Switching from spectacles to spherical-equivalent soft contact lenses may produce changes in selected binocular vision measures among patients with low myopic astigmatism, but the observed differences may not represent clinically meaningful dysfunction.
Researchers conducted an acute, single-visit comparative study involving 36 patients aged 15 to 35 years with low myopic astigmatism. Each patient underwent binocular vision testing with spectacles followed by spherical-equivalent soft contact lenses after a 30-minute stabilization period, allowing within-patient comparisons. The patients had at least −0.50 to −3.00 diopters of myopia in both principal meridians of both eyes and 0.75 to 2.00 diopters of astigmatism. Habitual contact lens users and patients new to contact lenses were included.
Assessments included accommodative amplitude and facility, stereoacuity, horizontal phoria, near point of convergence (NPC), negative relative accommodation, positive relative accommodation (PRA), positive and negative fusional vergence, and accommodative lag. The researchers recorded the average of 3 measurements for each parameter and used spherical hydrogel soft contact lenses rather than toric lenses.
Compared with spectacles, contact lenses showed changes in accommodative lag (from 0.70 to 0.81 diopters), NPC (from 6.67 to 7.02 cm). and PRA (from −2.81 to −3.17 diopters).
Despite their statistical significance, the absolute changes were modest and remained within established normative clinical ranges. The researchers noted that the differences were within commonly reported test-retest variability for binocular and accommodative measurements in young adults. They characterized the changes as subtle functional adaptations rather than clinically significant deterioration in binocular performance.
Most other measures did not change statistically significantly between correction methods. Four patients developed exophoria when switching from spectacles to contact lenses; 9 patients had exophoria with spectacles compared with 13 with contact lenses.
In secondary analyses, accommodative amplitude and facility were positively correlated between spectacle and contact lens wear. Accommodative lag, negative relative accommodation, PRA, and fusional vergence measures showed moderate positive correlations across correction conditions.
There were several study limitations. The testing order was not randomized, adaptation to contact lenses was limited to a short period, and the study did not include a toric contact lens comparator. Multiple binocular and accommodative outcomes were also evaluated without formal adjustment for comparisons. Because spherical-equivalent lenses may leave residual uncorrected astigmatism, the findings should be interpreted as reflecting the acute effects associated with spherical-equivalent correction rather than contact lens wear in general.
“Further studies comparing toric and spherical soft contact lenses are warranted to determine the specific contribution of residual astigmatism,” wrote lead study author Arjun Sapkota, MOptom, and Nabin Baral, MOptom, of the Department of Optometry at the Himalaya Eye Institute of Pokhara University in Nepal, and colleagues.
The study authors reported no conflicts of interest.
Source: Annals of Medicine & Surgery
