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

kanski 7th

Fig. 14.68 (A) Choroidal folds; (B) FA shows alternating hypofluorescent and hyperfluorescent streaks

(Courtesy of JS Schuman, V Christopoulos, DK Dhaliwal, MY Kahook and RJ Noecker, from Lens and Glaucoma, in Rapid Diagnosis in Ophthalmology, Mosby 2008 – fig. B)

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

819 / 1137

kanski 7th

Hypotony maculopathy

Pathogenesis

Maculopathy is common in eyes developing hypotony, defined as IOP less than 5 mmHg. The most common cause is excessive drainage following glaucoma filtration surgery (higher risk with adjunctive antimetabolite), other causes including trauma (cyclodialysis cleft, penetrating injury), chronic uveitis (by directly impairing ciliary body function and by tractional ciliary body detachment due to cyclitic membrane), and retinal detachment. The development of secondary choroidal effusion may act to perpetuate the hypotony. With time the hypotonous process can itself lead to further damage, including sclerosis and atrophy of ciliary processes. Prolonged severe hypotony may lead to phthisis bulbi and loss of the eye. Treatment is aimed at restoring normal IOP.

Diagnosis

•Vision is variably affected. Delayed normalization of IOP may result in permanent visual impairment, though substantial improvement has been reported following hypotony reversal after several years.

•Chorioretinal folds that may radiate outwards in branching fashion from the optic disc (Fig. 14.69); these are due to scleral collapse with resultant chorioretinal redundancy.

•Fine retinal folds radiating outwards from the foveola which may also show CMO.

•Other features that depend on aetiology, including a shallow anterior chamber, choroidal effusion, cataract, corneal decompensation, optic disc oedema, uveitis, wound leak or an inadvertent filtering bleb adjacent to a wound.

•Ultrasound biomicroscopy may show a cyclitic membrane or cyclodialysis cleft if there is clinical reason to suspect this.

•B-scan ultrasonography will demonstrate choroidal effusions.

•A-scan will show reduced axial length (compared with pre-operatively or with the fellow eye).

Fig. 14.69 Radial chorioretinal folds due to chronic hypotony

(Courtesy of P Gili)

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

820 / 1137

kanski 7th

Vitreomacular traction syndrome

1Pathogenesis. In vitreomacular traction syndrome (VMT), the vitreous cortex remains attached to the fovea but is detached from the perifoveal region, with resultant exertion of persistent anteroposterior traction on the fovea. Changes at the posterior hyaloid membrane and retina similar to those involved in EMM and macular hole formation may be involved in the pathogenesis.

2Presentation is usually in adult life with decreased vision, metamorphopsia, photopsia and micropsia. A mild variant of VMT has been reported following cataract surgery, when it may be mistaken for pseudophakic CMO.

3Signs. The macula may show retinal surface wrinkling, distortion, EMM or CMO.

4OCT shows incomplete posterior vitreous separation with persistent attachment of vitreous to the fovea (Fig. 14.70). The posterior vitreous surface often gives rise to a prominent signal.

5Treatment in marked or progressive disease involves pars plana vitrectomy to relieve macular traction, usually with good results. Spontaneous resolution may also occur.

Fig. 14.70 OCTin vitreomacular traction shows incomplete posterior vitreous separation with persistent attachment at the fovea

(Courtesy of C Barry)

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

821 / 1137

kanski 7th

Idiopathic choroidal neovascularization

Idiopathic CNV is an uncommon condition which affects patients under the age of 50 years and is usually unilateral. The diagnosis is one of exclusion of other possible associations of CNV in younger patients such as angioid streaks, high myopia and chorioretinal inflammatory conditions such as presumed ocular histoplasmosis, MEWDS or PIC. The condition carries a better visual prognosis than that associated with AMD and in some cases spontaneous resolution may occur. The CNV lies predominantly above the RPE (type 2), often encircled by reactive RPE growth. PDT has met with variable results, but anti-VEGF agents show promise.

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

822 / 1137

kanski 7th

Solar retinopathy

1Pathogenesis. Retinal injury is caused by photochemical effects of solar radiation by directly or indirectly viewing the sun (eclipse retinopathy).

2Presentation is within 1–4 hours of solar exposure with unilateral or bilateral impairment of central vision and a small central scotoma.

3VA is variable according to severity.

4Fundus

•A small yellow or red foveolar spot which fades within a few weeks (Fig. 14.71A).

•The spot is replaced by a sharply defined foveolar defect with irregular borders (Fig. 14.71B) or a lamellar hole.

5OCT shows foveal thinning with a focal hyporeflective area, the depth of which correlates with the extent of visual acuity loss but which generally includes the photoreceptor inner and outer segments.

6Treatment is not available.

7Prognosis is good in most cases with improvement of visual acuity to normal or near-normal levels within 6 months; in a minority, significantly reduced vision persists.

Fig. 14.71 Solar maculopathy. (A) Yellow foveolar spot; (B) foveolar defect

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

823 / 1137

kanski 7th

Chapter 15 – Hereditary Fundus Dystrophies

INTRODUCTION 648 INVESTIGATIONS 648 Electroretinography

 648 Electro-oculography  649

Dark adaptometry 650 Colour vision tests 650

GENERALIZED PHOTORECEPTOR DYSTROPHIES 651 Typical retinitis pigmentosa 651

Atypical retinitis pigmentosa 654 Important systemic associations 654 Progressive cone dystrophy 656 Leber congenital amaurosis 656

Stargardt disease and fundus flavimaculatus  657

Bietti corneoretinal crystalline dystrophy 660 Alport syndrome 661

Familial benign fleck retina 661

Pigmented paravenous chorioretinal atrophy 661 Congenital stationary night blindness 662 Congenital monochromatism (achromatopsia)  664

MACULAR DYSTROPHIES 665 Juvenile Best macular dystrophy 665

Multifocal vitelliform lesions without Best disease  665

Pattern dystrophy 665

North Carolina macular dystrophy 667 Familial dominant drusen 668

Sorsby pseudoinflammatory dystrophy 669 Benign concentric annular macular dystrophy 669 Central areolar choroidal dystrophy 670 Dominant cystoid macular oedema 670 Sjögren–Larsson syndrome 670

Familial internal limiting membrane dystrophy 670

GENERALIZED CHOROIDAL DYSTROPHIES 670 Choroideremia 670

Gyrate atrophy 671

Generalized choroidal dystrophy 674 Progressive bifocal chorioretinal atrophy  674

VITREORETINAL DYSTROPHIES 674 Juvenile X-linked retinoschisis 674 Stickler syndrome 675

Wagner syndrome 676

Familial exudative vitreoretinopathy 678

Enhanced S-cone syndrome and Goldmann–Favre syndrome  678

Snowflake vitreoretinal degeneration 679

Dominant neovascular inflammatory vitreoretinopathy 679 Dominant vitreoretinochoroidopathy 681

Kniest dysplasia 681

824 / 1137

kanski 7th

ALBINISM 681 Introduction 681

Tyrosinase-negative oculocutaneous albinism  682

Tyrosinase-positive oculocutaneous albinism  683

Ocular albinism 683

CHERRY-RED SPOT AT MACULA 683 Pathogenesis 683

GM1 gangliosidosis (generalized)  684

Mucolipidosis type I (sialidosis) 684 GM2 gangliosidosis 684 Niemann–Pick disease 684

Farber disease 685

Introduction

Applied anatomy

The hereditary fundus dystrophies are a rare but important group of disorders that primarily involve the outer retina (RPE-photoreceptor complex) and its blood supply (choriocapillaris). It is uncommon for the inner retina or the retinal vasculature to be the primary target. There are two types of photoreceptor cells:

1The rods are the most numerous (120 million) and are of the highest concentration in the mid-peripheral retina. They are most sensitive in dim illumination and are responsible for night and peripheral vision. If rod dysfunction occurs earlier or is more severe than cone dysfunction, it will result in poor night vision (nyctalopia) and peripheral field loss, the former usually occurring first.

2The cones are fewer in number (6 million) and have their highest concentration at the fovea. They are most sensitive in bright light and mediate day vision, colour vision and central visual acuity. Cone dysfunction therefore results in poor central vision, impairment of colour vision (dyschromatopsia) and occasionally problems with day vision (hemeralopia).

Inheritance

1Autosomal dominant (AD) dystrophies often manifest more variable expression, have a later onset and a milder course as compared with recessive disorders.

2Recessive dystrophies may be autosomal (AR) or X-linked (XL). They have an earlier onset and more severe course that AD dystrophies. In some cases female carriers of XL conditions show characteristic fundus findings (see below).

3X-linked dominant conditions are extremely rare and typically lethal in boys (e.g. Aicardi syndrome).

Classification

The dystrophies can be subdivided into two main groups: (a) generalized which involve the entire fundus and (b) local in which only the macula is affected. Further subclassification of each is based on the presumed site of primary pathology (e.g. photoreceptors, RPE or choroid).

Copyright © 2011 Elsevier Inc.All rights reserved. Read our Terms and Conditions of Use and our PrivacyPolicy.

If you find this useful please saythanks in your way: dramroo

825 / 1137

kanski 7th

Investigations

Electroretinography

Principles

The electroretinogram (ERG) is the record of an action potential produced by the retina when it is stimulated by light of adequate intensity. The recording is made between an active electrode either in contact with the cornea or a skin electrode placed just below the lower eyelid margin, and a reference electrode on the forehead. The potential between the two electrodes is then amplified and displayed (Fig. 15.1). The normal ERG is biphasic (Fig. 15.2).

1The a-wave is the initial fast negative deflection generated by photoreceptors.

2The b-wave is the next slower positive large amplitude deflection. Although it is generated from fluxes of potassium ions within and surrounding Müller cells, it is directly dependent on functional photoreceptors and its magnitude makes it a convenient measure of photoreceptor integrity. The amplitude of the b-wave is measured from the trough of the a-wave to the peak of the b-wave. It is enhanced with dark adaptation and increased light stimulus. The b-wave consists of b-1 and b-2 subcomponents; the former probably represents both rod and cone activity and the latter mainly cone activity. It is possible to single out rod and cone responses with special techniques.

Fig. 15.1 Principles of electroretinography

826 / 1137

kanski 7th

Fig. 15.2 Components and origins of the electroretinogram

Standard ERG

The normal ERG consists of five recordings (Fig. 15.3). The first three are elicited after 30 minutes of dark adaptation (scotopic), and the last two after 10 minutes of adaptation to moderately bright diffuse illumination (photopic). It may be difficult to dark adapt children for 30 minutes and therefore dim light (mesopic) conditions can be utilized to evoke predominantly rod-mediated responses to low intensity white or blue light stimuli.

1Scotopic ERG

aRod responses are elicited with a very dim flash of white or blue light, resulting in a large b-wave and a small or nonrecordable a-wave.

bCombined rod and cone responses are elicited with a very bright white flash, resulting in a prominent a-wave and b-wave.

cOscillatory potentials are elicited by using a bright flash and changing the recording parameters. The oscillatory wavelets occur on the ascending limb of the b-wave and are generated by cells in the inner retina.

2Photopic ERG

aCone responses are elicited with a single bright flash, resulting in an a-wave and a b-wave with small oscillations.

bCone flicker is used to isolate cones by using a flickering light stimulus at a frequency of 30 Hz to which rods cannot respond. It provides a measure of the amplitude and implicit time of the cone b-wave. Cone responses can be elicited in normal eyes up to 50 Hz, after which point individual responses are no longer recordable (‘critical flicker fusion’).

827 / 1137

kanski 7th

Fig. 15.3 Normal electroretinographic recordings

Multifocal ERG

Multifocal ERG is a method of producing topographical maps of retinal function (Fig. 15.4). The stimulus is scaled for variation in photoreceptor density across the retina. At the fovea, where the density of receptors is high, a lesser stimulus is used than in the periphery where receptor density is lower. As with conventional ERG, many types of measurements can be made. Both the amplitude and timing of the troughs and peaks can be measured and reported and the information can be summarized in the form of a three-dimensional plot which resembles the hill of vision. The technique can be used for almost any disorder which affects retinal function.

Fig. 15.4 Multifocal electroretinogram

Electro-oculography

1Principle. The electro-oculogram (EOG) measures the standing potential between the electrically positive cornea and the electrically negative back of the eye (Fig. 15.5). It reflects the activity of the RPE and the photoreceptors. This means that an eye blinded by lesions proximal to the photoreceptors will have a normal EOG. In general, diffuse or widespread disease of the RPE is needed to significantly affect the response.

2Interpretation. As there is much variation in EOG amplitude in normal subjects, the result is calculated by dividing the maximal height of the potential in the light (‘light peak’) by the minimal height of the potential in the dark (‘dark trough’). This is expressed as a ratio (Arden ratio) or as a percentage. The normal value is over 1.85 or 185%.

828 / 1137