CTFFIND4: Fast and accurate defocus estimation from electron micrographs

CTFFIND is a widely-used program for the estimation of objective lens defocus parameters from transmission electron micrographs. Defocus parameters are estimated by fitting a model of the microscope's contrast transfer function (CTF) to an image's amplitude spectrum. Here we describe modifications to the algorithm which make it significantly faster and more suitable for use with images collected using modern technologies such as dose fractionation and phase plates. We show that this new version preserves the accuracy of the original algorithm while allowing for higher throughput. We also describe a measure of the quality of the fit as a function of spatial frequency and suggest this can be used to define the highest resolution at which CTF oscillations were successfully modeled.

Changes in falling risk depending on induced axis directions of astigmatism on static posture

[Purpose] To assess the changes in falling risk depending on the induced axis direction of astigmatism using cylindrical lenses in a static posture. [Subjects and Methods] Twenty subjects (10 males, 10 females; mean age, 23.4 ± 2.70 years) fully corrected by subjective refraction participated. To induce myopic simple astigmatism conditions, cylindrical lenses of +0.50, +1.00, +1.50, +2.00, +3.00, +4.00, and +5.00 D were used. The direction of astigmatic axes were induced under five conditions with increased cylindrical powers:, 180°, 90°, and 45° on both eyes; 180°/90° right/left eye, and 45°/135° right/left eye. Changes in the fall risk index were analyzed using the TETRAX biofeedback system. Measurements were performed for 32 seconds for each condition. [Results] The fall risk index increased significantly from C+4.00 D in 180°/90° right/left eye, C+3.00 D in 45°/135° right/left eye, and C+3.00 D in 45° on both eyes versus corrected emmetropia. Among the five axis conditions with the same cylindrical power lenses, the increase in the fall risk index was highest at 45° in both eyes. [Conclusion] Uncorrected oblique astigmatism may increase falling risk compared to with-the-rule and against-the-rule astigmatism. Clinical specialists should consider appropriate correction of astigmatism for preventing falls, especially for uncorrected oblique astigmatism.

Characteristics of Astigmatism in a Population of Tunisian School-Children

Purpose:

To evaluate the characteristics of astigmatism in a cross-sectional study of schoolchildren in Tunisia.

Materials and Methods:

A random cluster design was used to recruit children from primary schools across urban and rural settings in Tunisia, from 2008 to 2010. A total of 6192 students aged 6–14-years old were enrolled. All students whose uncorrected visual acuity was worse than 20/20 underwent a complete ophthalmic examination. Astigmatism was defined as the cylinder power of 0.75 diopter (D) or greater.

Results:

The prevalence of astigmatism was 6.67%. Mean cylinder power was - 1.89 ± 0.79D. The prevalence of astigmatism increased statistically significantly with age (P = 0.032). The prevalence of astigmatism was not significantly related to gender (P = 0.051). Of those with cylinder, 63.6%, 17.8%, and 18.6% schoolchildren had with with-the-rule, against-the-rule, and oblique astigmatism, respectively. ATR astigmatism was significantly higher in males (P = 0.033). There was no significant association between the student's area of residence and astigmatism (P = 0.059).

Conclusion:

Comparisons with other studies show that the prevalence of astigmatism in Tunisia is higher than in some countries. The prevalence of astigmatism increased with age but not gender. The majority of schoolchildren had with-the-rule astigmatism.

Customized photorefractive keratectomy to correct high ametropia after penetrating keratoplasty: A pilot study

PURPOSE

To evaluate preliminarily the safety and efficacy of customized photorefractive keratectomy (PRK) to correct ametropia and irregular astigmatism after penetrating keratoplasty (PK).

METHODS

This pilot study included five eyes of five patients with a mean spherical equivalent of -5.1±1.46D (range from -2.75 to -6.50D). In all cases, ametropia and irregular astigmatism was corrected with topography-guided customized PRK. Ocular examinations with topographic analysis were performed preoperatively as well as at 1, 3 and 6 months after surgery.

RESULTS

All eyes gained postoperatively at least three Snellen lines of uncorrected visual acuity. Mean refractive spherical equivalent was 0.62±0.63D (range from -0.25 to -1.75D) at 6 months postoperatively.

CONCLUSION

Our pilot study suggests that customized PRK can be a safe and effective method for treating ametropia and irregular astigmatisms after PK. Future studies with larger samples and longer follow-ups should be performed to confirm these results.

Meta-analysis to Compare the Safety and Efficacy of Manual Small Incision Cataract Surgery and Phacoemulsification

PURPOSE

A systematic review and meta-analysis comparing the safety, efficacy, and expenses related to phacoemulsification versus manual small incision cataract surgery (SICS).

METHODS

PubMed, Cochrane, and Scopus databases were searched with key words manual SICS 6/18 and 6/60; astigmatism and endothelial cell loss postoperatively, intra- and post-operative complications, phacoemulsification, and comparison of SICS and phacoemulsification. Non-English language manuscripts and manuscripts not indexed in the three databases were also search for comparison of SICS with phacoemulsification. Data were compared between techniques for postoperative uncorrected and corrected distance visual acuity (UCVA and best corrected visual acuity [BCVA], respectively) better than 6/9, surgical cost and duration of surgery. The Oxford cataract treatment and evaluation team scores were used for grading intraoperative and postoperative complications, uncorrected near vision.

RESULT

This review analyzed, 11 comparative studies documenting 76,838 eyes that had undergone cataract surgery considered for analysis. UCVA of 6/18 UCVA and 6/18 BCVA were comparable between techniques (P = 0.373 and P = 0.567, respectively). BCVA of 6/9 was comparable between techniques (P = 0.685). UCVA of 6/60 and 6/60 BCVA aided and unaided vision were comparable (P = 0.126 and P = 0.317, respectively). There was no statistical difference in: Endothelial cell loss during surgery (P = 0.298), intraoperative (P = 0.964) complications, and postoperative complications (P = 0.362). The phacoemulsification group had statistically significantly less astigmatism (P = 0.005) and more eyes with UCVA of 6/9 (P = 0.040). UCVA at near was statistically significantly better with SICS due to astigmatism and safer during the learning phase (P = 0.003). The average time for SICS was lower than phacoemulsification and cost <½ of phacoemulsification.

CONCLUSION

The outcome of this meta-analysis indicated there is no difference between phacoemulsification and SICS for BCVA and UCVA of 6/18 and 6/60. Endothelial cell loss and intraoperative and postoperative complications were similar between procedures. SICS resulted in statistically greater astigmatism and UCVA of 6/9 or worse, however, near UCVA was better.

[Perforating keratoplasty versus Descemet stripping automated endothelial keratoplasty in the partner eye: Functional results and patient satisfaction]

BACKGROUND

This study compared the postoperative results and patient satisfaction between penetrating keratoplasty (PK) and Descemet stripping automated endothelial keratoplasty (DSAEK) in patients who underwent PK in one eye and DSAEK in the other eye.

METHODS

A total of 15 patients were identified from the corneal database register and the medical charts were analyzed for best corrected visual acuity (BCVA), keratometric astigmatism, endothelial cell density and postoperative complications. Patient satisfaction was evaluated by a standardized interview.

RESULTS

Median follow-up time for PK was 55 months and 18 months for DSAEK (p < 0.01). Median BCVA in PK was 0.8 and 0.5 in DSAEK (p = 0.01) at the end of follow-up. Median keratometric astigmatism was 3.1 diopters after PK and 1.9 diopters after DSAEK (p = 0.2). Median endothelial cell density was 831 cells/mm(2) after PK and 860 cells/mm(2) after DSAEK (p = 0.63). For the interventions 57 % of the patients preferred PK, 36 % preferred DSAEK and 7 % were undecided. Patients assigned the better performing eye to the PK side in 64 % and in 29 % to the DSAEK side and 7 % perceived equal visual performance in both eyes.

CONCLUSION

The results leave doubt about the superiority of DSAEK compared to PK; however, exceptionally good refractive results of the 15 PK eyes analyzed and significantly longer follow-up times after PK could be the reason for the unexpectedly high patient preference for PK.

Assessment of aberrations and visual quality differences between myopic and astigmatic eyes before and after contact lens application

OBJECTIVE:

To evaluate the aberration and visual quality differences between myopic and astigmatic eyes before and after contact lens application by using corneal aberrometer and low- contrast sensitivity chart.

METHODS:

Eighty eyes of 40 patients were included in this study. Patients were divided into two groups as myopic (40 eyes, n=20) and astigmatic groups (40 eyes, n=20). We used aspheric Balafilcon A (Purevision and Purevision Toric Bausch&Lomb, Rochester, USA) lenses for each group. Corneal aberrations and low-contrast sensitivity values were measured and compared for each patient in both groups.

RESULTS:

There were no statistically significant differences between myopic and astigmatic groups when we compared low-contrast sensitivity values for both on- and off-eyes. Mean total higher-order aberration (HOA) values for off-eye, were 0.29±0.10 μm, and 0.33±0.10 μm for on-eye in the myopic group, while they were 0.42±0.14 μm in off-eye and 0.37±0.23 μm in on-eye in the astigmatic group. Off-eye mean coma, irregular astigmatism and total higher-order aberration RMS (root-mean-square) values were significantly higher in the astigmatic group compared to the myopic group (p=0.006, p=0.001, p=0.001) but mean on-eye RMS values were not.

CONCLUSION:

Myopic and astigmatic patients differ in terms of high-order aberrations and these differences cannot be equalized after contact lens application, but visual quality can be improved in both patients by using contact lenses.

[Laser Blended Vision for presbyopia: Results after 3 years]

PURPOSE

Retrospective study of the first 173 patients with presbyopia who underwent LASIK with a non-linear aspheric ablation profile and micro-monovision for the correction of presbyopia with myopia, astigmatism, hyperopia or emmetropia: Laser Blended Vision(®) Program by Carl Zeiss Meditec(®) (Jena, Germany).

METHODS

We retrospectively studied the first consecutive 173 patients with presbyopia who underwent LASIK with the wavefront-guided Laser Blended Vision(®) Program by Zeiss(®) in our Excimer Laser Zeiss Mel-80 by Carl Zeiss Meditec(®) (Jena, Germany) over the last three years in our clinic (Optima Laser Clinic, Valence, Spain). The program has a non-linear aspheric ablation profile that increases the spherical aberration in both eyes. A slight myopia of -1.5 diopters (D) in the non-dominant eye is also programmed. We analysed the results and patient satisfaction. The patients were separated into two groups: less than 50 years old and 50 years or more. Follow-up was from 1 to 28 months. We also separated two groups: follow-up under 12 months and follow-up of 12 months or more. We analysed the efficacy, safety and predictability of the procedure.

RESULTS

Seventy-nine male and 94 female patients between 42 and 69 years old were studied, for a total of 337 eyes. Only eight patients (4.62%) were between 42 and 44; 55 (31.79%) were between 45 and 49; 110 patients (63.58%) were 50 years or more. Nine patients underwent the surgery in the non-dominant eye only. Twelve (6.94%) patients were emmetropic (0.5 or less spherical equivalent), 42 (24.28%) were myopic or myopic astigmatic, and 119 (68.79%) were hyperopic or hyperopic astigmatic. One hundred and thirty-six patients (78.61%) had pre-operative near vision between J4 and J10. One hundred and seventy-one patients (98.84%) had post-operative near vision between J1 and J3; 150 (86.7%) had J1 (efficacy). Post-operative visual acuity without correction for distance was 20/20 or better in 159 patients (91.91%) (binocular). The predictability within 0.5 D was 87.86%. Safety 99.7% (336/337 eyes): one eye of a diabetic patient lost two lines BCVA. A total of 93.64% were satisfied with the procedure, 2.89% used eye-glasses for certain activities, 1.73% reported dry eye, 0.58% reported a nonspecific lack of adaptation, and there were no serious complications; 3.47% did not achieve their expectations. Twenty-four patients (13.87%) needed an enhancement, 18 of them (75.5%) for only one eye, with 88.89% of these being the non-dominant eye. Forty-nine patients (28.32%) had over 12 months follow-up, with 95.92% still satisfied.

CONCLUSIONS

Laser Blended Vision(®) is an excellent option, well tolerated, stable and effective for patients with presbyopia and myopia, astigmatism, hyperopia or emmetropia, also avoiding an intraocular procedure.

[Long-term results of lasik refractive error correction after penetrating keratoplasty in patients with keratoconus]

OBJECTIVE

To evaluate the long term results of Lasik for residual refractive errors (RE) after penetrating keratoplasty (PKP) for keratoconus (KC).

DESIGN

Retrospective cohort.

METHOD

Records of 14 consecutive patients (19 eyes) who had Lasik after PKP for KC were retrospectively reviewed. In all eyes with refractive stability and suture removed before Lasik, far distance Visual Acuity with (AVCC) and without correction (AVSC), spherical equivalent (EE), refractive (Ast) and keratometric (dK) astigmatism were analyzed pre- and post-operatively before and after one year of follow up. Data were analyzed using Shapiro-Wilk normality test, Student t test and Mann-Whitney test. A P-value of <0,05 was considered statistically significant.

RESULTS

The mean follow-up time was 3.16 months for the follow-up before one year postoperative and 5.8 years for the follow-up after one year postoperative. The best spectacle corrected visual acuity of 0,11 LogMAR (DE 0,07) before Lasik remained stable throughout the study. The SE decreased from -2.6 (DE 3.53) to -0,36 D (DE 1.33) (P<.05) for the follow-up before one year postoperative and -1.28 D (DE 1.63) (P=.07) for the follow-up after one year postop. The refractive cylinder was reduced from -3.43 (DE 1.35) preoperative to -1.37 D (DE 1.24) (P<.05) and -3.21 D (DE 2.29) (P=.36) in the long term after one year of follow-up.

CONCLUSIONS

Lasik refractive results regress one year after the operation; therefore it is not an effective long-term surgical refractive procedure for residual refractive errors after PKP for KC.

[SMILE: refractive lenticule extraction for myopic correction]

PURPOSE

It is currently possible to obtain refractive correction without using an excimer laser; the technique is called ReLEx(®) (Refractive Lenticule extraction) and uses the femtosecond laser VisuMax(®) (Carl Zeiss Meditec, Jena, Germany). We present initial clinical experience with small-incision (4mm) lenticule extraction (SMILE) for the treatment of moderate to high myopia via a retrospective study of 106 myopic and astigmatic eyes.

MATERIALS AND METHODS

This retrospective study of 106 eyes measures postoperative visual acuity to determine the safety, efficacy and predictability of the technique. For SMILE, an intrastromal lenticule is cut with the VisuMax(®) femtosecond laser; it is then dissected and detached from the anterior and posterior stromal planes and finally removed through a 4mm incision. This procedure does not require the creation of a flap. The study is based on 106 eyes of 54 patients who underwent the surgery for moderate to high myopia, with or without associated astigmatism. Patient selection was the same as for LASIK.

RESULTS

The average age of the patients was 33 ± 9 (20-54). The mean preoperative spherical equivalent was -6.22 ± 1.6 (-3; -9.75 D). The mean preoperative sphere was -5.88 D ± 1.52 (-3; -9.75 D) with a mean cylinder of -0.68 D ± 0.58 (0.00; -2.25). Postoperatively, 95% of patients had distance vision greater than or equal to 8/10. No loss of BCVA was noted. The mean postoperative spherical equivalent was -0.16 ± 0.35 D (-1.38; +0.88) with a mean sphere of 0.00 ± 0.34 D (-1,25; +1) and a mean cylinder of -0.31 ± 0.37 D (0; -1.5). One eye was converted to PRK because the incision site was covered by conjunctiva during the last 5 seconds of the laser phase.

CONCLUSION

SMILE is a predictable and safe technique for the surgical correction of moderate to high myopia.

The use of toric intraocular lens to correct astigmatism at the time of cataract surgery

Background:

To evaluate the visual and refractive outcomes of cataract surgery with toric intraocular lens (IOL) implantation at a teaching hospital of the United Kingdom.

Design:

Prospective interventional case series.

Materials and Methods:

This study compared the outcome of 3 groups of patients: Group 1 included 25 eyes with cataract and more than 2.5 diopters (D) of corneal astigmatism receiving a toric monofocal IOL; Group 2 had 18 patients with cataract and more than 2.5 D of astigmatism but receiving a non-toric monofocal IOL; while Group 3 had 25 patients with cataract and less than 1.5 D of astigmatism and receiving a non-toric monofocal IOL. Data collected included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction and corneal keratometry. Postoperative examinations were scheduled at 1 and 6 weeks.

Results:

Postoperatively the mean UDVA was LogMAR 0.27 ± 0.20 (equivalent snellen acuity of 20/37) in Group 1, 0.54 ± 0.22 (20/69) in Group 2 and 0.16 ± 0.20 (20/29) in Group 3. The mean CDVA was LogMAR 0.08 ± 0.13 (20/24) in Group 1, 0.23 ± 0.16 (20/34) in Group 2 and 0.04 ± 0.13 in Group 3 (20/22). The mean preoperative keratometric cylinder was 3.78 ± 1.0 D in Group 1, 3.41 ± 1.47 D in Group 2 and 0.97 ± 0.43D in Group 3; the mean postoperative subjective cylinder was 1.2 ± 0.68 D in Group 1, 3.23 ± 1.41 D in Group 2 and 0.95 ± 0.58 D in Group 3. The difference was statistically significant for the postoperative refractive cylinder values when comparing Group 1 to Group 2 (P = <0.0001) but the difference was insignificant between Group 1 and Group 3 (P = 0.23).

Conclusion:

Toric IOL implantation is an effective option to manage corneal astigmatism at the time of cataract surgery and to optimise visual outcomes for astigmatic patients when comparing to outcomes for their non-astigmatic counterparts.

Low toric soft contact lens acceptance study

PURPOSE

The aim of the study was to evaluate the objective and subjective visual performance of custom toric contact lenses (TL) and their spherical off-the-shelf counterparts (SL) in subjects with low amounts of astigmatism.

METHODS

Twenty-three habitual soft lens wearers (40 eyes, 25-35 years) manifesting 0.50-1.00DC and ≤±3.00DS were recruited. Air Optix Aqua (Lotrafilcon B) was fit using the spherical equivalent of the manifest refraction. Intelliwave toric in Efrofilcon A (Definitive) was fit using the manifest refraction and keratometric data. Comprehensive visual performance tests were done through manifest refraction in a trial frame; in SL; and in TL. A subjective evaluation of quality of vision was also obtained.

RESULTS

ANOVA revealed that, at the morning visit (AM), high contrast logMAR distance visual acuity (HCDVA) was significantly better (p<0.01) in spectacles as compared to SL. A similar trend was noted at the afternoon visit (PM). In addition, at the PM visit, HCDVA was significantly better (p<0.01) for TL as compared to their SL. ANOVA revealed that, at the PM visit, low contrast distance visual acuity (LCDVA) was significantly better (p=0.05) in spectacles as compared to SL. None of these differences were clinically significant. In addition, no statistically significant difference (p>0.05) in subjective vision rating scores was noted between SL and TL.

CONCLUSIONS

The present investigation found no clinically significant difference in visual performance between spherical and toric soft contact lenses in low astigmats.

Cataract Surgery in Eyes with Low Corneal Astigmatism: Implantation of the Acrysof IQ Toric SN6AT2 Intraocular Lens

PURPOSE

To assess the refractive and visual outcomes following cataract surgery and implantation of the AcrySof IQ Toric SN6AT2 intraolcular lens (IOL) (Alcon Laboratories, Inc., Fort Worth, TX, USA) in patients with low corneal astigmatism.

METHODS

This study is a retrospective, consecutive, single surgeon series of 98 eyes of 88 patients (with low preoperative corneal astigmatism) undergoing cataract surgery and implantation of the AcrySof IQ Toric SN6AT2 IOL. Postoperative measurements were obtained 1-month postsurgery. Main outcome measures were monocular distance visual acuity and residual refractive astigmatism.

RESULTS

Mean preoperative corneal astigmatic power vector (APV) was 0.38±0.09 D. Following surgery and implantation of the toric IOL, mean postoperative refractive APV was 0.13±0.10 D. Mean postoperative distance uncorrected visual acuity was 0.08±0.09 logMAR. Postoperative spherical equivalent refraction (SER) resulted in a mean of -0.23±0.22 D, with 96% of eyes falling within 0.50 D of the target SER.

CONCLUSION

The AcrySof IQ Toric SN6AT2 IOL is a safe and effective option for eyes undergoing cataract surgery with low levels of preoperative corneal astigmatism.

The Unevenness and Non-orthogonal State of Distribution of Corneal Thickness and the Influence on Correction of Myopic Astigmatism by LASEK

To observe and calculate the unevenness and the non-orthogonal state of distribution of corneal thickness and the relationship between them using Pentacam and to investigate the influence of unevenness and the non-orthogonal state on correction of myopic astigmatism by laser subepithelial keratomileusis (LASEK). 230 eyes with myopic astigmatism treated with LASEK were divided into two groups: 114 eyes as the low astigmatism group (-0.25 to -0.75 DC) and 116 eyes as the midrange-high astigmatism group (-1.00 to -4.50 DC). With the help of the diagram of keratoconus evaluation program of the Pentacam, the D 3.0 and D 6.5 were calculated for the index of distribution of unevenness of the corneal thickness, and the absolute value of the angle between the maximum and minimum progression-index orientation (M 90) for the index of non-orthogonal states. The correction of myopic astigmatism by LASEK was based on standard vector analysis and power vector analysis. The follow-up period was for 3 months. The preoperative M 90 was 22.14° ± 20.87°, D 6.5 was 58.66 ± 21.32 μm, and D 3.0 was 16.11 ± 4.28 μm for the 230 eyes that were tested. The D 6.5 of low astigmatism group (55.62 ± 20.81) μm was significantly lower than that of midrange-high astigmatism group (61.65 ± 21.48) μm (P < 0.05). Of the 230 eyes, the M 90 was positively correlated with D 6.5 (r = 0.37, P < 0.001), and D 6.5 was positively correlated with D 3.0 (r = 0.56, P < 0.001). 3 months postoperatively, the absolute error vector (|EV|) of low astigmatism group (0.46 ± 0.34) was significantly lower than that of midrange-high astigmatism group (0.53 ± 0.29) (P < 0.01). The error of magnitude of low astigmatism group (-0.10 ± 0.31) was significantly lower than that of midrange-high astigmatism group (0.08 ± 0.41) (P < 0.001). The absolute error of angle (|EA|) of low astigmatism group (26.10 ± 27.24) was significantly higher than that of midrange-high astigmatism group (9.99 ± 17.32) (P < 0.001). The correction ratio of low astigmatism group (1.45 ± 1.21) was significantly higher than that of midrange-high astigmatism group (0.94 ± 0.33) (P < 0.01). The error ratio (ER) of low astigmatism group (1.34 ± 1.40) was significantly higher than that of midrange-high astigmatism group (0.42 ± 0.27) (P < 0.001). In low astigmatism group, M 90 was positively correlated with |EV| (r = 0.30, P < 0.001). In midrange-high astigmatism group, M 90 was positively correlated with ER (r = 0.31, P < 0.001) and D 6.5 was positively correlated with |EV| and B, respectively (r = 0.34, 0.33, P < 0.001). The relationship between unevenness and non-orthogonal state of distribution of corneal thickness could influence the correction of astigmatism by LASEK. Therefore, more attention should be paid to the correction of midrange-high astigmatism group by excimer surgery.

Refractive, anterior corneal and internal astigmatism in the pseudophakic eye

PURPOSE

To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes.

METHODS

The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to net curvital and net torsional powers with the steeper corneal plane as the reference meridian. Curvital power is the force acting along a given meridian, and torsion is the power twisting the astigmatic direction out of that plane. The internal astigmatism (IA) was calculated as the difference between RA and ACA.

RESULTS

For curvital powers, the refractive astigmatism (KP(Φ)RA ) could be described as a function of anterior corneal astigmatic magnitude (KP(Φ)ACA ) and direction α by the multiple linear regression equation: KP(Φ)RA = -0.09 + 0.61*KP(Φ)ACA + 0.33*cos2α, (r(2) = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92° relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle α of the steeper anterior corneal meridian, averaging 0.86 D at 91° for with-the-rule, 0.37 D at 95° for oblique and 0.17 D at 97° for against-the-rule corneal astigmatisms.

CONCLUSIONS

The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patient candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism.

Prediction of residual astigmatism after cataract surgery using swept source fourier domain optical coherence tomography

PURPOSE

To compare corneal measurements obtained by a swept source fourier domain OCT (CASIA SS-1000), an autokeratometer (Haag-Streit Lenstar), a hybrid topographer (Tomey TMS-5), a Placido topographer (Tomey TMS-5 in Placido mode) and a Scheimpflug tomographer (Oculus Pentacam) to manifest subjective refraction.

METHODS

One hundred and four pseudophacic patients with non-toric IOLs were measured at least 6 months after surgery. Corneal astigmatism as measured on the anterior corneal surface as well as total corneal astigmatism including posterior surface data was compared to manifest refractive cylinder (cross-cylinder strategy) by computing difference vectors and correlation analysis of power vectors.

RESULTS

The OCT (0.43 ± 0.25 D) and the hybrid topographer (0.44 ± 0.25 D) yielded the smallest difference vector to subjective cylinder and by far the lowest percentage of outliers >0.75 D (≈10%). The rotating Scheimpflug camera showed the largest (0.70 ± 0.41 D) difference vector. The best predictive precision (0.37 ± 0.22) could be achieved by vector averaging Lenstar keratometry and OCT.

CONCLUSIONS

Autokeratometry yielded the least measuring noise but OCT as well as hybrid topography had better predictive precision due to posterior curvature data. Scheimpflug tomography suffered from high measuring noise. Combination of keratometry and OCT data yielded the best precision for planning of toric IOL implantation. To get a reliable target cylinder for TIOL calculation, accuracy of the measuring device is crucial. Keratometry and Placido topography lack the information of the posterior corneal curvature while Scheimpflug devices suffer from higher measuring noise. In this paper, a combination of ssOCT with autokeratometry yielded the best predictive quality.

Laser-assisted in situ keratomileusis for correction of astigmatism and increasing contact lens tolerance after penetrating keratoplasty

Purpose

To determine effectiveness of laser-assisted in situ keratomileusis (LASIK) in the treatment of astigmatism following penetrating keratoplasty (PK).

Methods

We performed a retrospective review of medical records of patients who underwent LASIK following PK and had over 1 year of follow-up data.

Results

Twenty-six patients (26 pairs of eyes) underwent LASIK following PK. Mean age of the patients at the time of LASIK was 40.7 years (range, 26 to 72 years). Following LASIK, the mean cylinder was reduced by 2.4 diopters and mean reduction of cylinder after LASIK was 65.4% from the preoperative values at the last follow-up visit. Uncorrected visual acuity became 20 / 50 or better in 69.2% of the eyes after LASIK. Best-corrected visual acuity became 20 / 50 or better in 73.1% of the eyes after LASIK. All of them were intolerable to contact lenses before LASIK. After LASIK, 6 pairs (23.1%) did not need to use contact lenses and 18 pairs (69.2%) were tolerable to using contact lenses or spectacles. There were no significant endothelial cell density changes 12 months after LASIK (p = 0.239).

Conclusions

LASIK is effective in the treatment of astigmatism following PK and increases contact lens and spectacle tolerance.

Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation

PURPOSE

To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness.

MATERIALS AND METHODS

Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences.

RESULTS

The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3-6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis.

CONCLUSION

Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

Management of extreme ametropia after penetrating keratoplasty: a series of surgical procedures for high myopia and astigmatism

A series of surgical interventions – relaxing corneal incisions, intraocular lens, and intrastromal rings – were used to correct a case of extreme ametropia in a thin cornea after a penetrating keratoplasty in an 18-year-old patient who presented with a −10.25 −8.50 × 120 preoperative refraction and 20/200 best-corrected visual acuity (BCVA). After a series of surgical procedures, the patient's BCVA in his left eye improved to 20/30 with +0.50 −1.00 × 170, the slit lamp examination showed no significant findings, and the patient's visual complaints disappeared. At the 1-year follow-up, the BCVA was 20/25, without visual complaints. The process of individualizing the surgical procedure in the present case was employed in an outcome-based approach, that is, the next surgical procedure was defined after the surgery and postoperative evaluation. The patient did not present complications during the follow-up period of 2.5 years.

Corneal astigmatism change and wavefront aberration evaluation after cataract surgery: "Single" versus "paired opposite" clear corneal incisions

Background:

Correcting the pre-existing astigmatism is an optimal goal in cataract surgery. The aim of this study is to compare the astigmatic correcting effect of a single regular 3.2 mm clear corneal incision (CCI) with paired opposite CCI in cataract patients and effect of these incisions on optical aberrations using the wavefront quantitative analysis.

Materials and Methods:

This was a randomized controlled trial study undertaken in an ophthalmology referral center on 50 patients planned for cataract surgery who were randomized to either single 3.2 mm CCI or paired opposite CCI group. Post-operative evaluation was performed at 12 weeks and included refraction, keratometery, corneal topography and wavefront analysis. Corneal astigmatism and post-operative values were compared in two groups.

Results:

The mean pre-operative corneal astigmatism was 2.58 ± 1.03 D in the single incision group and 2.70 ± 0.94 D in the paired opposite incisions group. After 12 weeks of surgery, the corneal astigmatism was reached to 2.15 ± 0.82 D in single incision group and 1.63 ± 1.21 in the paired opposite incisions group. There was a statistically significant difference in two arms of treatment regarding to surgically induced astigmatism after 3 months. The mean post-operative total and higher order aberrations and values were not significantly different in two groups.

Conclusion:

The results of our study showed that paired opposite incisions is an effective procedure for reducing pre-existing corneal astigmatism in cataract surgery. Paired incisions did not show any beneficial effect regarding wavefront aberrations compared with conventional single incision method.

A new approach based on Machine Learning for predicting corneal curvature (K1) and astigmatism in patients with keratoconus after intracorneal ring implantation

Keratoconus (KC) is the most common type of corneal ectasia. A corneal transplantation was the treatment of choice until the last decade. However, intra-corneal ring implantation has become more and more common, and it is commonly used to treat KC thus avoiding a corneal transplantation. This work proposes a new approach based on Machine Learning to predict the vision gain of KC patients after ring implantation. That vision gain is assessed by means of the corneal curvature and the astigmatism. Different models were proposed; the best results were achieved by an artificial neural network based on the Multilayer Perceptron. The error provided by the best model was 0.97D of corneal curvature and 0.93D of astigmatism.

Biometric risk factors for corneal neovascularization associated with hydrogel soft contact lens wear in Korean myopic patients

PURPOSE

To investigate the biometric risk factors for corneal surface complications associated with hydrogel soft contact lens (SCL) fitting in myopic patients in Korea.

METHODS

This is a retrospective case-control study. The records of 124 subjects (124 eyes) who wore SCLs on a daily basis were reviewed. Thirty-one patients (31 eyes) who were diagnosed with corneal neovascularization (NV) while wearing SCLs were included in the complication group. Ninety-three age- and sex-matched patients (93 eyes) who wore SCLs, who did not have corneal NV and who visited our clinic for correction of refractive errors were included in the control group. The degree of spherical equivalent, astigmatism and corneal base curve radius (BCR) were compared in both groups.

RESULTS

Patients with NV exhibited poorer best corrected visual acuity and more myopia than controls (p = 0.008 and 0.006, respectively). In univariate analysis, highly myopic patients (-9 diopters [D] or higher) were more likely to experience NV (odds ratio [OR], 2.232; 95% confidence interval [CI], 1.602 to 3.105). High astigmatism (≥2 D) increased the risk of complications (OR, 2.717; 95% CI, 1.141 to 6.451). Steep cornea, in which BCR was <7.5 mm, also raised the risk of complications (OR, 4.000; 95% CI, 1.661 to 9.804). Flat cornea was not a risk factor for the development of NV.

CONCLUSIONS

High myopia, high astigmatism, and steep cornea seemed to be risk factors in the development of corneal NV in SCL wearers.

The prevalence of astigmatism and its determinants in a rural population of Iran: the "Nooravaran Salamat" mobile eye clinic experience

Purpose:

The prevalence of astigmatism, and the astigmatic axis, and their determinants were evaluated in a rural population of Iran.

Materials and Methods:

In a cross-sectional study conducted from May to August 2011, 13 villages in the vicinity of the city of Khaf in northeast Iran were investigated in this study. All the examinations including visual acuity, refraction, slit-lamp biomicroscopy and fundoscopy were performed in a Mobile Eye Clinic. Written informed consent was obtained from all participants. Only phakic eye that could be reliably refracted without a previous history of ocular surgery were included.

Results:

Out of 2635 participants who were screened, 2124 were analysed for this study of whom 52% were female. The prevalence of astigmatism was 32.2% (95% confidence intervals (CI): 30.2-34.2). Astigmatism significantly increased from 14.3% in the under 15-year-old age group to 67.2% in the age group of over 65-years old (P < 0.001). The prevalence of With-The-Rule (WTR), Against-The-Rule (ATR), and oblique astigmatism was 11.7%, 18.1%, and 2.4 %, respectively. ATR significantly increased with age (P < 0.001). The mean corneal astigmatism was 0.73 D which linearly increased with age (P < 0.001).

Conclusion:

Attention must be paid to astigmatism in rural areas due to the high prevalence. Further studies are suggested to discover the role of the environmental and genetic factors. It seems that environmental and occupational factors in the villages cause a significant increase in the prevalence of astigmatism with age. A high percentage of participants had ATR astigmatism, which was more common at older ages.

[The cornea in high axial myopia]

PURPOSE

To compare corneal characteristics of eyes with high myopia with those of eyes with no spherical ametropia using Orbscan and ultrasonic pachymetry.

METHODS

Orbscan and ultrasonic pachymetry values were prospectively recorded in a study group of 105 patients with high myopia (i.e., axial length greater than 26mm in both eyes) and in a control group of 105 patients with no spherical ametropia (absolute value of spherical equivalent less than 1.25D regardless of cylinder value). Astigmatism data were expressed by rectangular coordinates in a dioptric plane. Axis was decomposed in 2 components (WTR/ATR and oblique) which were analyzed by Cos2axis and Sin2axis trigonometric functions. Enantiomorphism (mirror-image symmetry) between fellow eyes was quantified by a Euclidean distance for the location of the thinnest point and by the difference (in absolute value) between 180° and the sum of both axes for astigmatism.

RESULTS

In the study group, the mean axial length and subjective spherical equivalent were, respectively, 27.82±2.14mm (26.00 to 34.06) and -9.00±3.46D (-4.71 to -19.82). The mean corneal astigmatism was +0.92D×91.3° in the study group and +0.65D×89.3° in the control group. The mean corneal cylinder was higher in the study group (1.44D versus 0.91D; P<0.001) whereas axis showed no significant differences between both groups. The mean maximal keratometry was steeper in the study group (44.53D versus 44.13D; P=0.03) whereas the mean keratometry and minimal keratometry displayed no significant differences between both groups. No significant differences in central corneal thickness (540.2μm versus 546.9μm; P=0.10), peripheral corneal thickness, corneal diameter, corneal irregularity, asphericity, and irregular astigmatism were found between both groups. There were no significant differences in enantiomorphism parameters between both groups. In the study group, correlation with axial length was significant only for spherical equivalent (r=-0.86; P<0.001) and corneal cylinder (r=0.16; P=0.04).

CONCLUSION

High myopia exhibits corneal characteristics similar to corneas of eyes with no spherical ametropia, except for toricity. While the posterior segment elongates, development of high myopia appears not to affect corneal characteristics. Corneal toricity may be associated with evolution toward high myopia by perturbing mechanisms of emmetropization.

Manual intrastromal corneal keratotomy: An alternate encouraging approach for refractive error correction

Results of femtosecond based intrastromal astigmatic keratotomy have been reported to be encouraging for correction of Astigmatism. We report a new surgical technique-manual intrastromal corneal keratotomy (MICK) for correction of simple refractive astigmatism (−1.5 DC against the rule). The technique involves the creation of a 100 μm thickness corneal flap creation using Moria M2 evolution LSK MicroKeratome and 300 μm depth, 4 mm long manual transverse astigmatic keratotomy on both sides of the steep axis 3 mm from the pupillary center along with four incision peripheral radial keratotomy outside the optic zone (based on the mesopic pupil). The flap was repositioned and routine post-operative regimen was followed. Patient achieved 20/20 vision in both eyes post-operatively on the first day, which was maintained even at the 1 month follow-up. This simple technique could be useful as an alternative method for correction of refractive errors in patients not suitable for excimer and/or femtosecond laser treatment.