Effects of font design and electronic display parameters upon text legibility were determined using a threshold size method. Participants' visual acuity (inverse of the minimum detection size, representing the threshold legibility for each condition) was measured using upper- and lowercase letters and lowercase words in combinations of 6 fonts, 3 font-smoothing modes, 4 font sizes, 10 pixel heights, and 4 stroke widths. Individual lowercase letters were 10% to 20% more legible than lowercase words (i.e., lowercase words must be 10%-20% larger to have the same threshold legibility). This letter superiority effect suggests that individual letters play a large role and word shape plays a smaller role, if any, in word identification at threshold. Pixel height, font, stroke width, and font smoothing had significant main effects on threshold legibility. Optimal legibility was attained at 9 pixels (10 points). Verdana and Arial were the most legible fonts; Times New Roman and Franklin were least legible. Subpixel rendering (ClearType) improved threshold legibility for some fonts and, in combination with Verdana, was the most legible condition. Increased stroke width (bold) improved threshold legibility but only at the thinnest width tested. Potential applications of this research include optimization of font design for legibility and readability.

Previous investigators have observed that some subjects show large amounts of accommodative lag. We hypothesized that less accurate accommodation might be associated with poorer visual acuity and/or smaller pupil sizes. Sixty subjects (30 emmetropes and 30 myopes) aged 20-30 years, participated. All had best-corrected visual acuity of 6/6 or better [mean = -0.10 +/- 0.07 logarithm of the minimum angle of resolution (logMAR)]. Subjects monocularly viewed reduced Bailey-Lovie charts through a +6.50 D Badal lens on a Canon R1 auto-refractor. Visual acuity, accommodative response and pupil diameter were measured for 0, 2 and 4 D accommodative stimuli. For accommodation measurements (N= 10) subjects were instructed to fixate the smallest letters that they could read. The mean accommodative response was +0.22 +/- 0.28, +1.83 +/- 0.23 and +3.71 +/- 0.27 D for the 0, 2 and 4 D stimuli, respectively. The mean visual acuity was -0.06 +/- 0.10, -0.11 +/- 0.07 and -0.11 +/- 0.07 logMAR for the 0, 2 and 4 D stimuli, respectively. Visual acuity for the 0 D stimulus was significantly poorer than for other conditions (p < 0.001) and associated with increased accommodative lead (p < 0.01). There was also an association between visual acuity and accommodative response (or lag) for the 4 D stimulus (p=0.002). The emmetropes showed significantly better visual acuity than the myopes (p= 0.004). No significant difference was observed in the accommodative response between emmetropes and myopes. Pupil diameter was not associated with the accuracy of the accommodative response (p > 0.17). Increased accommodative lead (0 D stimulus) and accommodative lag (4 D stimulus) are associated with decreased visual acuity. Smaller pupil diameters are not associated with increased accommodative lag.

PURPOSE: To develop and test the efficacy of myopic treatment, based on preoperative manifest refraction and higher order aberrations, in enhancing the postoperative refractive error following customized LASIK treatment and compare results with the manufacturer-recommended sphere offset Zyoptix treatment nomogram, which does not account for the preoperative higher order aberrations. METHODS: One hundred seventy-five myopic eyes (89 patients) were treated based on the Rochester nomogram, which specified the amount of myopia to be treated based on preoperative manifest refraction and higher order aberrations, including third order aberrations and spherical aberration. Postoperative refractive error was measured at 1 month and compared to that theoretically estimated with the Zyoptix nomogram. RESULTS: The mean preoperative sphere and cylinder were -4.52±2.05 diopters (D) and -0.81±0.70 D, respectively. The mean postoperative spheres were +0.04±0.33 D and +0.31±0.54 D, using the Rochester and Zyoptix nomograms, respectively. The mean postoperative spherical equivalent refractions were -0.11±0.34 D and +0.15±0.53 D using the Rochester and Zyoptix nomograms, respectively. The Rochester nomogram reduced the range of postoperative spherical equivalent to ±1.00 D, which was significantly better than that using the Zyoptix nomogram (t=5.46, P<.0001), which would have resulted in 8% of eyes with a postoperative spherical equivalent refraction >±1.00 D. Using the Rochester nomogram, 93.1% of eyes attained a postoperative UCVA ≥20/20. The percentage of postoperative hyperopic overcorrection decreased to 2.8% in the Rochester nomogram group from 22.3% using the Zyoptix nomogram, which only adjusts spherical values based on preoperative sphere and does not account for preoperative aberrations. CONCLUSIONS: The Rochester nomogram compensates for the effect of preoperative higher order aberrations on sphere and provided reduced range of postoperative spherical equivalent refraction. [J Refract Surg. 2007;23:435-441.]

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