Mean Modulation Transfer Function Research Articles

The visual impact of higher-order aberrations in patients with pediatric blepharokeratoconjunctivitis.

To analyze higher-order aberrations (HOAs) and their visual impact in a pediatric blepharokeratoconjunctivitis (PBKC) cohort compared with healthy controls. Prospective case-control study of pediatric patients (≤ 16 years old). Subjects underwent wavefront aberrometry analysis to compare HOAs and their impact on visual quality. A total of 150 eyes from 76 patients were included in the analysis. The PBKC group consisted of 50 eyes and the control group of 100 healthy eyes. Mean age was 10.39 ± 3.81 years for the PBKC group and 10.80 ± 3.61 years for the controls. Mean corrected-distance visual acuity (CDVA) was 0.24 ± 0.21 logMAR in the PBKC group and 0.07 ± 0.1 in the controls (P < 0.001). Mean astigmatism was 1.6 ± 1.98D in the PBKC group vs. 0.67 ± 0.76D in the control group (P = 0.01). Mean RMS of HOAs was 1.05 ± 1.7mm in the PBKC group and 0.41 ± 0.18mm in the controls (P < 0.001). The mean modulation transfer function (MTF) in the PBKC group was significantly lower (16.37 ± 16.32) than controls (30.3 ± 23.57) (P < 0.001). Corneal leukomas, stromal vascularization, peripheral nummular subepithelial scars, and pannus formation are associated with increased HOAs. There was a significant increase in total HOAs of eyes with PBKC compared to healthy controls. Corneal opacity, vascularization, and scarring are associated with increased HOAs. The PBKC eye aberration profile: coma, secondary astigmatism, quadrafoil, and pentafoil, were associated with decreased CDVA and visual quality (PSF and MTF).

Modulation transfer function formula for different age ranges.

The modulation transfer function (MTF) is one of the most complete tools to study the optical performance of the eye. We present the average radial MTF profiles measured in 68 subjects grouped in six age ranges (from 20 to 80years) and a general formula to estimate the radial profile of human MTF as a function of pupil size and age. The mean MTF for each age group was fitted to an analytical expression to compute two parameters related to aging. The proposed formula fitted reasonably well to experimental data available in previous works and predicted the average changes with aging of different optical quality parameters obtained from MTF.

Evaluation of the Effects of Vitrectomy with Primary Epiretinal Membrane Peel on Optical Quality Using Double-Pass Aberrometry

Introduction: We performed a prospective, single-center, cohort study in order to evaluate the effects of vitrectomy with epiretinal membrane (ERM) peel on optical quality in patients with primary ERM. Methods: Thirty patients treated for primary ERM by vitrectomy with ERM peel were included from our tertiary university hospital ophthalmology department. The main study outcome was a variation in optical quality parameters measured using the HD Analyzer™ between preoperative and 2-month postoperative evaluations in operated eyes. Optical quality parameters comprised point spread function (PSF) width at 10% and 50%, objective scatter index (OSI), and modulation transfer function (MTF) cutoff. Contralateral non-operated eyes were used as an internal control for measurement reproducibility. Results: Mean PSF width at 10% (42.22 vs. 27.37 arc/min; p = 0.0002) and mean OSI (3.32 vs. 2.32; p = 0.0003) were significantly improved between pre- versus postoperative evaluations. Mean PSF width at 50% and mean MTF cutoff showed no changes. Subgroup analysis according to crystalline lens status gave similar results, demonstrating that improvements in mean PSF width at 10% and OSI were not lens-related. Non-operated eyes showed no changes in any of the parameters analyzed. Conclusion: Reduced light scattering measured by OSI indicates improved optical quality following vitrectomy with ERM peel among patients with primary ERM. OSI measurement could thus be a new parameter of interest in the preoperative assessment of primary ERM and other pre-vitrectomy assessments.

Laboratory and Clinical Experience With a Diffractive Trifocal Intraocular Lens Sutured to an Artificial Iris.

To determine in vitro, using a translational research approach before realizing the procedure in a patient with iatrogenic aphakia and partial aniridia, whether suturing a trifocal intraocular lens (IOL) to an artificial iris degrades the IOL's optical quality. Optical quality was analyzed by measuring the modulation transfer function (MTF) at a 3-mm aperture and at 50 and 100 lp/mm spatial frequencies. The FineVision Pod F GF IOL (PhysIOL) was assessed in two powers: two +20.00 diopters (D) (20A and 20B IOLs) and two +30.00 D (30A and 30B IOLs). The IOLs' decentration in relation to the artificial iris's center was evaluated. The laboratory results provided empirical evidence in the informed consent for surgical intervention in a patient with iatrogenic aphakia and iris defect in one eye. Clinical results were measured using the parameter of corrected distance visual acuity plus a patient self-assessment of the cosmetic appearance of the operated eye. The 20A and 20B IOLs demonstrated a mean MTF reduction of up to 1.1%, whereas the 30A and 30B IOLs showed a decrease of up to 5.2% for both spatial frequencies. All lenses showed good centration levels. In the clinical case, the patient showed corrected distance visual acuity, distance-corrected near visual acuity, and distance-corrected intermediate visual acuity of 0.20, 0.20, and 0.22 logMAR, respectively. The patient was satisfied with the cosmetic outcome. There was merely a slight reduction in trifocal IOL optical quality after it was sutured to an artificial iris. Clinically, the combined implantation of the artificial iris and FineVision IOL provided good functional and cosmetic outcomes. [J Refract Surg. 2022;38(1):61-68.].

Evaluation of optical quality in pterygium patients with a new modified sutureless and glue-free method

BackgroundModified sutureless and glue-free method is an effective and novel surgical approach for pterygium. We aim to evaluate optical quality in pterygium treated with the new method and investigate the clinical application of the Optical Quality Analysis System (OQAS) and Anterior segment optical coherence tomography (AS-OCT) to evaluate the pterygium surgery.MethodsA total of 52 eyes of 52 patients with pterygium were randomly divided into 2 groups. After surgical excision, the bare sclera was placed with a tight fit limbal conjunctival autograft fixed via the modified sutureless and glue-free method in group 1 (26 eyes) and conventional sutures in group 2 (26 eyes). Objective scattering index (OSI), modulation transfer function (MTF) and Strehl ratio (SR) were measured using OQAS in both groups during the perioperative period. Pterygium diameter was measured on AS-OCT. Ocular surface disease index (OSDI) questionnaire also was used.ResultsThe group 1 had significantly lower mean OSI, higher mean MTF, and higher mean SR at 1 month and 3 months after surgery (p < 0.05). The group 1 had significantly lower mean OSDI at 1 month (p < 0.05), while was similar to group 2 at 3 months (p > 0.05). Pterygium diameter positively correlated with OSI (r = 0.528, p < 0.001), while it negatively correlated with MTF (r = − 0.501, p < 0.001) and SR (r = − 0.174, p = 0.217) before operation.ConclusionsThe modified sutureless and glue-free method might be more advantageous in improving the optical quality during early postoperative recovery times and pterygium diameter affected optical quality. OQAS can be reliably used to evaluate postoperative outcomes.

Implantable collamer lens with a central hole for residual refractive error correction after corneal refractive surgery.

The present study aimed to assess the visual and refractive outcomes of an implantable collamer lens with a central hole (ICL V4c) for residual refractive error correction after corneal refractive surgery in individuals with myopia. A total of 16 eyes of eight consecutive patients with myopia undergoing ICL V4c implantation after corneal refractive surgery were investigated. The uncorrected visual acuity (VA) and best-corrected VA were examined prior to surgery and at 1, 3 and 6 months after surgery. The post-operative values of the modulation transfer function (MTF) cutoff frequency, Strehl ratio (SR), objective scattering index (OSI) and Optical Quality Analysis System (OQAS) values (OVs) were quantitatively assessed using an OQAS. At 6 months after surgery, the mean uncorrected LogMAR VA was 0.06±0.10 and the values had improved in 100% of the eyes. The mean MTF cutoff frequency, SR, OSI, OV 100%, OV 20% and OV 9%, were 31.294±4.321 cycles/degree, 0.187±0.039, 1.399±0.274, 1.066±0.261, 0.748±0.287 and 0.509±0.229, respectively. In conclusion, ICL V4c implantation for the correction of residual refractive error after corneal refractive surgery appeared feasible and safe and also had an excellent optical performance. However, long-term changes in visual quality require further investigation.

In vitro optical quality assessment of a monofocal IOL sutured to an artificial iris.

To assess whether the combined implantation of a monofocal IOL and an artificial iris had an effect on the IOL's optical performance. David J. Apple International Laboratory for Ocular Pathology, Heidelberg, Germany. In vitro laboratory study. IOL optical quality was assessed using an OptiSpheric IOL Pro II to measure the IOL's modulation transfer function (MTF) at 3.0 mm pupil size and spatial frequency of 100 lp/mm. Three ASPIRA-aAY IOLs with different base powers, 10.0 diopter (D) (IOL A), 20.0 D (IOL B), and 30.0 D (IOL C) were measured before and after suturing the IOL to an ArtificialIris (AI). The degree of IOL decentration about the center of the AI was also evaluated. The mean MTF values prior to suturing were 0.57, 0.65, and 0.63 for IOLs A, B, and C, respectively. After suturing to the AI, the mean MTF values were 0.52, 0.54, and 0.55 for IOLs A, B, and C, respectively. The decentration values in vertical direction were 0.20 mm, 0.00 mm, and 0.02 mm for IOLs A, B, and C, respectively. In horizontal direction, the decentration values were 0.42 mm, 0.10 mm, and 0.03 mm for IOLs A, B, and C, respectively. The MTF decreased slightly in all 3 IOLs after they were sutured to the AI. The small differences, however, should be clinically irrelevant. This laboratory assessment showed that suturing of the IOL to the AI can be performed in a reliable and reproducible manner without deteriorating optical quality.

Influence of angle kappa and angle alpha on visual quality after implantation of multifocal intraocular lenses

To assess the influence of angle kappa (κ) and angle alpha (α) on visual quality after multifocal intraocular lens (IOL) implantation. Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China. Prospective case series. Patients with cataract had phacoemulsification with TECNIS Symfony IOL implantation. The preoperative angle κ and angle α were measured using the iTrace device. Distance, intermediate, and near visual acuities were recorded 3months postoperatively. The Optical Quality Analyzing System was used to measure the objective scatter index (OSI), modulation transfer function (MTF) cutoff frequency, and Strehl ratio. A patient questionnaire was also administered. The study comprised 29 patients (57 eyes). Monocularly, the mean postoperative logarithm of the minimum angle of resolution (logMAR) uncorrected distance, intermediate, and near visual acuities were 0.03±0.09 (SD), 0.05±0.11, and 0.11±0.09, respectively. The mean postoperative logMAR corrected distance, distance-corrected intermediate, and distance-corrected near visual acuities were -0.01±0.05, 0.04±0.09, and 0.11±0.08, respectively. The mean OSI, MTF cutoff, and Strehl ratio were 1.27±0.84, 32.03±10.80 cycles per degree, and 0.17±0.05, respectively. The OSI (r=0.398, P=.005), MTF (r=-0.437, P=.002), and Strehl ratio (r=-0.419, P=.003) values were significantly correlated with angle κ. There was no correlation with angle α. Angle κ affected the objective visual quality multifocal after IOL implantation. The decision to implant a multifocal IOL should be carefully considered for patients with a large angle κ.

Optical Performance of the Cornea One Year Following Keratoconus Treatment with Corneal Collagen Cross-Linking

ABSTRACT Purpose The purpose of the study is to assess changes in optical performance of the cornea in patients with keratoconus following treatment with corneal collagen crosslinking (CXL). Materials and Methods One hundred and eleven eyes of 111 consecutive keratoconus patients with 12-month follow-up after CXL were included. The changes in the visual acuity, manifest refractive errors, and corneal topographic parameters were evaluated. Sirius dual-scanning corneal tomography was used to determine the effectiveness of CXL on each patient’s total corneal optical quality; preoperative and 12-month postoperative measurements were analyzed over a 4-mm stimulated pupil and were compared with regards to higher order corneal aberrations (total amount of higher order aberrations [HOAs], vertical coma, horizontal coma, vertical trefoil, oblique trefoil, and spherical aberration), vertical and horizontal modulation transfer function (MTF), and Strehl ratio of point spread function (PSF). Results At 12 months, there was a significant improvement in mean uncorrected visual acuity (UCVA) (P < 0.001), best corrected visual acuity (BCVA) (P < 0.001), spherical equivalent refraction (P = 0.007), and manifest astigmatic refraction (P < 0.001). The corneal topographic measurements revealed a significant decrease in the mean simulated keratometry-1, simulated keratometry -2, and maximum keratometry compared with the baseline measurements (P < 0.001, for all). In addition, there were significant improvements in mean root mean square error values for corneal total HOA (P < 0.001), vertical coma (P < 0.001), and vertical trefoil (P = 0.008) following CXL. Mean MTF and Strehl ratio did not change after CXL (P > 0.05). The improvement in UCVA significantly correlated with the changes in vertical trefoil (r = −0.191, P = 0.044), and the improvement in BCVA and the changes in manifest astigmatic correction were also significantly correlated (r = −0.247, P = 0.009) 12 months after CXL. Conclusions CXL treatment for keratoconus led to an improvement in visual, refractive, topographic, and most corneal HOAs outcomes at the 12-month follow-up. However, these improvements were not enough to increase corneal MTF and the Strehl ratio of PSF.

Comparison of optical quality after implantable collamer lens implantation and wavefront-guided laser in situ keratomileusis.

To compare the optical quality after implantation of implantable collamer lens (ICL) and wavefront-guided laser in situ keratomileusis (WG-LASIK). The study included 40 eyes of 22 patients with myopia who accepted ICL implantation and 40 eyes of 20 patients with myopia who received WG-LASIK. Before surgery and three months after surgery, the objective scattering index (OSI), the values of modulation transfer function (MTF) cutoff frequency, Strehl ratio, and the Optical Quality Analysis System (OQAS) values (OVs) were accessed. The higher order aberrations (HOAs) data including coma, trefoil, spherical, 2nd astigmatism and tetrafoil were also obtained. For patients with pupil size <6 mm, HOAs data were analyzed for 4 mm-pupil diameter. For patients with pupil size ≥6 mm, HOAs data were calculated for 6 mm-pupil diameter. Visual acuity, refraction, pupil size and intraocular pressures were also recorded. In both ICL and WG-LASIK group, significant improvements in visual acuities were found postoperatively, with a significant reduction in spherical equivalent (P< 0.001). After the ICL implantation, the OSI decreased slightly from 2.34±1.92 to 2.24±1.18 with no statistical significance (P=0.62). While in WG-LASIK group, the OSI significantly increased from 0.68±0.43 preoperatively to 0.91±0.53 postoperatively (Wilcoxon signed ranks test, P=0.000). None of the mean MTF cutoff frequency, Strehl ratio, OVs showed statistically significant changes in both ICL and WG-LASIK groups. In the ICL group, there were no statistical differences in the total HOAs for either 4 mm-pupil or 6 mm-pupil. In the WG-LASIK group, the HOA parameters increased significantly at 4 mm-pupil. The total ocular HOAs, coma, spherical and 2nd astigmatism were 0.12±0.06, 0.06±0.03, 0.00±0.03, 0.02±0.01, respectively. After the operation, these values were increased into 0.16±0.07, 0.08±0.05, -0.04±0.04, 0.03±0.01 respectively (Wilcoxon signed ranks test, all P<0.05). At 6 mm-pupil, the induction of total HOAs was not statistically significant in the WG-LASIK group. ICL implantation has a less disturbance to optical quality than WG-LASIK. The OQAS is a valuable complementary measurement to the wavefront aberrometers in evaluating the optical quality.

Optical aberrations, accommodation, and visual acuity with a bioanalogic continuous focus intraocular lens after cataract surgery

PurposeTo evaluate the visual outcomes, pseudoaccommodation, and wavefront aberrometry after implantation of Wichterle IOL-Continuous Focus (WIOL-CF®, Gelmed International, Kamenne Zehrovice, Czech Republic) by i-Trace aberrometry. MethodsIn this retrospective interventional case series study, after cataract surgery with implantation of accommodative WIOL-CF®, the patients were evaluated with i-Trace aberrometer for measurement of modulation transfer function (MTF), point spread function (PSF), total aberrations, higher order aberrations (HOAs) at far and near and pseudoaccommodation. The pre and postoperative visual acuity at near and distance were also measured. ResultsForty eyes of 20 patients (aged 40–77 years) were enrolled in this study with mean follow-up time of up 13.10 ± 5.52 months. The mean logMAR corrected distance visual acuity (CDVA) improved from 0.20 ± 0.14 preoperatively to 0.10 ± 0.09 at the last follow-up after surgery (P = 0.002). The results were 60% J1, 70% J2, 85% J3, 90% J4, 95% J5 and 100% for J6. The mean pseudoaccommodation, range of accommodation volume, and average of peak accommodation were −2.52 ± 1.56 diopters (D), 1.50 to 5.25 D and −3.25 ± 1.25 D, respectively. The mean MTF at 5 cycles per degree at far was 0.200 ± 0.10 and for near was 0.207 ± 0.10. PSF at far and near was 0.0002 and 0.001, respectively. The mean root mean square (RMS) value of HOAs; total, coma spherical aberration, trefoil, and secondary astigmatism were 1.08 ± 0.48 μm, 0.89 ± 0.45 μm, −0.33 ± 0.23 μm, 0.25 ± 0.17 μm, and 0.15 ± 0.13 μm for far and 0.88 ± 0.49 μm, 0.73 ± 0.46 μm, −0.25 ± 0.22 μm, 0.19 ± 0.16 μm and 0.11 ± 0.10 μm for near, respectively. There was a decrease in HOAs at near relative to far (P < 0.05). ConclusionWIOL-CF® seems to be an acceptable accommodative intraocular lens (IOL) in terms of uncorrected near and distant visual outcomes, MTF and HOA.

Optical performance of hydrophobic acrylic intraocular lenses with surface light scattering

To evaluate the potential effect of surface light scattering on the optical performance of hydrophobic acrylic intraocular lenses (IOLs) made of Acrysof material. Alcon Laboratories, Inc., Fort Worth, Texas, USA. Experimental study. Explanted IOLs from cadaver eyes with more than 50 computer-compatible tape (CCT) units of scatter were selected, yielding 7 IOLs. Clinically explanted IOLs (n = 4) were obtained after IOLs had been implanted 8.5 to 10.5 years. Explanted IOLs were matched to unused control IOLs. After proteins were removed, scatter was measured for IOLs dry, wetted (2 minutes in a balanced salt solution), and hydrated (24 hours). Badal imaging, ultraviolet-visible transmission, and modulation transfer function (MTF) measurements were performed with hydrated IOLs. Hydrated scatter values ranged from 80 to 221 CCT for explanted IOLs and 2 to 7 CCT for controls. No differences in Badal image resolution were observed between explanted IOLs and controls. The mean MTF values at 100 line pairs per mm (representing 20/20 visual acuity) were similar between explanted IOLs and controls. Over the range of 400 to 700 nm, a small reduction (mean 2.1% ± 1.4% [SD]) in transmission was observed. Surface light scattering of explanted IOLs did not affect image resolution or MTF values. Although light transmission was slightly decreased, the magnitude appeared to be inconsequential for optical performance.

Clinical Evaluation of Optical Quality and Intraocular Scattering after Posterior Chamber Phakic Intraocular Lens Implantation

We assessed the optical quality and intraocular scattering after posterior chamber phakic intraocular lens implantation. We examined prospectively 38 eyes of 19 consecutive patients undergoing implantable contact lens (ICL) implantation (mean age ± SD 36.3 ± 5.7 years), and 38 age-matched normal eyes of 19 healthy volunteers (mean age 36.4 ± 4.9 years). We assessed quantitatively the values of modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI), and the Optical Quality Analysis System (OQAS) values (OVs). We compared these variables in eyes undergoing ICL implantation to those in healthy eyes. The mean MTF cutoff frequency, Strehl ratio, OSI, OV 100%, OV 20%, and OV 9% were 28.69 ± 8.59 cycles/degree, 0.17 ± 0.04, 1.06 ± 0.48, 0.96 ± 0.29, 0.83 ± 0.31, and 0.83 ± 0.32, respectively, 3 months after ICL implantation. We found no significant differences in the MTF cutoff frequency (Mann Whitney U test, P = 0.31), Strehl ratio (P = 0.46), OSI (P = 0.30), or OVs at contrasts of 100% (P = 0.51), 20% (P = 0.46), and 9% (P = 0.36), between the ICL and control groups. The optical quality parameters, such as the MTF cutoff frequency, Strehl ratio, OSI, or OVs in the ICL group, were not significantly different from those in the control group, suggesting that the optical quality and intraocular scattering of eyes undergoing ICL implantation essentially was equivalent to those of healthy eyes.

Visual quality after posterior chamber phakic intraocular lens implantation in keratoconus

To quantify image-quality characteristics after correction of refractive error with a posterior chamber phakic intraocular lens (PC pIOL) in eyes with stable or stabilized keratoconus. Narayana Nethralaya Postgraduate Institute of Ophthalmology, Bangalore, India. Case series. Eyes with stable or stabilized keratoconus that had V4 Visian PC pIOL implantation for correction of refractive error were evaluated postoperatively for visual-quality metrics. Ten eyes of 7 patients had PC pIOL implantation. The preoperative mean refractive spherical equivalent of -7.21 diopters (D) ± 2.25 (SD) decreased to -0.55 ± 1.53 D at 6 weeks and -0.44 ± 1.21 D at 6 months. The efficacy index was 0.72 and the safety index, 1.13. The mean modulation transfer function (MTF) was 18.96 ± 14.16 (≥ 30 cycles per degree = good), the Strehl ratio was 0.11 ± 0.07 (1 = perfect), and the objective scatter index (OSI) was 4.45 ± 3.29 (≥ 1.5 = significant scatter). The MTF correlated inversely with secondary coma (P=.026), negative vertical coma (P=.014), and the root mean square (RMS) of total aberrations (P=.010) and higher-order aberrations (HOAs) (P=.015). The OSI was directly correlated with secondary coma (P=.021), secondary trefoil (P=.016), the RMS of total aberrations (P=.032), and HOAs (P=.050). In keratoconus, the refractive error could be corrected with the PC pIOL; however, the associated aberrations had an adverse impact on the ultimate visual quality and have to be addressed.

Image quality improvement in megavoltage cone beam CT using an imaging beam line and a sintered pixelated array system

To quantify the improvement in megavoltage cone beam computed tomography (MVCBCT) image quality enabled by the combination of a 4.2 MV imaging beam line (IBL) with a carbon electron target and a detector system equipped with a novel sintered pixelated array (SPA) of translucent Gd(2)O(2)S ceramic scintillator. Clinical MVCBCT images are traditionally acquired with the same 6 MV treatment beam line (TBL) that is used for cancer treatment, a standard amorphous Si (a-Si) flat panel imager, and the Kodak Lanex Fast-B (LFB) scintillator. The IBL produces a greater fluence of keV-range photons than the TBL, to which the detector response is more optimal, and the SPA is a more efficient scintillator than the LFB. A prototype IBL + SPA system was installed on a Siemens Oncor linear accelerator equipped with the MVision(TM) image guided radiation therapy (IGRT) system. A SPA strip consisting of four neighboring tiles and measuring 40 cm by 10.96 cm in the crossplane and inplane directions, respectively, was installed in the flat panel imager. Head- and pelvis-sized phantom images were acquired at doses ranging from 3 to 60 cGy with three MVCBCT configurations: TBL + LFB, IBL + LFB, and IBL + SPA. Phantom image quality at each dose was quantified using the contrast-to-noise ratio (CNR) and modulation transfer function (MTF) metrics. Head and neck, thoracic, and pelvic (prostate) cancer patients were imaged with the three imaging system configurations at multiple doses ranging from 3 to 15 cGy. The systems were assessed qualitatively from the patient image data. For head and neck and pelvis-sized phantom images, imaging doses of 3 cGy or greater, and relative electron densities of 1.09 and 1.48, the CNR average improvement factors for imaging system change of TBL + LFB to IBL + LFB, IBL + LFB to IBL + SPA, and TBL + LFB to IBL + SPA were 1.63 (p < 10(- 8)), 1.64 (p < 10(- 13)), 2.66 (p < 10(- 9)), respectively. For all imaging doses, soft tissue contrast was more easily differentiated on IBL + SPA head and neck and pelvic images than TBL + LFB and IBL + LFB. IBL + SPA thoracic images were comparable to IBL + LFB images, but less noisy than TBL + LFB images at all imaging doses considered. The mean MTFs over all imaging doses were comparable, at within 3%, for all imaging system configurations for both the head- and pelvis-sized phantoms. Since CNR scales with the square root of imaging dose, changing from TBL + LFB to IBL + LFB and IBL + LFB to IBL + SPA reduces the imaging dose required to obtain a given CNR by factors of 0.38 and 0.37, respectively. MTFs were comparable between imaging system configurations. IBL + SPA patient image quality was always better than that of the TBL + LFB system and as good as or better than that of the IBL + LFB system, for a given dose.

Optical Quality Measurements of Hydrophobic Acrylic Intraocular Lenses

To compare the optical quality of several models of hydrophobic acrylic intraocular lenses (IOLs). Modulation transfer function (MTF) measurements were performed using a model eye system on four models of hydrophobic acrylic IOLs. Models tested were the AcrySof SA60AT, MA60AC, and MA60BM (Alcon, Ft Worth, Tex), as well as the model VA-60BB (Hoya, Tokyo, Japan). For benchmarking, the Alcon model MZ60BD polymethylmethacrylate (PMMA) lens was also measured. Three lenses of each model were tested at frequencies of 50 and 100 line pairs (lp)/mm (corresponding to 20/40 and 20/20, respectively). With a 3-mm aperture, the Alcon AcrySof models had mean MTF values ranging from 58.5% to 60.3% at 100 lp/mm and 78.0% to 79.7% at 50 lp/mm. The Hoya model VA-60BB provided statistically significantly lower (P<.05) MTF values than the Alcon AcrySof models at both frequencies (47.3 +/- 1.2% at 100 lp/mm and 71.8 +/- 1.9% at 50 lp/mm). With a 5-mm aperture, the Alcon AcrySof models had MTF values ranging from 32.9% to 34.3% at 100 lp/mm and 45.2% to 46.7% at 50 lp/mm. Under these larger aperture conditions, the Hoya model VA-60BB also had statistically significantly lower MTF values (20.9 +/- 0.8% at 100 lp/mm and 27.2 +/- 1.1% at 50 lp/mm). Under both apertures and frequencies, the Alcon PMMA lens had statistically significantly higher MTF values than the Hoya lens and statistically significant lower MTF values than all AcrySof models. Using both 3- and 5-mm aperture settings as well as frequencies corresponding to 20/20 and 20/40 vision, statistically significantly higher MTF values were obtained for AcrySof lenses, which were greater than the PMMA lens, which were greater than the Hoya model VA-60BB. The differences in MTF values between lens models are more exaggerated with a 5-mm aperture and may highlight differences in lens manufacturing processes.

Comparison of edge analysis techniques for the determination of the MTF of digital radiographic systems

The modulation transfer function (MTF) is well established as a metric to characterize the resolution performance of a digital radiographic system. Implemented by various laboratories, the edge technique is currently the most widespread approach to measure the MTF. However, there can be differences in the results attributed to differences in the analysis technique employed. The objective of this study was to determine whether comparable results can be obtained from different algorithms processing identical images representative of those of current digital radiographic systems. Five laboratories participated in a round-robin evaluation of six different algorithms including one prescribed in the International Electrotechnical Commission (IEC) 62220-1 standard. The algorithms were applied to two synthetic and 12 real edge images from different digital radiographic systems including CR, and direct- and indirect-conversion detector systems. The results were analysed in terms of variability as well as accuracy of the resulting presampled MTFs. The results indicated that differences between the individual MTFs and the mean MTF were largely below 0.02. In the case of the two simulated edge images, all algorithms yielded similar results within 0.01 of the expected true MTF. The findings indicated that all algorithms tested in this round-robin evaluation, including the IEC-prescribed algorithm, were suitable for accurate MTF determination from edge images, provided the images are not excessively noisy. The agreement of the MTF results was judged sufficient for the measurement of the MTF necessary for the determination of the DQE.

Monochromatic aberrations as a function of age, from childhood to advanced age.

To describe monochromatic optical aberrations of the eye as a function of age. One hundred fourteen subjects with a spherical equivalent within +/-3.50 D from emmetropia, corrected visual acuity of 20/40 or better, and normal findings in an ophthalmic examination were enrolled. The mean age was 43.2 +/- 24.5 years (range, 5.7-82.3). Monochromatic optical aberrations were measured with a Hartmann-Shack wavefront sensor after pharmacological dilation and cycloplegia. For a 5-mm pupil and for third- to seventh-, third-, fourth-, and fifth- to seventh-order aberrations, as well as for coma and spherical aberrations, the root mean square (RMS) error as a function of age was modeled by a second-order polynomial regression. It decreased progressively through childhood, adolescence, and early adulthood; reached a minimum level during the fourth decade of life, then increased progressively with age, to age 82. For a 5-mm pupil, the mean modulation transfer function (MTF) was reduced in both the child-teenage (5-20 years; n = 29) and the elderly (61-82 years; n = 37) groups versus the middle-aged adult group (41-60 years; n = 24; P < 0.05). In young adults (21-40 years; n = 23) and elderly subjects, the MTF curves were very close and almost superimposed at spatial frequencies higher than 38 cyc/deg. Aberrations of the whole eye were objectively measured from early childhood to an advanced age, and the relationship between monochromatic aberrations and age has been shown to fit a quadratic model. The results suggest that the definition of emmetropization should be broadened to include the reduction of higher order aberrations.

Monochromatic modulation transfer function of the human eye for different pupil diameters: an analytical expression.

The modulation transfer function (MTF) of human eyes for different pupil sizes was measured in a group of normal young subjects by use of a double-pass method. Measurements were carried out in the fovea, with monochromatic red light, paralyzed accommodation, artificial pupils, and optimum spherical refraction in each subject. For each pupil size both the averaged MTF and the intersubject variability were calculated. MTF's were approximated by the sum of two exponential functions. This three-parameter function provides a better approximation to our ocular MTF's than do most of the previous parametric models (usually one exponential), especially at intermediate and high spatial frequencies. Further curve fitting of the parameters allowed us to obtain a general expression for the mean MTF as a function of both pupil diameter and normalized spatial frequency. This equation summarizes our estimates of the average monochromatic retinal image quality of the human eye for any pupil diameter with good accuracy and in a compact way, which allows one to incorporate the eye's image quality easily in any particular study.