The accurate detection and quantification of metamorphopsia allows the retinal physician to have a more complete understanding of the correlation between visual symptomatology and disease severity, aiding in the identification of additional indications for surgical intervention. Besides subjective Amsler grid testing, there are currently several ways to detect and quantify metamorphopsia; however, the most commonly used tool in prospective clinical trials is the M-CHARTS metamorphopsia tool (Inami & Co., Ltd., Tokyo, Japan).1–5
The M-CHARTS tool is an analog testing booklet which an examiner presents to a patient with subjective reports of visual distortion; the first page of the booklet displays a solid, objectively straight line bisecting a central fixation point. The patient is asked to focus on the central point, and if distortion is perceived at any point along the line, a second dotted line with decreased spatial frequency is presented in the same configuration. This process is repeated, with each new line comprising regularly spaced dots of decreasing spatial frequency, until the patient no longer perceives a distorted line.1 The distance between each dot of the final line, measured in degrees of visual angle, represents the patient's effective metamorphopsia score, or “M-score,” along that axis. Standard use of the test — as described by the manufacturer — only involves performing these steps with vertical and horizontal lines; thus, visual distortions that lie outside the 90° and 180° axes may not be detected by the tool, and the test may yield inaccurate or incomplete information about the severity of a patient's symptoms. Given the heterogeneity of macular anatomic derangement in complex vitreoretinal interface disorders such as epiretinal membrane and vitreomacular traction syndrome, it is quite possible that only testing the vertical and horizontal meridians would result in many false negative results.
We present a novel use for the M-CHARTS tool in which the testing cards are rotated about the fixation point until the patient perceives the greatest amount of distortion. Sequential M-CHARTS testing can then take place along that axis, which will more accurately reflect the severity of any reported distortion. This method was attempted on a patient with vitreomacular traction with significant symptoms of metamorphopsia, and we believe it was better able to detect and quantify her visual symptoms than standard M-CHARTS testing. This case report was exempt from institutional review board review but was carried out in line with the tenets of the Declaration of Helsinki.
The patient is a 60-year-old female with no known ocular comorbidities who was referred to our retina clinic for evaluation of possible vitreomacular traction in the left eye (OS). At presentation, the patient exhibited a complaint of persistent floaters for an unknown amount of time but otherwise denied any symptoms. Her corrected visual acuity (VA) at presentation was 20/20 in both eyes (OU), with a normal-appearing Amsler grid testing OU. Slit-lamp examination revealed trace nuclear sclerosis OU but an otherwise normal anterior segment. Fundus examination demonstrated blunted foveal reflexes OU, but the remainder of the fundus appeared to be within normal limits. Spectral-domain optical coherence tomography (SD-OCT) images showed a normal foveal contour in the right eye (OD) with vitreomacular adhesion (VMA), and focal vitreomacular traction (VMT) with cystoid foveal edema OS consistent with a Gass stage 1 macular hole (MH) (Figure 1A). A decision was made at the time to monitor at regular intervals for evolution of a full-thickness MH (FTMH), at which time surgery would be offered to the patient.
(A) Spectral-domain optical coherence tomography (SD-OCT) of the patient's left eye at her initial visit demonstrating focal vitreomacular traction with cystoid foveal edema. Only horizontal slices were obtained at the time of image capture, so this image represents a horizontal slice through the fovea. (B) SD-OCT of the patient's left eye taken in at her follow-up visit demonstrating interval release of traction, yet persistent parafoveal fluid cysts. The contour of her central fovea has almost fully returned to a physiologic position. This image represents a cross-sectional slice oriented 30° above the horizontal axis, along approximately the same plane as that of the M-CHARTS testing booklet at which the patient saw maximal distortion. (C) Schematic diagram demonstrating the axis of rotation of the M-CHARTS testing booklet about an axis perpendicular to the center of the page, emanating from the central fixation point. The solid vertical line represents the index test figure for detection of metamorphopsia. Our patient noted no metamorphopsia when presented, as recommended, with both a vertical a horizontal testing target separately. (D) After presenting the patient with a variety of M-CHARTS testing target orientations over 360°, maximal distortion was reported by our patient at a meridian located 30° above the X axis.
At her 3-month follow-up appointment, SD-OCT images revealed an interval release of traction OS but persistent parafoveal edema (Figure 1B) and also showed the development of some mild traction OD. The patient's VA measured OD 20/25+1 with no improvement with pinhole testing, OS 20/30 with improvement to 20/25+1 with pinhole testing. At this visit, the patient noted a small area of distortion in the paracentral right upper quadrant of the Amsler grid in her left eye that did not cross the vertical or horizontal axes. She denied perceiving any distortion with her right eye while viewing the Amsler grid. Anterior and posterior examinations were otherwise unchanged.
Description of M-Charts Testing
In an effort to quantify her perceived distortion, M-CHARTS metamorphopsia testing was performed, and despite distortions that she had seen on the Amsler grid with her left eye, both eyes yielded an M-CHARTS metamorphopsia score of 0 along both the vertical and horizontal axes. Another attempt at M-CHARTS was made, this time slowly rotating the card containing a solid line around an imaginary axis perpendicular to the central fixation point (Figure 1C). The patient was advised to alert the examiner when she perceived the greatest distortion along the line. The orientation with the greatest amount of perceived distortion occurred at approximately 30° above the positive X axis (Figure 1D); the patient, once again, described the distortion as occurring in the area a small distance above and to the right of the central fixation point. The examiner then proceeded to iterate the testing targets through dotted lines of decreasing spatial frequency until the distortion was no longer perceivable, which occurred at an inter-dot distance of visual angle 0.3°. We would therefore report this patient's metamorphopsia or “M-score” as “0.3° axis 30°.”
As of the time of her most recent metamorphopsia assessment, due to the release of traction in her left eye and the absence of symptoms in her right eye, there are no plans for operative intervention. However, the purpose of this report was not to demonstrate treatment response, but rather to highlight the limitations of what is emerging as a gold-standard for the quantitative assessment of metamorphopsia.2–5 We anticipate this patient's metamorphopsia will likely subside as her parafoveal anatomic changes resolve in the absence of ongoing traction, and we have plans to repeat this method of M-CHARTS testing at future visits.
In cases such as ours, in which the patient experiences minimal change in VA but still reports noticeable visual distortions, the detection and accurate quantification of metamorphopsia — although inherently subjective — may represent an important additional metric of objective visual dysfunction. It also reassures the patient that the symptom they are noticing has been objectively validated and characterized. Doing so also allows the retinal physician to either justify or avoid intervention and to monitor response to treatments in a systematic way over time.
The recommended use of the M-CHARTS metamorphopsia tool involves the presentation of lines solely along the vertical and horizontal axes.1 Using this method, investigators have found the result achieved with the M-CHARTS tool correlates moderately, yet statistically significantly, with results achieved via subjective metamorphopsia questionnaires (r = 0.59, P = .0004), with a sensitivity for detecting metamorphopsia lying between 74% to 89% depending on the subject's underlying disease.2 This case demonstrates a failure of this method to detect a patient's metamorphopsia and introduces a new way of performing the test that was able to detect distortions otherwise missed. We believe that rotating the M-CHARTS tool as previously described may help increase the sensitivity of M-CHARTS and would yield a metamorphopsia score even more closely aligned with patient-perceived severity.
Further studies are needed to validate this proposed modification of the usual testing method; however, we believe our proposed method is safe, easy to implement, and provides a more complete representation of a patient's visual distortions than traditional M-CHARTS testing. In the future, a simple hand-held frame for the M-CHARTS booklet or digital equivalent could be fashioned that would allow the user to pivot the M-CHARTS testing booklet to any angle and an attached protractor could measure the angle-from-horizontal with greater precision. In the meantime, when reporting M-scores, it should now be necessary to denote the axis of greatest distortion in addition to the scores achieved at the standard vertical and horizontal sampling axes.
- Matsumoto C, Arimura E, Hashimoto S, et al. A new method for quantification of metamorphopsia using M-CHARTS. Rinsho Ganka. 2000;54:373–377.
- Kitagawa T, Yuzawa M. [Intravitreal pegaptanib sodium for myopic choroidal neovascularization: 1 year results of a prospective pilot study]. Nippon Ganka Gakkai Zasshi. 2013;117(4):344–50. PMID:.23767190
- Medical University of Lublin. The Application of M-Charts and Microperimetry for the Assessment of Visual Function in Patients After Vitrectomy Due to the Full Thickness Macular Hole. Identifier NCT03701542. ClinicalTrials.gov. https://clinicaltrials.gov/ct2/show/NCT03701542?term=m-charts&rank=1. Published on October 8, 2018.
- Dal Vecchio M (2015). Mid-Term Evaluation of Metamorphopsia in Epiretinal Membrane Surgery. Identifier NCT03045367. ClinicalTrials.gov. https://clinicaltrials.gov/ct2/show/NCT03045367?term=NCT03045367&rank=1. Published February 7, 2017.
- Arimura E, Matsumoto C, Nomoto H, et al. Correlations between M-CHARTS and PHP findings and subjective perception of metamorphopsia in patients with macular diseases. Invest Ophthalmol Vis Sci. 2011;52(1):128–135. https://doi.org/10.1167/iovs.09-3535 PMID: doi:10.1167/iovs.09-3535 [CrossRef]