Metamorphopsia - an overview | ScienceDirect Topics (2023)

Cortical Visual Distortions

Positive visual phenomena frequently develop in patients with visual field defects and even in migraine: distortions of shape calledmetamorphopsia, scintillating scotomas, irregular shapes (teichopsia, or fortification spectra), macropsia and micropsia, peculiar changes of shape and size known as theAlice in Wonderland syndrome (described by Golden in 1979), achromatopsia (loss of color vision), akinetopsia (loss of perception of motion), palinopsia (perseveration of visual images), visual allesthesia (spread of a visual image from a normal to a hemianopic field), and even polyopia (duplication of objects). All these phenomena are disturbances of higher visual perception rather than agnosias.

Two types of color vision deficit are associated with occipital lesions. First, a complete loss of color vision, or achromatopsia, may occur either bilaterally or in one visual hemifield with lesions that involve portions of the visual association cortex (Brodmann areas 18 and 19). Second, patients with pure alexia and lesions of the left occipital lobe fail to name colors, although their color matching and other aspects of color perception are normal. Patients often confabulate an incorrect color name when asked what color an object is. This deficit can be calledcolor agnosia, in the sense that a normally perceived color cannot be properly recognized. Although this deficit has been termedcolor anomia, these patients can usually name the colors of familiar objects such as a school bus or the inside of a watermelon.

Metamorphopsia

Metamorphopsia is a syndrome in which the shape of objects appears distorted. It can be permanent, affect parts of the visual field, and may have a retinal, cortical, or even subcortical origin. In some instances, however, metamorphopsia may be restricted to faces, either permanently or transiently when associated with epilepsy. Faces or parts of the face are then seen as larger (macropsia) or smaller (micropsia), facial elements may be misaligned or turned sideways by several degrees, etc. Metamorphopsia does not necessarily prevent identification. It is usually considered a visuosensory deficit. As for prosopagnosia, whether face metamorphopsia is related to face-specific mechanisms or not is matter of debate.

Idiopathic Central Serous Chorioretinopathy

One of the more commonly seen etiologies of serous retinal detachment is idiopathic central serous chorioretinopathy (ICSC), which often affects young, otherwise healthy individuals in the third to fourth decade of life. A significant male predominance exists, and there is likely an association with both type A personalities and patients using exogenous corticosteroids. Pregnancy also carries an increased risk of ICSC (Fig. 6.40.1).³ These patients experience decreased vision, metamorphopsia, and decreased color vision, and although spontaneous return of vision is common, long-term dysphotopsias are a frequent complaint.

In ICSC, fluorescein angiography (FA) reveals defects in the integrity of the RPE, most commonly as an “expansile dot” of leakage or, classically, a “smokestack” pattern of focal leakage. Late pooling within the areas of retinal detachment is also seen. Additionally, two other forms of ICSC have been reported: a chronic form, also known asdiffuse retinal pigment epitheliopathy, and a more bullous form, which often manifests in the inferior retina.¹

Debate continues as to whether ICSC is primarily a defect of the RPE or the choroid. The primary finding on FA is a focal loss of integrity of the RPE; however, more recent studies using indocyanine green angiography (ICGA) have shown that underlying these focal RPE defects are areas of choroidal hyperpermeability, seen in the middle phases of angiography. Observation of hyperpermeable choroid, interspersed with areas of delayed filling, has led some researchers to propose a pathological mechanism of primary choroidal vasculopathy or thrombosis, perhaps leading to focal RPE defects and subsequent overlying retinal detachment. This theory implicates a thrombotic mechanism leading to focal disruption or necrosis of the RPE and may represent a pathological mechanism similar to that which produces serous retinal detachments in some diseases, such as immunoglobulin A nephropathy, type II glomerulonephritis, and cryoglobulinemia.²

Treatment has traditionally been observation, as most cases resolve spontaneously. However, in atypical or recurrent cases, or in rare cases with associated choroidal neovascularization, one can consider focal laser photocoagulation or anti–vascular endothelial growth factor (VEGF). In addition, reduced fluence photodynamic therapy (PDT) with verteporfin has been employed, most commonly for the chronic form of ICSC.³ Finally, oral agents that block aldosterone, primarily spironolactone and eplerenone, have demonstrated reductions in subretinal fluid and improved visual acuity.

3.7.5 Interpretation

Metamorphopsia may indicate macular oedema. Although this can be advantageous clinically, great care must be taken when choosing the suitability of a patient for home monitoring with the test, as it can point out otherwise unnoticed problems that subsequently greatly annoy patients. For other patients, compliance can be poor (Fine et al. 1986). The step in the Amsler chart manual that suggests that you ask the patient to look for movement of lines, shining, or colours (entoptic phenomena) has been omitted as it can produce many artefacts.

Distortion (dysmetropsia, metamorphopsia, and “Alice in Wonderland” syndrome)

Dysmetropsia and metamorphopsia are related visual illusions where object shapes appear distorted and straight lines bent. Metamorphopsia is best assessed with an Amsler grid. Even relatively young children will be able to say whether the lines are straight or not and report “funny lines.” Visual distortions are either optical (common), macular (occasional), or cerebral (rare) in origin. Optical causes include high corneal, lenticular, or retinal (staphylomatous) astigmatism, high ametropia, anisometropia, and new glasses. Macular causes include macular edema and choroidal neovascularization (e.g. associated with myopic Fuchs maculopathy, inflammatory ocular disease, and macular dystrophies). Rarely visual distortion is of cerebral origin, as in the “Alice in Wonderland” syndrome. A cerebral cause is likely to be accompanied by other neurologic symptoms and signs.

If the Amsler grid confirms the presence of distortions, the management includes refraction and detailed slit-lamp examination of the anterior and posterior segments. Investigations may include optical coherence tomography or fundus fluorescein angiography with macular disease, corneal topography (if keratoconus is suspected) and neuroimaging (magnetic resonance imaging [MRI]) if a cerebral cause is suspected.

Metamorphopsia, micropsia, macropsia, and the Alice in Wonderland syndrome more commonly accompany childhood than adult migraine. Alice in Wonderland syndrome is frequently associated with migraine, but may also be due to epilepsy, drugs/medication (topiramate), varicella infection, or infectious mononucleosis.

Visual Distortions and Illusions in Migraine

Metamorphopsia. Distortion of the shapes of objects may be experienced by patients with migraine (objects may appear too fat, too thin, too short, or too tall, for instance); however, metamorphopsia is a much more common complaint among patients with macular disease.

Micropsia and macropsia. In a variation of metamorphopsia, patients with migraine may complain that objects appear too small (micropsia) or too large (macropsia). In teleopsia, objects seem too far away. People may appear too small in lilliputianism. These symptoms can also be caused by seizures.

Alice in Wonderland syndrome. This condition is described here because it is classically associated with migraine; migraine is one its most commonly identified etiologies, and some affected patients without a history of migraine later develop migraine.²³ However, the underlying cause of the Alice in Wonderland syndrome may remain uncertain in some patients.²³

Lippman²⁴ described seven patients with classic migraine who experienced episodes of distorted body image. Each had fascinating illusions characterized by enlargement, diminution, or distortion of part of or the whole body, and each patient knew the sensations were not real. One 38-year-old woman reported attacks of feeling “about 1 foot high” accompanied by headache. Another elderly woman complained of migraine headaches preceded by the feeling of her left ear “ballooning out 6 inches or more.” His Patient 7 reported headaches accompanied by sensations of body size distortion “as if someone had drawn a vertical line separating the two halves; the right half seems to be twice the size of the left half.”

Lippman²⁴ recalled that Lewis Carroll (Charles Lutwidge Dodgson), also a migraineur, had described similar hallucinations in his book, Alice in Wonderland. It has been speculated that Dodgson had experienced distortions in body image during his migraine events, and incorporated the hallucinations into the fictional story about the young girl who, during her adventures in Wonderland, shrinks and grows numerous times. Todd²⁵ then coined the condition Alice in Wonderland syndrome. Rolak²⁶ pointed out the similarity between original illustrations in Dodgson's book (Figs. 12.3 and 12.4) and some of the descriptions cataloged by Lippman.²⁴

For unclear reasons Alice in Wonderland syndrome is more common in children. We agree with Lanska and Lanska²⁷ that patients with the Alice in Wonderland syndrome can be divided into those with illusions involving their own body (intrapersonal, or pure Alice in Wonderland syndrome) versus those with illusions involving objects around them (extrapersonal, or Alice in Wonderland–like syndrome). The extrapersonal variety is more common, and micropsia and teleopsia are the most common complaints, but macropsia and metamorphopsia also occur. Some children have both intrapersonal and extrapersonal complaints. Hachinski et al.¹⁹ described a 6-year-old child who thought people around her were smaller than normal. Once, while playing in the snow, this same child felt that she was “unusually large” and that an ordinary snowball had become “huge and turned blue.”

Metamorphopsia, micropsia/macropsia, and Alice in Wonderland syndrome have been attributed to migrainous cortical dysfunction in the nondominant posterior parietal lobule.²⁸ In contrast, single photon emission computed tomography (SPECT) imaging in one report²⁹ demonstrated occipital and temporal lobe abnormalities. Frontal lobe epilepsy,³⁰ encephalopathy due to infectious mononucleosis,³¹ topiramate use,³² and varicella infection have also been reported causes of Alice in Wonderland syndrome. In patients with Alice in Wonderland syndrome and Alice in Wonderland–like syndrome, magnetic resonance imaging (MRI) and electroencephalograph (EEG) are generally unhelpful. The condition is often self-limited,^23,33 or it can persist,^23,34 but nonetheless it is typically benign.³⁵

Other distortions and illusions. Migraine may also produce the perception of multiple images and should be included in the differential diagnosis of cerebral diplopia.³⁶ Kosmorsky,³⁷ in a report of his own acephalgic migraine, described the duplication of images within a scintillating scotoma. The double vision was present with either eye covered and did not change with either monocular or binocular viewing. Migraineurs may also complain of palinopsia (see later discussion), the persistence of visual images. However, palinopsia is more characteristically a symptom of parietooccipital lobe damage. Fig. 12.5 illustrates one patient's depiction of her visual illusion associated with migraine.

Visual function

Metamorphopsia or a scotoma may be present in the early stages of the disease.¹³ When patients are asked specifically for symptoms of metamorphopsia, a majority will admit to such symptoms, even among those with early disease.²¹ Visual impairment may be mild; however, loss of vision in one eye is frequently reported.⁶ Vision may decrease gradually with the progression of the disease. Visual acuity less than 20/200 (legal blindness) is rare but may be seen in the advanced stages with marked atrophy of the central photoreceptors or secondary to a large area affected by neovascularization.^6,7,18,22 In the Mac Tel Project, the mean visual acuity at baseline was 20/40 in 522 eyes that had not previously received therapy.¹¹ Visual acuity was 20/20 or better in 16% and 20/32 or better in approximately 50%. The most common risk factors associated with lower visual acuity in this cohort were characteristics found in more advanced disease, namely retinal pigment hyperplasia and the right-angle venules. Similar visual acuity results were reported by Gass and Blodi.⁶ In a retrospective study, 25% of eyes (6/24) remained stable during a follow-up period of 10–17 years.²²

Despite the mild visual impairment, the vision-related quality of life is impacted markedly. In the Mac Tel Project, the National Eye Institute Visual Functioning Questionnaire (NEI-VFQ-25) was administered to all participants.²³ They reported significantly lower vision-related function in all domains compared to a group of participants in a study of age-related macular degeneration and who had similar visual acuities. A subset of these participants, enrolled in the Mac Tel Project, were tested using the Impact of Vision Impairment questionnaire.²⁴ Similar results were seen in this second study.

Symptoms

Macular edema

Although metamorphopsia on Amsler grid testing is characteristic of central serous retinopathy, there is an accompanying mild central depression which varies in size from 2 to 5 degrees (Fig. 12-25). The scotoma is usually substantially larger using SWAT rather than white-on-white perimetry. Even after resolution of edema, the majority of patients have residual Amsler and perimetric defects⁴⁶ (Fig. 12-26). Similar changes may result from other causes of fluid accumulation in the macula, such as diabetic retinopathy, Irvine–Gass syndrome, trauma (Berlin's edema), and retinal vasculitis.²

SWAP studies on patients with early diabetic maculopathy demonstrated a correlation between the decrease in mean thresholds and the increase in size of the foveal avascular zone and the perifoveal intercapillary area. These changes were not observed with standard white-on-white perimetry.⁴⁷ In patients with clinically significant diabetic macular edema, Hudson et al.⁴⁸ found all patients had abnormal SWAP 10-2 fields compared to only one-third using standard perimetric fields. Further, the area of abnormal sensitivities was greater than that expected by clinical assessment.

Using microperimetry, macular scotomas were found in 74% of 19 patients with clinically significant macular edema.⁴⁹ Hudson et al.⁵⁰ followed 24 diabetic patients with macular edema before grid laser treatment and up to 12 weeks following treatment with microperimetry. They found correlation between the edema index and visual function to correlate in some, but not all patients. In another study of 30 patients, eight eyes remained stable, 15 improved mean deviation after treatment, and laser scars showed marked loss of function.⁵¹

Distortion (dysmetropsia, metamorphopsia and “Alice in Wonderland syndrome”)

Dysmetropsia and metamorphopsia are related visual illusions where object shapes appear distorted and straight lines bent. Metamorphopsia is best assessed with an Amsler grid. Even relatively young children will be able to say whether the lines are straight or not and report “funny lines.” Visual distortions are either optical (common), macular (occasional), or cerebral (rare) in origin: optical causes include high corneal, lenticular or retinal (staphylomatous) astigmatism, high ametropia, anisometropia, and new glasses. Macular causes include macular edema and choroidal neovascularization (e.g. associated with myopic Fuchs’ maculopathy, inflammatory ocular disease, and macular dystrophies). Rarely visual distortion is of cerebral origin, as in the “Alice in Wonderland syndrome.” With a cerebral cause, other associated neurologic symptoms and signs will likely be found.

If the Amsler grid confirms the presence of distortions, management includes refraction, corneal topography (if keratoconus is suspected ) and detailed slit-lamp examination of the anterior and posterior segments. Investigations may include optical coherence tomography or fundus fluorescein angiography with macular disease and neuroimaging (MRI) if a cerebral cause is suspected.

Metamorphopsia, micropsia, macropsia, and the Alice in Wonderland syndrome are more common in children than in adults with migraine. Alice in Wonderland syndrome is frequently associated with migraine, but may also be due to epilepsy, drugs/medication (topiramate), varicella infection, or infectious mononucleosis (see Chapter 9).