Age-Related Macular Disease Part 2 – Detection of Wet AMD
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Continuing education CET Age-related macular disease Part 2 – Detection of wet AMD In the second part of this series, Dr Frank Eperjesi looks at the clinical evaluation of suspect maculopathy with particular emphasis on the early detection of the wet form. C7881, one general CET point, suitable for optometrists and DOs he first article in this three- part series (Optician, October 19) looked at the classifica- tion of AMD and described the clinical features of dry TAMD as: discrete yellow spots at the macula (drusen), hyperpigmentation of the RPE, sharply demarcated areas of RPE depigmentation (hypopigmenta- tion) with focal hyperpigmentation of the RPE a high-risk feature for subse- quent wet AMD development. The clinical features of wet AMD were described as geographic atrophy of the RPE with visible underlying choroidal Figure 1 Dry AMD Figure 2 Wet AMD vessels, pigment epithelial detachment (PED) with or without neurosensory and halt vision loss or even reverse vision onset of the inevitable and progressive detachment, subretinal or sub-RPE loss with smaller and less central lesions. significant visual loss associated with neovascularisation, fibroglial scar tissue, According to recent studies investigating the condition. haemorrhage and exudates. the outcome of these treatment modali- While dry AMD is a slowly progres- ties, the larger the lesion at baseline the Using symptoms to detect wet sive disease with vision loss taking place smaller the treatment benefit in terms of AMD over many years, wet AMD is a much the absolute level of visual acuity at two Detection of wet AMD often involves more rapidly progressive disease and years after the initiation of treatment. instructing patients to report symptoms is the main cause of catastrophic and The natural history of CNV is that such as distorted lines, blurriness, permanent vision loss, which can occur it gradually increases in size by an reduced vision and dark areas in their over a matter of a few days. It is estimated average of 10 to 18µm daily2 and that visual field or use of the Amsler grid that 18 per cent of patients with inter- it grows closer to the foveal centre in and being alert to new symptoms of mediate AMD (many medium-sized about 50 per cent of cases.3 Therefore, metamorphopsia, visual field scotoma drusen >63µm but <125µm or one large early detection of AMD-related lesions and blurred vision or micropsia. Many drusen >125µm – the central retinal is crucial in the management of these investigators have pointed out that the vein is about 125µm in diameter at the patients. Reeves4 estimates that in her patients who notice these symptoms optic nerve head) in at least one eye and experience the transition to early wet or changes in the Amsler grid are 43 per cent of patients with advanced AMD is not recognised soon enough in detected relatively late in the stage of AMD in one eye only develop choroi- approximately 15 per cent of patients. the disease when a large scotoma is dal neovascularisation (CNV), in other By the time an ophthalmologist sees already present.8,9 words wet AMD, within five years.1 these patients they have severe, irrevers- Wet AMD accounts for only 10 per ible vision loss for which treatment has Change in refractive error cent of all AMD but accounts for 95 minimal impact. She goes onto state that In the author’s experience it is worth per cent of serious vision loss. This takes ‘ideally, diagnosis and treatment should further investigating older patients the form of a localised loss of vision occur right after conversion to wet (especially those with more than one (scotoma) and or distortion of vision AMD before vision loss has occurred’. risk factor for AMD – see article three (metamorphopsia). This article will Recent publications have emphasised in this series) who present with a reduc- review techniques that can be used in the benefits of treating AMD lesions tion in myopia or an increase in hyper- primary care optometric setting in the while they are still relatively small.5,6 opia (hyperopic shift), particularly for timely detection of wet AMD. Loewenstein7 reported a case where a those without cortical lens opacities patient with a small extrafoveal lesion (these have been reported to cause this Early detection of wet AMD and visual acuity of 6/12 presented two type of refractive error change). Research has shown that the major current months later with 6/36 and an extensive A hyperopic shift without cortical lens techniques used in the treatment of wet subfoveal CNV without treatment. opacities could be due to type 2 diabetes AMD (anti-VEGF and photodynamic This reflects the importance of identi- (however, this most commonly causes a therapy) are more likely to be successful fying the presence of CNV before the myopic shift) or due to CNV elevation 36 | Optician | 16.11.07 opticianonline.net CET Continuing education of RPE or neurosensory retina. Further were evaluated the detection rate was investigation could involve slit-lamp even lower.11 indirect binocular ophthalmoscopy, There are several reasons for the poor referral for an ophthalmological opinion performance of the Amsler grid: or both. Elevation due to a subtle hyper- ● Awareness of visual field defects opic shift such as 0.75DS may result in is limited, with the patient not being retinal elevation that is too subtle to cognisant of any defect until the detect using slit-lamp indirect binocu- scotoma is considerably large and lar ophthalmoscopy, so it is useful to ask already includes central vision because the patient if they have experienced any of foveal involvement of the lesion. metamorphopsia or micropsia to help This can be partly explained by cortical with the differential diagnosis. completion or the ‘filling in’ phenome- non.16 The correlation relation between Ophthalmoscopy scotoma size and detection rate has been Certain types of wet AMD are very demonstrated.11 easy to detect even when using a direct Figure 3 Forsee PHP from Notal Vision ● The inability to properly maintain ophthalmoscope through an undilated fixation during testing pupil (Figure 1 dry AMD and Figure 2 a screen-based Amsler grid is reduced ● The crowding effect caused by the wet AMD). Early CNV changes may progressively and just before the target multiple lines that are peripherally not be detectable using a monocular disappears altogether relative scotomata presented in the Amsler grid causing technique and it would be good practice become apparent to the patient. With low sensitivity of the test and adding to investigate patients presenting with the standard and threshold Amsler to its poor performance symptoms of distorted lines, blurriness, tests mydriasis and ophthalmoscopy ● The non-interactive nature of the reduced vision, dark areas in their visual should be avoided immediately prior to Amsler grid, rendering it unsuitable field, metamorphopsia or micropsia using the Amsler grid especially with for monitoring patients because factors with slit-lamp-based binocular indirect suspected AMD.10 Neither the standard such as quality of examination perform- ophthalmoscopy. However, slit-lamp nor threshold versions are as good as ance and reliability measures, such as indirect biomicroscopy’s clinical utility conventional perimetry when it comes false positives and false negatives is variable and depends to a great extent to detecting scotomata less than 6º (the cannot be assessed upon the expertise of the examiner and average optic nerve head is 7º) in diame- ● Low compliance to perform the lesions may still be missed. ter.11 It seems common practice for eye Amsler grid at home. care professionals to supply patients Using the Amsler grid to detect with a copy of the recording sheet Preferential hyperacuity wet AMD (black grid on a white background) for perimeter As the early detection of wet AMD is home testing. This may result in spuri- To try to address some of the shortcom- crucial, patients at risk are encouraged ous results as bright backgrounds with ings of the Amsler grid a new method to perform self-monitoring, often using black detail have been shown to result in using the hyperacuity function has been an Amsler grid. The Amsler grid can anomalous illusions of shape and colour developed. This was initially named the be used to detect scotomata (missing akin to the pattern glare described by ‘Macular Computerised Psychophysical or blurred lines) and metamorphopsia Wilkins and colleagues in their work Test’ and described by Loewenstein and (bowed or distorted lines) and the likely on reading problems.12 It would be colleagues in 200317 but has become position of the associated lesion. The better to guide patients or carers to known as the ‘Preferential Hyperacuity basic grid (Amsler chart 1) is printed an appropriate website from which Perimeter’ (PHP). The test was origi- in white on a dull black background. they can print a white grid on black nally marketed by Zeiss as the ‘Preview It is intended for use at 30cm (with the background version for themselves or PHP’ and is now available from Notal patient fully corrected for that distance) use a screen-based grid for self-testing. Vision (www.notalvision.com) as the when each square subtends an angle of Unfortunately, Franklin10 and others13 Forsee PHP (Figure 3). In this second- 1º and the whole chart 20º. Amsler have reported that compliance with generation format it has a number of chart 2 has guidelines to help those self-testing is low. The most common improvements over its first incarnation patients who already have a central presenting symptom of wet AMD is in terms of improved speed and ease of scotoma to estimate where the central blurred vision and distortion when interpretation. This system was origi- fixation is located.