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PubMed1988

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 depending upon the age of the patient. The use of the surgical keratometer is helpful in assessing a proper endpoint during surgical correction of astigmatism.

Adrenal Cortex Hormones↗

PubMed1988

The effect of selective suture removal on astigmatism following penetrating keratoplasty.

We retrospectively evaluated selective removal of interrupted nylon sutures to reduce astigmatism following penetrating keratoplasty in 68 eyes with eight or 12 interrupted sutures and one running suture. Following removal of one to four interrupted sutures at one visit (N = 234 visits), corneal astigmatism had changed 2 to 3 diopters (range 0 to 12 D) by the next visit. The astigmatism decreased greater than or equal to 1 D in 54%, changed 0 to .87 D in 28%, and increased greater than or equal to 1 D in 18%. When a total of five or six sutures were removed during the 5 months following surgery, less than 3 D of residual astigmatism was present in 50 eyes (74%). The axis of astigmatism changed less than or equal to 40 degrees in 74% (n = 65). In a second group of 20 eyes with double running sutures, removal of the 10-0 running suture in all 20 eyes produced an average change of 1.8 D (range = 0 to 3.75 D), with an equal number of increases and decreases. Vector analysis showed the total induced change in astigmatism was approximately twice the absolute keratometric change.

Astigmatism↗

PubMed1979

Astigmatic considerations in corneal graft.

Some fictions about astigmatism should be dispelled: 1) Sutures determine astigmatism. They do not. 2) The size of the graft is contributory to astigmatism. It is not contributory. 3) Anterior or posterior cutting of the graft makes no difference. It does make a difference. 4) Same size trephine can be used to cut graft and recipient opening. Not when graft is cut from posterior surface or significant flattening will result. 5) A small cutting error is of no consequence. A small cutting error can cause a great deal of astigmatism. Tissue factors are paramount. Sutures must maintain wound apposition primarily. Posterior cutting requires a larger diameter trephine. A one-half-mm cutting error can cause an astigmatism of five diopters. Excessive corneal astigmatism, when it does occur, can be controlled by corneal wedge resection. The surgical keratometer identifies and limits surgical and suture-induced errors. Success in microsurgical keratoplasty can no longer be defined only as a clear graft. It must include also minimal or no residual optical error.

Astigmatism↗

PubMed1978

Resolution acuity in astigmats: evidence for a critical period in the human visual system.

Astigmats, who have been fully optically corrected, show an acuity configuration highly characteristic of the uncorrected astigmatism when they are tested with gratings of different orientations. This phenomenon, which is called meridional amblyopia, has been supposed to be neural in origin. This paper attempts to show that there is evidence for a critical period in the visual system of humans. In the experiment described here twelve astigmatic subjects were tested against a control group of six non-astigmatic (emmetropic) subjects. The astigmatic subjects differed in the ages at which they had been initially optically corrected. Square-wave gratings were used to test the subjects and measures of acuity for different orientations were recorded. It was found that those astigmatic subjects corrected above the age of seven showed the usual acuity decrement while those corrected below seven showed significantly smaller meridional amblyopia. The age of seven, therefore, was taken to mark the end of a critical period in the development of the human visual system, after which the system ceases to be structurally influenced by visual input.

Adult↗

PubMedDate not supplied

Treatment of myopic astigmatism with photorefractive keratectomy using an erodible mask.

The Summit Technology erodible mask treatment of astigmatism does not alter the keratometric astigmatism significantly, even though the refractive astigmatism appears to improve by about 50%. Myopia is satisfactorily treated with the erodible mask, but there is slightly more undercorrection compared to photorefractive keratectomy (PRK) using an expanding diaphragm. Increasing the minus power in ordering the mask cylinder improves the myopia result, but not the keratometric astigmatism result. The following factors do not influence the keratometric astigmatism result: 1) The type of astigmatism (with-, against-the-rule, or oblique); 2) The initial keratometry readings; and 3) The time from the commencement of epithelial removal to laser treatment.

Astigmatism↗

PubMed1995

[A comparison analysis on methods of astigmatism examinations for children].

70 children 140 eyes with astigmatic refractive error were reported. The methods of examination included retinoscopy, autorefraction and keratometry. The data of eye astigmatism and keratic astigmatism measured by the methods were analyzed. It revealed that there existed a good identity among the three methods, and the relationship between eye astigmatism (EAs) and keratic astigmatism (KAs) shown by the formula EAs = 0.94 KAs - 0.13 was similar to that of previous reports. It is suggested that the keratometry be necessary as an assistant method of refraction to assure to get a reliable astigmatism result for children.

Adolescent↗

PubMed1994

A comparison of two semi-quantitative surgical keratometers: the modified Hyde ruler and the Barrett keratoscope with "astigmatic dial".

The Hyde astigmatic ruler is an inexpensive, semiquantitative, hand-held, surgical keratometer that we modified by geometrically calculating the correct shape of its ellipses. The Barrett keratoscope is a cheap, disposable, qualitative keratometer that, unlike the Hyde ruler, produces a bright corneal image. We designed a transparent overlay, or "astigmatic dial," to use with the keratoscope. This overlay determines the magnitude of astigmatism and sets the distance the keratoscope is held from the cornea by direct comparison with the corneal image. Using a model cornea, we compared our modified Hyde ruler with the Barrett keratoscope and astigmatic dial to determine the accuracy of measurement provided by each. Both instruments had good predictive values for the true astigmatism; however, the Barrett keratoscope/astigmatic dial provided more consistent measurements of the astigmatism. We believe the keratoscope and dial provide a cheap, convenient, and accurate alternative to the more expensive microscope-mounted keratometers.

Astigmatism↗

PubMed1994

Clinical utility of the Barrett keratoscope with astigmatic dial.

Intraoperative keratometry allows some degree of control over corneal astigmatism during cataract surgery. I describe the clinical use of the Barrett keratoscope combined with an astigmatic dial that quantifies the information obtained by this simple, inexpensive, hand-held surgical keratometer. Based on a comparison of intraoperative measurements with those taken after extracapsular cataract surgery with an automated keratometer, I conclude that intraoperative keratometry reliably predicted the postoperative astigmatism. For those who had the intraocular pressure (IOP) set between 15 and 20 mm Hg intraoperatively, the mean deviation of the first postoperative measurement from the intraoperative measurement of astigmatism was +/- 1.03 D (standard error, 1.56 diopters; 95% confidence interval 0.712 to 1.35 D). When the IOP was not set, the postoperative astigmatism differed from the intraoperative reading by more than 2.00 D for 50% of the cases. Setting the IOP prior to intraoperative keratometry significantly improved the reliability of the measurement. Intraoperative keratometry by the simple device used in this study is of sufficient utility to allow the surgeon to adjust for the predicted changes in the corneal astigmatism at the time of surgery.

Astigmatism↗

PubMed1993

Postoperative astigmatism following phacoemulsification with sutured vs. unsutured wounds.

A total of 293 cases of phacoemulsification cataract surgery with a 5.0- or 6.0-mm frown incision were analysed retrospectively to compare postoperative astigmatism between cases with sutured wounds and those with unsutured wounds. Astigmatic analysis was done with a simplified method (keratometric readings with steep meridians between 46 degrees and 134 degrees were considered "with-the-rule" [WTR], and those with steep meridians less than 46 degrees and greater than 134 degrees, "against-the-rule" [ATR]). Among patients with WTR astigmatism preoperatively, the mean keratometric cylinder in the sutureless group (n = 53) was significantly lower at 1 day and at 4 to 6 months postoperatively than before surgery (p < or = 0.001); in the suture group (n = 120) the mean cylinder was significantly higher at 1 day and significantly lower at 4 to 6 months than before surgery (p < 0.05). Among patients with ATR astigmatism preoperatively, the mean keratometric cylinder in the sutureless group (n = 22) was significantly higher at 1 day than before surgery (p < 0.01); in the suture group (n = 98) the mean cylinder was significantly lower at 1 day than before surgery (p < 0.001), and the difference at 4 to 6 months almost reached statistical significance (p = 0.052). Vector analysis showed that surgically induced cylinders in the suture and sutureless groups were similar. Our findings suggest that in the short term patients with preoperative WTR astigmatism may benefit from unsutured wounds, and those with preoperative ATR astigmatism may benefit from sutured wounds if the incision is placed in the vertical meridian.

Astigmatism↗

PubMed1993

Limbus-parallel keratotomies and compression sutures in excessive astigmatism after penetrating keratoplasty.

From 1986 to 1991, among 980 penetrating keratoplasties, all 22 patients were studied retrospectively who had undergone 28 refractive procedures because of high corneal astigmatism after penetrating keratoplasty. In 8 procedures, only relaxing incisions were made, and in 20 procedures, additional compression sutures were placed at 90 degrees to the former. In 7 cases the relaxing incisions were located on the patient's peripheral cornea and in 21 cases, inside the graft margin. The absolute preoperative corneal astigmatism was 7.25-20.0 D (mean, 11.5 +/- 3.1 D). Immediately after surgery it was 0-14.0 D (mean, 7.0 +/- 3.6 D). The vector-corrected astigmatism immediately after surgery was 1.0-28.9 D (mean, 13.2 +/- 7.8 D). After a mean follow-up of 20.6 months, the mean residual astigmatism was 1.0 +/- 11.25 D (mean, 5.4-2.5 D). The mean postoperative vector-corrected astigmatism was 0-19.3 D (mean, 9.1 +/- 4.6 D). The best-corrected preoperative visual acuity was 0.12-0.9 (mean, 0.4), the best postoperative visual acuity was 0.3-1.2 (mean, 0.6). The approach described may reduce disturbing postkeratoplasty astigmatism--although the predictability remains unsatisfactory.

Adolescent↗

PubMed1996

[Results of photorefractive keratectomy for myopic astigmatism].

In 54 patients, 92 eyes with different degrees of compound, myopic astigmatism underwent photorefractive keratectomy with the VISX 20/20 excimer laser. The eyes were grouped by degree of refractive astigmatism into: high (-2.75 to -5.0 diopters), moderate (-1.25 to -2.50 diopters), and low (< -1.0 diopter) astigmatism. At 6 months after the procedure the mean reduction from the preoperative refractive cylinder was 80.7% in the high, 68.4% in the moderate, and 47.6% in the low astigmatism group. 89.2% of the eyes with low, 81.8% with moderate, and 85% with high cylinders had achieved a final, uncorrected visual acuity of between 6/6 and 6/10. The VISX laser is an effective tool for the correction of high and moderate astigmatism, but is less effective for low astigmatism.

Adult↗

PubMed1997

Excimer laser correction of astigmatism using erodible masks.

PURPOSE: The latest development in the erodible mask technology is an excimer laser containing the mask in the laser optical pathway. This paper reports the results of the first human series of consecutive treatments performed for the correction of compound myopic astigmatism. METHODS: We have treated 83 eyes. Spherical equivalent attempted correction ranged between -1.75 and -11.75 D (mean -7.07 +/- 2.45 D), astigmatic attempted correction ranged between -1.00 and -5.00 D (mean -2.42 +/- 1.02 D). The sphere correction was made by diaphragm using a multi-zone software with three ablation zones: 100% of the total attempted correction for the central 5.0 mm zone, 70% for the second 6.0 mm zone, 30% for the outer 6.5 mm zone. Cylinder correction was made sequentially after myopic correction using the appropriate mask. RESULTS: One month after treatment, mean refractive error was +1.07 +/- 1.24 D (range +4.50/-1.75 D) for spherical equivalent, and -0.49 +/- 0.57 D (range +0.75/-2.00 D) for astigmatism. Forty-eight eyes (57.8%) had uncorrected visual acuity of 20/40 or better. At six months, mean refractive error was +0.42 +/- 0.97 D (range +3.75/-1.00 D) for spherical equivalent, and -0.44 +/- 0.51 D (range +0.25/-3.00 D) for astigmatism. Vector analysis showed that 57 eyes (68.7%) had 5 or less degrees rotation. Seventy-two (86.7%) and 54 eyes (65.1%) had uncorrected visual acuity equal or better than 20.40 and 20/25 respectively. One eye (1.2%) showed a best corrected visual acuity loss of more than one line, but 8 eyes (9.6%) had a gain of more than one line. One-year results on a smaller series (33 eyes) overlap the six-month results. CONCLUSIONS: The mask in-the-rail excimer laser delivery system appears to be effective and predictable in the correction of compound myopic astigmatism. We observed no significant regression of the astigmatic correction over time. Longer follow-up on larger series is necessary to draw final conclusions.

Adolescent↗

PubMed1996

[Corneal astigmatism following trabeculectomy].

OBJECTIVE: The study was designed to investigate the change of corneal astigmatism following trabeculectomy. METHODS: Before and after the operation at different periods, the corneal astigmatism of 42 eyes was evaluated by Topcon-OM-3 keratometer. RESULTS: Almost the corneal astigmatism of all the cases was with-the-rule in the early stage after trabeculectomy. Among them, the astigmatism in 41.03% of cases was more than 2.00D, 3 months post-operatively 17.50% shifted towards against-the-rule, and 9.50% remained more than 2.00D which was induced by the surgery. CONCLUSION: Trabeculectomy may cause certain with-the-rule corneal astigmatism. The corneal astigmatism in most of the cases may decrease as time passes by.

Adolescent↗

PubMed1999

Long-term results of single continuous suture adjustment to reduce penetrating keratoplasty astigmatism.

PURPOSE: To evaluate the long-term effect of single continuous corneal suture adjustment on reducing penetrating keratoplasty astigmatism after suture removal. METHODS: Patients were identified from the original study of single continuous penetrating keratoplasty suture adjustment to reduce corneal astigmatism who were followed for more than a year after suture removal. A matching unadjusted control group was selected in the same way from those patients in the original study undergoing penetrating keratoplasty during the 2 years before the development of suture adjustment. The corneal astigmatism was compared before adjustment (study group) or <3 months after surgery (control group), >4 months after suture adjustment, and >12 months after suture removal in both groups. RESULTS: A study group of 54 patients with suture adjustment and a control group of 45 patients without suture adjustment were identified. Before suture adjustment, the study group had an average keratometric astigmatism of 6.44 diopters (standard deviation [SD] = 2.51, range = 0.38-12.25), and the control group had 6.38 diopters (SD = 3.29, range = 2.75-16.00, p = 0.536). Compared to that in the unadjusted control group, the average penetrating keratoplasty astigmatism in the suture-adjusted group was reduced by 44.6% (2.36 diopters) 4.5 months after surgery and before suture removal (p = 0.0002) and by 25.4% (1.19 diopters) at least 12 months after suture removal (p = 0.011). CONCLUSION: Postoperative adjustment of a single continuous corneal suture significantly reduces penetrating keratoplasty astigmatism after suture removal.

Adolescent↗

PubMed1997

[The correction of myopic astigmatism by refractive keratotomy].

PURPOSE: To determine the efficacy and the predictability of refractive keratotomy in the myopic astigmatism. METHOD: 15 patients (23 eyes) who had been operated on with myopic astigmatism; 4 eyes with simple astigmatism and 19 eyes with compound astigmatism, 1 patient had myopia at one eye and myopic astigmatism at the other. It were performed tangential incisions ("T"), curved incisions ("C") and simple Ruiz with or without radial incisions. The patients were reviewed after 3.6 and 12 month from the operation. RESULTS: Better visual acuity with no correction. The only postoperative complication was under correction. CONCLUSIONS: Refractive keratotomy is recommended in myopic astigmatism and especially with anisometropia.

Adult↗

PubMed1986

Trapezoidal astigmatic keratotomy. Quantification in human cadaver eyes.

The mechanism by which surgical procedures correct astigmatism are incompletely understood and, therefore, the results are often unpredictable. In this study, a Terry keratometer was used to analyze the effect of each component part of a 3-, 4-, and 5-mm trapezoidal astigmatic keratotomy. Semiradial incisions along the horizontal meridian produced corneal flattening along the horizontal meridian twice that of the vertical meridian, therefore inducing positive cylinder astigmatism at 90 degrees. A single pair of tangential incisions placed 5 mm apart, when added to the semiradial incisions, accounted for 100%, 87%, and 78% of the maximal effect from the 3-, 4-, and 5-mm completed trapezoidal astigmatic keratotomies, respectively. This study suggests that maximal correction of astigmatism may be attained with a single set of tangential incisions placed 5 mm apart between two sets of semiradial incisions.

Astigmatism↗

PubMed1991

Photorefractive keratectomy for astigmatism. Initial clinical results.

Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to perform toric ablations designed to correct cylindrical errors. An expanding slit was used to flatten the cornea in the steep meridian. Four contact lens-intolerant patients underwent this procedure for correction of astigmatism (two patients after penetrating keratoplasty, one patient after corneal ulcer, and one patient with naturally occurring high astigmatism). In each patient, surgery reduced the regular component of the astigmatism; residual irregular astigmatism limited spectacle-corrected acuity in one patient. All patients experienced a shift in spherical equivalent toward hyperopia. Toric ablations with the excimer laser appear to represent a promising strategy for the correction of compound myopic astigmatism that does not rely on creation of deep corneal incisions, excisions, or compression sutures.

Astigmatism↗

PubMed1992

Comparison between postoperative astigmatism after classic extracapsular lens extraction and after phacoemulsification with implantation of a Pearce tripod or Pearce vaulted Y-loop intraocular lens.

We compared the surgically induced astigmatism after standard extracapsular cataract extraction (ECCE) with the astigmatism following cataract extraction by phacoemulsification. The surgically induced corneal astigmatism was assessed on several occasions, ranging from one day to one year postoperatively. After phacoemulsification, this astigmatism was considerably slighter than after ECCE on day 1 postoperatively and after two and six weeks. However, one year postoperatively, this difference was less clear. We then measured slight against-the-rule astigmatism for both surgical techniques.

Astigmatism↗