Ординатура / Офтальмология / Английские материалы / Moorfields Manual of Ophthalmology_Jackson_2007

Retinal Laser Guidelines

General points

■The laser spot size is affected by lens selection. For example, selecting 100 μm on the laser produces the following spot size on the retina:

1.Volk Area Centralis: 100 μm.

2.Volk Transequator: 143 μm.

3.Volk Quadraspheric: 200 μm.

■For macular treatment use an Area Centralis, for panretinal photocoagulation use a Transequator or Quadraspheric lens.

■Identify the foveal centre using fluorescein angiogram or clinical examination and a fixation target. Do not do this at the laser. In general, perform macular treatments with a 100–

200μm retinal spot size, 0.1–0.2 second duration, one spot size apart.

■In general, perform peripheral treatments with a 500 μm retinal spot size, 0.05–0.1 second, one spot size apart. Treatment is more uncomfortable in the far periphery, the horizontal meridia, and over previous laser scars or pigmentation.

■Shorter duration burns (0.05 sec) are more comfortable.

Longer burns (0.1–0.2 sec) are more effective and less likely to rupture Bruch’s membrane.

■Reduce power when treating pigmented fundi.

■Topical anaesthesia is usually adequate but some patients require peribulbar or sub-Tenon’s anaesthetic for akinesia or analgesia, e.g. perifoveal treatment in a young, mobile patient.

■Some lasers offer both green or yellow laser light. Green light is attenuated by nuclear sclerosis, and power delivery may vary depending on the light path through the lens. Avoid green laser immediately after angiography as residual vitreous fluorescein provides troublesome fluorescence with green illumination. Green laser is also absorbed by luteal pigment when treating near the fovea. In these settings, yellow light is preferable.

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Retinal laser guidelines

Macular Grid Laser

■Indications : Macular oedema, particular in diabetics, or following branch retinal vein occlusion.

■Consent: Benefit – improved visual prognosis. Risks – risks will vary with the indication for treatment but may include: blindness from foveal burn; paracentral scotoma; altered colour vision; re-treatment; subretinal neovascularization.

■Method :

1.See General points, above.

2.Select an Area Centralis lens or equivalent and set the laser to 100 μm (100 μm retinal spot size), 0.05–0.2 seconds duration.

3.Test burn intensity and Bell’s reflex (risk of foveal burn) using low-power burns (60 mW), near the temporal arcade.

4.Increase the power to give light-grey burns. More power will be needed in areas of oedema.

5.Avoid retinal haemorrhage, exudates, pigmentation, and scars. These produce variable laser absorption and more collateral damage. Avoid laser within the foveal avascular zone (FAZ).

6.Apply burns one burn width apart, over the area of oedema. A fluorescein angiogram may help define the area of leakage. For diffuse leakage, use a grid pattern (Fig. 10.13). For circinate leakage, treat locally.

7.For more specific protocols see the sections on individual diseases.

■Follow-up : Usually 3–4 months.

Panretinal Photocoagulation (PRP)

■Indications : Iris, retinal, or optic disc neovascularization secondary to retinal ischaemia, most commonly proliferative diabetic retinopathy or following retinal vein occlusion.

■Consent: Benefit – reduced risk of visual loss but explain that PRP does not improve vision. Risks – reduced vision including blindness from foveal burn; reduced night vision; macular

Laser for Macroaneurysm

■Indications : Macular oedema or exudates caused by a leaking retinal arteriolar macroaneurysm.

■Consent: Benefit – improve or stabilize vision. Risks – blindness from foveal burn; paracentral scotomas; altered colour vision; failure to prevent leakage; re-treatment;

subretinal neovascularization. Offer a guarded prognosis if there is chronic (>3 months) macular oedema suggested by cyst formation, subfoveal pigmentation, fibrosis or

exudates.

■Investigations : Perform fluorescein angiography, as some macroaneurysms bleed then stop leaking.

■Method :

1.See General points, above.

2.Set the laser to 200 μm and use an Area Centralis lens (200 μm retinal spot size). Start with 60 mW and increase the intensity to produce grey-white burns.

3.Treat around the macroaneurysm with a single confluent line.

4.If leakage persists, repeat the procedure and treat macroaneurysms directly.

5.Consider grid treatment (technique above) in areas of retinal telangiectasia with persistent oedema.

■Follow-up : 2 weeks after first treatment for possible direct treatment, then 3 months to consider macular grid.

Laser for Choroidal Neovascularization

■Indications : Extraand juxtafoveal choroidal neovascularization secondary to age-related macular degeneration (AMD). If secondary to a presumed inflammatory cause, consider oral corticosteroid cover.

■Consent: Benefit – for AMD, laser reduces the 3-year risk of severe visual loss from 63% to 45% (extrafoveal) or 58% to 49% (juxtafoveal), relative to the natural history. Risk – loss of vision including blindness from foveal or parafoveal burn, permanent paracentral scotoma, and re-treatment. Recurrence occurs in 50% and is often aggressive and subfoveal.

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Risks – transient or permanent loss of vision; acute vision loss occurs in 1–4%; photosensitivity (avoid sunlight for 48 hours, wear protective clothing and sunglasses); injection site complications; back pain; liver dysfunction; re-treatment; multiple fluorescein angiograms.

■Method :

1.Dilute verteporfin (6 mg/m2 body surface area) in 5% dextrose.

2.Administer intravenously at 3 mL/min over 10 minutes, using a syringe pump and in-line filter.

3.Laser spot size = greatest linear dimension of the lesion

angiographically (including contiguous blood, blocked fluorescence, or RPE detachment) + 1000 μm. This gives a 500 μm treatment margin around the lesion.

4.At 15 minutes postinfusion, centre the aiming beam over the lesion and activate the laser. The laser is a nonthermal diode and produces red light (689 nm) at an intensity of 800 J/sec or 600 mW/cm² for 83 s.

■Follow-up : 10–12 weeks, or earlier if the patient has symptoms. Re-treatment is often required.

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Differential diagnoses

Differential Diagnoses

Rubeosis iridis

■Retinal ischaemia, e.g. diabetes, retinal vein occlusion (Fig. 10.15), Eales’ disease.

■Ocular ischaemic syndrome, e.g. atherosclerotic carotid artery disease.

■Intraocular inflammation, e.g. Fuchs’ heterochromic iridocyclitis.

■Intraocular tumour, e.g. melanoma.

■Iris ischaemia (rare).

Retinal neovascularization

■Diabetes mellitus (Fig. 10.16).

■Retinal vein occlusion.

■Hypertension.

■Sickle cell retinopathy.

■Ocular ischaemic syndrome.

■Retinopathy of prematurity.