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PubMedDate not supplied

Improved technique of circular keratotomy for the correction of corneal astigmatism.

BACKGROUND: Based on Gauss' law governing the comparison of hyperbaric pressure in the eye and atmospheric pressure, the authors present a procedure to correct astigmatism. The present paper describes an improvement of a technique for circular keratotomy that was published previously. METHODS: We present data on a consecutive series of 32 eyes with a mean corneal astigmatism of 4.66 diopters (D) (range -2.25 to -6.00 D) with a variety of clinical diagnoses. The astigmatic cornea was trephined with a diameter of 7 mm and a depth of 300 microns. After deepening of the trephination with a diamond knife to 550 microns over the steeper semimeridians, the intraocular pressure created a rounding of the cornea. The amount of astigmatic correction and extent of deepening were controlled intraoperatively with a keratoscope. No sutures were placed. RESULTS: In 32 consecutive eyes, corrections were between 50 and 90% of the initial cylindrical values after 1 week to 1 month. In 29 eyes (91%), the results obtained remained stable during a 1-year follow-up; in two eyes (6%), the 1-month results worsened by more than 1.00 D and in one eye (3%), results improved by more than 1.00 D. There were no complications during or after surgery. Wound gaping resulting in epithelial plugs did not occur. No patient lost one or more lines of spectacle-corrected visual acuity, but 13 eyes (40%) gained one or more lines. CONCLUSION: The technique of correcting corneal astigmatism by trephining to a depth of 300 microns, with deepening of the wound to 550 microns along the steep meridian and using no sutures can correct up to 10.00 D of astigmatism with reasonable stability.

Astigmatism↗
PubMedDate not supplied

Treatment of irregular astigmatism with a broad beam excimer laser.

BACKGROUND: Four basic types of irregular astigmatism are described: central elevation, central flat area, eccentric elevation, and eccentric flat area. METHODS: The importance of the Munnerlyn formula is shown for the treatment of irregular astigmatism. A new diagnostic entity is described, the steep/flat ratio, modeled on the inferior/superior ratio described previously in keratoconus. Calculation of the steep/flat ratio is described using the cross sectional view of videokeratography, leading to specific treatments for the four types of irregular astigmatism. Surgical technique using the VISX Star excimer laser for repeated laser in situ keratomileusis (LASIK) is described. RESULTS: Case studies are given for each of the forms of irregular astigmatism showing improved topographic appearance and indicating treatment parameters. In each case, improvement of both uncorrected and spectacle-corrected visual acuity is demonstrated. CONCLUSIONS: Irregular astigmatism is an important complication of refractive surgery. Four basic forms of irregular astigmatism can be treated with a broad beam excimer laser.

Adult↗
PubMed1998

Laser in situ keratomileusis for simple myopic, mixed, and simple hyperopic astigmatism.

PURPOSE: To summarize initial results of astigmatic laser in situ keratomileusis (LASIK) for 41 eyes of 26 patients using the EC-5000 Nidek system and assess its safety, efficacy and predictability. METHODS: The EC-5000 Nidek excimer laser was used to correct simple myopic, mixed, and simple hyperopic astigmatism with manifest cylinder from 2.00 to 6.50 D. Ablation zone diameters were 6.5 mm (steep meridian ablation) to 7.5 mm (flat meridian ablation) with a repetition rate of 40-41 Hz. In eyes with simple myopic and mixed astigmatism, ablation was performed in both meridians; in eyes with simple hyperopic astigmatism, ablation was performed in the flat meridian alone. Follow-up was 3 months in all eyes. RESULTS: Uncorrected visual acuity was 20/40 or better in 85% of the eyes. Uncorrected visual acuity was equal to the preoperative spectacle-corrected visual acuity in 63% of the eyes. Intended cylinder correction was within 1.00 D in 95% of eyes. No eyes lost lines of spectacle-corrected visual acuity. CONCLUSION: LASIK using the EC-5000 excimer laser appears to effective in the treatment of simple myopic, mixed, and simple hyperopic astigmatism, with favorable results as compared to those previously described for astigmatic keratotomy.

Astigmatism↗
PubMed1998

Laser in situ keratomileusis for hyperopia and hyperopic astigmatism.

BACKGROUND: The correction of hyperopia by excimer laser remains challenging because the procedure is followed by regression and loss of effect. We evaluated excimer laser in situ keratomileusis (LASIK) to correct hyperopia and hyperopic astigmatism using the NIDEK scanning slit excimer laser and a modified nomogram. METHODS: The study included the first consecutive 58 eyes treated for hyperopia and hyperopic astigmatism by one surgeon. All eyes were operated at the Alexandria Eye Center, Alexandria, Egypt using the Nidek excimer laser and the Chiron automated corneal shaper. Astigmatic correction was done first by myopic ablation using a 5.0 mm ablation zone and a 5.5 mm transition zone, followed by narrow hyperopic ablation using a 5.5 to 7.5 mm zone. RESULTS: Mean preoperative cycloplegic spherical equivalent refraction was +3.75 D (range, +1.00 to +6.00 D). Mean preoperative astigmatism was 2.75 D (range 0 to 4.00 D). After hyperopic LASIK, all eyes had a reduction in their hyperopia, but regression occurred gradually until the last follow-up examination. At 6 months follow-up, the mean cycloplegic refraction was +2.25 D (range, 0 to +3.25 D). The postoperative astigmatism had a mean of 1.25 D (range 0 to 2.75 D). Four eyes had a reduction in the quality of vision due to a decentered ablation and a small ablation zone, but no other vision threatening complications were reported. CONCLUSION: LASIK to correct hyperopia and hyperopic astigmatism is safe, effective, and repeatable. Predictability and long-term stability needs improvement. A better ablation profile and modified algorithm need to be provided by excimer laser manufacturers.

Adolescent↗
PubMedDate not supplied

Laser in situ keratomileusis retreatment for residual myopia and astigmatism.

PURPOSE: To evaluate the visual and refractive results of laser in situ keratomileusis (LASIK) retreatment on eyes with residual myopia with or without astigmatism. METHODS: LASIK retreatment was performed on 35 eyes of 23 patients for correction of residual myopia, with or without astigmatism, with a mean manifest spherical equivalent refraction of -2.17+/-0.82 D (range, -1.00 to -3.87 D) and mean refractive astigmatism of -0.55+/-0.61 D (range, 0 to -1.75 D). Retreatment was performed 3 to 18 months after primary LASIK (mean, 5.1+/-2.6 mo). The corneal flap of the previous LASIK was lifted and laser ablation was performed using the Chiron-Technolas Keracor 116 excimer laser. Follow-up was 12 months for all eyes. RESULTS: At 1 year after retreatment, manifest spherical equivalent refraction was reduced to a mean -0.23+/-0.28 D (range, 0 to -0.87 D), and refractive astigmatism was reduced to a mean -0.16+/-0.25 D (range, 0 to -0.75 D). Thirty-two eyes (91.5%) had a manifest spherical equivalent refraction within +/-0.50 D of emmetropia, and 33 eyes (94.3%) had 0 to 0.50 D of refractive astigmatism. Uncorrected visual acuity was 20/20 or better in 11 eyes (31.4%). Spectacle-corrected visual acuity was not reduced in any eye after retreatment. There were no significant complications. CONCLUSION: LASIK retreatment was effective for correction of residual myopia or astigmatism after primary LASIK. Refractive results were predictable with good stability after 3 months. Lifting the flap during LASIK retreatment was relatively easy to perform and did not result in visual morbidity in eyes treated from 3 up to 18 months after primary LASIK.

Adult↗
PubMedDate not supplied

Holmium laser thermal keratoplasty for hyperopia and astigmatism after photorefractive keratectomy.

PURPOSE: To report results of holmium laser thermal keratoplasty used to treat induced hyperopia and induced, as well as pre-existing astigmatism after photorefractive keratectomy. METHODS: Sixteen eyes of 16 patients were included in this study. Contact holmium laser (Technomed Holmium 25) was used in 7 patients to correct hyperopia (8 spots at 8 or 9 mm) and in 9 patients to correct astigmatism (4 spots at 7, 8, or 9 mm). Follow-up evaluation was done after at least 6 months. The effectiveness, stability, and safety of the procedure were investigated. RESULTS: Spherical correction was ineffective (1.00 D or less) when applied at the 9-mm diameter treatment zone. Spherical correction applied at the 8-mm diameter treatment zone was ineffective in 1 eye. Three eyes achieved 1.00 to 2.00 D change, but 2 of these eyes showed an induced astigmatic change as well. Correction of astigmatism at the 7-mm diameter treatment zone resulted in a 0 to 4.00 D cylinder component change. Treatment at the 8-mm diameter treatment zone showed a 0 to 1.50 D effect and at the 9-mm treatment zone, 0.25 to 1.50 D. All eyes that achieved significant improvement (1.00 D or more change in cylinder component) showed significant overcorrection in the first postoperative phase. There were no sight threatening complications. CONCLUSION: Holmium laser thermal keratoplasty can be useful for the treatment of overcorrection and induced as well as pre-existing astigmatism after photorefractive keratectomy. However, predictability is low and astigmatism can be induced with the attempted spherical correction.

Adult↗
PubMedDate not supplied

Surgically-induced astigmatism after laser in situ keratomileusis for spherical myopia.

PURPOSE: To characterize the surgically-induced-astigmatism (SIA) associated with spherical LASIK. METHODS: Refractive outcomes in 70 eyes that underwent primary myopic LASIK with purely spherical ablation were analyzed. The Summit Apex Plus excimer laser was used. The Bausch & Lomb Hansatome with the 180-microm plate was used to produce superiorly hinged flaps. The relationship between refractive astigmatism and corneal topographic astigmatism was analyzed using linear regression and vector analysis. RESULTS: There was a statistically significant negative correlation (slope = -0.21) between refractive surgically-induced astigmatism and preoperative topographic cylinder. A 0.24-D with-the-rule shift was also found. Surgically-induced astigmatism was not correlated with the magnitude of laser ablation. CONCLUSION: The lamellar keratotomy portion of LASIK reduces pre-existing corneal astigmatism and produces a relative steepening of the hinge meridian.

Adult↗
PubMedDate not supplied

Photorefractive keratectomy for astigmatism with the Meditec MEL 60 laser.

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) in eyes treated with astigmatic refractive errors. METHODS: Nine hundred forty eyes were treated with the Aesculap Meditec MEL 60 ArF excimer laser. Treatment groups were: Group 1 (n=746) eyes with compound myopic astigmatism, Group 2 (n=104) eyes with compound hyperopic astigmatism, Group 3 (n=75) eyes treated for mixed astigmatism, and Group 4 (n=15) eyes with simple myopic astigmatism (negative cylinder). RESULTS: In Group 1, the preoperative spherical equivalent refraction of -6.10 D with an average of -1.50 D cylinder decreased to -0.95 D with -0.13 D cylinder; uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 86% (642/746 eyes); 20/20 or better in 58% (433/746 eyes); 0.8% (6/746 eyes) lost two lines of spectacle-corrected visual acuity (SCVA); 74% (552/746 eyes) were within +/-0.50 D and 93% (694/746 eyes) were within +/-1.00 D of target refraction. In Group 2, preoperative mean +4.57 D spherical equivalent refraction with an average of +1.57 D cylinder decreased to +1.13 D with +0.38 D cylinder; UCVA of 20/40 or better was achieved in 84% (87/104 eyes); 20/20 or better in 46% (48/104 eyes); 14,4% (15/104 eyes) lost two or more lines of SCVA; 52% (54/104 eyes) were within +/-0.50 D and 82% (85/104 eyes) were within +/-1.00 D of target refraction. In Group 3, mean preoperative -4.20 D cylinder and +3.00 D spherical equivalent refraction decreased to -0.50 D cylinder and -0.50 D spherical equivalent refraction; UCVA of 20/40 or better was achieved in 83% (62/75 eyes); 20/20 or better in 32% (24/75 eyes); 13.3% (10/75 eyes) lost two or more lines of SCVA. In Group 4, mean preoperative -3.98 D cylinder decreased to -0.62 D cylinder; UCVA of 20/40 or better was achieved in 60% (9/15 eyes); none of the eyes achieved 20/20 or better; SCVA remained stable in 6.6% (1/15 eyes) and decreased two or more lines in 20.0% (3/15 eyes); 20% (3/15 eyes) were within +/-0.50 D and 53.3% (8/15 eyes) were within +/-1.00 D of target refraction. CONCLUSION: PRK with the Meditec MEL 60 laser produced the best results in eyes with compound myopic astigmatism (Group 1). In all other groups, results were less predictable.

Adult↗
PubMedDate not supplied

Laser in situ keratomileusis for astigmatism greater than -3.50 D with the Nidek EC-5000 excimer laser.

PURPOSE: LASIK with the Nidek EC-5000 excimer laser was used to treat high astigmatism. METHODS: The Nidek EC-5000 excimer laser and ACS microkeratome were used in regular LASIK procedures. Results of 74 eyes with astigmatism of more than 3.50 D and up to 10.00 D were evaluated. RESULTS: With Nidek algorithms, it was possible to eliminate refractive error completely or reduce it to a satisfactory amount, especially in difficult cases of mixed astigmatism with high astigmatic components. CONCLUSION: The Nidek software for mixed and high astigmatism was efficient, predictable, and produced good results in difficult cases of high astigmatism.

Adult↗
PubMedDate not supplied

A comparison of induced astigmatism in conventional and wavefront-guided myopic LASIK using LADARVision4000 and VISX S4 platforms.

PURPOSE: To evaluate and compare the surgically induced astigmatism in myopic eyes undergoing conventional and wavefront-guided LASIK. METHODS: A retrospective review was performed of the charts of 200 myopic eyes of 121 patients who underwent either custom or conventional treatments via the VISX S4 or LADARVision4000 platforms (50 consecutive eyes in each of the four groups). The primary outcome measure was manifest refraction, which was evaluated preoperatively and at 3 months postoperatively. The magnitude and axis of the unintended surgically induced astigmatism were calculated using vector analysis. The Student t test was used to compare the magnitudes of the surgically induced astigmatism and the absolute angle of error. RESULTS: The mean preoperative manifest cylinder was 0.66 +/- 0.38 diopters (D) for conventional VISX S4 and 0.68 +/- 0.39 D for VISX CustomVue (P = .795), and 0.76 +/- 0.56 D for LADARVision and 0.61 +/- 0.36 D for LADAR CustomCornea (P = .114). The success index was 0.19 +/- 0.41 for VISX S4 and 0.49 +/- 0.49 for VISX CustomVue (P = .0013), and 0.25 +/- 0.47 for LADARVision and 0.20 +/- 0.39 for LADAR CustomCornea (P = .5721). The absolute mean angle of error was 4.4 +/- 13.9 degrees for VISX S4 versus 14.9 +/- 23.9 degrees for VISX CustomVue (P = .0085), and 6.1 +/- 12.30 for LADARVision versus 3.9 +/- 11.1 degrees for LADAR CustomCornea (P = .3501). Of the VISX CustomVue eyes, 32% had an absolute angle of error > 10 degrees, as compared to 10% for both the VISX S4 and LADAR CustomCornea eyes (P = .013), and 16% for the LADARVision group (P = .056). CONCLUSIONS: Wavefront-guided ablation is associated with higher surgically induced astigmatism and larger astigmatic axis shift on the VISX platform as compared to the LADAR CustomCornea and the LADAR and VISX conventional platforms. Care should be emphasized mainly during registration/alignment to minimize surgically induced astigmatism in wavefront-guided LASIK.

Adult↗
PubMed1976

What causes astigmatism?

Although spectacles were invented in the 13th century, methods of testing for astigmatism have been developed only within the past one hundred years. Even today, the etiological factors responsible for corneal astigmatism are not well understood. A mechanism which may account for the existence of corneal astigmatism is proposed, on the basis of data concerning changes in astigmatism with age, racial variations in astigmatism and changes in astigmatism due to the wearing of contact lenses.

Adolescent↗
PubMed2000

[Surgical correction of astigmatism after wedge resection keratoplasty].

PURPOSE: To analyse the results of astigmatism correction after keratoplasty using wedge resection technique. MATERIAL AND METHODS: Eleven patients underwent a wedge resection for postkeratoplasty astigmatism. The average postoperative astigmatism was 13.9 diopters (range 11.0 to 17.0 D). Among the patients there were 5 women and 6 men, aged 25 to 70 years. All of the grafts were in static phase, after suture removal. The indications for keratoplasty were: keratoconus--8, pseudophakic and aphakic corneal edema--3. The follow-up period after wedge resection was 6 to 24 months. The astigmatism was evaluated by videokeratometer (ORC Masterviue Ultra). RESULTS: Postoperatively, the average astigmatism was 7.25 D by 6 months, 8.1 D by 12 months, 8.45 D by 24 months. The visual acuity corrected with spectacles was 0.2 to 1.0. 8 patients (72.7%) gained better visual acuity. Complications included: 1) growing vessels through the wound, 2) delay of epithelization. CONCLUSION: Wedge resection is an effective technique for managing postkeratoplasty high astigmatism.

Adult↗
PubMed2001

[Clinical observation of astigmatism induced by corneal incision after phacoemulsification].

OBJECTIVE: To evaluate the changes of astigmatism induced by corneal incision after phacoemulsification. METHODS: Phacoemulsification was performed on 62 cases (78 eyes) without suture for a corneal incision. The changes of corneal astigmatism before and after operation in group A (incision at the superior nasal or superior temporal) and B (incision at the steepest corneal meridian) were compared. RESULTS: Three months after the operation, the surgical induced astigmatism was (0.83 plus minus 0.65) D and (0.72 plus minus 0.55) D in group A and B respectively. There was no significant difference, statistically (P > 0.05). The changes of corneal astigmatism were 0.11 D and 0.39 D in group A and B respectively, the difference being statistically significant (P < 0.05). CONCLUSION: Surgically induced astigmatism is very small after a corneal incision in phacoemulsification without a suture. If the incision is placed on the steepest meridian, the corneal astigmatism can be significantly reduced postoperatively.

Adolescent↗
PubMedDate not supplied

[Possibilities of prophylaxis of the induced "suture" astigmatism in cataract extraction].

Due to a number of reasons, the traditional methods of cataract extraction, i.e. through 8-12 mm limbic incisions, are still widely used in the clinical practice. A frequent occurrence of a high postoperative astigmatism, even if the operation is successful, is the main shortcoming of different variations of the traditional method of cataract extraction. Possibilities of how to neutralize the induced "suture-like" corneal astigmatism were investigated in this study by using two methods: A. a modified technique of applying a continuous corneal Pirs' suture with elements of an accentuated impact in the projection of the horizontal meridian. B. Meridian keratorraphia--application, in the cornea, of an additional compensatory suture in the projection of the horizontal meridian. Studies were made in two groups of patients after extracapsular cataract extraction (ECE) with intraocular lens (IOL) implantation--a total of 30 patients, 30 eyes. The main group was divided into two subgroups--A and B--(10 patients and 10 eye in each) in accordance with a used method of compensating the induced astigmatism. 10 patients were in the control group. A comparative evaluation of changes of a degree of the original astigmatism, which occurred under the influence of the sealing suture, showed that the parameters of induced astigmatism in the control group essentially and reliably (p < 0.001) exceeded the similar parameters registered in both subgroups of the main group; finally, the efficiency of method B in respect to neutralizing the "suture" astigmatism out did the possibilities of method A (p < 0.01).

Astigmatism↗
PubMedDate not supplied

Results of transverse keratotomies for astigmatism after penetrating keratoplasty: a retrospective study of 48 consecutive cases.

BACKGROUND: High astigmatism is still a common complication of penetrating keratoplasty which often limits the final corrected visual acuity. Surgical correction of high astigmatism persistent after suture removal remains rather controversial. In our present study, we used the technique of transverse keratotomies for the surgical correction of high astigmatism following penetrating keratoplasty because of its simplicity and corrective potential. METHODS: We present a retrospective clinical study based on the results of 48 consecutive transverse keratotomy procedures performed on the graft. Three eyes were operated on twice, for a total of 51 procedures. The astigmatism had to be stable for at least 6 months after suture removal, with poor corrected visual acuity with spectacles or contact lenses. The operative protocol (number of incisions, optical zone size) was decided based on the degree of astigmatism. The mean post-operative observation period was 5.11 +/- 3.93 months (range, 1 to 24 months). RESULTS: The mean preoperative cylinder was 8.96 +/- 2.22 diopters and 4.91 +/- 1.79 D postoperatively. The mean cylindrical change was 4.51 +/- 2.77 D. The spherical equivalent remained unchanged in most cases. In a majority of cases, the corrected visual acuity for distance and near vision was improved. No cases of persistent graft edema caused by immunologic rejection or endothelial failure were observed. Moreover, in no case was there worsening of the best corrected visual acuity. CONCLUSIONS: The technique of transverse incisions in the graft to correct or reduce high postkeratoplasty astigmatism is simple, efficient, and relatively safe. The main problem was poor predictability.

Adult↗
PubMed1991

Paired relaxing incisions for the control of astigmatism.

The problem of astigmatism, occurring both congenitally and in conjunction with cataract and refractive surgery, is a common and significant one. A review of patients in this study shows 18% greater than 2 diopters and 6% greater than 3 diopters of astigmatism measured by keratometry. Many methods for correcting this astigmatism have developed, including long peripheral incisions, both straight and curved, the many varieties of the Ruiz procedure, and short paired relaxing incisions. I have reviewed my results for short paired incisions following cataract surgery, congenital astigmatism, and radial keratotomy at 6 months following surgery. The average change in astigmatism was 2.69 +/- 0.78 (manifest)/2.35 +/- 1.09 (keratometry) for the 5-mm optic zone following cataract surgery. Paired relaxing incisions following radial keratotomy showed a change in astigmatism of 0.92 +/- 0.19 (manifest)/1.29 +/- 1.29 (keratometry) diopters for the 6-mm optic zone and 2.12 +/- 0.34 (manifest)/2.25 +/- 0.49 (keratometry) diopters for the 5.5-mm optic zone. No significant complications and no large overcorrections were encountered.

Adolescent↗
PubMed1990

[The effect of the incision in cataract extraction on corneal astigmatism].

Postoperative corneal astigmatism has been studied in 130 eyes after cryoextraction of senile cataract depending in the cataractous incision: perpendicular, step-shaped alone, step-shaped with additional scleral "cap peak", 5 x 3 mm. On discharge, most frequently (in 75% of cases) a direct kind of corneal astigmatism was observed. Astigmatism invariably decreased and became stable after 4--7 months, direct astigmatism became rarer (44%), but the number of eyes with reversed astigmatism increased (40%). The lowest degree of corneal astigmatism (1.8 +/- 16D) and consequently the highest surgical visual outcomes were recorded after a step-shaped incision.

Astigmatism↗
PubMedDate not supplied

Surgical correction of postoperative astigmatism.

The photokeratoscope has increased the understanding of the aspheric nature of the cornea as well as a better understanding of normal corneal topography. This has significantly affected the development of newer and more predictable models of surgical astigmatic correction. Relaxing incisions effectively flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. The net change in spherical equivalent is, therefore, negligible. Poor predictability is the major limitation of relaxing incisions. Wedge resection can correct large degrees of postkeratoplasty astigmatism, Resection of 0.10 mm of tissue results in approximately 2 diopters of astigmatic correction. Prolonged postoperative rehabilitation and induced irregular astigmatism are limitations of the procedure. Transverse incisions flatten the steeper meridian an equivalent amount as they steepen the flatter meridian. Semiradial incisions result in two times the amount of flattening in the meridian of the incision compared to the meridian 90 degrees away. Combination of transverse incisions with semiradial incisions describes the trapezoidal astigmatic keratotomy. This procedure may correct from 5.5 to 11.0 diopters dependent upon the age of the patient. The use of the surgical keratometer is helpful in assessing a proper endpoint during surgical correction of astigmatism.

Astigmatism↗