Articles and journal
By Montani Giancarlo
To manage presbyopia with contact lenses there are several available options, including single vision contact lenses and spectacle overcorrection for near, monovision, rigid gas permeable (RGP) and soft multifocal and bifocal lens designs (1,2). Although there is an increasing demand for presbyopic contact lens corrections with the aging population (3) the number of wearers is still low (4,5). One reason for this result is related to higher drop out associated to patients aged over 40 years induced by vision issues that represent the most important reason for ceasing to wear contact lenses (6-8). Generally, although multifocal RGP contact lenses use an alternating vision design and multifocal soft contact lenses use a simultaneous vision design, multifocal RGP contact lens wearers have a higher degree of satisfaction in their corrected vision than multifocal soft contact lens wearers have (9). The aim of new developed lenses is to deliver better vision and higher comfort to increase the success rate of this increasing contact lens segment.
This prospective study was designed to evaluate subjectively the performance of a progressive translating RGP contact lens (Expert Progressive, Precilens). The design of the lens tested present a prismatic front surface with an inferior slab off and a quadric-curve back surface. The optical zone, similar to an ophthalmic progressive lens, present an area for distance vision, an area for near vision and a progressive zone between them (Figure1).
A total of 8 subjects were enrolled in the study. Five subjects were habitual monofocal RGP contact lens (CL) wearers and three no contact lens wearers. A minimum of best-corrected visual acuity for far of 0,1 logMAR in each eye, a minimum addition needs of 1,50D and no more than 0.75D of residual astigmatism with RGP contact lens were considered . Subjects with a history of refractive surgery, binocular vision abnormalities, ocular and systemic diseases, Dry Eye, Meibomian Gland Dysfunction or other contact lens contraindications were excluded. For the study were used a progressive translating RGP contact lens fitted considering the best subjective refraction (best distance correction / minimum addition) and according to the manufacturers’ fitting rules. Before to take the measurements the subjects were adapted to the best lenses for a minimum of two weeks and the day of the visit the lenses were used for a minimum of two hours. During the visit the visual performance of the lenses were evaluated, under photopic conditions (85 cd/m2), measuring visual acuity (VA) with a Sloan letters acuity chart in logMAR scale at high (95%) and low (25%) Michelson contrast for far (5m), intermediate (1m) and near (40 cm) distances. Stereoacuity was measured also using a Randot stereo test at 40 cm. The results obtained were compared with those obtained with the best ophthalmic correction for the distances tested. Overall subjective quality of vision ( for far, intermediate and near distances) , comfort, speed of stabilization of the lenses and stability of vision were also assessed with a numerical rating scale (NRS) from 10 to 100 (with higher scores for better performance).
Figure 1 Lens design and optimal fluorescein pattern
The study participants presented a mean age of 51,6± 3 years (from 48 to 56 years of age), a mean spherical refraction of -0.75±2.62D (from +2.00 to -4.50D), a mean near spectacle addition of +2.10 ±0.18D (range +1.75 to +2.50D) and a mean pupil diameter of 3.55±0.70 under photopic conditions. No statistically significant differences (paired t-test, p > 0.05) in monocular and binocular VA at high contrast for all distances tested and in monocular and binocular VA at low contrast for near were found between the lenses tested and the best ophthalmic correction.Monocular VA at high and low contrast with contact lenses were respectively for far -0,05 ±0.05logMAR and 0.04 ±0.05 logMAR , for intermediate -0.07±0.04 logMAR and 0.05 ±0.05logMAR and for near -0.02±0.04logMAR and 0.09 ±0.06logMAR (Figure 2 and 3). Binocular VA at high and low contrast with contact lenses were respectively for far -0.07 ±0.03logMAR and 0.04 ±0.05 logMAR, for intermediate -0,06 ±0.05logMAR and 0,03 ±0.05logMAR and for near -0.03 ±0.05logMAR and 0.07 ±0.06 logMAR. Mean value of stereopsis obtained with contact lenses in respect to the ophthalmic correction were not statistically significant different and the result were 40 sec of arc. The subjects rated the performance of the lenses for far vision 91±7, intermediate vision 93±5, near vision 96±2, comfort 82±9, speed of stabilization 77±7 and stability of vision 85±5 (Figure 4).
Figure 2 Monocular and Binocular high contrast visual acuity
Figure 3 Monocular and Binocular low contrast visual acuity
Figure 4 Subjective performance measured with NRSs
Monocular and binocular high contrast VA with Expert Progressive was not significant different in respect to best ophthalmic correction. A statistical significant reduction was found only for the monocular and binocular low contrast VA for far and intermediate distances although this result was not clinically significant since the differences were lower than one VA line. Subjective performance of the CLs evaluated by the wearers showed an high score for vision at every distances. Interesting to evaluate the higher score for near vision even though high an low contrast VA at near were lower in respect to other distances. This results can be explained considering the different “metric” used by wearers to judge their visual performance at near using target from the “real world” like smartphone, book or newspapers with bigger letter than limits of VA. In spite of the greater thickness of the lens tested in respect to monofocal RGP CLs both habitual and no CL wearers rated comfort more than acceptable. In conclusion the results of this study demonstrate that the progressive translating RGP CL tested provide an optimal visual results for all distances comparable with the best ophthalmic compensation representing an option indicated not only for RGP monofocal CL wearers but also for new wearers and for patients experienced poor vision results with soft multifocal contact lens.
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