angiography in AMD
83AMD However, if there is doubt as to whether a neovascular
component is present or treatable, then urgent fl uorescein angio- graphy is indicated (Fig. 4.2). Angiography is also indicated to defi ne the type and extent of a choroidal neovascular membrane prior to laser photocoagulation. More recently, indocyanine green (ICG) angiography, which was initially pioneered 20 years ago, has enjoyed a come-back. This technique images the choroidal circula- tion using wavelengths in the infrared region and can be useful in cases where the limits of the neovascular membrane are obscured by haemorrhage.13 Although theoretically promising, the practical usefulness of ICG angiography remains limited.
4.2.4 Genetic factors in AMD
AMD is a disorder of complex inheritance. Numerous studies have now shown that genetic predisposition is important in AMD, but that this is likely to be modifi ed signifi cantly by environmental factors. Until 3–4 years ago, studies on the genetics of AMD were Figure 4.2 Late-phase fl uorescein angiogram of an extensive subfoveal
choroidal neovascular membrane in ‘wet’ age-related macular degeneration. The white arrow indicates the vessels in the neovascular complex, the white arrowheads indicate intraretinal haemorrhage and the black arrow indicates leakage of dye from the neovascular membrane.
few in number and limited to several reports noting a positive family history of the condition in their patients. More recently, several workers have readdressed the question of genetic input in the pathogenesis of AMD. In a study comparing the characteristics of drusen (early clinical markers of AMD) in the spouses and siblings of affected patients with AMD, Piguet and co-workers14 revealed marked concordance between siblings but not between spouses, suggesting that genetic factors are more important than the environmental factors shared by spouses. Two other studies assessed the concordance of fundal changes for AMD in monozy- gotic and dizygotic twins.15,16 Both studies show a high rate of concordance for fundal fi ndings in AMD in the monozygotic pairs: 23 of 23 pairs in one study and 8 of 9 pairs in the other. As would be expected, the level of concordance for fundal fi ndings was much less striking in the dizygotic twins. Recently a case-control study by the authors concluded that the risk of developing AMD was 19 times greater for the sibling of an affected person than for the sibling of an unaffected control.17 More recently, several genome-wide scans have identifi ed several hotspots for AMD on the human genome. Over the past 12 months studies by several groups have shown that more than 50% of cases of AMD are caused by sequence changes in the genes controlling the pathway of the ‘complement’ cascade, which is involved in the body’s response to infl ammation. Although several potential genes have been implicated, the most important player seems to be comple- ment factor H (CFH). These are exciting fi ndings, which may in time offer signifi cant possibilities for advances in therapies.18
4.2.5 Treatment for AMD
At present, only 5% of patients with ‘wet’ AMD are treatable by argon laser photocoagulation. The position and nature of the cho- roidal neovascular membrane (CNVM) is critical when assessing the feasibility of treatment. Extrafoveal CNVMs respond well to conventional laser (Fig. 4.3), juxtafoveal CNVMs are variable in their response, whereas subfoveal CNVMs, on average, lose six lines of Snellen acuity after treatment. The position of these mem- branes is depicted in Figure 4.4. However, even those patients who respond to laser treatment with regression of the neovascular process have a recurrence rate over the next 3 years of 60%.19
CNVMs can be classifi ed as classical or occult. Classical mem- branes are those that are not obscured by blood or exudate and
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A B
Figure 4.3 Treated extrafoveal CNVM (A) with corresponding post-
treatment scotoma shown on an Amsler chart (B).
Figure 4.4 Position of CNVMs. FAZ, foveal avascular zone. Position of CNVMs a - extrafoveal >200 μm b - juxtafoveal >1<199 μm c - subfoveal a b c FAZ - 350 μm in diameter Retinal capillaries in perifoveal area Ch004-H1815.indd 85 9/15/2006 12:08:56 PM
are completely visible on fl uorescein angiography. Classical membranes also fi ll early during fl uorescein angiography. Occult CNVMs are obscured by overlying blood or exudate, are poorly defi ned, and often fi ll slowly. Many other treatment modalities such as radiation therapy, photodynamic therapy (PDT), subreti- nal surgery, intravitreal and subtenon steroid injections, intravit- real anti-vascular endothelial growth factor (VEGF) aptamer and antibodies have been, and are currently being, evaluated.20–23 To date, PDT has been the most successful and is now recommended by the National Institute for Clinical Excellence (NICE) for patients with AMD-related 100% classical CNVM, whose vision is LogMAR 1.0 (6/60) or better. The evidence for benefi t for membranes other than 100% classical is said to be less strong. Treatment with PDT for this group of patients can be performed only within the confi nes of an approved centre. Detailed information can be found at http://www.nice.org.uk/pdf/49pressreleasepdt.pdf.
For patients with geographic atrophy, no specifi c treatment is available. Recent epidemiological studies suggest that those who eat diets high in lutein and zeaxanthin, and those who have higher levels of the antioxidant vitamins A, C and E, may have a reduced incidence of progression of the disease. The recent Age-Related Eye Disease Study (AREDS) supplementa- tion trial demonstrated a benefi t in terms of reduced progres- sion in patients with moderate drusen who had dietary supplementation.24
4.2.6 Visual prognosis
AMD is a clinically heterogeneous condition with a wide spec- trum of clinical manifestations. The visual prognosis therefore varies greatly depending on the disease subtype, as shown for different subgroups in Table 4.3.25,26 From a visual rehabilitation viewpoint, it is often in the early stages of neovascularisation, when vision is relatively good and metamorphopsia very dis- abling, that the condition is most diffi cult to manage. At this stage patients are often better using their spectacle correction, good lighting and large, high contrast, good quality print rather than magnifying aids. The patient’s willingness to accept low vision intervention and low vision aids can improve dramatically once they begin to focus attention on the degree of useful vision retained rather than the vision lost.
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4.3 Cataract
4.3.1 Prevalence
The term cataract describes the opacifi cation of the crystalline lens of the eye. The type and position of the opacifi cation can vary greatly; however, from the patient’s viewpoint, it is the degree of visual compromise that is important. Owing to the multifactorial aetiology of cataract, the true incidence is diffi cult to assess. Data from the Framingham Eye Study indicated a 5-year incidence of 10% at 55–59 years, increasing to 37% at 75–79 years.26 Others have
Table 4.3 Visual Prognoses in AMD
Fundal change Risk of visual loss
Hard drusen only (>8) 10% risk of CNVM in 5 years Drusen with pigmentary changes 58% risk of CNVM in 5 years Visual loss in a CNVM 60% of eyes show more than
six lines of visual loss at
18 monthsa
Risk of second eye becoming involved 13% per year by disciform scar
Risk of a PED developing a CNVM 25% at 10 years Risk of a PED developing GA 75% at 10 years Loss of central vision to <6/60 60% in 18 months [LogMAR 1.0] in a PED
Risk of a PED developing a ripb 4–10% in 18 months
Risk of PED in the second eye 80% in 3 years The risk of a rip in the second eye 33% – year 1
60% – year 2 80% – year 3
Geographic atrophy Average interval between diagnosis and visual loss of 3/60 [LogMAR 1.3] is 9 years
a Reduced to 25% having more than six lines of visual loss in 18 months by
argon laser photocoagulation.
b Tear of the retinal pigment epithelium. CNVM, choroidal neovascular
membrane; GA, geographic atrophy; PED, pigment epithelial detachment.
reported senile lens changes to be present in 91% of the 75–85 years age group.27
4.3.2 Clinical presentation
The patient who is developing cataracts usually complains of gradual onset of blurred vision for distance. In contrast, reading acuity is usually well preserved and the acquired myopic shift may even cause the patient to boast that the eyes have improved as reading is now possible without the aid of reading glasses. Other symptoms include foggy or misty vision, glare that is typi- cally not improved by wearing sunglasses but is improved by shielding (i.e. by the use of hats or sun visors), and monocular diplopia or triplopia.
Most patients are assessed in the outpatient setting using a basic Snellen acuity chart. The Snellen chart, although very serviceable, has the disadvantage of measuring visual acuity at 95% contrast. Daily tasks, however, are not usually carried out at 100% contrast but rather in a setting of various shades of grey. Thus, it is hardly surprising that patients who are found to have 6/9 [LogMAR 0.2] vision by Snellen acuity may still complain that their quality of vision is poor. Although contrast sensitivity reduc- tion is not typical of all cataracts, some patients are signifi cantly disabled in low luminance situations despite having 6/6 [LogMAR 0.0] vision recorded on the Snellen chart.28 This is especially true for posterior subcapsular cataract.
Practical advice
If a patient complains of poor vision and diffi culty with daily tasks despite good visual acuity, measurement of contrast sensitivity will often reveal the patient’s true disability.
4.3.3 Treatment for cataract
Surgery for cataract is now an excellent procedure, with most units carrying out small incision phacoemulsifi cation day-case surgery under local anaesthesia. This is a painless, safe procedure with a low rate of complications. The most recent survey from the Royal College of Ophthalmologists (UK) is the National Cataract
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