Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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Retinopathy in blood disorders

Leukaemia

Classification

The leukaemias are malignancies of the haematopoietic stem cells characterized by abnormal proliferation of white blood cells. Acute leukaemias are characterized by replacement of bone marrow with very immature (blast) cells (Fig. 13.77A). Chronic leukaemias are associated, at least initially, with well-differentiated (mature) leucocytes (Fig. 13.77B) and occur almost exclusively in adults. The four major variants of leukaemia are:

1Acute lymphocytic (lymphoblastic) that predominantly affects children; overall, 90% of cases respond to treatment and approximately 70% are cured.

2 Acute myelocytic (myeloblastic) is most frequently seen in older adults and is curable in 30% of those under the age of 60 years. 3 Chronic lymphocytic has a very chronic course and many patients die from an unrelated cause.

4Chronic myelocytic has a progressive clinical course and a less favourable prognosis.

Fig. 13.77 Blood filmin leukaemias. (A) Bone marrow aspirate in acute myeloid leukaemia shows immature blast cells; (B) peripheral blood smear in chronic lymphatic leukaemia shows many mature lymphocytes

Ocular features

Ocular involvement is more commonly seen in the acute than the chronic forms and virtually any ocular structure may be involved. It is, however, important to distinguish the fairly rare primary leukaemic infiltration from the more common secondary changes such as those associated with anaemia, thrombocytopenia, hyperviscosity and opportunistic infections; these may manifest as intraocular bleeding, infection and vascular occlusion.

1Fundus changes

•Retinal haemorrhages, cotton wool spots and retinal haemorrhages with white centres (Roth spots – Fig. 13.78A) occur in acute leukaemias.

•Peripheral retinal neovascularization is an occasional feature of chronic myeloid leukaemia (Fig. 13.78B).

•Choroidal deposits in chronic leukaemia may give rise to a ‘leopard skin’ appearance (Fig. 13.78C).

•Optic nerve infiltration may cause swelling and visual loss.

2Other ocular features

•Orbital involvement, particularly in children.

•Iris thickening, iritis and pseudohypopyon.

•Spontaneous subconjunctival haemorrhage and hyphaema.

•Cranial nerve palsies.

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Fig. 13.78 Fundus changes in haematological disorders. (A) Retinal haemorrhages, cotton wool spots and Roth spots in acute leukaemia and anaemia associated with thrombocytopenia; (B) peripheral retinal neovascularization in chronic myeloid leukaemia; (C) ‘leopard-skin’ appearance due to choroidal infiltration in chronic leukaemia; (D) retinal haemorrhages, and gross venous dilatation and segmentation in hyperviscosity

(Courtesy of P Saine – fig. A; P Morse – fig. B)

Anaemia

The anaemias are a group of disorders characterized by a decrease in the number of circulating red blood cells, a decrease in the amount of haemoglobin in each cell, or both, that occurs when the equilibrium between blood loss and production are disturbed. Retinal changes in anaemia are usually innocuous and rarely of diagnostic importance.

1Systemic features include pallor, atrophic glossitis, koilonychia and angular stomatitis.

2Retinopathy

•Retinal venous tortuosity is related to the severity of anaemia but may occur in isolation, particularly in patients with betathalassaemia major.

•Dot/blot and flame-shaped haemorrhages, cotton wool spots and Roth spots are more common with co-existing thrombocytopenia in aplastic anaemia (see Fig. 13.78A). The duration and type of anaemia do not influence the occurrence of these changes.

3Optic neuropathy with centrocaecal scotomas may occur in patients with pernicious anaemia. Unless treated with vitamin B12 supplements, permanent optic atrophy may ensue. Pernicious anaemia may also cause dementia, peripheral neuropathy and subacute combined degeneration of the spinal cord; the latter is characterized by posterior and lateral column disease.

Hyperviscosity

The hyperviscosity states are a diverse group of rare disorders characterized by increased blood viscosity due to polycythaemia or to abnormal plasma proteins (e.g. Waldenström macroglobulinaemia).

1Polycythaemia is caused by neoplastic proliferation of erythrocytes leading to hyperviscosity and increased bone marrow activity; plethora, splenomegaly, pruritus, hypertension, angina, gout, thrombosis and haemorrhage.

2Waldenström macroglobulinaemia is a malignant lymphoproliferative disorder with monoclonal IgM production that most frequently affects elderly men. It is characterized by fatigue, easy bruising, lymphadenopathy, hepatosplenomegaly, Raynaud phenomenon and peripheral vascular disease.

3Fundus features include retinal haemorrhages and venous dilatation (Fig. 13.78D), occasionally retinal vein occlusion and conjunctival telangiectasia.

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Congenital vascular anomalies

Retinal macrovessel

1Signs. A unilateral, large, aberrant retinal vessel, usually a vein, is present in the posterior pole and may cross the foveal region and horizontal raphe (Fig. 13.79A). Because arteriovenous anastomoses are also often present the condition may be considered to be a variant of racemose angiomatosis (see Ch. 12).

2FA may show early filling and delayed emptying of the vessel; a dilated capillary bed surrounding the macrovessel is often present. Areas of capillary non-perfusion and foveal cysts may also be seen.

Fig. 13.79 Congenital retinal vascular anomalies. (A) Retinal macrovessel; (B) arteriovenous communication; (C) FA shows filling but no leakage

(Courtesy of C Barry – figs B and C)

Arteriovenous communications

Congenital arteriovenous communications usually present on routine examination, with unilateral involvement in single or multiple sites of the same fundus. They have a predilection for the papillomacular bundle and the superotemporal quadrant. Occasionally reported complications include haemorrhage, exudation and vascular occlusion. Some patients may harbour similar systemic lesions. The malformations can be divided into the following three types on the basis of severity.

Group 1 consists of an anastomosis between a small arteriole and venule with the interposition of an abnormal capillary or arteriolar plexus. It is non-progressive and associated with good visual acuity.

Group 2 demonstrates direct arteriovenous communications between a branch retinal artery and vein (Fig. 13.79B and C). Group 3 consists of diffuse marked dilatation of the vascular tree with many large-calibre anastomosing channels.

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Chapter 14 – Acquired Macular Disorders

INTRODUCTION 594

CLINICAL EVALUATION OF MACULAR DISEASE 595 Symptoms 595

Slit-lamp biomicroscopy  595

Visual acuity 596 Contrast sensitivity 598 Amsler grid 598

FUNDUS FLUORESCEIN ANGIOGRAPHY 601 INDOCYANINE GREEN ANGIOGRAPHY 608 OPTICAL COHERENCE TOMOGRAPHY 611 AGE-RELATED MACULAR DEGENERATION 611

Introduction 611

Drusen 613

Prophylactic antioxidant supplementation in AMD  615

Non-exudative (dry) AMD 616

Retinal pigment epithelial detachment 616 Retinal pigment epithelial tear 619 Choroidal neovascularization 620 Haemorrhagic AMD 627

Retinal angiomatous proliferation 627

POLYPOIDAL CHOROIDAL VASCULOPATHY 628 AGE-RELATED MACULAR HOLE 629

MACULAR MICROHOLE 631

CENTRAL SEROUS CHORIORETINOPATHY 632 CYSTOID MACULAR OEDEMA 633 EPIMACULAR MEMBRANE 635 DEGENERATIVE MYOPIA 637

ANGIOID STREAKS 641 Ocular considerations 641 Systemic associations  641

CHOROIDAL FOLDS 643

HYPOTONY MACULOPATHY 644

VITREOMACULAR TRACTION SYNDROME 645

IDIOPATHIC CHOROIDAL NEOVASCULARIZATION 645

SOLAR RETINOPATHY 645

Introduction

Anatomical landmarks

1The macula (Fig. 14.1A) is a round area at the posterior pole, lying inside the temporal vascular arcades. It measures between 5 and 6 mm in diameter, and subserves the central 15–20° of the visual field. Histologically, it shows more than one layer of ganglion cells, in contrast to the single ganglion cell layer of the peripheral retina. The inner layers of the macula contain the yellow xanthophyll carotenoid pigments lutein and zeaxanthin in far higher concentrations than the peripheral retina (hence the full name ‘macula lutea’ – yellow plaque).

2The fovea is a depression in the retinal surface at the centre of the macula, with a diameter of 1.5 mm (Fig. 14.1B and Fig. 14.2), about the same as the optic disc.

3The foveola forms the central floor of the fovea and has a diameter of 0.35 mm (Fig. 14.1C). It isthe thinnest part of the retina and is devoid of ganglion cells, consisting only of a high density of cone photoreceptors and their nuclei, together with Müller cells.

4The umbo is a depression in the very centre of the foveola which corresponds to the foveolar light reflex, loss of which may be an early sign of damage.

5The foveal avascular zone (FAZ), a central area containing no blood vessels but surrounded by a continuous network of capillaries, is located within the fovea but extends beyond the foveola. The exact diameter varies with age and in disease, and its limits can be determined with accuracy only by fluorescein angiography (FA); an average is 0.6 mm.

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Fig. 14.1 Anatomical landmarks. (A) Normal foveal light reflex; (B) OCTshows the foveal depression; (C) fovea (yellow circle); foveal avascular zone-approximate (red circle); foveola (lilac circle); umbo (central white spot)

Fig. 14.2 Cross-section of the fovea

Retinal pigment epithelium

1Structure

•The retinal pigment epithelium (RPE) is composed of a single layer of cells, hexagonal in cross-section. The cells consist of an outer non-pigmented basal element containing the nucleus, and an inner pigmented apical section containing abundant melanosomes.

•The cell base is in contact with Bruch membrane, and at the cell apices multiple thread-like villous processes extend between the outer segments of the photoreceptors.

•At the posterior pole, particularly at the fovea, RPE cells are taller and thinner, more regular in shape and contain more numerous and larger melanosomes than in the periphery.

2Functions

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•RPE cells and intervening tight junctional complexes (zonula occludentes) constitute the outer blood–retinal barrier, preventing extracellular fluid leaking into the subretinal space from the choriocapillaris, and actively pump ions and water out of the subretinal space.

•Its integrity, and that of Bruch membrane, is important for continued adhesion between the two, thought to be due to a combination of osmotic and hydrostatic forces, possibly with the aid of hemidesmosomal attachments.

•Facilitation of photoreceptor turnover by the phagocytosis and lysosomal degradation of outer segments following shedding.

•Preservation of an optimal retinal milieu. Maintenance of the outer blood–retinal barrier is a key factor, as are the inward transport of metabolites (mainly small molecules such as amino acids and glucose) and the outward transport of metabolic waste products.

•Storage, metabolism, and transport of vitamin A in the visual cycle.

•The dense RPE pigment serves to absorb stray light.

Bruch membrane

1Structure. Bruch membrane separates the RPE from the choriocapillaris and on electron microscopy consists of five distinct elements:

•The basal lamina of the RPE.

•An inner collagenous layer.

•A thicker band of elastic fibres.

•An outer collagenous layer.

•The basal lamina of the inner layer of the choriocapillaris.

2Function. The RPE utilizes Bruch membrane as a route for the transport of metabolic waste products out of the retinal environment. Changes in its structure are thought to be important in the pathogenesis of many macular disorders – for example, its integrity may be important in the suppression of choroidal neovascularization (CNV).

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Clinical evaluation of macular disease

Symptoms

1Blurred vision and difficulty with close work may be an early symptom. Onset can be rapid in some conditions such as CNV.

2A positive scotoma, in which patients complain of something obstructing their central vision, is a symptom of more severe disease. This is in contrast to optic neuropathy which typically causes a missing area in the visual field (a negative scotoma).

3 Metamorphopsia (distortion of perceived images) is a common symptom that is not present in optic neuropathy. 4 Micropsia (decrease in image size) is caused by a spreading apart of foveal cones, and is less common.

5Macropsia (increase in image size) is due to crowding together of foveal cones, and is uncommon.

6Colour discrimination may be disturbed, but is generally less evident than in even relatively mild optic neuropathy.

7Difficulties related to dark adaptation such as poor vision in dim light and persistence of after-images may occur.

Slit-lamp biomicroscopy

Indirect slit-lamp ophthalmoscopy (Fig. 14.3A) utilizes high power convex lenses designed to obtain a wide field of view of the fundus which is vertically inverted and laterally reversed (Fig. 14.3B). The technique is as follows:

Fig. 14.3 (A) Indirect slit-lamp biomicroscopy; (B) fundus view

(Courtesy of B Tompkins – fig. B)

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Visual acuity

Snellen visual acuity

Distance visual acuity (VA) is directly related to the minimum angle of separation (subtended at the nodal point of the eye) between two objects that allow them to be perceived as distinct. It is usually carried out using black letters or symbols (optotypes) of a range of sizes set on a white chart at a standard distance.

1Normal VA equates to 6/6 (metric notation; 20/20 in non-metric ‘English’ notation) on Snellen testing (see below, Fig. 14.4). This should be regarded as only a reference or screening standard because normal corrected VA in healthy young adults is usually superior (6/4 – roughly 20/12) and then drops to 6/6 (20/20) by around the 7th decade.

2Best-corrected VA denotes the level achieved with optimal refractive correction.

3Pinhole VA. A pinhole (PH) aperture consists of an opaque occluder perforated by one or more holes of about 1 mm diameter (Fig. 14.5). It compensates for the effect of refractive errors. However, PH acuity in patients with macular disease and posterior lens opacities may be worse than with spectacle correction.

Fig. 14.4 Snellen visual acuity chart

Fig. 14.5 Pinhole occluder

Very poor visual acuity

If the patient is unable to read any letters at any distance, VA is recorded as follows:

1Counting fingers (CF) denotes that the patient is able to tell how many fingers the examiner is holding at a specified distance (Fig. 14.6).

2Hand movements (HM) is the ability to distinguish whether the examiner's hand is moving when held just in front of the patient.

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3Perception of light (PL) means that the patient can discern only light. The quadrant from which the light can be perceived (projected) should be noted on a chart (Fig. 14.7).

Fig. 14.6 Testing of ‘counting fingers’ visual acuity

Fig. 14.7 Notation for the projection of light test (right eye); the patient cannot detect light directed towards the superior and temporal quadrants

LogMAR acuity

LogMAR charts address many of the deficiencies of the Snellen chart (Table 14.1), and are the standard means of VA measurement in research and increasingly in clinical practice.

•LogMAR is an acronym for the base-10 logarithm of the minimum angle of resolution, and refers to the ability to resolve the elements of an optotype. Thus, if a letter on the 6/6 (20/20) equivalent line subtends 5′ of arc, and each limb of the letter has an angular width of 1′, an MAR of 1′ is needed for resolution. For the 6/12 (20/40) line, the MAR is 2′, and for the 6/60 (20/200) line it is 10′.

•The logMAR score is simply the base-10 log of the MAR, so as the log of the MAR value of 1′ is zero, 6/6 is equivalent to logMAR

0.00.The log of the 6/60 MAR of 10′ is 1, so 6/60 is equivalent to logMAR 1.00. The log of the 6/12 MAR of 2′ is 0.301, giving a logMAR score of 0.30. Scores better than 6/6 have a negative value.

•As letter size changes by 0.1 logMAR units per row and there are five letters in each row, each letter can be assigned a score of

0.02.The final score can therefore take account of every letter that has been read correctly and the test should continue until half of the letters on a line are read incorrectly.

Table 14.1 -- Comparison of Snellen and logMAR visual acuity testing

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LogMar charts

1The Bailey–Lovie chart (Fig. 14.8) is the best-known, and is designed to be used at 6 m. Each line of the chart comprises five letters and the spacing between each letter and each row is related to the width and the height of the letters.

•The distance between two adjacent letters on the same row is equal to the width of a letter from the same row, and the distance between two adjacent rows is the same as the height of a letter from the lower of the two rows.

•Snellen VA values and logMAR VA are listed to the right and left of the rows respectively.

•VA can also be recorded on the Bailey–Lovie chart using the Visual Acuity Rating (VAR) score in which the 6/6 equivalent line read correctly gives a score of 100, with one point taken away or added for each letter fewer or more than this.

2Other charts are calibrated for 4 m. The early treatment diabetic retinopathy study (ETDRS) charts utilize balanced rows comprising Sloan optotypes, developed to confer equivalent legibility between individual letters and rows. ETDRS letters are square, based on a 5 × 5 grid, i.e. 5′ × 5′ for the 6/6 equivalent letters at 6 m. In the Bailey–Lovie chart, a 6/6 letter is 5′ in height by 4′ in width.

Fig. 14.8 Bailey–Lovie chart

Contrast sensitivity

1Principles. Contrast sensitivity is a measure of the ability of the visual system to distinguish an object against its background. A target must be sufficiently large to be seen, but must also be of high enough contrast with its background; a light grey letter will be

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