What is logmar visual acuity

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Shivanii Agnihotri. Show More. Views Total views. Actions Shares. No notes for slide. Log mar chart 1. This has been in use since and more recently a newer LogMAR fig 2 chart has been introduced into clinical practice. Initially used as a research tool because it is more accurate than other acuity charts, this accuracy is also valuable in the clinical setting and many eye departments now use it routinely. This chart was designed to enable a more accurate estimate of acuity than do other charts e.

For this reason, the LogMAR chart is recommended, particularly in a research setting. An observer who can resolve details as small as 1 minute of visual angle scores LogMAR 0, since the base logarithm of 1 is 0.

Two versions of modified and standard logMAR charts were designed, constructed, and used to assess the visual acuity of 50 individuals drawn from a typical out-patient population. A comparison of the testing time was carried out using paired t -test. Both the versions of modified logMAR charts produced the results which agreed well with those of the standard logMAR charts. The outcomes of the current study demonstrates that the modified logMAR chart with three optotypes offers a comparable result to the standard logMAR charts for assessing distant visual acuity in routine clinical examination set up with a much lesser testing time.

Visual acuity VA measurement is the most commonly adapted method for the assessment of visual function in clinical as well as research settings. In the year , Snellen developed the first letter acuity chart to assess visual function which worked on the principle of measuring the finest spatial details that the visual system can discriminate.

The reliability of the Snellen chart later came under criticism due to 1 disparity in the number of letters in each line causing a varying level of difficulty for the subjects; 2 huge variation in the contour interaction throughout the chart due to non-uniformity in spacing between the letters and lines, 3 varying size progression of optotypes between the acuity levels, 4 lack of standardized scoring system, 5 poor repeatability and reliability, etc.

The development of logarithmic progression charts in the s have negated the limitations pertaining to design and precision, but failed to acquire the preference of clinicians mainly due to unfamiliar scoring system and extended time taken to complete the test. The group included patients with cataract, pseudophakia, glaucoma, myopia, and emmetropia. The study was approved by the institutional review board and all the participants signed the informed consent before taking part in the study.

The acuity charts were designed, constructed, and printed on white panels based on Bailey Lovie's principle to test the VA at 4 m. The combination of Sloan letters used to construct both versions of modified and standard charts was different. All the four charts had 14 acuity levels with 0.

VA assessment was carried out monocularly RE with subject's habitual refractive correction if any. Each of them was tested using all the four charts after giving initial instructions on testing procedure and ensured that sufficient break was given between the tests. Charts were presented in a random order in order to avoid the effect of learning and getting accustomed to the test charts.

The whole procedure was conducted under consistent indoor environments with artificial lighting. Total time taken to complete the acuity measurements was documented using a stop watch. The time was measured from the start of first optotype until the subject erroneously read all the five or three letters in a line. Monitoring of the time and documentation of acuity scores were done by two individual examiners.

Subjects were prompted to read the letters one-by-one from the left upper corner and the end point was defined as the subject misread a line completely. As the scale increment in a standard logMAR chart is 0. But in modified logMAR, it was 0. The VA of a patient who had read all the optotypes correctly upto 0. The mean age of the subjects recruited for the study was Among the subjects chosen, 30 subjects had cataract, 13 were pseudophakic, 5 were emmetropic, 11 were myopic, and 4 had glaucoma.

To further illustrate the reliability of the modified logMAR chart, the Bland—Altman analysis was applied. From the data [ Table 3 ], it can be observed that the mean difference between the two designs is very less and the confidence limits constructed around the mean difference are very narrow. Hence, the results illustrate that the modified logMAR charts produce a valid assessment of VA which is comparable with the standard one.

The mean and range of testing time to complete the acuity measurements were noted as The clinicians all over the globe are in consensus about the type of VA chart to be used for research purpose. This study demonstrated that the modified logMAR chart can produce acuity data that agree very well to the data produced by the gold standard logMAR chart [ Table 3 ].

This observation is consistent with the previous studies. This could probably be due to the fact that all the acuity measurements were done with best-corrected visual acuity BCVA and by the same examiner. Moreover, all the four charts were presented to the subjects in a single visit with specific interval between the tests. Subsequent to the points mentioned above, the data were recorded using an interpolated single-letter acuity score method compared to the line assignment method favored in routine clinical practice.

The line assignment method is known to demonstrate more test-retest variability compared to the single-letter scoring technique. Results of this study are supported by the literature too. Although this study did not involve a comparison of logMAR designs with the Snellen type, previous articles have already documented its poor test-retest variability especially for the line assignment method.

As per the literature, the testing time observed to complete the Snellen chart was only marginally better than the time required for reduced logMAR charts. Source of Support: Nil. Conflict of Interest: None declared. National Center for Biotechnology Information , U. Journal List Oman J Ophthalmol v.

Oman J Ophthalmol.