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 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.

Macular pucker

Prognosis

Clinical features

Vasoproliferative retinal tumors usually present in the third or fourth decade and both sexes are equally affected.⁹ The majority of primary tumors are solitary (87%), in contrast to secondary tumors, where multiple lesions were found in 42% of cases.

Vitreoretinal interface diseases remain common causes of vision loss or metamorphopsia in spite of recent advances in vitreoretinal surgery. Previous studies revealed that various types of cells, such as retinal pigment epithelial cells, glial cells, retinal vascular endothelial cells, macrophages, and myofibroblast-like cells, organize into preretinal proliferative membranes and contribute to the pathogenesis of various diseases. Under physiological conditions, only small numbers of cells named hyalocytes are present in the vitreous and these are located mainly in the vitreous cortex abutting inner surface of the retina. Accumulating evidence has demonstrated that hyalocytes play pivotal roles in the vitreous cavity both under physiological and pathological conditions, in addition to the cells mentioned above. In this article, we describe the functional characteristics of hyalocytes, and ultimately indicate promising therapeutic strategies that target cell signaling especially in hyalocytes.