Ординатура / Офтальмология / Английские материалы / Moorfields Manual of Ophthalmology_Jackson_2007

carrier

P

2

Fig. 10.1: Drawing a family tree. Example shows autosomal dominant inheritance.

Autosomal recessive

■For rare genes, affected individuals are born of phenotypically normal parents and offspring are rarely affected, unless there is consanguinity.

■There is a 25% risk to each offspring of two carriers.

■Males and females are equally affected.

X–linked recessive

■Affected individuals are usually born of phenotypically normal parents.

■Affected males have unaffected sons, but all daughters are

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Taking a family history for inherited disease

■A female carrier has a 50% risk of her son being affected or her daughter being a carrier. Carriers may show abnormal signs, such as the tapetal retinal reflex that occurs in X-linked retinitis pigmentosa.

Mitochondrial inheritance

■Mitochondrial DNA is found in the egg but not sperm, so inheritance is maternal.

■Children of affected males are unaffected.

■Children of affected females all have the mutation, but the phenotype varies with the proportion of mitochondria with faulty genes.

Simplex

■These are usually autosomal recessive but without a known family history. There is therefore an increased risk of recurrence in any offspring.

Sporadic

■Originally used to describe disorders such as Down’s syndrome (trisomy 21) in which there is no calculable risk of recurrence.

Fluorescein Angiography

Background The fluorophore, sodium fluorescein, is injected into an antecubital vein and circulates to the eye. A fundus camera fitted with an illumination source and barrier filter is then used to selectively photograph the retinal and choroidal circulation.

In health, fluorescein passes rapidly through the eye but the inner and outer blood–retinal–barriers prevent staining of the retinal substrate. Retinal vessels are clearly visible but an intact RPE reduces the apparent fluorescence of the choroid. Diseases that damage the ocular circulation, RPE, or blood–retinal–barrier can all potentially be detected angiographically.

Indications Retinal vascular disease; macular oedema; RPE disease; subretinal neovascularisation; choroidal ischaemia; iris angiography.

Method

1.Ask if fundus fluorescein angiography (FFA) would alter management and is it the most appropriate investigation. Would clinical examination, optical coherence tomography (OCT), autofluorescence imaging, or indocyanine green angiography be better?

2.Exclude contraindications, e.g., fluorescein, iodine, or shellfish allergy. For use in pregnancy see page 702.

3.Explain the risks (see below) and benefits. Obtain written consent.

4.Indicate to the photographer the area of interest and presumed diagnosis.

5.Insert a 23-gauge butterfly cannula into an antecubital vein. Some clinicians prefer to use a Venflon for more secure access. A dorsal hand vein may be used, but this increases the transit time and dilutes the bolus.

6.Inject 5 mL of 20% fluorescein over 4–6 seconds whilst looking for extravasation (swelling, pain, resistance to injection), then turn off the lights.

7.Retain i.v. access in case of anaphylaxis.

Adverse events

■Yellowing of the skin and urine : these last 24 hours and occur in all patients.

■Nausea : occurs in 5% (vomiting <1%) shortly after injection

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Fluorescein angiography

previous injections, consider warming the ampoule to body temperature, injecting more slowly, and giving promethazine (Phenergan) 30 mg p.o., 1 hour prior.

■Extravasation : if this occurs then stop injecting, elevate the arm, and apply an icepack for 10 minutes. Extravasation rarely causes periphlebitis, skin necrosis, and granulomas, but pain is common and may last a few hours.

■Vasovagal syncope : this is the commonest cause of collapse. Patients have a transient reduction in pulse rate, blood pressure and conscionsness. Lie the patient flat, and elevate the lower limbs. Exclude other causes of collapse by history, examination, ECG, and blood glucose. Repeat observations in 1–2 hours, and discharge if well.

■Skin rash and itch : treat with oral antihistamines if itch alone or mild rash. Exclude anaphylaxis by auscultating the chest and checking respiratory rate, pulse, and blood pressure. If there is facial or other soft tissue swelling secure a 20-gauge Venflon or larger, give i.v. antihistamine (e.g. chlorpheniramine 10 mg over 1 minute), monitor extremely closely for bronchospasm or shock, and liaise immediately with physicians.

■Anaphylaxis : signs include reduced consciousness, pallor, facial swelling, tachycardia, hypotension, and bronchospasm. Provide immediate emergency care as shown on page 687.

Reading and reporting fluorescein angiograms When asked to comment on angiograms, it is often better to start with a clear description, rather than a diagnosis. In general, most abnormalities are hyperor hypofluorescent, and can be described with four terms: vascular filling defects, masking, leakage, and window defects.

■Hypofluorescence

1.Vascular filling defect : absent or obstructed retinal or choroidal vessels produce focal or diffuse hypofluorescence. Areas of capillary nonperfusion are suggested by leakage at the margin, and staining of the large vessel walls passing through the area, and telangiectasia (tiny, sacular vessel dilatations)

(Fig. 10.2).

2.Masking : most commonly occurs when retinal haemorrhage, exudates, or other opacities block

suggests ischaemia. Drop-out of the fine, lacy capillaries at the FAZ margin may give a ‘moth-eaten’ appearance compared to normal. Check the notes for a corresponding reduction in VA (Fig. 10.6).

A

B

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