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Ocular Causes of Visual Distortions

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Ocular Causes of Visual Distortions FOCUS | CLINICAL Ocular causes of visual distortions Corey J Rowland, Lawrence R Lee VISUAL DISTORTION is a common including their age, sex and race, should presentation in general practice. Patients be noted. A systemic history is important can find it challenging to convey the to highlight any co-existing risk factors, Background Patients with complaints of visual subjective nature of their visual distortions such as diabetes, hypertension and distortions may first present to their and often describe the changes as ‘blurred hypercholesterolaemia. A personal and general practitioners (GPs) for vision’ or ‘vision loss’. Metamorphopsia, family ocular history should be obtained. A assessment. Visual distortions can micropsia, macropsia, scotomas and social history, inclusive of smoking history, present in various forms, from blurred paracentral scotomas are all symptoms of is also relevant. A detailed medication images to aberrations of colour. It is visual function disturbance described in history is important as numerous important to clarify any complaints of various macular disorders.1 These visual medications are associated with visual distortion to uncover potentially vision- threatening pathology. This can be symptoms can often herald or precede an phenomena. Vasodilators such as erectile achieved through a directed history underlying maculopathy. Visual distortion dysfunction drugs (eg sildenafil) may and examination. secondary to macular haemorrhage result in cyanopsia, a distinctive bluish can lead to potentially irreversible loss tinge in vision. Vasodilators such as beta Objective of vision if not treated promptly. Visual blockers and anti-anginal medications The aim of this article is to provide a guide to clarifying complaints of visual distortion secondary to macular oedema are known to cause phenomena such distortions, outlining the common in central retinal vein occlusion (CRVO) as shimmering, halos or scintillations. ocular causes, with a focus on macular could indicate malignant hypertension, Systemic corticosteroids are associated pathologies. leading to stroke and other end-organ with central serous chorioretinopathy damage if left undiagnosed. Thus, visual (CSCR) and resultant visual distortions. Discussion Targeted clues in the cause of visual distortions should be clarified and not distortions can be obtained through a overlooked. It is through a comprehensive Nature of visual distortion directed history. Simple office-based assessment that a general practitioner Distortions in vision can be described examination techniques such as visual (GP) can identify red flags to potentially in terms of shape (metamorphopsia), acuity, the use of Amsler’s grid and sight-threatening or life-threatening size (micropsia or macropsia) and fundoscopy are useful to identify conditions and refer appropriately. This colour (dyschromatopsia), and possible pathology responsible for visual distortions. A basic assessment and article focuses on visual distortions aetiologies can be localised to the knowledge of macular pathologies can secondary to maculopathies and other orbit itself or to the occipital cortex. assist GPs’ appropriate assessment, ocular causes; however, it is important to Metamorphopsia is defined as a treatment and referral of patients who consider neurogenic causes in assessment. deviation of either vertical or horizontal present with visual distortions. lines in central vision as described by the patient, and commonly indicates History macular pathology.1 Patients may Obtaining a detailed history is important complain of typically straight objects, to elicit potential causes of visual such as doorways or window frames, distortions. A patient’s demographic, looking bent or twisted, or simply objects © The Royal Australian College of General Practitioners 2019 AJGP VOL. 48, NO. 8, AUGUST 2019 | 525 FOCUS | CLINICAL OCULAR CAUSES OF VISUAL DISTORTIONS ‘changing shape’. Distortions can manifest in particular sectoral field changes, to test for a relative afferent pupil defect as objects appearing disproportionately months or years prior to central distortion (RAPD), whereby a dilatory response is large (macropsia) or small (micropsia). development can be a sign of retinal vein elicited because of a reduction in afferent Dyschromatopsia or colour aberrations can occlusion with subsequent CMO.1 impulses from the optic nerve. An RAPD is also be implicated, but generally indicate generally observed in optic nerve disease.2 optic nerve pathology. Hemeralopia (day Associated symptoms blindness) or nyctalopia (night blindness) Any associated symptoms should be Visual fields can indicate retinal dystrophies. It is noted. Weakness or numbness on Visual fields to confrontation can important to elicit the location of the one side of the body, diplopia, slurred help define whether the pathology is visual distortion. Is it a sectoral field speech, headaches, difficulty swallowing, neurological or retinal. Sitting directly change suggestive of detachment, optic word-finding problems and imbalance across from the patient, the GP occludes neuropathy or retinal vascular disease? Or should be evaluated to rule out a one eye at a time, mirroring the patient. is it a central or paracentral abnormality, neurological cause of visual distortions. The patient, looking directly ahead, should seen in maculopathies or glaucomatous indicate when a moving target (usually the disease? Has the patient’s ability to read GP’s finger) is seen being brought in from deteriorated because of sections of the page Examination the periphery in all four quadrants. The being missing or are they having issues Vital and other signs patient’s visual field is compared with the with face perception due to a darkened A patient’s vital signs should be taken. GP’s to assess for any abnormalities. central scotoma? Determining whether Systemic hypertension is particularly the visual disturbance is present in one important and may manifest as Colour vision eye (monocular) or both eyes (binocular) hypertensive retinopathy/neuropathy and Colour vision testing using Ishihara plates can also aid in localising the pathology. retinal vein occlusion (RVO), leading to helps differentiate neurogenic from A monocular disturbance suggests that macular oedema. It may also be pertinent non-neurogenic vision changes. Acquired the lesion is anterior to the optic chiasm to check blood sugar levels or to conduct dyschromatopsia can be seen with lesions (eg retina, optic nerve, cornea); in cardiovascular and/or neurological of the optic nerve, retina or the visual contrast, binocular disturbances are more examinations depending on the nature cortex. Cerebral dyschromatopsia caused likely to be neurological. Associated visual of the presentation. by lesions at the occipital–temporal lobe symptoms such as photopsia, floaters and junction is usually accompanied by other transient scintillating colours may indicate Visual acuity focal neurology, including homonymous aetiologies such as tears, detachments and Visual acuity testing should be performed visual field defects.1 ocular migraines, respectively. using a Snellen chart and with appropriate refractive correction (ie the patient should Amsler grid Onset, duration and evolution wear their glasses if that is usual), or The Amsler grid was the first functional of symptoms using a pinhole. This can be performed test proposed to evaluate visual distortions A transient visual obscuration such as using a handheld chart or conventional (Figure 1A).1 It has application in general that experienced in embolic phenomena charts positioned at three and six metres’ practice to discover the presence and (eg amaurosis fugax) is likely to require distance from the patient. If the patient is location of defects in the central field more urgent evaluation than a central unable to see any letters, evaluate whether of vision and can also be used for home visual distortion of 12 months’ duration. the patient can count fingers, observe monitoring by patients. Magnetised Onset, duration and evolution of symptoms hand movements or simply perceive light. Amsler grids can be ordered from the helps triage the urgency of referral. A Visual distortions are often coupled with Macular Disease Foundation Australia static, central distortion of longer duration impaired visual acuity. website and are accessible on various can be suggestive of maculopathies such device applications. The Amsler grid as chronic, dry, age-related macular Intraocular pressure allows for simple and rapid qualitative degeneration (AMD), macular hole, Various forms of tonometry exist to evaluation of alterations of visual function epiretinal membrane (ERM) and diabetic measure intraocular pressure. Rebound in the central 10 degrees around a fixation macular oedema (DMO). Conversely, a tonometry, such as iCare, is the most point. It consists of a black or white card rapidly worsening central distortion can prevalent portable device and uses a small on which vertical and horizontal parallel be indicative of wet AMD with choroidal plastic-tipped probe that bounces gently lines are drawn, subdivided every 5 mm to neovascular membrane (CNVM) or CRVO against the cornea to obtain a reading. form a 10 cm square. The Amsler grid can with insipient cystoid macular oedema be used with patients using the following (CMO). Associated history of previous Pupils instructions: visual distortions in a young middle-aged Pupils should be examined for size and • wear your reading glasses and hold the male
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