Transactions from the Xth International Orthoptics Congress 2004

Visual acuity at all distances (AS-15, KOWA), contrast sensitivity at middle distance,
fusional amplitude and near stereoacuity (Titmus stereo tests) were measured. Questionnaire
was used as assessment of satisfaction.
Results
The average refraction of dominant eye was 0.11 D (-0.50 ~ +0.88 D) and that of
nondominant eye was -2.41 D (-1.50 ~ - 4.00 D). The mean amount of anisometropia was
2.53 D (1.50 ~ 4.25 D).
The binocular visual acuity was 20/25 or better at all distances and especially
binocular visual acuity at middle distances (0.7 m and 1.0 m) was greater than the monocular
visual acuity (Fig.1).
At low spatial frequencies (0.5 ~ 2.0 cpd), the binocular contrast sensitivity was
greater than the monocular contrast sensitivity and it was statistically significant. At high
spatial frequencies (greater than 4.0 cpd), the binocular contrast sensitivity was equal to or
below the monocular contrast sensitivity (Fig.2).
The median of stereoacuity in monovision was 80 seconds of arc (40 ~ 800 seconds of
arc) and 40 seconds of arc (40 ~ 200 seconds of arc) under full correction of refractive error.
81 % of patients, the stereoacuity was better than 100 seconds of arc (Fig.3).
The mean of fusional amplitude in monovision was 44.7 prism diopter (10 ~ 84 prism
diopter) and 64.9 prism diopter (22 ~ 118 prism diopter) under full correction of refractive
error (Fig.4).
77.4% of patients satisfied monovision. The rate of using glasses was 15.5%.
Discussion
It is well known that less than + 1.50 D add power is recommended in monovision with
contact lens (2) or LASIK (3). This study revealed that best add power in monovision by IOL
is +2.25 ~ +2.50 D since pseudophakic patients lost their accommodation completely.
Binocular visual acuity at middle distance was obviously better than each monocular visual
acuity. Thus, it indicates obvious binocular summation of visual acuity was observed in
middle distance. In contrast, anisometropic blur reduced binocular summation of contrast
sensitivity, particularly at high spatial frequencies, since blurred image lacks high frequency
detail (4). It has been indicated that the suppression of anisometropic blur plays an important
role in binocular summation (4, 5). It seemed that the difference of binocular summation
between visual acuity and contrast sensitivity was due to a discrepancy of each stimulus
condition such as contrast, background luminance and optical arrangement of device.
Although stereoacuity in monovision reduced as compared to that of under full correction of
refractive error, 81 % of patients showed within normal limits. Consequently, 77.4% of
patients were satisfied monovision. This value is in good agreement with the previous report
(6). However, some patients complained about asthenopia and reduced near or middle
distance acuity. Larger add power and / or larger interocular differences in visual acuity must
inevitably reduce binocular visual functions. Likewise, strong ocular dominance interrupts
blur suppression as well as the switching of eye, i.e., smooth alternation of fixation.
In summary, most of patients showed good visual quality and were satisfied with
monovision. Therefore, it is strongly suggested that monovison by IOL is effective method to
compensate for loss of accommodation after cataract surgery. Careful selection of patients as
well as precise measurement of IOL power is needed to improve patient’s satisfaction
furthermore.
2