<P> Macropsia may be a result of optical magnification differences between the eyes, retinal receptor distribution, or the cortical processing of the sampled image . The current hypothesis for the occurrence of dysmetropsia is due to the stretching or compression of the retina leading to the displacement of receptors . Macropsia arises from a compressed receptor distribution leading to a larger perceived image size and conversely, micropsiaresults from stretching of the retina leading to a more sparse receptor distribution that gives a smaller perceived image size . In the case of macropsia, the greater density of photoreceptor cells leads to greater stimulation making the object seem larger . In some cases, the effects of macropsia have been shown to be field dependent, in that the degree of visual distortion is related to the visual field angle . Non-uniform stretching or compression of the receptor distribution could explain the field dependency of the macrospia . If the compression forces were closer to the fovea the resulting compression would cause a greater amount of macropsia at lower field angles with little effect at higher field angles where the receptor distribution is not as compressed . Alterations in receptor distribution can be the result of epiretinal membrane, neuroretina detachment and / or re-attachment, or retinoschisis . Macropsia caused by surgical re-attachment of macula - off rhegmatogenous retinal detachment is not symmetrical around the fovea, resulting in differences size changes in the horizontal and vertical meridians . Asymmetry has also been observed with retinoschisis, in which macropsia generally results in the vertical direction while micropsia presents in the horizontal direction . </P> <P> Macropsia is generally diagnosed once a patient complains of the characteristic symptoms, such as disproportionally large objects in their visual field . The Amsler Grid test can be used to diagnose macropsia, along with other visual maladies depending on the subjective disturbance reported by the patient after looking at the Amsler Grid . Outward bulging of the lines on an Amsler Grid is consistent with patients experiencing macropsisa . The New Aniseikonia Test (NAT) can quantify the degree of macropsia or micropsia independently in the vertical and horizontal meridians . The test consists of red and green semicircles on a black background with a white round fixation target . The size of the red semicircle is held constant while the green semicircle is varied in size in 1% increments . The patient wears a pair of red / green goggles so that one eye is tested at a time, and the patient attempts to determine when the semicircles are the same size . This is termed the reversal threshold and the size difference between the semicircles is reported as the degree of aniseikonia . A positive value indicates that the object was perceived bigger and thus corresponds to macropsia, and conversely a negative value indicates micropsia . The Aniseikonia Inspector contains an aniseikonia test based on the same principles as the NAT, but the test is run on a computer screen, it is based on a forced choice method, and it can measure the size difference as a function of the size of the objects . The functionality of being able to measure the size difference as function of the size (i.e. field dependent testing) is especially important when the macropsia (or micropsia) has a retinal origin . </P> <P> The most common way to treat forms of aniseikonia, including macropsia, is through the use of auxiliary optics to correct for the magnification properties of the eyes . This method includes changing the shape of spectacle lenses, changing the vertex distances with contact lenses, creating a weak telescope system with contact lenses and spectacles, and changing the power of one of the spectacle lenses . Computer software, such as the Aniseikonia Inspector, has been developed to determine the prescription needed to correct for a certain degree of aniseikonia . The problem with correction through optical means is that the optics do not vary with field angle and thus cannot compensate for non-uniform macropsia . Patients have reported significantly improved visual comfort associated with a correction of 5 - 10% of the aniseikonia . </P> <P> With regard to drug - induced or virus - induced macropsia, once the underlying problem, either drug abuse or viral infection, is treated, the induced macropsia ceases . </P>

Is resolution the condition when objects appear larger than they really are