Stargardt's disease is usually through an autosomal recessive gene but autosomal dominant cases have also been reported. The autosomal recessive form of the disease has been mapped to the short arm of chromosome 1. The ABCR gene has been identified as the causative gene. This gene locus has also been implicated in age-related macular degeneration (see later), autosomal recessive Retinitis Pigmentosa, and autosomal recessive cone-rod dystrophy.

In Stargardt's disease, the presentation is during childhood with bilateral, gradual impairment of central vision. The clinical course is slowly progressive with increasing central atrophy. The visual prognosis is poor, and VA typically ranges between 6/24 and 6/60. Because the ABCR gene is also involved in processing Vitamin A, dietary supplementation with Vitamin A or beta-carotene supplements may actually worsen the clinical condition.

In the condition fundus flavimaculatus, there are bilateral ill-defined yellow white spots or flecks at the level of the RPE scattered throughout the posterior pole and the periphery. These flecks may be round, oval, or disciform in shape. The visual prognosis for fundus flavimaculatus is better than Stargardt's disease, and patients may remain asymptomatic unless a fleck involves the fovea.

Best's disease

Best's disease is an autosomal dominant inherited condition. It shows highly variable clinical expression and penetration. The gene for Best's disease has been mapped to chromosome 11 and mutations have been found in the bestrophin gene.

In childhood, bilateral symmetrical large yellow yolk-like (vitelliform) lesions appear at the maculae. As the disease progresses, these lesions break down (vitelliruptive) with resultant scarring and atrophy. Multifocal Best's disease has also been described. Best's disease can be complicated by choroidal neovascularisation.

All affected individuals have an abnormal electrooculogram (EOG) and this is a useful diagnostic tool. The VA is generally good during childhood although in adulthood the VA tends to fall.

The inheritance pattern of Cone Dystrophy is generally autosomal dominant. Early symptoms experienced include a reduction in VA, particularly in bright light. The patient experiences difficulty with colour vision and suffers from central visual field defects. On examination, the initial fundal changes are a pigmentary stippling of the posterior pole. This progresses to a "bulls-eye" pattern in advanced disease. Electrodiagnostic testing shows a grossly abnormal electroretinogram (ERG). Visual loss is gradual but may be profound.

Pattern dystrophies

The pattern dystophies encompass a group of disorders whose inheritance pattern tends to be autosomal dominant. There is a symmetrical accumulation of pigmented deposits in the maculae. However, few of the dystrophies are exclusive to the macula; pan-retinal involvement is evident following electrodiagnostic testing.

There are several patterns of deposition. The most commonly observed subtype is the "butterfly" pattern. There is a symmetrical reticular pattern of pigmentation and it is from this morphological appearance that the dystrophy takes its name. The lesions are more easily seen using fluorescein angiography. This disorder becomes manifest in the second to fifth decades of life and is accompanied by normal or only slightly decreased vision.

Juvenile retinoschisis

X-linked juvenile retinoschisis was first described by Haas in 1898. It is an X-linked recessive condition with 100% penetration. The abnormal gene has been mapped to the short arm of the X chromosome and therefore only males are affected by this condition. Electroretinographic testing indicates that the abnormality is at the level of the Muller cell. Female carriers have both a normal clinical examination and normal electrophysiological testing.

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In X-linked juvenile retinoschisis there is a split between the nerve fibre and ganglion cell layers of the retina. There is a spectrum of phenotypical presentations. The pathognomonic finding is a radial cystic maculopathy. Peripheral retinoschisis is present in 50% of patients. This may be complicated by retinal detachments and vitreous haemorrhages.

The visual outcome of X-linked juvenile retinoschisis is variable and cannot be predicted based on the fundus findings alone. The VA is usually in the region of 6/18 in the affected young adult, and it may remain stable for many years, with gradual deterioration to about 6/36 by the sixth decade of life. Most affected patients are legally blind by the seventh decade of life.

North Carolina Dystrophy

North Carolina Dystrophy becomes apparent in early childhood when there are scattered drusen and pigment dispersion within the foveae. Visual function is initially good. However, with time there is progression to total pigment epithelial and choriocapillary atrophy at the maculae and consequently poor visual function.

Age-Related Macular Degeneration

Age-related Macular Degeneration (AMD) is becoming very prevalent due to the ageing population. It is the leading cause of irreversible visual impairment among the elderly worldwide, affecting 30-50 million individuals. Risk factors include a positive family history, uncontrolled hypertension, exposure to harmful ultraviolet (UV) light, light coloured irides and smoking. AMD is divided into two subgroups--the non-neovascular or dry form and the neovascular or wet form. The dry subgroup is the more common, comprising over 85% of cases of AMD. Macular signs in this group include soft drusen, hyperpigmentary changes and geographic atrophy. Patients with this form of AMD have an insidious pattern of visual loss. They will notice central scotomas and have difficulty with fine print and contrast sensitivity. In the wet form of AMD, the visual loss is sudden and profound. Once advanced AMD develops in one eye, there is an increased likelihood of geographic atrophy or neovascularization occurring in the fellow eye. The key finding in wet AMD is a choroidal neovascular membrane (CNVM). This manifests as a grey-green lesion and is comprised of subretinal blood vessels. There may be associated subretinal fluid and haemorrhages (Figure 8). The CNVMs may be classified according to their location as subfoveal, juxtafoveal or extrafoveal. They may also be classified according to their angiographic appearances as being either classic or occult in nature (Figure 9). Indocyanine Green Angiography (ICG) is useful in classifying further subtypes of AMD such as Idiopathic Polypoidal Choroidal Vasculopathy (IPCV) and Retinal Angiomatous Proliferation (RAP).

OCT provides useful non-invasive imaging in AMD (Figure 10) whilst Scanning Laser Ophthalmoscopy (SLO) is a useful adjunct in the management of AMD. In cases of AMD, fluorescence is increased in a sick RPE and is extinguished when these cells die. An accumulation of lipofuscin accounts for increased signal activity measured with SLO in AMD.

There is currently no effective treatment for the dry form of AMD but significant advances have occurred in recent times for the treatment of the wet form of AMD. Previously, the standard treatment for wet AMD was to ablate the CNVM with laser photocoagulation. However, if the CNVM were sub- or juxtafoveal, there tended to be collateral damage and macular function would inevitably suffer following the laser treatment. A better outcome was noted in parafoveal CNVMs but patients would notice a paracentral scotoma. This treatment was nevertheless shown to be better than the natural history of wet AMD in the Macular Photocoagulation Study. (1)

Photodynamic therapy (PDT) was developed in order to target only the CNVM and minimise collateral damage. It involves the intravenous injection of a photosensitive dye called Verteporfin, which is activated by low energy laser light. The photochemical reaction that ensues activates a thrombotic pathway and closes the CNVM. The Treatment of AMD with Photodynamic Therapy (TAP) study reported the success of PDT in reducing visual loss in cases of subfoveal classic CNVMs. (2) However, it is only with use of anti-VEGF agents that visual recovery has been demonstrated in all types of AMD.

VEGF is an important component in angiogenesis and its inhibition reduces the development of CNVMs. The anti-VEGF compounds are injected directly into the vitreous cavity. With this treatment however, there are risks of endophthalmitis, cataract, retinal tears and haemorrhage, as it is an invasive procedure. Commercially available preparations such as Pegaptanib sodium (Macugen), which is VEGF-A isform 165 specific, and Ranibizumab (Lucentis), which binds all active forms of VEGF-A, as well as off-label preparations such as Avastin (Bevacizumab), are in current use.

Two important trials--the MARINA (Minimally Classic/Occult Trial of the Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular AMD) and ANCHOR (Anti-VEGF Antibody Ranibizumab for the Treatment of Predominantly Classic Choroidal Neovascularization in AMD)--showed the beneficial effect of Lucentis for neovascular AMD, regardless of lesion subtype. (3,4) Lucentis was the first agent to result in a sustained VA improvement in the treated patient groups.

There are a number of international trials currently underway comparing the efficacy of Avastin and Lucentis including the IVAN (Inhibit VEGF in Age-related choroidal Neovascularisation) and CATT (Comparison of Age-Related Macular Degeneration Treatments Trials) studies. The results of these trials will have massive economic implications, as Lucentis is several times more expensive then Avastin. Combination treatments of anti-VEGF agents with either intravitreal or subtenons injections of steroids such as anecortave acetate (RETAANE study) as well as PDT are under investigation. If successful, this form of combination treatment will reduce the number of intravitreal injections required. Future treatments of wet AMD include a VEGF trap that is smaller and binds to VEGF more avidly then its predecessors. Other therapies in clinical trials directly reduce the amount of VEGF being produced, by modulating its RNA activity. Surgical translocation of CNVMs in eyes is also a recognized treatment for wet AMD. In all cases, the advent of OCT has reduced the need for frequent fluorescein angiograms in monitoring the response of AMD to treatment, aiding larger scale studies to be conducted.

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Prevention of AMD is however better then any cure. The Age-Related Eye Disease Study (AREDS) showed a beneficial effect of anti-oxidant supplementation on retarding the progression to advanced AMD. (5) The AREDS formulation included vitamins C, E, beta-carotene and zinc with copper. The formulation was shown to be statistically significant in reducing the progression to advanced AMD by 25% in patients with bilateral large drusen as well as in patients with advanced AMD already affecting one eye. Oxidative stress is thought to play a significant role in the pathogenesis of AMD.

Beta-carotene should not be prescribed to smokers as it increases their risk of lung cancer. The antioxidant capabilities of lutein and zeaxanthin may be useful in the prevention of AMD. Some studies have recommended omega-3 fatty acids and vitamin B (including the variants) in the prevention of wet AMD. The AREDS 2 study is looking to see whether oral supplementation with lutein and zeaxanthin or omega-3 long-chain polyunsaturated fatty acids will decrease the progression to advanced AMD compared to control patients.

Myopic Maculopathy

Choroidal neovascularization can also be a feature of myopic maculopathy. Myopic maculopathy is a complication of patients whose refractive error is greater then -6.00DS. There is attenuation of the RPE and this may be complicated by the development of lacquer cracks. Macular haemorrhages or "coin lesions" may also cause a drop in central vision. Patients who have excessive myopia can also have strabismus, typically an exophoria or exotropia, and they are more likely to develop early cataracts.

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The prevalence of glaucoma is related to the degree of myopia. Determination of glaucomatous changes can be difficult in cases with highly tilted optic discs or where there is an adjacent posterior staphyloma. Among the other serious complications of progressive myopia are vitreous syneresis and rhegmatogenous retinal detachment that results from peripheral tears. Such detachments are usually spontaneous, but they may occur after blunt ocular trauma or subsequent to cataract surgery, especially when complicated by capsular rupture and vitreous loss.

Peripheral retinal disease

Symptoms of peripheral retinal disease are rod-determined and therefore disruption of night vision may be a commonly reported symptom. Photopsia and floaters may indicate a peripheral retinal tear that requires immediate investigation, whilst a constricted visual field may suggest dysfunction of the rod photoreceptors. In many other cases of peripheral retinal disease, the patient may be completely asymptomatic and therefore diagnosis is made purely based on objective examination.

Retinitis Pigmentosa

Retinitis Pigmentosa (RP) comprises a group of hereditary disorders. They are associated with a primary abnormality of the photoreceptor-RPE complex. Patients with RP may complain of difficulties with their vision in dimly lit surroundings or total nyctalopia. On examination, typical findings are a constricted visual field, retinal bone-spicule pigmentation, arteriolar attenuation and waxy optic disc pallor.

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Although central vision may be preserved for many years in the autosomal dominant form of RP, this can be affected in the X-linked or autosomal recessive forms. Posterior subcapsular cataract formation and CMO can complicate RP and reduce central vision.

Electrodiagnostic testing confirms the diagnosis of RP. Affected patients will have abnormal dark adaptometry and electroretinography (ERG) as well as electrooculography (EOG). EOG is a useful tool in identifying female carriers of X-linked RP as their fundal examination is normal.

Approximately 25% of patients maintain reading vision throughout their lives. The RP variant with the best visual prognosis is the autosomal-dominant form. The X-linked form has the least favourable prognosis.

There are some systemic diseases associated with RP. Kearns-Sayre syndrome combines a pigmentary retinopathy with Chronic Progressive External Ophthalmoplegia (CPEO), and complete heart block. This cardiac complication can result in death. Usher's syndrome refers to the combination of RP and sensory-neural deafness. Usher's syndrome accounts for 50% of cases of blind-deaf individuals. A white cane will alert people to a visually impaired individual, whilst those who have a concurrent hearing impairment carry a white cane with a red stripe.

Rubella Retinopathy

Congenital infection with the rubella virus can cause a number of abnormalities. The classic triad presentation of congenital rubella syndrome consists of sensory-neural hearing loss, ocular abnormalities and congenital heart disease. Congenital heart disease includes patent ductus arteriosus (PDA) and pulmonary artery stenosis. Sensory-neural hearing loss is the most common manifestation of congenital rubella syndrome. The hearing impairment may be bilateral or unilateral and may not be apparent until the second year of life.

Ocular abnormalities including cataract, infantile glaucoma, and pigmentary retinopathy occur in children with congenital rubella syndrome. Both eyes are affected in the majority of patients, and the most frequent findings are cataract and rubella retinopathy. Rubella retinopathy consists of a salt-and-pepper pigmentary change or a mottled, blotchy, irregular pigmentation, usually with the greatest density in the macula (Figure 11). The retinopathy is benign and non-progressive and in general there is preservation of good vision.

Congenital Hypertrophy of the Retinal Pigment Epithelium

Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE) is a benign congenital lesion of the RPE. They are grey or deep black in appearance, well-defined, thin, circular or oval lesions, found deep in the sensory retina at the level of the RPE. They can be solitary or multifocal and may be typical or atypical. The solitary lesion can measure between 1mm and 6mm in diameter. There may be a surrounding ring of hypopigmentation. Although generally black, the lesion may have some lacunar areas of depigmentation. The multifocal lesions can also be termed "bear tracks" (Figure 12). Groups of 3 to 30 small (0.1-2mm) lesions typically have a sectoral distribution within the fundus. The atypical, bilateral, multifocal CHRPE lesions associated with familial adenomatous polyposis (FAP) of the colon are relatively uncommon, occurring in only about one in 100,000 persons.

Choroidal Naevus

A choroidal naevus is a benign lesion commonly observed in the posterior fundus (Figure 13). It is usually flat or minimally elevated. It is more commonly found in the Caucasian population. A choroidal naevus should be photographed where possible or a detailed drawing made as these lesions may transform to become malignant choroidal melanomas. Suspicious findings for melanoma associated with naevi include large size, proximity to the optic disc, symptoms (flashing lights or a change in their vision), and overlying yellow pigment lipofuscin. The mnemonic TFSOM ("To Find Small Ocular Melanoma") is a useful aid attributed to the Ocular Oncology Department of the Wills Eye Hospital, Philadelphia (Table 1).

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Retinal Breaks & Tears

A peripheral retinal break or tear is a full thickness retinal defect. They occur more commonly following trauma or in patients with myopia or who are pseudophakic. Patients with lattice and snail-track degeneration carry an increased risk of developing a retinal tear. Lattice degeneration is found in patients with Marfan and Stickler syndromes. It consists of spindle shaped areas of retinal thinning containing a branching network of fine white lines.

Alerting symptoms of a retinal tear are flashing lights and floaters. A strongly associated ophthalmic sign is "tobacco dust"--pigment cells in the vitreous. Where there is a high clinical suspicion of a retinal tear, patients should be referred for immediate examination using indirect ophthalmoscopy and to include scleral depression. Approximately 60% of retinal breaks are situated in the upper temporal quadrant. Early detection allows treatment of the tear with argon laser photocoagulation.

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When a retinal detachment follows a retinal tear it is termed rhegmatogenous. The patient may become aware of an advancing peripheral field defect. In eyes with an extensive retinal detachment there is a RAPD. The intraocular pressure (IOP) in the eye with the detachment is typically lower then its fellow eye. The retinal detachment is then treated surgically, either internally with a pars plana vitrectomy or externally by buckling.

A tractional retinal detachment occurs without a retinal break. In contrast to the rhegmatogenous retinal detachment, which often has a convex, even bullous surface, the typical tractional retinal detachment has a more concave surface and is likely to be more localized, often not extending to the ora serrata. Tractional retinal detachments complicate proliferative retinopathy and are seen in advanced diabetic eye disease and Retinopathy of Prematurity (ROP).

A choroidal tumour can cause an exudative retinal detachment. An exudative detachment occurs when there is a passage of fluid from the choroid into the subretinal space and consequent elevation of the retina. Posterior scleritis, severe hypertension and heavy pan-retinal photocoagulation can cause an exudative retinal detachment. Retinal telangiectasia and choroidal neovascularisation can also cause exudative retinal detachments. Treatment of this condition is to treat the underlying cause.

Mgc in Clinical Optometry

CITY UNIVERSITY and OT have joined forces allowing readers to achieve CET points through to a full Masters in Clinical Optometry. MSc courses running at City University include: Principles of Therapeutics (apply anytime--web-based), Independent Prescribing (June 20-22nd 2010), Glaucoma (July 18-20 2010), Posterior Segment Eye Disease (September 5-7 2010) and Binocular Vision (November 14-16 2010). For further information please contact Dr Michelle L Hennelly by emailing (m.hennelly@ city.ac.uk) or call 0207 040 8352.

References

See www.optometry.co.uk/references

Louise O'Toole MMed Sci, FRCSI(Ophth) MRCOphth, FEBO is a consultant medical ophthalmologist in the Mater Private Hospital, Eccles Street, Dublin. She is also a lecturer to undergraduate optometrists in the Dublin Institute of Technology She has been involved in teaching on the MSc in Clinical Optometry at City University, London, particularly in the area of Ocular Therapeutics, and has written several articles in the field for Optometry Today.

Module questions

1. Which of the following statements about the macula is FALSE?

a. The macula measures 5.5-6.0cm in diameter

b. The most central point is termed the umbo

c. The umbo has a very high concentration of cones

d. The centre of the macula is situated temporal and inferior to the optic disc

2. All of the following are signs and/or symptoms of maculopathy EXCEPT?

a Micropsia

b. Image distortion

c. Photosensitivity

d. Relative afferent pupillary defect (RAPD)

3. Which of the following statements about macular holes is FALSE?

a. Women are more affected than males

b. Visual loss is painless

c. The majority of cases are idiopathic

d. They are always treated with surgery

4. Which of the following statements about epiretinal membranes is FALSE?

a. Symptoms include metamorphopsia

b. They are more easily seen using a yellow light

c. They appear as a hyper reflective band on the anterior surface of the retina using OCT

d. They may be associated with a macular pseudohole

5. Which of the following statements about central serous retinopathy is FALSE?

a. It is associated with the use of steroids

b. It is more common in males

c. It always requires laser photocoagulation

d. Patients may complain of micropsia

6. Which of the following statements about Stargardt's disease is FALSE?

a. It is generally autosomal recessive

b. It is one of the most common inherited macular dystrophies

c. It may be worsened by Vitamin A supplementation

d. No genetic abnormality has been determined

7. Which of the following statements about Retinitis Pigmentosa is FALSE?

a. There may be retinal bone spicule pigmentary changes

b. Arteriolar attenuation is a feature

c. Optic disc hyperaemia is a typical finding

d. It may be associated with cataracts

8. Which of the following statements about Intravitreal injections for age-related macular degeneration (AMD) is FALSE?

a. They may be complicated by haemorrhage

b. They may be complicated by endophthalmitis

c. They are generally administered under local anaesthesia

d. They are not indicated for subfoveal choroidal neovascular membranes

9. Which of the following statements about the AREDS formula for AMD is FALSE?

a. It includes Vitamin C

b. It includes Vitamin E

c. It includes zinc

d. It includes magnesium

10. Which of the following statements about congenital hypertrophy of the retinal pigment epithelium (CHRPE) is FALSE?

a. it is a benign lesion

b. It may be solitary or multifocal

c. Atypical CHRPE lesions are associated with cardiomyopathy

d. It may be surrounded by a hypopigmentary ring

11. Which of the following statements about retinal detachments is FALSE?

a. They are always preceded by a retinal tear

b. They are more common in myopic eyes compared to hypermetropic eyes

c. They may present with a history of photopsia and floaters

d. They are a feature of Marfan's syndrome

12. Which of the following statements about age-related macular degeneration (AMD) is FALSE?

a. It is generally bilateral

b. It is worsened by smoking

c. It may present with metamorphopsia

d. It causes peripheral visual loss
Table 1
Mnemonic to aid in the identification of a suspected
ocular melanoma

T Thickness > 2mm
F Fluid--sub-retinal fluid present
S Symptoms
O Orange pigment (lipofuscin)
M Margin--touching the optic disc
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Title Annotation:CONTINUING EDUCATION & TRAINING
Author:O'Toole, Louise
Publication:Optometry Today
Geographic Code:4EUUK
Date:May 7, 2010
Words:5745
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