Ординатура / Офтальмология / Английские материалы / Handbook of Retinal Screening in Diabetes_Taylor_2006

National Retinopathy Screening Systems

The practical information presented in this book should be equally applicable to the slightly different approaches taken in England (http://www. nscretinopathy.org.uk/), Scotland (http://www.nsd.scot.nhs.uk/services/drs/), Wales (http://www.wales.nhs.uk/sites/page.cfm?orgid=351&pid=1903) and Northern Ireland.

Despite slightly different organizational practices in the separate countries, each retinal screener is still dealing with people who need to know about the state of their eyes and their doctors who need to know how retinopathy is changing in order to arrange appropriate management. It is likely that practices will converge to a large degree once the cost effectiveness of different methods has been compared.

Laser therapy

Laser therapy sounds alarming to patients but it is simple and well tolerated. For the patient, it means sitting at a device rather like the screening camera, looking at one place. The ophthalmologist aims the laser beam through the pupil at a precise spot on the retina and administers repeated flashes of laser light. It is not usually painful, and the laser pulses are felt rather as though something was tapping on the eyeball. The eye may ache for a few hours afterwards, and simple analgesics such as paracetamol may be advised. The commonest complaint of patients is that it takes rather a long time and is a tedious procedure. However, it saves sight.

There are two main types of laser therapy.

Pan-retinal photocoagulation is used for proliferative retinopathy. It involves applying several thousand laser dots all over the retina except between the disc and the fovea. Several sessions are usually needed to complete this. Provided that proliferative retinopathy is picked up early enough, pan-retinal photocoagulation is over 95 per cent successful in stopping the process. If vision is preserved after a few months, then the long-term outlook is excellent. For reasons not well understood, once complete treatment has been given and proliferative change has been halted, further new vessel formation is relatively unlikely to reoccur in the future. Naturally, annual retinal screening should be continued.

Grid photocoagulation is used for exudative maculopathy. It involves applying laser spots in a grid pattern lateral to the fovea. It is reasonably successful, but only if visual acuity is better than 6/24 and even then in only about 60 per cent of patients.

The word laser is merely an acronym for the process of producing this form of light. It stands for Light Amplification by the Stimulated Emission of Radiation. Laser light is purely of one wavelength, the waves are all synchronous and the beam is perfectly parallel. It can deliver energy which is targeted to specific cells or tissues because of these special properties. In treating diabetic retinopathy, the energy is absorbed by blood in capillaries and by the pigment epithelium layer.

The only practical problem experienced by people who have required very heavy laser therapy relates to dim lighting conditions. The pale areas of laser scar allow internal reflection of light inside the eye with consequent ghost images. Some visual field defects will be detectable, and formal perimetry is required to ensure that vision meets the legal requirement to hold a driving licence.

Vitrectomy

If a large pre-retinal haemorrhage fails to clear, or if fibrous bands threaten to detach the retina, an operation can be performed to take away the abnormal tissue. This is done under general anaesthetic. Vitrectomy is performed by introducing fine instruments through the conjunctiva into the vitreous humour, with direct vision for the surgeon through the pupil. The abnormal tissue is cut and sucked out, and clear fluid replaces the volume. If necessary, laser therapy can be delivered from within the eye. Vision can be dramatically restored. However, it is a major eye operation and prevention of advanced changes by effective screening and timely laser therapy is far preferable.

Ophthalmoscopy

Use of the ophthalmoscope can be helpful for retinal screeners, even though it is not regarded as an essential skill. The ophthalmoscope shines a beam of light into the eye and allows a view of all the structures from cornea to retina. It is most useful to sort out what may be preventing a clear view of the retina

(e.g. corneal scarring, cataracts of various sorts and vitreous opacities including asteroid hyalosis). The view is magnified about 15 times, so that some appearances which cannot be assessed fully on the image, even with image manipulation, can be visualized. At first you will be surprised that you can only see an area about the size of the disc at any one time, and you have to move this ‘searchlight’ back and forth across the retina to build up a full picture. It is a difficult skill, but once obtained makes screening easier and more interesting.

1.Getting started. Hold the ophthalmoscope in your right hand (this is easier to start for right handers). Switch on the light (usually by rotating a collar) and check that the lens is set to zero by rotating the focus wheel, going through the circle of convex and concave lenses at the head of the scope. Rest the top of the instrument firmly in the angle between your right eyebrow and nose so that (with some jiggling) you can see through the viewing hole. Look around the room. Find the light switch. You should get used to moving your head and the scope as a single unit.

2.Look in an eye. With your subject sitting comfortably and you standing in front, decide where to ask him/her to look. This should be at a distinct point, not in the middle of a blank wall. It should be in a position so that your subject’s line of gaze passes the level of your eyes (usually at about 60° elevation). Place your left hand on your subject’s forehead with your thumb along the right eyebrow. Close your left eye. Starting at arm’s length, look through the scope at the right pupil. Move slowly towards the eye. You should see redness when 30–50cm from the eye. Closer up, everything will appear pink and blurred. You can confidently move to within 2.5cm of the eye as your forehead will make contact with your left thumb safely before the scope gets too close to the eye. Look around. You may see a blood vessel or two.

3.Relax. Go back to looking round the room through the scope. This time place your right forefinger on the focus wheel and click it round, one step at

a time. Your view will get fuzzier, then change suddenly as the lens gets to the point of the strongest + correction next to the strongest – correction. Get used to focusing without moving the scope.

4.Now you have learned the basic moves you can start on the clinically useful systematic approach. Repeat step 2, but ensure that you move towards

the eye along a line about 15° to the side of the line of gaze. This will mean that you are lined up on the optic disc. Ask yourself these questions: (a) cornea OK?; (b) lens clear?; (c) vitreous clear? If you encounter no abnormalities you should be looking at the retina at or near the optic disc. Pivot your line of sight through your subject’s pupil. When you can see a blood vessel, turn the focus wheel one way then the other to get the sharpest possible view. Next, follow that blood vessel one way then the other until you come to the optic disc.

5.And then the other eye. For right handers, using the left eye and the left hand is more awkward at first. All the above instructions should be left–right reversed. You will stand in front and just to the left of your subject, looking into his / her left eye with your left eye, holding the scope with your left hand. Ophthalmoscopy is not easy, and needs months of practice before you can expect to be confident.

6.Common problems crop up such as: I cannot close one eye, I wear glasses, I can’t focus. The brief answers are: cover it with a hand rather than resting it on the forehead, take them off, practice focusing on your hand from about 10cm away. Ask an expert to help with your ophthalmoscopy.

For treatment of type 1 diabetes, insulin:

(a)No – into the fat layer

(b)Yes

(c)Yes

(d)Yes

(e)Yes

Eating in type 1 diabetes:

(a)No – around carbohydrate counting and low fat content

(b)No – by estimating the carbohydrate content

(c)Yes

(d)No – a small potato is one 10g portion

(e)Yes

Hypoglycaemia:

(a)Yes

(b)No – hypoglycaemic unawareness is dangerous if present

(c)Yes

(d)No – too large a dose of insulin

(e)Yes

Ketoacidosis:

(a)Yes

(b)Yes

(c)No – it is always preceded by some degree of illness

(d)Yes

(e)Yes

Microvascular complications in type 1 diabetes:

(a)Yes

(b)Yes

(c)No – retinas, nerves and kidney

(d)No – the susceptibility to complications varies

(e)Yes

Chapter 2

Type 2 diabetes:

(a)Yes

(b)Yes

(c)Yes

(d)Yes

(e)Yes

Tablet treatment:

(a)Yes

(b)Yes

(c)No – gliclazide can cause hypos

(d)No – the ability to produce insulin gradually decreases and control worsens

(e)No – pioglitazone and rosiglitazone are new insulin sensitizers

Blood glucose:

(a)Yes

(b)Yes

(c)Yes

(d)No – good if pre-meal readings are under 7mmol/l

(e)Yes

The following are true of complications:

(a)Yes

(b)Yes

(c)Yes

(d)Yes

(e)Yes

Chapter 3

In the eye:

(a)Yes

(b)Yes

(c)No – the retina lets the light through and the black choroid absorbs it

(d)Yes

(e)Yes

Background retinopathy:

(a)Yes

(b)Yes

(c)Yes

(d)Yes

(e)Yes

New vessels:

(a)Yes

(b)No – from either the retina or the optic disc

(c)Yes

(d)Yes

(e)Yes

Chapter 4

Blindness:

(a)Yes

(b)No – only in the working age population (macula degeneration is commonest in the elderly and overall in the UK)

(c)No – it may be sudden in proliferative disease

(d)No – reduced by screening programmes in both Sweden and Newcastle

(e)No – maculopathy is the more common cause of blindness

In a quality assurance programme:

(a)Yes

(b)Yes

(c)Yes

(d)Yes

(e)Yes

The following statements are true:

(a)Yes

(b)No – around 20 per cent will have exudative maculopathy after 25 years

(c)Yes

(d)Yes

(e)No – laser therapy will not restore vision in exudative maculopathy

Chapter 5

In the course of retinal screening:

(a)No – all information is confidential

(b)Yes

(c)No – visual acuity must be tested before mydriasis

(d)No – 6 metres

(e)No – a pinhole device is used when glasses are not available or if VA appears low

Visual acuity:

(a)No – refraction, the clarity of lens/vitreous and retinal function are tested

(b)Yes

(c)No – only a two line difference is significant

(d)Yes

(e)Yes

Mydriatic drops:

(a)No – full precautions must always be taken

(b)Yes

(c)Yes

(d)No – young people can be sometimes imaged satisfactorily without mydriasis but time must be left between image acquisitions for the pupil to re-dilate

(e)No – they are rapidly spread across the conjunctiva and cornea by blinking

Obtaining the image:

(a)No – joystick first then fine focusing knob

(b)No – essential for all images

(c)No – disc-centred and macula-centred

(d)Yes

(e)No – pale streaks at the edge of the image

When examining the image:

(a)Yes

(b)No – a red blur on the disc may indicate new vessels – examine closely

(c)Yes

(d)No – common in younger people

(e)No – after the second branch points

The person with diabetes:

(a)No – the image is theirs

(b)No – waiting for results can be a cause of anxiety

(c)Yes

(d)Yes

(e)Yes