Astigmatism and LASIK

BCLA CLEAR Presbyopia: Management with corneal techniques

Corneal techniques for enhancing near and intermediate vision to correct presbyopia include surgical and contact lens treatment modalities. Broad approaches used independently or in combination include correcting one eye for distant and the other for near or intermediate vision, (termed monovision or mini-monovision depending on the degree of anisometropia) and/or extending the eye's depth of focus [1]. This report provides an overview of the evidence for the treatment profile, safety, and efficacy of the range of corneal techniques currently available for managing presbyopia. The visual needs and expectations of the patient, their ocular characteristics, and prior history of surgery are critical considerations for patient selection and preoperative evaluation. Contraindications to refractive surgery include unstable refraction, corneal abnormalities, inadequate corneal thickness for the proposed ablation depth, ocular and systemic co-morbidities, uncontrolled mental health issues and unrealistic patient expectations. Laser refractive options for monovision include surface/stromal ablation techniques and keratorefractive lenticule extraction. Alteration of spherical aberration and multifocal ablation profiles are the primary means for increasing ocular depth of focus, using surface and non-surface laser refractive techniques. Corneal inlays use either small aperture optics to increase depth of field or modify the anterior corneal curvature to induce corneal multifocality. Presbyopia correction by conductive keratoplasty involves application of radiofrequency energy to the mid-peripheral corneal stroma which leads to mid-peripheral corneal shrinkage, inducing central corneal steepening. Hyperopic orthokeratology lens fitting can induce spherical aberration and correct some level of presbyopia. Postoperative management, and consideration of potential complications, varies according to technique applied and the time to restore corneal stability, but a minimum of 3 months of follow-up is recommended after corneal refractive procedures. Ongoing follow-up is important in orthokeratology and longer-term follow-up may be required in the event of late complications following corneal inlay surgery.

Topographic and surgical risk factors for high postoperative residual astigmatism after small incision lenticule extraction in patients with different degrees of myopia: a retrospective cohort study

BACKGROUND

To evaluate the possible topographic and surgical risk factors for high postoperative residual astigmatism in patients who undergo small-incision lenticule extraction (SMILE) surgery and have different myopia degrees.

METHODS

A retrospective cohort study was conducted, and patients who underwent SMILE surgery were enrolled. A total of 80 and 150 eyes from 40 to 75 individuals, respectively, were selected as the low myopia and high myopia groups. The demographic data, visual acuity, refraction, topographic parameters and surgical settings were recorded. Multiple linear regression with interaction tests were performed to survey the risk factors for high postoperative residual astigmatism in each group.

RESULTS

Five (6.25%) and 9 (6.00%) eyes presented with high postoperative residual astigmatism in the low myopia and high myopia groups, respectively, but these differences were not significant (P = 0.569). A steep corneal curvature was correlated with a greater risk of high postoperative residual astigmatism in the low myopia group (P = 0.015), while a higher degree of cycloplegic cylinder power, steeper corneal curvature, greater topographic cylinder power, smaller optic zone and longer incision length were associated with a high rate of postoperative residual astigmatism in the high myopia group (all P < 0.05). In addition, the interaction effects of cycloplegic and topographic cylinder power and longer incision length on the incidence of high postoperative residual astigmatism development were more evident in the high myopia group than in the low myopia group (all P < 0.05).

CONCLUSIONS

A steep corneal curvature correlates with a high risk of high postoperative residual astigmatism after SMILE surgery, and a higher degree of cycloplegic and topographic cylinder and longer incision are associated with high postoperative residual astigmatism in individuals with high myopia.

Comparison of refractive and visual acuity results after Contoura® Vision topography-guided LASIK planned with the Phorcides Analytic Engine to results after wavefront-optimized LASIK in eyes with oblique astigmatism

PURPOSE

To compare visual acuity and refractive results between topography-guided laser in situ keratomileusis (LASIK) planned with the Phorcides Analytic Engine (PAE) to results after wavefront-optimized (WFO) LASIK in subjects with preoperative oblique astigmatism in their manifest refraction.

METHODS

This was a retrospective chart review of clinical results from eyes treated with topography-guided LASIK planned with PAE compared to eyes treated with WFO LASIK using the same Wavelight® excimer laser system. All included subjects had preoperative oblique astigmatism. Residual refractive error and visual acuity (uncorrected and corrected) were the measures of interest, at the visit closest to 90 days postoperative.

RESULTS

A matched data set from 100 WFO and 97 PAE eyes was extracted from clinical records. At the postoperative visit the PAE group showed lower residual refractive cylinder (p = 0.04), uncorrected distance visual acuity (UDVA) (-0.06 PAE vs. -0.02 WFO, p < 0.01) and distance corrected visual acuity (CDVA) (p < 0.01). The percentage of eyes with a mean refraction spherical equivalent (MRSE) magnitude within 0.25 D and 0.50 D of plano was statistically significantly higher in the PAE group (p = 0.04 and 0.01, respectively). A statistically significantly higher percentage of eyes in the PAE group had UDVA better than or equal to -0.10 logMAR (20/16 Snellen, 36% vs 22%, p = 0.04). More eyes gained CDVA after surgery in the PAE group (53% vs 32%, p < 0.01). There were five enhancements in the WFO group versus none in the PAE group, a statistically significant difference (p = 0.03).

CONCLUSIONS

Visual acuity and refractive outcomes after LASIK using PAE in eyes with oblique astigmatism in their preoperative refraction were statistically significantly better than those obtained when WFO treatment was used. The number of refractive outliers and the number of retreatments were also significantly lower with PAE treatment.

Comparison of clinical outcomes after femtosecond laser in situ keratomileusis in eyes with low or high myopia

AIM

To compare the clinical results of femtosecond (FS) laser in situ keratomileusis (LASIK) in high myopic patients and low myopic patients.

METHODS

This study included 212 myopic eyes undergoing LASIK using a VisuMax 500kHz FS laser. All treated eyes were assigned to one of two groups according to preoperative manifest spherical refraction: low myopia group (A, >-4.0 D) and high myopia group (B, ≤-4.0 D). Uncorrected and corrected distance visual acuity (UDVA, CDVA), refractive errors, and higher-order aberrations (HOAs) were measured preoperatively and 1wk, 1, 3 and 6mo postoperatively.

RESULTS

At 6mo of follow-up, 92% and 76% had a UDVA of 20/20 or better in group A and B, respectively (P=0.037) and UDVA was significantly different between two groups (P=0.042). Six and seven percentage lost one line of CDVA in group A and B, respectively (P=0.572) and no eyes in both groups lost more than two lines. Each group had 87% and 76% of treated eyes within ±0.5 D of the intended correction (P=0.186), and 13% and 43% with a change of >0.50 D in spherical equivalent from 1wk to 6mo postoperatively (P=0.005). In terms of postoperative astigmatism, each group had 89.1% and 76.6% within ±0.50 D, respectively and there was significant difference (P=0.006). Group A tends to induce smaller HOAs than group B.

CONCLUSION

FS LASIK is effective and safe for correcting high myopia as well as low myopia. However, high myopic eyes showed more postoperative astigmatism and HOAs which affect visual acuity.

Correction of Myopic Astigmatism with Topography-Guided Laser In Situ Keratomileusis (TOPOLINK)

We aim to assess the feasibility of topography-guided laser in situ keratomileusis (TOPOLINK) for correcting pre-existing and surgical-induced astigmatism. A retrospective, single center cohort study was conducted. Patients with pre-existing irregular myopic astigmatism were recruited into the primary group and those with irregular myopic astigmatism following laser in situ keratomileusis (LASIK) were recruited into the enhancement group. The changes in uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), maximum astigmatism, spherical equivalent (SE) and patient satisfaction were recorded. The Chi-square test, Mann-Whitney U test and Generalized Linear Mixed Model were utilized for the analysis in the current study. A total of 18 eyes were studied in the primary group and 14 eyes were examined in the enhancement group. One year postoperatively, the UCVA, BCVA, maximum astigmatism and SE improved significantly in both the primary and the enhancement groups (all p < 0.05). The UCVA (p = 0.046) and SE (p = 0.003) were worse in the primary group preoperatively but became similar in both groups postoperatively, while the BCVA and maximum astigmatism remained identical between groups throughout the study period (all p < 0.05). In addition, the rate of high and moderate satisfaction reached 90.0% in the primary and the enhancement groups, without significant differences (p = 0.871). In conclusion, the TOPOLINK showed high predictability and will contribute to similar outcomes between primary and postoperative irregular myopic astigmatism concerning visual acuity, refractive status and subject satisfaction.

Astigmatismus

Der Astigmatismus ist der weltweit häufigste Refraktionsfehler vor Hypermetropie und Myopie. Man unterscheidet den äußeren vom inneren Astigmatismus. Der äußere Astigmatismus kann weiter in „mit der Regel“, „gegen die Regel“ und „schräg“ unterteilt werden. Die Summierung des äußeren und inneren Astigmatismus ergibt den refraktiven Zylinder. Astigmatismus wurde lange als zweidimensionales Phänomen gesehen, doch erst die dreidimensionale Betrachtung hat den Blick auf bestehende Analyseverfahren (Topo- und Tomographie) erweitert. Die Vektoranalyse nach Alpins ist hierbei eine bekannte Methode zur Therapieplanung. Zur Therapie des Astigmatismus stehen konservative Optionen wie Brille oder torische Kontaktlinse sowie unterschiedlichste chirurgische Verfahren wie photorefraktive Keratektomie, Femtosekundenlaser-assistierte Keratotomie, Laser-in-situ-Keratomileusis, „small-incision lenticule extraction“ und die Implantation torischer Intraokularlinsen zur Verfügung.

[Astigmatism]

Astigmatism is the most frequent refractive error worldwide followed by hyperopia and myopia. Internal astigmatism has to be differentiated from external astigmatism. Furthermore, external astigmatism can be divided into "with the rule", "against the rule" and "oblique". The summation of internal and external astigmatism results in the refractive cylinder. Astigmatism has for a long time been regarded as a two-dimensional phenomenon; however, only a three-dimensional consideration expanded the view on existing analytical methods (topography and tomography). Alpins' vector analysis is a commonly used method for treatment planning. Multiple options exist for treatment of astigmatism with conservative approaches, such as eyeglasses or toric contact lenses as well as various surgical procedures, such as photorefractive keratectomy, femtosecond laser-assisted keratotomy, laser in-situ keratomileusis, small incision lenticule extraction and toric intraocular lens implantation.

[Visual improvement by aberration-free excimer laser retreatment : Therapy after combined photorefractive keratectomy and keratome laser in situ keratomileusis treatment]

A 23-year-old male patient presented with reduced visual acuity of the right eye, along with halos and starbursts in both eyes after a one-stage tissue-saving treatment, a combination of myopic photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). After an extensive preliminary examination and analysis of the examination results, aberration-free LASIK retreatment for reducing astigmatism and enlargement of the optical zone with an excimer laser was performed on the right eye. The visual performance and the subjectively perceived optical quality improved postoperatively.

Accuracy of Scheimpflug Holladay equivalent keratometry readings after corneal refractive surgery in the absence of clinical history

BACKGROUND AND OBJECTIVE

To identify the most accurate combination of Pentacam's equivalent keratometry readings (EKR) and intraocular lens power formula when the clinical history is unavailable.

PATIENTS AND METHODS

A total of 18 patients underwent cataract surgery after refractive surgery. The Pentacam 4.5- and 3.0-mm EKR were combined with the SRK II, SRK/T, Hoffer-Q, and Holladay I and II formulas.

RESULTS

The smallest deviation from the predicted value was achieved by combining the 4.5 EKR with the Holladay II formula (mean arithmetic deviation, -0.2 ± 0.4 dpt).

CONCLUSION

The 4.5-mm EKR + Holladay II formula can accurately calculate intraocular lens power in patients with previous refractive surgery.

Do outside temperature and sunlight duration influence the outcome of laser refractive surgery? Results from the Hamburg Weather Study

PURPOSE

To examine the impact of temperature and sunlight duration on refractive and visual outcome of laser-assisted in situ keratomileusis (LASIK) in myopic eyes.

SETTING

University Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany.

DESIGN

Retrospective, cross-sectional data analysis.

METHODS

This study comprised 1,052 eyes of 1,052 consecutive myopic patients (419 males, 633 females; mean age at surgery 35.0±9.0 years) with a mean preoperative refractive spherical equivalent (SE) of -3.88±1.85 diopters (D). Two subgroups were defined, comprising patients undergoing surgery during either meteorological winter or summer. Manifest refraction, uncorrected, and corrected distant visual acuity (UDVA and CDVA) were assessed pre- and postoperatively. We applied robust regression analysis with efficiency index (EI), safety index (SI), and postoperative SE (in D) as dependent variables.

RESULTS

At the 1-month (33.0±5.0 days) follow-up, the mean postoperative SE was -0.18±0.44 D. Bivariate comparisons showed that statistically significant better EI was related to days with lower temperature. We obtained a significant difference for SI which suggested that low temperature had a positive influence on SI. No change by more than one line on LogMAR scale was obtained.

CONCLUSION

Although being statistically significant, there was no clinically relevant difference in the outcome of LASIK, which demonstrates its highly standardized quality. Prospective, longitudinal studies are warranted to address meteorotropic reactions through evaluating defined meteorological parameters.

Variation in the effectiveness of refractive surgery during the year: results from the Hamburg Weather Study

PURPOSE

To examine the impact of seasonality on the refractive and visual outcomes of laser in situ keratomileusis (LASIK) in myopic eyes.

SETTING

Department of Ophthalmology and Care Vision Refractive Centers, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

DESIGN

Retrospective cross-sectional data analysis.

METHODS

Two subgroups were defined. The first comprised patients having surgery during meteorological winter and the second, patients having surgery during meteorological summer. The manifest refraction and uncorrected and corrected visual acuities were assessed preoperatively and postoperatively. Robust regression analysis was applied with the efficacy index, safety index, and postoperative SE as dependent variables.

RESULTS

This study comprised 1052 eyes of 1052 consecutive myopic patients (419 men, 633 women; mean age at surgery 35.0 years ± 9.0 [SD]) with a mean preoperative refractive spherical equivalent (SE) of -3.88 ± 1.85 diopters (D). At the 1-month follow-up (mean 33.0 ± 5.0 days), the mean postoperative SE was -0.18 ± 0.44 D. The efficacy index was 0.023 higher in eyes with refractive surgery during summer than in eyes treated during winter (P=.032), indicating less efficacy during winter. The differences in the safety index and postoperative SE between summer and winter were not statistically significant. No eye had a change of more than 1 line on the logMAR scale (corrected distance visual acuity).

CONCLUSIONS

Although the difference in the efficacy index was statistically significant, the difference in the outcomes of LASIK was not clinically relevant, which shows the procedure's highly standardized reliability. Prospective longitudinal studies are warranted to address meteorotropic reactions by evaluating defined meteorological parameters.

FINANCIAL DISCLOSURE(S)

No author has a financial or proprietary interest in any material or method mentioned.

Do air pressure and wind speed influence the outcome of myopic laser refractive surgery? Results from the Hamburg Weather Study

Laser in situ keratomileusis (LASIK) is one of the dominant procedures for the surgical correction of refractive errors. Meteorotropic reaction has been described regarding the field of ophthalmology. This study was thus initiated to assess the impact of air pressure and wind speed on the refractive and visual outcome of LASIK in myopic eyes. Our study comprised 1,052 eyes of 1,052 consecutive myopic patients (419 males, 633 females; mean age at surgery 35.0 ± 9.0 years) with mean preoperative refractive spherical equivalent (SE) of -3.88 ± 1.85 diopters (D). Two subgroups were defined, which had undergone surgery either during meteorological winter or summer. Manifest refraction, uncorrected and corrected visual acuity were assessed pre- and post-operatively. We applied robust regression analysis with efficiency index (EI), safety index, and postoperative SE (D) as dependent variables. At the 1-month (33.0 ± 5.0 days) follow-up, the mean postoperative SE was -0.18 ± 0.44 D. Bivariate comparisons showed that statistically significant better EI was related to days with low to moderate air-pressure. This was confirmed by robust regression analysis. Moderate to high wind speed was related to more appropriate postoperative SE. No change by more than one line on logMar scale was obtained. Although being statistically significant, there is no clinically relevant difference in outcome of LASIK, which demonstrates its highly standardized quality. Prospective, longitudinal studies are warranted to address meteorotropic reactions through evaluating individual risk profiles.

Laser in situ keratomileusis for astigmatism ≤ 0.75 diopter combined with low myopia: a retrospective data analysis

Background

This study examined the refractive and visual outcome of wavefront-optimized laser in situ keratomileusis (LASIK) in eyes with low myopia and compound myopic astigmatism ≤ 0.75 diopter (D).

Methods

153 eyes from 153 consecutive myopic patients (74 male, 79 female; mean age at surgery 40.4 ± 10.4 years) who had a preoperative refractive cylinder ≤ 0.75 D and a manifest sphere between -0.25 D and -2.75 D, and who had completed 4-month follow-up. Three subgroups defined by the magnitude of preoperative manifest refractive cylinder (0.25, 0.50, and 0.75 D) were formed. Manifest refraction, uncorrected and corrected visual acuity were assessed pre- and postoperatively. The astigmatic changes achieved were determined using the Alpins vector analysis.

Results

After 4 months (120.0 ± 27.6 days) of follow-up, a mean uncorrected distant visual acuity of 0.07 ± 0.11 logMAR and a mean manifest refraction spherical equivalent of -0.06 ± 0.56 D were found. There was no statistically significant difference in efficacy and safety between the preoperative cylinder groups. Astigmatic overcorrection for preoperative cylinder of ≤ 0.50 D was suggested by the correction index, the magnitude of error, the index of success, and the flattening index.

Conclusions

Low myopic eyes with a preoperative cylinder of ≤ 0.50 D were significantly overcorrected with regard to cylinder correction when combined with low myopic LASIK. Accordingly, we are cautious in recommending full astigmatic correction for eyes with low myopia and manifest cylinder of ≤ 0.50 D.

Efficacy and predictability of laser in situ keratomileusis for low astigmatism of 0.75 diopter or less

PURPOSE

To examine the refractive and visual outcomes of wavefront-optimized laser in situ keratomileusis (LASIK) in myopic eyes with low astigmatism of 0.75 diopter (D) or less.

SETTING

University Medical Center Hamburg-Eppendorf, Germany, and Care Vision private clinics, Germany and Austria.

DESIGN

Retrospective cross-sectional data analysis.

METHODS

This study comprised consecutive myopic patients with a preoperative refractive cylinder of 0.75 D or less and a preoperative subjective sphere between -2.75 D and -11.50 D. Three subgroups were formed based on preoperative refractive cylinder magnitude (0.25 D, 0.50 D, and 0.75 D). Manifest refraction, uncorrected distance visual acuity (UDVA), and corrected distance visual acuity were assessed preoperatively and postoperatively. The astigmatic changes were determined using Alpins vector analysis.

RESULTS

This study enrolled 448 eyes of 448 patients (145 men, 303 women; mean age at surgery 37.8 years ± 9.4 [SD]). By 4 months (mean 116.8 ± 27.7 days) postoperatively, the mean UDVA was 0.10 ± 0.13 logMAR and the mean manifest refraction spherical equivalent (MRSE) -0.05 ± 0.68 D. There was no statistically significant difference in efficacy or safety between the preoperative cylinder groups. Astigmatic overcorrection for a preoperative cylinder of 0.25 D and 0.50 D was suggested by the correction index, the magnitude of error, the index of success, and the flattening index.

CONCLUSIONS

Although the mean UDVA and mean MRSE obtained by the 4-month follow-up were appropriate, a preoperative cylinder of 0.50 D or less was significantly overcorrected. Accordingly, caution should be used when considering full astigmatic correction for manifest cylinder of 0.50 D or less.

Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D

BACKGROUND

The purpose of this study was to evaluate surgically-induced astigmatism after spherical ablation in photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) for myopia with astigmatism < 1.00 D.

METHODS

The charts of patients undergoing spherical PRK or LASIK for the correction of myopia with minimal astigmatism of <1.00 D from 2002 to 2012 at the John A Moran Eye Center in Salt Lake City, UT, were retrospectively reviewed. Astigmatism was measured by manifest refraction. The final astigmatic refractive outcome at 6 months postoperatively was compared with the initial refraction by Alpins vector analysis.

RESULTS

For PRK, average cylinder increased from 0.39 ± 0.25 (0.00-0.75) preoperatively to 0.55 ± 0.48 (0.00-1.75) postoperatively (P = 0.014), compared with an increase in LASIK eyes from 0.40 ± 0.27 (0.00-0.75) preoperatively to 0.52 ± 0.45 (0.00-2.00) postoperatively (P = 0.041). PRK eyes experienced an absolute value change in cylinder of 0.41 ± 0.32 (0.00-1.50) and LASIK eyes experienced a change of 0.41 ± 0.31 (0.00-1.50, P = 0.955). Mean surgically-induced astigmatism was 0.59 ± 0.35 (0.00-1.70) in PRK eyes, with an increase in surgically-induced astigmatism of 0.44 D for each additional 1.00 D of preoperative cylinder; in LASIK eyes, mean surgically-induced astigmatism was 0.55 ± 0.32 (0.00-1.80, P = 0.482), with an increase in surgically-induced astigmatism of 0.29 D for each 1.00 D of preoperative cylinder.

CONCLUSION

Spherical ablation can induce substantial astigmatism even in eyes with less than one diopter of preoperative astigmatism in both PRK and LASIK. No significant difference in the magnitude of surgically-induced astigmatism was found between eyes treated with PRK and LASIK, although surgically-induced astigmatism was found to increase with greater levels of preoperative astigmatism in both PRK and LASIK.

Relationships between keratometry and collagen fibrillar structure of cornea by circular polarization biomicroscopy

PURPOSE

To evaluate the relationships between keratometry and collagen fibrillar structure of cornea by circular polarization biomicroscopy.

METHODS

Thirty-four subjects (63 eyes) were included in this study. Intraocular pressure (IOP) was measured, and keratometry was done with an automated keratometer. When the corneal astigmatism was larger than 0.75 diopter, corneal topography was done. After pupil dilation, the examiner placed a circular polarizing filter in front of the subject's eye. The images were captured by a camera connected to the slit lamp. Interfocal distance and angle were measured with ImageJ. The correlations between corneal astigmatism and interfocal distance-angle were examined by double angle vector diagram. Scalar analyses were done for the correlations between subject age and interfocal distance, between IOP and interfocal distance, and between mean cornea power and interfocal distance.

RESULTS

The mean age of the 34 subjects was 59 ± 16 years. Mean interfocal distances and angles determined by double angle vector diagram were 4.67 mm and -20.5 degrees in the right eye and 3.73 mm and +24.2 degrees in the left eye. The correlation between age and interfocal distance and between IOP and interfocal distance were statistically insignificant (P = 0.913 and 0.361, respectively). The interfocal distance and angle showed no statistically significant correlation with corneal astigmatism by vector analysis (P = 0.221 and 0.850, respectively). The fibrillar structure pattern in circular polarizing biomicroscopy showed no statistically significant relationship with the bow tie pattern in corneal topography (P = 0.762). However, analysis of the correlation between mean corneal power and interfocal distance showed a statistically significant, but weak positive correlation (r = 0.326, P = 0.019).

CONCLUSIONS

Interfocal distance determined through circular polarizing biomicroscopy showed a positive correlation with mean corneal power. But age, IOP, and corneal astigmatism did not show a significant correlation with interfocal distance and angle.

Prospective study of exclusive strontium-/yttrium-90 beta-irradiation of primary and recurrent pterygia with no prior surgical excision. Clinical outcome of long-term follow-up

PURPOSE

To evaluate the consecutive treatment results regarding pterygium recurrence and the efficacy of exclusive strontium-/yttrium-90 beta-irradiation for primary and recurrent pterygia and to analyze the functional outcome.

PATIENTS AND METHODS

Between October 1974 and December 2005, 58 primary and 21 recurrent pterygia were exclusively treated with strontium-/yttrium-90 beta-irradiation with doses ranging from 3,600 to 5,500 cGy. The follow-up time was 46.6 +/- 26.7 months, with a median of 46.5 months.

RESULTS

The treatment led to a size reduction in all pterygia (p < 0.0001). Neither recurrences nor side effects were observed during therapy and follow-up in this study. Best-corrected visual acuity increased (p = 0.0064). Corneal astigmatism was reduced in recurrent pterygia (p = 0.009).

CONCLUSION

Exclusive strontium-/yttrium-90 beta-irradiation of pterygia is a very efficient and well-tolerated treatment, with remarkable aesthetic and rehabilitative results in comparison to conventional treatments, especially for recurrent lesions which have undergone prior surgical excision.

High-order aberrations and preoperative associated factors

PURPOSE

The purpose of this study was to determine which preoperative factors are associated with the presence of high-order aberrations.

METHODS

A total of 93 eyes of 52 subjects were evaluated preoperatively between 1 January and 31 March 2003, using a Hartmann-Shack-based aberrometer. Age, gender, cycloplegic refraction, pupil size, keratometry readings, anterior chamber depth, white-to-white tests, intraocular pressure and basic secretion tests were evaluated.

RESULTS

Factors associated with high-order aberrations included age > or = 40 years (mean 4.39 +/- 2.95 microm; p = 0.03, Mann-Whitney test), higher keratometry values (44.96 +/- 1.57 D) (r = 0.447, p < 0.001, Spearman's correlation coefficient), higher degrees of myopia (> or = - 6.1 D) (p < 0.001, Kruskall-Wallis test) and increasing pupil size (p < 0.001, anova). Other factors including anterior chamber depth, white-to-white results, intraocular pressure and basic secretion test results did not correlate with the presence of high-order aberrations preoperatively.

CONCLUSIONS

Ocular wavefront aberrations varied greatly from subject to subject. Treatment should be customized for each laser based on patient characteristics in order to ensure the optimal treatment profile for the aberration.

Transverse keratotomy followed by LASIK for the treatment of naturally occurring astigmatism

PURPOSE

To evaluate the efficacy of transverse keratotomy followed by LASIK for patients with high amounts of naturally occurring astigmatism.

METHODS

Thirteen eyes with naturally occurring astigmatism ranging from -3.75 to -6.50 diopters (D) underwent sequential transverse keratotomy (60 degrees at 6 mm) and LASIK procedures. The effect of these two procedures on the amount of astigmatism was studied.

RESULTS

Transverse keratotomy led to a 46% reduction in refractive cylinder from -5.50 +/- 0.80 D to -3.00 +/- 1.00 D. After LASIK, the initial refractive astigmatism was reduced by 90% to -0.50 +/- 0.50 D with a minimum follow-up of 6 months.

CONCLUSIONS

The combined technique of transverse keratotomy followed by LASIK is an effective and accurate way to treat high amounts of naturally occurring astigmatism, allowing the size of the optical zone of the excimer laser ablation to be maximized.

Comparison of Cross Cylinder Ablation Using the Optimized Ablation Transition Zone and the Torsion Error Detector for Correction of Astigmatism

PURPOSE

To compare the safety and efficacy of laser in situ keratomileusis (LASIK) in correcting high myopic astigmatism using two different ablation profiles using the Nidek EC-5000 CX II laser).

METHODS

Fifteen patients (25 eyes) had LASIK for compound myopic astigmatism, using the Optimized Ablation Transition Zone (OATz) ablation profile and activated torsion error detection (TED). Results were compared with those obtained with a cross cylinder ablation profile for myopic astigmatism.

RESULTS

For eyes treated with TED, on postoperative day 7, 76% had visual acuity equal to or better than baseline best spectacle-corrected visual acuity (BSCVA) and 56% of eyes had overcorrected astigmatism. On postoperative day 20, none of the eyes had residual astigmatism more than 1.00 D and 72% eyes were within +/-0.50 D cylinder; 92% of eyes had residual astigmatism within 30 degrees of the preoperative axis and 12% remained astigmatically overcorrected at 20 days. Eighty-eight percent of eyes were either fully corrected or had mild myopic astigmatism. Comparison of results with cross cylinder ablation showed that 24% had overcorrection and 60% of patients with high astigmatism were overcorrected up to 1.75 D and developed hyperopic astigmatism in the opposite axis. Results with the cross cylinder ablation profile were good up to 2.00 D of myopic astigmatism.

CONCLUSIONS

Correction of astigmatism using the OATz profile and TED with the Nidek EC-5000 CX II laser produced good results in high as well as pure astigmatism treatments, compared to the cross cylinder ablation profile. Ablation depth was greater in OATz with TED-based corrections. Overcorrections were less with OATz with TED, and residual astigmatism was at the same baseline axis, thereby increasing patient satisfaction.

Contact Lens Prescribing in a Specialist Medical Contact Lens Clinic Based in an NHS Hospital

PURPOSE

To describe the range of indications for contact lenses and the types of lenses being used in an NHS hospital-based specialist medical contact lens clinic and contrast this with information from 12 years ago.

METHODS

A retrospective audit of 596 clinic attendances was performed in the contact lens clinic at the Western Eye Hospital between April 2002 and March 2003. The results were compared with a similar audit performed in 1991. We used the hospitals electronic records, and information on contact lens prescribing was obtained directly from the receipts generated by the contact lens department and the accounts department.

RESULTS

We saw 392 patients with 88.5% of patients requiring 2 or less visits per year. The majority of referrals are for high myopia (28.6%) closely followed by aphakia (25.2%) and keratoconus (24.7%). This is in contrast to 1991 when 68% of referrals were for aphakia and twice as many myopes (17%) were seen as keratoconus patients (8%). A total of 560 lenses were prescribed with 68 different types of lens in use. The seven most commonly used lens types accounted for 61% of all lenses prescribed.

CONCLUSIONS

Medical contact lens clinics provide a specialist service and also provide an important training resource for junior ophthalmologists. Safer cataract surgical techniques have had a significant impact on the case mix seen in our clinic, with the emphasis moving away from aphakic and myopic patients and toward the more challenging to fit eyes with keratoconus or postcorneal surgery.