Abstract
purpose. The present investigation compared recognition acuities (ETDRS chart) with resolution acuities (Landolt-C chart) in a sample of patients with idiopathic macular holes (MH). Traditionally, visual acuity in a clinical setting is measured with a letter chart. Yet, the ability to recognize a letter differs from a resolution task, such as detecting the direction of a gap in a ring. It was hypothesized that resolution acuity would be more impaired than recognition acuity in patients with MH, because component cues in letter optotypes are not available in Landolt-Cs.
method. Visual acuities of 23 patients with MH (age range, 52–82) were tested, using standard ETDRS and Landolt-C charts. Optical coherence tomography was used to confirm the diagnosis of MH.
results. Acuities correlated strongly, before and after surgery (r = 0.92 and r = 0.95, respectively). However, paired t-tests determined that resolution acuity was significantly more impaired at both time points than was recognition acuity (P < 0.001). Using Bland-Altman plots, the limits of agreement between the two acuity types indicated that resolution acuity differed from recognition acuity by up to five lines before surgery and up to 3 lines after surgery.
conclusions. ETDRS and Landolt-C acuities differ in a clinically significant way in patients before and after MH surgery. Measuring recognition acuity by reading letters may lead to an overestimate of visual ability at the retinal level in patients with MH by including compensatory top-down cognitive processes that are unavailable for resolution tasks.
The assessment of visual acuity forms one of the cornerstones in the detection, evaluation, and treatment of vision impairment. However, its proper measurement and interpretation remain a challenge, especially within the constraints of a clinical setting. Various acuity tasks are in use, many of which reflect unique properties of visual function. Researchers and clinicians worldwide use different optotypes in their investigations, and it becomes difficult to compare acuity outcomes across studies. Specifically, the comparison of recognition acuity (i.e., reading individual letters) and resolution acuity (i.e., detecting a gap in a Landolt-C) pose the question of whether these two types of measures evaluate visual function equally.
The Snellen chart has become the most frequently used tool for recognition acuity in the applied setting. Detailed evaluation of this measure has revealed several flaws in its design, resulting in the constant development of improved eye charts,
1 2 3 4 5 including the ETDRS chart, which has become the scientific measure of choice. Resolution tasks are used when examining children, patients who are unfamiliar with the Latin alphabet, or those who are unable to communicate verbally. Here, the optotypes generally consist of one repeating symbol, where only the orientation of the target varies. The most commonly used resolution acuity charts are the Landolt-C and the Tumbling-E. Generally, recognition and resolution acuities are considered equivalent in their ability to assess visual function in normal observers, as differences were small and deemed clinically insignificant (Raasch TW, et al.
IOVS 1984;25:ARVO Abstract 87).
1 6 It has been pointed out that the letter C, which is also contained in the ETDRS chart and is the sole symbol of the Landolt-C chart, is more difficult to identify than other letter optotypes.
1 5 7 Although the letters T and Z have been considered easier to recognize than a Landolt-C, the letter R has been found to be more difficult.
8 Furthermore, letter confusion has been particularly problematic among letters that contain curved components, such as C, S, D, and O.
9 A scaling factor of 0.95 for letter optotypes has been suggested to obtain the same acuity as with Landolt rings.
8 Whether these two types of acuities are comparable in the presence of visual disease has only been investigated in patients with amblyopia
10 and remains to be fully evaluated in other diseases.
One form of disease in which surgical intervention is evaluated with the use of eye charts is macular hole (MH), an age-related condition that affects the central area of the retina (macula). In addition to declining acuity, this condition creates distortions and/or blind spots (scotomas) in the central visual field. Because of the central scotoma created by the presence of an MH, patients are forced to fixate eccentrically. Therefore, a decrease in acuity is expected, as both recognition and resolution acuity have been demonstrated to decline as a function of retinal eccentricity.
11 12 13 14 Previous work with a scanning laser ophthalmoscope (SLO) has indicated that patients fixate at or near the edge of the MH before surgery and that fixation returns toward the central area of the macula after successful surgical closure of the defect.
15 16 Nakabayashi et al.
15 used the amount of fixation shift and its associated improvement of visual acuity to define functionally successful MH closure, in addition to the established standards for successful MH surgery.
17
In the present study, we investigated whether differences exist between acuity-chart types in patients with a diagnosis of MH. It was hypothesized that, even though recognition (ETDRS) and resolution (Landolt-C) acuities would be highly correlated, resolution acuity would be more impaired, and this difference would be clinically significant in the presence of MH as well as after MH surgery.
The participants were 18 women and 5 men with a mean age of 71.0 ± 7.7 years (SD; range, 52–82), currently being treated by one retinal surgeon. The sample consisted of 23 eyes of these 23 patients with a diagnosis of idiopathic MH in only one eye, with no concomitant retinal disease and a healthy second eye. MH diameter was measured with optical coherence tomography (OCT 3; Carl Zeiss Meditec Inc., Dublin, CA) and ranged from approximately 200 to 900 μm (∼0.8–3.4° of visual angle). Information on duration of symptoms was not available. Eight eyes had clear intraocular lens implants at the time of diagnosis whereas, of the remaining 15 eyes, 2 (patients 15 and 22) showed clinically significant signs of cataract formation during the study. All patients were scheduled to undergo 25-gauge transconjunctival sutureless vitrectomy with gas tamponade between June 2004 and July 2005. Postsurgically, MH status was evaluated by OCT scan.