A recent study of common complaints of dissatisfied refractive surgery patients showed that 59% were unhappy because of blurred distance vision and 43.5% because of poor night vision.1 A novel method for improving vision in these post-refractive surgery patients without further surgery is being tested using NeuroVision (NeuroVision Pte Ltd, Singapore). NeuroVision is a computer-based treatment interface where a repetitive set of visual exercises is performed for 10 to 12 weeks. It is founded on the concept of perceptual learning previously described for the treatment of amblyopia.2 3
Figure. A) Change in unaided visual acuity and B) contrast sensitivity during the NeuroVision treatment.
A healthy 45 -year old man underwent LASIK in November 2000 to correct -9.50 -1.00 X 180 (20/20) in the right eye and -9.00 -1.25 X 175 (20/20) in the left eye with targeted emmetropia in both eyes. In January 2005, the patient returned complaining of blurred distance vision. Unaided vision was 20/32 2 (0.24 logMAR) in the right eye and 20/40 (0.30 logMAR) in the left eye with a refraction of -0.25 -0.75 X 155 (20/20) in the right eye and -1.00 -0.50 X 50 (20/20) in the left eye. Although presbyopic, he did not have any problems with unaided near vision but had begun using glasses when driving at night 1 year after the initial LASIK. Cycloplegic refraction did not reveal any accommodative element in the residual myopia. The patient underwent a full ophthalmic assessment to ensure that his eyes were free from pathology. A LASIK enhancement was discussed and the patient was discouraged from correcting his unintended monovision, as it would lead to loss of near vision.
The patient enrolled for the NeuroVision treatment and upon completing treatment (after 35 sessions) in early June 2005, his unaided visual acuity was 20/16-3 (-0.04 logMAR) in the right eye and 20/20"1 (0.02 logMAR) in the left eye with no change in the manifest or cycloplegic refraction (Fig). This represents 2.8 lines of visual improvement in the right eye and 1.6 lines in the left eye. The repeatability (95% limits of agreement) of this set of logMAR charts in our clinic setting was previously tested and found to be 0.09 logMAR units.4 This shows the improved visual acuity reported by the patient is actual improvement and not an artifact of noise in the visual acuity measurements. The contrast sensitivity function measured with the Sine Wave Contrast Test (Stereo Optical Co Ltd, Chicago, 111) also showed improvement at every measured spatial frequency (see Fig). The patient reported marked improvement in photopic and mesopic vision and no longer relied on glasses.
As described in the literature on perceptual learning,5 in neurons in the primary visual cortex, stimuli present within the receptive field can be facilitated or suppressed by other stimuli present outside the receptive field. Modulation of neuronal responses by stimuli falling outside the receptive field represents a neural mechanism for enhancing visual perception. By repetitively stimulating this neural mechanism, the enhanced visual perception may be transferred to other higher-level visual tasks such as visual acuity and contrast sensitivity.
The availability of a noninvasive treatment to improve unaided visual acuity and contrast sensitivity in patients following refractive surgery is a benefit to any refractive surgery practice especially in cases where enhancement is contraindicated.
1. Jabbur NS, Sakatani K, O'Brien TP. Survey of complications and recommendations for management in dissatisfied patients seeking a consultation after refractive surgery. / Cataract Refract Surg. 2004;30:1867-1874.
2. Levi DM, Polat U. Neural plasticity in adults with amblyopia. Proc Natl Acad Sci USA. 1996;93:6830-6834.
3. Karni A, Sagi D. Where practice makes perfect in texture discrimination: evidence for primary visual cortex plasticity. Proc Natl Acad Sci USA. 1991;88:4966-4970.
4. Farn HB, Lim KL. Effect of higher-order wavefront aberrations on binocular summation. J Refract Surg. 2004;20:S570-S575.
5. Polat U, Mizobe K, Pettet MW, Kasamatsu T, Norcia AM. Collinear stimuli regulate visual responses depending on cell's contrast threshold. Nature. 1998;391:580-584.