Effect of laser in situ keratomileusis on vision analyzed using preoperative optical quality

Comparison of the optical quality after SMILE and FS-LASIK for high myopia by OQAS and iTrace analyzer: a one-year retrospective study

BACKGROUND

To compare the correction effect and optical quality after small-incision lenticule extraction (SMILE) and femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) for high myopia.

METHODS

51 high myopia eyes after SMILE and 49 high myopia eyes after FS-LASIK were enrolled and divided into two groups retrospectively. The OQAS and iTrace analyzer were used for optical quality inspection. Between the two groups the spherical equivalent (SE), astigmatism, uncorrected distant visual acuity (UDVA), strehl ratio (SR), modulation transfer function cutoff frequency (MTF cutoff), objective scatter index (OSI) and wavefront aberrations were analyzed and compared before surgery and at 1, 6 and 12 months after surgery.

RESULTS

After the operation: (1) SE and astigmatism declined and UDVA increased significantly in both groups, and UDVA was better after SMILE than FS-LASIK. (2) SR and MTF cutoff reduced and OSI increased significantly after SMILE and FS-LASIK. SR and MTF cutoff were significantly higher after SMILE than FS-LASIK. OSI was significantly lower after SMILE than FS-LASIK. (3) The total wavefront aberration, total low-order wavefront aberration, defocus and astigmatism aberration as well as trefoil aberration reduced significantly in both groups. The total high-order wavefront aberration increased significantly after FS-LASIK. The spherical and coma aberration increased significantly in both groups. The total high-order wavefront aberration and coma aberration at 1 month were higher after FS-LASIK than SMILE.

CONCLUSION

The optical quality descended after SMILE and FS-LASIK. SMILE was superior to FS-LASIK at the correction effect and optical quality for high myopia. The combination of OQAS and iTrace analyzer is a valuable complementary measurement in evaluating the optical quality after the refractive surgery.

TRIAL REGISTRATION

This is a retrospective study. This research was approved by the ethics committee of Xiangya Hospital and the IRB approval number is 201612074.

Strehl Ratio and Myopia in Chinese Adolescents: The Tuyou County Pediatric Eye (TYPE) Study

Aim

To investigate the relationships between property of the visual quality, Strehl ratio (SR) and the degree of myopia.

Methods

A total of 444 anatomically normal eyes of 222 adolescents were enrolled in the TYPE study. Based on spherical equivalent (SE), subjects were divided into four groups: emmetropia/control (SE: +0.75 to −0.75 D), low myopia (SE: −0.75 to −3.00D), moderate myopia (SE: −3.00 to −5.00D), high myopia (SE: <−5.00D). Axial length (AL) was measured. SR was attained with an OPD-III SCAN and calculated under a 3 mm pupil diameter.

Results

The overall SR (mean ± SD) was 0.40 ± 0.08. Among all included eyes, the SR in eyes with the emmetropia, low myopia, moderate myopia and high myopia was 0.80 ± 0.11, 0.31 ± 0.04, 0.21 ± 0.11, and 0.11 ± 0.02, respectively. Furthermore, the K2 in eyes with the emmetropia, low myopia, moderate myopia and high myopia was 43.83±1.50, 43.96±1.37, 43.4±5.52, and 45.16±1.43, respectively. Significant differences were detected within the four groups in terms of SR and K2 (P < 0.001). Multiple regression analysis confirmed that AL negatively affected SR independently (P < 0.001).

Conclusion

Our findings provide a useful basis for the conclusion that myopia affects visual quality SR in Chinese adolescents. Besides, when performing visual quality SR, axial length must be taken into consideration, as it will influence SR.

Optical Quality Assessment in Patients with Unilateral Congenital Ptosis: A Matched Case-Control Study

Background. To evaluate the differences in the corneal higher-order aberrations (HOAs) and optical quality of the ptosis eyes compared with the normal fellow eyes in the unilateral congenital ptosis patients. Methods. A matched case-control study was performed in 17 pairs of eyes in 17 unilateral congenital ptosis patients. The ptosis eye was enrolled in the ptosis group while the normal fellow eye was enrolled in the normal group. The HOAs obtained from Pentacam HR and the optical quality parameters obtained from Optical Quality Analysis System (OQAS) were compared between the two groups. Results. There were significant differences in a vertical coma and vertical trefoil on the anterior corneal surface between the ptosis group and the normal group $\left(p<0.05\right)$ . The OQAS parameters in the ptosis group were significantly different from those in the normal group $\left(p<0.05\right)$ . The vertical fissure height (VFH) showed a significant correlation with the total HOAs, 3rd HOAs, and vertical coma on the anterior corneal surface $\left(p<0.05\right)$ . Conclusions. Compared with the normal fellow eyes, the ptosis eyes showed significantly degraded optical quality. The eyelid position was important for the changes of corneal HOAs in the ptosis eyes. The reasons for the discrepancy of the OQAS parameters between the ptosis eyes and normal fellow eyes were multiple.

Optical Quality and Intraocular Scattering in the Diabetic Eye without Diabetic Retinopathy

SIGNIFICANCE

This study suggests that despite having comparable best-corrected visual acuity and normal fundus appearance, objective measurements of optical quality showed that patients with diabetes but without overt retinopathy may have impaired visual function. Screening using the Optical Quality Analysis System might help identify those patients.

PURPOSE

Visual impairments are common in diabetes, but the status of the problem is unclear before the development of diabetic retinopathy. The aim of this pilot study was to investigate the optical quality and intraocular scattering in the diabetic eye without diabetic retinopathy.

METHODS

Twenty-seven patients with diabetes without diabetic retinopathy were enrolled. Twenty-seven age- and sex-matched healthy volunteers served as a control group. Optical quality parameters included modulation transfer function cutoff frequency, Strehl (two-dimensional) ratio, and Optical Quality Analysis System values at 100, 20, and 9 contrast levels. The objective scatter index was assessed using the Optical Quality Analysis System. Correlations were analyzed between the modulation transfer function cutoff, Strehl ratio, objective scatter index, and Optical Quality Analysis System value, and the age of the patient and the duration of diabetes mellitus.

RESULTS

The diabetic group exhibited lower modulation transfer function cutoff, Strehl ratio, and Optical Quality Analysis System values at 100, 20, and 9% contrast levels and higher objective scatter index than did the controls (all, P < .01). There were no associations between the optical quality parameters and age or the duration of diabetes mellitus in the diabetic participants (all, P > .05). Moderate associations were found between all parameters obtained from the Optical Quality Analysis System and age in the control group (all, P < .01).

CONCLUSIONS

This pilot study suggests that optical quality was reduced, and intraocular scattering increased in the diabetic eye without diabetic retinopathy compared with controls.

Visual outcome of penetrating keratoplasty, deep anterior lamellar keratoplasty and Descemet membrane endothelial keratoplasty

PURPOSE

A single-center, cross-sectional study was designed to assess and compare objective and subjective quality of vision of patients intervened with penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK).

METHODS

Forty-six patients previously intervened with PK (22 eyes), DALK (7 eyes) and DMEK (17 eyes) were recruited. Visual evaluation included spherical and cylindrical refraction, distance corrected visual acuity (DCVA), photopic contrast sensitivity (CS), optical quality, measured with the HD Analyzer (objective scattering index [OSI], MTF cut-off and Strehl ratio), and ocular and corneal aberrometry, measured with the KR-1W Wavefront Analyzer.

RESULTS

Statistically significant between-group differences were found in age (p=0.006, DMEK patients were older) and time since surgery (p<0.001, longest time for PK patients). No statistically significant differences were found in DCVA between the techniques. Between-group differences were encountered in CS at 12 (p=0.007) and 18 (p<0.001) cycles per degree, with DMEK and DALK obtaining the best and worst outcomes, respectively. Differences in optical quality were found between the techniques (OSI, p=0.004; MTF cut-off, p=0.048; Strehl ratio p=0.022), with DMEK displaying the best outcomes. Highest and lowest values in ocular and corneal aberrations were for DALK and DMEK patients, respectively. Between-group differences were found in corneal astigmatism (p<0.001; -3.31±2.00 D in PK; -2.68±0.94 D in DALK; -1.09±0.62 D in DMEK).

CONCLUSION

Overall, DMEK proved superior over PK and DALK in terms of quality of vision, with PK offering slightly better outcomes than DALK in most visual function parameters under evaluation.

Response for light scattered in the ocular fundus from double-pass and Hartmann-Shack estimations

Double-pass (DP) and Hartmann-Shack (HS) are complementary techniques based on reflections of light in the ocular fundus that may be used to estimate the optical properties of the human eye. Under conventional data processing, both of these assessment modes provide information on aberrations. In addition, DP data contain the effects of scattering. In the ocular fundus, this phenomenon may arise from the interaction of light with not only the retina, but also deeper layers up to which certain wavelengths may penetrate. In this work, we estimate the response of the ocular fundus to incident light by fitting the deviations between DP and HS estimations using an exponential model. In measurements with negligible intraocular scattering, such differences may be related to the lateral spreading of light that occurs in the ocular fundus due to the diffusive properties of the media at the working wavelength. The proposed model was applied in young healthy eyes to evaluate the performance of scattering in such a population. Besides giving a parameter with information on the ocular fundus, the model contributes to the understanding of the differences between DP and HS estimations.

Effects of aging on optical quality and visual function

BACKGROUND

We assessed the effects of aging on visual function and optical quality in a healthy adult population and provide reference values for different age ranges.

METHODS

We conducted a prospective study with 198 healthy volunteers from 31 to 70 years of age. The visual acuity (VA) and contrast sensitivity (CS) at 3, 6, 12 and 18 cycles per degree (cpd) frequencies were assessed, together with values of optical quality and intraocular scattering obtained with a double-pass system (Optical Quality Analysis System - OQAS), specifically the modulation transfer function cutoff frequency (MTF_cutoff ), the Strehl ratio, the OQAS values (OV) at contrasts of 100, 20 and nine per cent and the objective scatter index (OSI). We studied the change of these variables with age and obtained standard values for optical quality and intraocular scattering parameters for four age groups: 31 to 40, 41 to 50, 51 to 60 and 61 to 70 years.

RESULTS

We found significant correlations between age and all variables analysed and significant differences among the age groups considered except for CS (3 cpd) (p = 0.067). Ageing particularly affected low-contrast parameters, such as the OV nine per cent and the OSI, which decreased to 37 and 50 per cent of their original values, respectively. The OSI was found to provide high sensitivity and specificity values, when healthy and caratactous eyes were considered. The results suggest that optical deficits are compensated until 50 years of age with sensory and perceptual factors, as smaller changes were found for visual function than for objective measurements of optical quality and intraocular scattering.

CONCLUSIONS

Measures of optical quality assessed by subjective psychophysical and objective techniques varied differently with age. Values obtained for each age group can be used to determine normal limits of optical quality and intraocular scattering for diagnosis of ocular conditions.

Optical Quality and Related Factors in Ocular Hypertension: Preliminary Study

Background. To evaluate the optical quality and related factors in patients with ocular hypertension (OHT). Methods. This was a prospective case-control study. A total of 12 eyes with OHT and 20 control eyes underwent testing with Optical Quality Analysis System II (OQAS II) to evaluate the modulation transfer function cut off frequency (MTF cutoff), the Strehl 2D ratio (SR), objective scatter index (OSI), tear-film mean OSI (TFOSI), and the OQAS values (OV100%,OV20%, and OV9%). Results. The optical quality of patients with OHT declined, with lower MTF cutoff (OHT 36.86 ± 7.11 cpd , controls 48.50 ± 4.04 cpd, t = −4.60, P < 0.05), lower SR (OHT 0.22 ± 0.04, controls 0.27 ± 0.05, t = −2.72, P < 0.05), lower OV100% (OHT 1.26 ± 0.25, controls 1.61 ± 0.14, t = −4.03, P < 0.05), lower OV20% (OHT 1.27 ± 0.27, controls 1.72 ± 0.20, t = −4.00, P < 0.05), and lower OV9% (OHT 1.30 ± 0.25, controls 1.69 ± 0.32, t = −2.28, P < 0.05). There were not any statistically significant differences in OSI and TFOSI. The MTF cutoff in patients with OHT was correlated significantly with age (r = −0.59, P < 0.05). Conclusions. Optical quality of patients with OHT is reduced, with lower MTF cutoff, SR, OV100%, OV20%, and OV9%. MTF cutoff is negatively related to age.

Visual Outcomes and Optical Quality After Femtosecond Laser Small Incision Lenticule Extraction: An 18-Month Prospective Study

PURPOSE

To investigate the long-term visual outcomes and optical quality after femtosecond laser small incision lenticule extraction (SMILE) for moderate to high myopia correction.

METHODS

Fifty-four patients (37 women, 17 men) who underwent SMILE were enrolled in this prospective clinical study. Patient ages ranged from 18 to 40 years, with a mean spherical equivalent of -6.50 ± 1.64 diopters. Data including refractive parameters, retinal image quality, intraocular scattering, and aberrations were collected at 6 and 18 months after surgery. Patient satisfaction was also evaluated.

RESULTS

At 18 months after surgery, both the mean safety index and the efficacy index were 1.23 ± 0.23 (range: 0.80 to 1.50); there was no significant difference with indices measured at 6 months (P > .05). No patient lost two or more lines of corrected distance visual acuity. Total higher-order aberrations (HOAs) and coma significantly increased after SMILE (P < .05), whereas total spherical aberrations and trefoil changed only slightly. The mean modulation transfer function cutoff frequency was 36.66 ± 8.54 cycles per degree (cpd) before surgery and 37.81 ± 6.89 cpd at 18 months postoperatively; the mean objective scatter index was 0.62 ± 0.33 before surgery and 0.71 ± 0.38 at 18 months postoperatively. No significant difference was found between the three time points (P > .05). Mean patient satisfaction was 9.31 ± 0.64 (with a maximum score of 10).

CONCLUSIONS

SMILE showed good safety, efficacy, and stability in correcting moderate to high myopia, and patients were highly satisfied. HOAs increased after SMILE, mainly due to the increase of coma, whereas retinal image quality and intraocular scattering barely changed.

Impact of scatter on double-pass image quality and contrast sensitivity measured with a single instrument

We compared objective Double-Pass (DP) image quality data with subjective visual parameters measured within the same modified instrument for different amounts of scatter. The original DP imaging channel of a clinical instrument was maintained intact and two additional channels were included, one for visual testing and another for tear film (TF) imaging by using a retro-illumination technique. Contrast sensitivity (CS) was compared with measurements of the Objective Scattering Index (OSI) obtained from DP retinal images corresponding to different scatter levels induced by pre-defined filters. OSI values were correlated with the change in CS for different spatial frequencies measured with the same instrument. Since TF and DP images were recorded at the same rate, this provided additional information about the dynamic spatial stability of the tear film. This new DP instrument has been proven to provide accuracy and repeatability, and to be suitable for clinical diagnosis, with a complete evaluation of the eye's performance by a simultaneous objective and subjective assessment under the same experimental conditions.

Intra- and Intersession Repeatability of an Optical Quality and Intraocular Scattering Measurement System in Children

Purpose

To evaluate intra- and intersession repeatability of objective optical quality and intraocular scattering measurements with a double-pass system in children.

Methods

Forty-two eyes of 42 children were included in the study. An optical quality analysis system (OQAS) was used to measure optical quality parameters, including modulation transfer function cutoff frequency (MTF_cutoff), Strehl ratio (SR), OQAS values (OV) at 3 different contrasts and objective scatter index (OSI). Three measurement sessions with 10-min intervals were operated by the same technician, and in each session four consecutive measurements were obtained.

Results

Mean values for MTF_cutoff, SR and OSI were 46.85 ± 7.45cpd, 0.27 ± 0.06 and 0.34 ± 0.22 respectively. 1) The intraclass correlation coefficients were ranged from 0.89 to 0.97 and coefficients of variation from 0.06 to 0.16 for all the parameters in the first session; the relative repeatability were 11.1% (MTF_cutoff), 22.5% (SR), 10.9% (OV100%), 16.6% (OV2%), 22.4% (OV9%) and 56.3% (OSI). Similar results were found in the second and third sessions. 2) Bland-Altman analysis showed that narrow 95% confidence intervals (compared between the first and second sessions) ranged from -5.42 to 5.28 (MTF_cutoff), -0.05 to 0.07 (SR), -0.18 to 0.18 (OV100%), -0.26 to 0.29 (OV20%), -0.33 to 0.39 (OV9%) and -0.11 to 0.09 (OSI); the comparison between any two of the three sessions showed similar results.

Conclusion

Measurements of optical quality and intraocular scattering in children by the double-pass system showed good intra- and intersession repeatability. Retinal image quality is high and intraocular scattering is low in children.

Optical quality and intraocular scattering after femtosecond laser small incision lenticule extraction

PURPOSE

To investigate objective optical quality and changes in light scatter after femtosecond laser small incision lenticule extraction (SMILE) for moderate to high myopia correction.

METHODS

Prospective clinical study of 66 eyes of 66 patients (23 males, 43 females) with a mean age of 28.67 ± 6.62 years, mean spherical refraction of -6.06 ± 1.57 diopters, and mean cylindrical refraction of -0.68 ± 0.46 diopters. Every patient had a 3-month follow-up after a standard SMILE procedure. An optical quality analysis system was used to measure modulation transfer function cutoff frequency (MTFcutoff), Strehl2D ratio, and objective scatter index (OSI).

RESULTS

At 3 months postoperatively, mean spherical equivalent was 0.03 ± 0.24 diopters and corrected distance visual acuities of all patients were equal to or better than preoperative values, with a mean safety index of 1.12 ± 0.17 (range: 0.80 to 1.50) and mean efficacy index of 1.18 ± 0.21 (range: 0.80 to 1.50). Mean OSI increased from 0.75 preoperatively to 1.09 at 20 days postoperatively (P < .05), and gradually declined to 0.94 at 40 days and 0.82 at 3 months postoperatively (P > .05). MTFcutoff and Strehl2D ratio did not change significantly compared with preoperative values (P > .05). Multiple linear regression analysis revealed that preoperative OSI was significantly correlated with optical quality at 3 months. Patients with less preoperative OSI tended to acquire higher MTFcutoff (b = -8.61) and lower OSI (b = 0.65) (P < .05).

CONCLUSIONS

SMILE had little impact on retinal image quality after myopia correction. Postoperative OSI showed a temporary increase and then returned to normal.

Non-cycloplegic spherical equivalent refraction in adults: comparison of the double-pass system, retinoscopy, subjective refraction and a table-mounted autorefractor

AIM

To evaluate the accuracy of spherical equivalent (SE) estimates of a double-pass system and to compare it with retinoscopy, subjective refraction and a table-mounted autorefractor.

METHODS

Non-cycloplegic refraction was performed on 125 eyes of 65 healthy adults (age 23.5±3.0 years) from October 2010 to January 2011 using retinoscopy, subjective refraction, autorefraction (Auto kerato-refractometer TOPCON KR-8100, Japan) and a double-pass system (Optical Quality Analysis System, OQAS, Visiometrics S.L., Spain). Nine consecutive measurements with the double-pass system were performed on a subgroup of 22 eyes to assess repeatability. To evaluate the trueness of the OQAS instrument, the SE laboratory bias between the double-pass system and the other techniques was calculated.

RESULTS

The SE mean coefficient of repeatability obtained was 0.22D. Significant correlations could be established between the OQAS and the SE obtained with retinoscopy (r=0.956, P<0.001), subjective refraction (r=0.955, P<0.001) and autorefraction (r=0.957, P<0.001). The differences in SE between the double-pass system and the other techniques were significant (P<0.001), but lacked clinical relevance except for retinoscopy; Retinoscopy gave more hyperopic values than the double-pass system -0.51±0.50D as well as the subjective refraction -0.23±0.50D; More myopic values were achieved by means of autorefraction 0.24±0.49D.

CONCLUSION

The double-pass system provides accurate and reliable estimates of the SE that can be used for clinical studies. This technique can determine the correct focus position to assess the ocular optical quality. However, it has a relatively small measuring range in comparison with autorefractors (-8.00 to +5.00D), and requires prior information on the refractive state of the patient.

The recovery of optical quality after laser vision correction

Purpose

To evaluate the optical quality after laser in situ keratomileusis (LASIK) or serial photorefractive keratectomy (PRK) using a double-pass system and to follow the recovery of optical quality after laser vision correction.

Methods

This study measured the visual acuity, manifest refraction and optical quality before and one day, one week, one month, and three months after laser vision correction. Optical quality parameters including the modulation transfer function, Strehl ratio and intraocular scattering were evaluated with a double-pass system.

Results

This study included 51 eyes that underwent LASIK and 57 that underwent PRK. The optical quality three months post-surgery did not differ significantly between these laser vision correction techniques. Furthermore, the preoperative and postoperative optical quality did not differ significantly in either group. Optical quality recovered within one week after LASIK but took between one and three months to recover after PRK. The optical quality of patients in the PRK group seemed to recover slightly more slowly than their uncorrected distance visual acuity.

Conclusions

Optical quality recovers to the preoperative level after laser vision correction, so laser vision correction is efficacious for correcting myopia. The double-pass system is a useful tool for clinical assessment of optical quality.

Comparison between an objective and a psychophysical method for the evaluation of intraocular light scattering

In this study we present the comparison of the performance of two systems to measure intraocular scattering. Measurements were made by using a psychophysical system based on a brightness comparison method that provides a glare index and a physical system based on the double-pass technique, which gives an objective scatter index by measuring the optical quality of the eye. Three external diffuser filters that simulated different grades of intraocular scattering were used in subjects with normal vision. The two measured indexes showed a graded rise with increasing level of scattering. The discrimination ability obtained for both systems showed that they were able to distinguish among conditions ranging from normal to early cataracts.

Optical quality after myopic photorefractive keratectomy and laser in situ keratomileusis: comparison using a double-pass system

PURPOSE

To use a double-pass system to compare the optical quality after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for mild to moderate myopia.

SETTING

Universitat Politècnica de Catalunya, Terrassa, Barcelona Institute of Ocular Microsurgery, Barcelona, Spain.

DESIGN

Comparative case series.

METHODS

Optical quality was assessed with a clinical double-pass system preoperatively and 3 months after PRK or LASIK. The modulation transfer function (MTF), retinal image quality parameters (MTF cutoff frequency, Strehl ratio), and intraocular scattering (objective scatter index [OSI]) were calculated.

RESULTS

This study evaluated 34 eyes that had PRK and 55 eyes that had LASIK. Both PRK and LASIK had a statistically significant impact on retinal image quality, although no significant differences between the techniques were observed. The MTF at 30 cycles per degree decreased by a factor of 1.50 in the PRK group and by a factor of 1.32 in the LASIK group. The MTF cutoff frequency decreased by a factor of 1.04 in the PRK group and by a factor of 1.06 in the LASIK group. The Strehl ratio decreased by a factor of 1.10 and 1.07, respectively. Photorefractive keratectomy and LASIK increased the objective scatter index by factors of 1.48 and 1.57, respectively. Significant correlations between the preoperative refraction and the OSI were found.

CONCLUSIONS

Retinal image quality was similarly reduced with PRK and LASIK, with no significant differences between the 2 methods. Some PRK patients had a residual refractive error that might have been related to corneal-wound healing still present 3 months postoperatively.