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PubMed1992

Photorefractive keratectomy for severe postkeratoplasty astigmatism.

We performed cylindric corneal ablations with the excimer laser on 12 patients to correct severe, disabling astigmatism after keratoplasty. In some patients, an additional ablation was performed to correct myopia. Patients were followed up for an average of eight months (range, six to 14 months). Uncorrected visual acuity improved in nine patients, and nine of the 12 patients had a decrease in refractive cylinder at last follow-up. The mean preoperative refractive cylinder was 7.0 +/- 3.6 diopters, which decreased to a mean of 3.1 +/- 2.6 diopters at one month (P = .0003) and 4.3 +/- 2.9 diopters at last follow-up (P = .03). Keratometric astigmatism decreased from 7.5 +/- 3.9 diopters preoperatively to 5.2 +/- 3.9 diopters at the last follow-up (P = .001). Mean spherical equivalent was reduced from -7.4 +/- 4.2 diopters preoperatively to -3.3 +/- 4.4 diopters postoperatively (P = .003). Postoperative corneal haze, when present, did not reduce visual acuity. Excimer laser superficial keratectomy thus appears to be safe when used for postkeratoplasty ametropia, although substantial regression may limit its effectiveness in some patients.

Adult↗
PubMed1991

Developing entry criteria for studies of severe postkeratoplasty astigmatism.

Investigators who use keratometry or topography systems to plan operations for the correction of severe postkeratoplasty astigmatism assume the study group is homogeneous. To test this hypothesis, we established four entry criteria we believed were necessary to ensure a homogeneous group. The criteria were as follows: (1) best-corrected or pinhole visual acuity greater than or equal to 20/40; (2) graft well centered relative to the corneal light reflex; (3) corneal light reflex within 0.5 mm of the center of the entrance pupil; and (4) a minimum of ten central keratoscope rings of the Corneal Modeling System accurately digitized. A retrospective analysis of the keratoscope images of 20 consecutive patients (20 eyes) referred for correction of postkeratoplasty astigmatism was performed to determine the percentage of patients who met the proposed criteria. Only seven (35%) simultaneously met all four entry criteria. Investigators interested in comparing techniques to correct this problem are faced with a dilemma. Strict entry criteria will ensure a homogeneous study group but will exclude most patients. More lenient entry criteria will increase the number of eligible subjects but will introduce heterogeneity, which may confound results.

Astigmatism↗
PubMed1998

Experimental correction of irregular corneal astigmatism using topography-based flying-spot-mode excimer laser photoablation.

PURPOSE: To present a novel experimental approach for treating irregular corneal astigmatism. METHODS: After decomposition of topographic analysis data into orthogonal Zernike polynomials, a regular target surface was defined, and the ablation profile was calculated. In a polymethylmethacrylate with an irregular surface, computer-controlled ablation was performed using a 193-nm excimer laser in "flying-spot mode." RESULTS: The difference between flattest and steepest hemimeridians in the 3-mm zone, surface regularity index, and surface asymmetry index were reduced from 8.7 to 1.1 diopters, 1.19 to 0.39, and 1.84 to 0.14, respectively. CONCLUSION: Tying corneal topography into laser software offers a straightforward concept for correction of irregular corneal astigmatism in an experimental model.

Astigmatism↗
PubMed2004

Myopia and astigmatism in retinopathy of prematurity after treatment with cryotherapy or laser photocoagulation.

BACKGROUND: Visual outcome studies have shown that laser photocoagulation may result in more favourable clinical outcomes than cryotherapy in threshold retinopathy of prematurity (ROP). Comparative refractive outcome studies have shown that patients treated with laser photocoagulation have less myopia than those treated with cryotherapy. We carried out a study to determine whether a difference in visual outcome or refraction exists in patients with threshold ROP who have been treated with cryotherapy vs. laser photocoagulation. METHODS: A retrospective cohort study was conducted comparing treatment results after at least 3 years of follow-up in patients with threshold ROP treated with cryotherapy or laser photocoagulation at a tertiary care children's hospital. Visual acuity and refraction were the outcomes studied. Covariates measured were sex, gestational age and birth weight. Analysis was performed with both bivariate analysis and multivariate models. RESULTS: Seventy-one eyes of 37 patients with threshold ROP were included in the study. Thirty-seven eyes received cryotherapy, and 34 eyes received laser photocoagulation. The mean spherical equivalent refraction was significantly lower in the cryotherapy group than in the laser photocoagulation group (-9.21 dioptres vs. -1.80 dioptres, p = 0.001). Patients in the cryotherapy group were more likely than those in the laser photocoagulation group to have against-the-rule astigmatism (odds ratio 6.86, p = 0.004). Laser photocoagulation did not significantly lower the frequency of an unfavourable visual outcome (visual acuity worse than 20/200) (p = 0.09). INTERPRETATION: Eyes with threshold ROP treated with laser photocoagulation were significantly less myopic and less likely to have against-the-rule astigmatism than those treated with cryotherapy.

Astigmatism↗
PubMed1985

Corneal astigmatism induced by oversized rigid anterior chamber implants.

Postoperative corneal astigmatism induced by implantation of an oversized rigid anterior chamber intraocular lens has been studied. Sources of error leading to the choice of an oversized lens as well as the mechanism by which an oversized lens induces corneal astigmatism are discussed.

Anterior Chamber↗
PubMed2000

Toric intraocular lenses for correcting astigmatism in 130 eyes.

OBJECTIVE: This study evaluated the results after implantation of toric intraocular lenses (IOLs) to correct preexisting corneal astigmatism in patients undergoing either cataract or clear lens extraction surgery. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: One hundred thirty eyes of 99 patients who underwent phacoemulsification and posterior chamber toric IOL implantation from January 1997 through February 1998 were included in the study. INTERVENTION: Implantation of a toric IOL was performed after cataract surgery (122 eyes) or clear lens extraction surgery (eight eyes). Both preoperative corneal cylinder and refractive cylinder powers were more than 1.50 diopters (D) for all the eyes included in this study. To provide a comparison, we also studied 51 eyes of 45 patients meeting the same preoperative criteria for degree of corneal and refractive cylinder who underwent implantation of a spherical (nontoric) IOL combined with limbal relaxing incisions. The data for both study and comparison groups were analyzed retrospectively. The selection for the two groups was arbitrary. MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA), mean spherical equivalent, residual refractive cylinder, and toric IOL axis. RESULTS: In the toric IOL group, 84% of eyes achieved 20/40 or better UCVA. In the spherical IOL group, 76% achieved 20/40 or better UCVA. The mean postoperative refractive cylinder was -1.03 +/- 0.79 D in the toric IOL group and -1.49 +/- 0.75 D in the spherical IOL group. CONCLUSIONS: Our results indicate that phacoemulsification and posterior chamber toric IOL implantation is a largely predictable new surgical option to correct preexisting corneal astigmatism in cataract or clear lens extraction surgery.

Adult↗
PubMed2002

Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy: a report by the American Academy of Ophthalmology.

OBJECTIVE: This document describes laser in situ keratomileusis (LASIK) for myopia and astigmatism and examines the evidence to answer key questions about the efficacy and safety of the procedure. METHODS: A literature search conducted for the years 1968 to 2000 retrieved 486 citations and an update search conducted in June 2001 yielded an additional 243 articles. The panel members reviewed 160 of these articles and selected 47 for the panel methodologist to review and rate according to the strength of evidence. A Level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a Level II rating is assigned to well-designed cohort and case-control studies; and a Level III rating is assigned to case series and poorly designed prospective and retrospective studies, including case-control studies. RESULTS: The assessment describes randomized controlled trials published in 1997 or later (Level I evidence) and more recent comparative and noncomparative case series (Level II and Level III evidence), focusing on results for safety and effectiveness. It is difficult to extrapolate results from these studies that are comparable to current practices with the most recent generation lasers because of the rapid evolution of LASIK technology and techniques. It is also difficult to compare studies because of variations in the range of preoperative myopia, follow-up periods, lasers, nomograms, microkeratomes and techniques, the time frame of the study, and the investigators' experience. CONCLUSIONS: For low to moderate myopia, results from studies in the literature have shown that LASIK is effective and predictable in terms of obtaining very good to excellent uncorrected visual acuity and that it is safe in terms of minimal loss of visual acuity. For moderate to high myopia (>6.0 D), the results are more variable, given the wide range of preoperative myopia. The results are similar for treated eyes with mild to moderate degrees of astigmatism (<2.0 D). Serious adverse complications leading to significant permanent visual loss such as infections and corneal ectasia probably occur rarely in LASIK procedures; however, side effects such as dry eyes, night time starbursts, and reduced contrast sensitivity occur relatively frequently. There were insufficient data in prospective, comparative trials to describe the relative advantages and disadvantages of different lasers or nomograms.

Academies and Institutes↗
PubMed1978

Surgical correction of astigmatism by microwedge resection of the limbus.

This paper presents a preliminary report on an approach to the surgical correction of corneal astigmatism, ie, the microwedge resection of the cornea, analyzes the quantitative aspects of the surgical treatment, and describes the Jensen double-bladed microsurgical knife designed for making calibrated-uniform microsurgical wedge resections of the cornea. This technique makes correction of even small increments of corneal astigmatism possible.

Astigmatism↗
PubMed1981

Disparate diameter grafting. Astigmatism, intraocular pressure, and visual acuity.

We studied 180 consecutive corneal transplants performed by one surgeon to determine the benefit obtained by using a 0.5 mm oversize (OS) graft. We compared 61 same size (SS) grafts to 119 oversize (OS) grafts, with a mean follow-up time of 24 and 13 months respectively. While the refractive error, recovery of visual acuity, and intraocular pressure were similar in both groups, the astigmatism was found to be significantly elevated in the (OS) group. Using a 0.5 mm oversize graft did not afford any protection against postkeratoplasty glaucoma, did not increase the speed of recovery of the patients' visual acuity, but produced significantly more astigmatism than a same size graft.

Adult↗
PubMed1987

Wound healing after astigmatic keratotomy in human eyes.

The authors analyzed three full-thickness corneal buttons and two corneal scleral rims obtained 5 1/2 to 44 months after three trapezoidal keratotomies (Ruiz), one "L," and one "TL" procedure. The indications for the penetrating keratoplasty were photophobia, corneal edema, and loss of best-corrected vision after the astigmatic keratotomy procedures. Epithelial plugs were seen in all five specimens. Complete basal lamina lined the wounds in two cases. Tangential incisions of the Ruiz procedure were shallower and demonstrated more advanced wound healing than the corresponding semiradial incisions. Two of the three Ruiz procedures demonstrated peripheral separation of the semiradial incisions. Wound healing events after astigmatic keratotomy procedures appear similar to those reported previously after standard radial keratotomy with the exception that tangential incisions appear to heal faster than the semiradial incisions.

Adult↗
PubMed1990

Low myopia with low astigmatic correction gives cataract surgery patients good depth of focus.

Multifocal intraocular lenses (IOLs) are being developed to improve the depth of focus of pseudophakic patients. However, the authors noted good uncorrected distance and near acuity in 32 pseudophakic patients with post-operative refraction of myopic astigmatism and round reactive pupils where a plano convex monofocal posterior chamber IOL was used. They suggest that for appropriate clinical assessment of the effectiveness and safety of multifocal IOLs, a randomized, controlled, double-masked clinical trial be undertaken to compare monofocal with multifocal IOLs. In such a trial, they suggest aiming for myopic astigmatism in the monofocal IOL group.

Astigmatism↗
PubMed1993

Results of radial and astigmatic keratotomy by beginning refractive surgeons.

BACKGROUND: There is little information available on the results of radial and astigmatic keratotomy surgery that is performed by beginning refractive surgeons. METHODS: A retrospective review of all refractive keratotomies performed by Corneal Fellows in the University of California, Los Angeles, Department of Ophthalmology between October 1985 and October 1991 was performed. Data from all eyes with at least 3 months of follow-up were analyzed. Visual acuity, refractive error, and complication rates were compared with published case series. RESULTS: The mean preoperative spherical equivalent for the 79 eyes analyzed was -3.97 diopters (D) (range, -0.75 to -8.50 D). The mean postoperative spherical equivalent was -0.44 D (range, +1.50 to -3.88 D). The postoperative spherical equivalent was within 1.00 D of emmetropia in 85% of eyes, and uncorrected visual acuity was 20/40 or better in 94% of eyes. There were no vision-threatening complications. No patient lost more than one line of best-corrected visual acuity. CONCLUSION: Radial and astigmatic keratotomies that are performed by beginning refractive surgeons in a supervised setting can be safe and effective procedures with results comparable with those obtained by experienced refractive surgeons.

Adult↗
PubMed1994

Correction of irregular astigmatism with the excimer laser.

BACKGROUND: Correction of irregular astigmatism has not been possible using available keratorefractive technology. METHODS: The authors used a topographic map as a guide and created a custom excimer ablation program, designed to create a more regular surface. The program consisted of a combination of phototherapeutic and photorefractive ablation patterns. The amount of tissue to be removed was calculated on the basis of the diameter and steepness of the irregular areas of the corneal surface. RESULTS: A more regular surface, as evidenced by topographic analysis, reduced astigmatism, and improved uncorrected visual acuity, was produced. CONCLUSION: Using the corneal topographical map as a guide, excimer laser ablation can be used to create a more regular optical surface with improved visual function.

Adult↗
PubMed1994

A piggyback contact lens for the correction of irregular astigmatism in keratoconus.

PURPOSE: Although the combination of a hard contact lens "piggybacked" on a soft lens base for the correction of severe astigmatism in keratoconus has existed for two decades, little is known about its effect on the corneal epithelium and endothelium. This study involves two parts: the measure of oxygen pressure in rabbits, and the long-term effects on patients with keratoconus wearing these hybrid lenses. METHODS: A polarographic sensor was used to measure the oxygen pressure on rabbit corneas under two types of piggyback lenses: oxygen-permeable hard lenses on high water-content soft lenses, and polymethylmethacrylate (PMMA) lenses on low water-content soft lenses. In the clinical evaluation, 11 patients with keratoconus (8 men, 3 women; 25.1 +/- 4.9 years of age) who could not wear hard contact lenses due to constant pain or inadequate lens fitting were given oxygen-permeable piggyback contact lenses and were observed for at least 9 months. RESULTS: In the animal study, the oxygen pressure under piggybacked oxygen-permeable hard contact lenses was 95 +/- 14 mmHg after 5 minutes wear, but it was only 34 +/- 14 mmHg when PMMA and low water-content lenses were used. Ten of 11 patients were successfully treated using this technique, whereas one patient had persistent contact lens loss, requiring penetrating keratoplasty. Specular microscopic observation of the corneal epithelium and endothelium did not show any changes during the follow-up period. CONCLUSIONS: These results suggest the efficacy and safety of the piggyback combination of oxygen-permeable hard and soft contact lenses for the correction of astigmatism in patients with keratoconus.

Adolescent↗
PubMed1997

Resolution of astigmatism after surgical resection of capillary hemangiomas in infants.

OBJECTIVE: The goal of the study was to assess the affect of early surgical resection of capillary hemangiomas on the induced astigmatism of infants. DESIGN: Cohort study. PARTICIPANTS: Three infants younger than 9 months of age are included. INTERVENTION: Total resection of the astigmatism-inducing hemangiomas was performed. MAIN OUTCOME MEASURES: Refractive change in the eye operated on was measured and the cosmetic results were observed. RESULTS: Preoperative and postoperative cylinder reduction in the three patients were 8 diopters (D) to 0 D, 3 D to 0 D, and 4.5 D to 1 D, respectively. All patients had excellent cosmetic results, and there were no postoperative complications. CONCLUSIONS: Surgical resection of adnexal hemangiomas in carefully selected infants can lead to excellent cosmetic results. If the mass-induced pressure on the infant sclera is relieved at a young enough age, anisometropia and resultant amblyopia can be eliminated.

Astigmatism↗
PubMed2000

Optical coherence tomography evaluation of the corneal cap and stromal bed features after laser in situ keratomileusis for high myopia and astigmatism.

OBJECTIVE: To study the corneal microstructure by optical coherence tomography (OCT) after laser in situ keratomileusis (LASIK) for high myopia with and without astigmatism. DESIGN: Nonrandomized self-controlled comparative trial. PARTICIPANTS: Sixty-three consecutive LASIK eyes with spherical equivalent refraction between -6.0 and -17.0 diopters (D) and astigmatism between 0.0 and -5.0 D were prospectively recruited for examination. INTERVENTION: LASIK was performed with the Chiron Hansatome microkeratome (160-microm fixed plate) and Summit Apex Plus excimer laser using a 5.5/6.0/6.5-mm multizone pattern. Proper preoperative calculations were performed to ensure stromal beds thicker than 250 microm. MAIN OUTCOME MEASURES: OCT imaging and measurement of corneal thickness was performed preoperatively. In addition, corneal cap and stromal bed thickness measurements were performed 1 day, 1 month, and 3 months postoperatively. RESULTS: The average central corneal pachymetry was 538.9 +/- 26.2 microm preoperatively. Mean corneal cap thickness measured 124.8 +/- 18.5 microm 1-day postoperatively. Mean stromal bed thickness was 295.2 +/- 37.1 microm on the first postoperative day. Compared with the 1-day postoperative examination, the average stromal bed thickness increased significantly by 5.9 microm (P = 0.001) and 7.2 microm (P = 0.001) at the 1-month and 3-month postoperative examinations, respectively. Mean difference between actual (118.7 +/- 27.8 microm) and predicted (104.1 +/- 20.8 microm) central ablation depths was 14.6 +/- 16.7 microm (P = 0.0001). A weak but statistically significant positive association was found between preoperative refraction and the difference between expected and real ablation depth values (R = 0.26; P = 0.042). Posterior stromal beds were more than 250-microm thick in 58 eyes (89.9%) 1 day postoperatively. This safety requirement improved at the 1-month postoperative examination, when the partial regression accounted for slightly thicker stromal beds and only two cases (3.2%) exhibited posterior stromal tissue thinner than 250 microm. These two cases were seen only for corrections exceeding 12 D (P = 0.04). CONCLUSIONS: OCT appears to be a useful tool for the evaluation of both the qualitative and quantitative anatomic outcome of LASIK. Corrections of higher degrees of ametropia run a higher risk of producing a thinner than expected central cornea. Particularly, corrections greater than 12 D may lead eventually to stromal beds thinner than 250 microm, despite proper preoperative calculations. Because corneal flaps are usually thinner than expected with the microkeratome used herein, adequate posterior corneal stroma is preserved in most instances.

Adolescent↗
PubMed2000

Early clinical experience using custom excimer laser ablations to treat irregular astigmatism.

PURPOSE: To assess the viability of custom excimer laser ablations for treating irregular astigmatism. SETTING: Single-center prospective study of a new custom-ablation technique. METHODS: Twelve patients received 15 custom ablations for irregular astigmatism resulting from keratoconus, penetrating keratoplasty for keratoconus, prior decentered laser in situ keratomileusis, or incisional refractive surgery. Follow-up ranged from 6 weeks to 14 months. Initially, the laser beam was manually decentered; later, the Contoured Ablation Patterns (CAP) method (VISX, Inc.) was used to automatically decenter the ablation over the corneal elevation. RESULTS: Results are presented in a case-by-case fashion. In the manual decentration group, the uncorrected visual acuity (UCVA) was 20/50 or better in 9 of 11 eyes (81.8%) and 20/40 or better in 7 eyes (63.6%). Surgery resolved or decreased visual symptoms when present. The best corrected visual acuity (BCVA) was maintained or improved in all eyes. Persistent </=grade 1 haze developed in the 2 patients (n = 3 eyes) treated for keratoconus. In the CAP group, the UCVA was between 20/40 and 20/80; the BCVA improved in 3 of 4 eyes (75.0%) and declined from 20/20 to 20/25 at 3 months in the remaining eye due to haze. The ablation produced some spherical flattening in both groups, resulting in induced hyperopia that was generally clinically insignificant. CONCLUSION: Early results of this experimental custom-ablation technique are promising.

Adult↗
PubMed2000

Tear secretion following spherical and astigmatic excimer laser photorefractive keratectomy.

PURPOSE: To evaluate the effect of spherical and astigmatic excimer laser photorefractive keratectomy (PRK and PARK, respectively) on tear secretion. SETTING: The Vlemma Eye Center, Athens, Greece. METHODS: Forty-eight eyes of 48 patients had PRK (28 eyes) or PARK (20 eyes) for the correction of myopia and combined myopic astigmatism. The fellow eye served as a control. The mean preoperative spherical equivalent was -3.96 diopters (D) +/- 1.00 (SD) in the PRK eyes (range -2.00 to -6.50 D) and -3.45 +/- 0.50 D in the PARK eyes (range -1.75 to -6.00 D). Attempted correction aimed at emmetropia. Schirmer I and II and tear film breakup time (BUT) tests were performed preoperatively and 1, 3, and 6 months postoperatively. All tests were correlated to the amount of attempted correction. RESULTS: In the PRK group, the preoperative mean values were Schirmer I, 16.20 mm; Schirmer II, 12.73 mm; and BUT, 16.46 sec. At 1 month, they were 12.23 mm, 8.46 mm, and 13.33 sec, respectively; at 3 months, 13.86 mm, 10.64 mm, and 14.42 sec, respectively; at 6 months, 14.32 mm, 11.32 mm, and 15.36 sec, respectively. In the PARK group, the mean Schirmer I, II, and BUT values were preoperatively 18.52 mm, 14.86 mm, and 17.42 sec, respectively; at 1 month, 14.5 mm, 10.4 mm, and 14.36 sec, respectively; at 3 months, 15.36 mm, 11.81 mm, and 14.72 sec, respectively; and at 6 months, 16.5 mm, 12.15 mm, 16.5 sec, respectively. No correlation to the amount of attempted correction was found. Fellow-eye tests were not affected at any interval. CONCLUSIONS: In the first 6 months after PRK and PARK, tear secretion test values decreased.

Adult↗