Search

Objectives: To evaluate corneal irregular astigmatism due to the anterior corneal surface using Fourier harmonic analysis with a Placido ring-based corneal topographer (Placido-based topographer) and three-dimensional anterior segment optical coherence tomography (OCT) in dry eyes., Methods: Forty-four eyes of 44 subjects with dry eye and 20 eyes of 20 normal control subjects were enrolled. Corneal topographic data were obtained using a Placido-based topographer and OCT. Dioptric data from the central 3-mm zone of the anterior corneal surface were decomposed using Fourier harmonic analysis. Spherical, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity) refractive error components of the cornea from the two imaging modalities were compared., Results: Both asymmetry and higher-order irregularity values were significantly greater in dry eyes than in control eyes for both the Placido-based topographer and OCT measurements (all P<0.05). In dry eyes, measured values of asymmetry and higher-order irregularities were significantly smaller when obtained with OCT than with the Placido-based topographer (both P<0.001). By contrast, these parameters were not significantly different between the two devices in control eyes. In dry eyes, severity of superficial punctate keratopathy in the central corneal region was correlated with irregular astigmatism., Conclusions: The amount of corneal irregular astigmatism, quantified using Fourier harmonic analysis, was significantly higher in dry eyes than in normal eyes. Measurements obtained with OCT and the Placido-based topographer differed in subjects with dry eyes. Therefore, caution should be practiced when trying to use these measurements interchangeably.

Background: The nonsuperimposable mirror-image symmetry of the body (enantiomorphism) is reflected in the wavefront error maps of eyes. Averaging the wavefront errors of right and left eyes has the potential to adversely affect correlations made between wavefront error and visual acuity or other factors. Not only are the results of past studies using Zernike terms suspected of being invalid, there is concern about possible errors in the algorithms used to create customized corneal ablations., Objective: To compare the results of analysis with and without correction for enantiomorphism., Methods: Fourteen TMS-1 corneal topographic maps from 7 patients having with-the-rule astigmatism in both corneas were selected for Zernike decomposition to 45 terms. The maps were distributed among 3 groups: 7 right eye maps, 7 left eye maps, and 7 left eye maps in which the topography was transposed about the vertical axial to correct for enantiomorphism (left eye-corrected). The wavefront error difference between the right and left eyes was compared with the difference between the right eyes and the left eyes in which enantiomorphism was corrected (right eye vs left eye-corrected). The left eye wavefront error was then compared with the left eye wavefront error after correction (left eye vs left eye-corrected)., Results: Correcting for enantiomorphism produced a statisticially significant difference in the first 5 radial orders of Zernike terms (P=.02). Of the 45 Zernike terms analyzed, 7 terms were significantly different at the P<.05 level in the right eye vs left eye category, compared with 4 terms in the right eye vs left eye-corrected category. Eleven terms were significantly different at the P<.05 level in the left eye vs left eye-corrected category., Conclusions: Correcting for enantiomorphism makes the Zernike terms in right and left eyes appear more similar. Failure to correct for enantiomorphism causes certain terms to cancel each other when averaged across right and left eyes. Wavefront error studies that do not consider enantiomorphism, including those used to adjust laser surgical nomograms, will introduce significant errors to certain Zernike terms.

Objective: To correlate new quantitative topographic indexes of corneal irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) following excimer laser photorefractive keratectomy (PRK)., Setting: Department of Ophthalmology, LSU Eye Center, and Refractive Surgery Center of the South, Ear, Nose & Throat Hospital, New Orleans, Louisiana; Manhattan Eye, Ear and Throat Hospital, New York, New York, USA., Methods: Videokeratography data (TMS-1) were obtained preoperatively and 1, 3, 6, 12, 18, and 24 months postoperatively from 100 eyes having PRK for low to mild myopia. Algorithms measured fine local irregularity with the surface regularity index (SRIp), varifocality with the coefficient of variation of corneal power (CVPp), and central islands with the elevation/depression magnitude (EDM)., Results: The SRIp and CVPp increased after surgery and remained significantly higher than the preoperative levels throughout the 24 month follow-up (P < .05). The increase in EDM was significant from 1 to 6 months (P < .05) but not thereafter. Multiple regression analysis revealed that variables having a statistically significant relationship with postoperative BSCVA were CVPp and EDM at 1 month, CVPp at 3 months, and CVPp, haze, and age at 6 months. No statistically significant correlation between any measures of irregular astigmatism and BSCVA was found after 1 year of follow-up., Conclusion: The quantitative measures used in this study are sensitive methods by which irregular astigmatism after keratorefractive procedures can be classified, evaluated, and compared.

Videokeratography has been available for a decade, and this test is essential for determining the presence and type of irregular corneal astigmatism. Three eyes diagnosed with myopic astigmatism and considered good candidates for refractive surgery with conventional examination were studied. Color-coded maps with videokeratography showed regular astigmatism in one eye and the existence of irregular astigmatism in two eyes. Videokeratography showed that one of these eyes had a keratoconus suspect pattern and the second showed a pattern consistent with pellucid marginal degeneration. Videokeratography can detect and classify irregular astigmatism in cases where routine examination shows no abnormal findings.

Purpose: Irregular corneal astigmatism has been reported in association with annular tinted hydrogel contact lenses. We report the abnormal videokeratographic findings of five patients wearing annular tinted contact lenses, who presented with bilateral blurred vision and revealed a loss of best corrected visual acuity., Methods/results: The corneal topographic analysis revealed a previously unreported distinct ring-shaped pattern of irregular astigmatism. The topographic circular band of irregular astigmatism was further characterized by concentric areas of relative steepening, flattening, and steepening with a diameter of approximately 4 mm. This pattern suggests that forces acting at the junctional zone between the tinted area and the clear pupillary area are inducing structural abnormalities of the corneal surface. At the time of presentation, the mean surface regularity index (SRI) was 2.06 (range: 0.61-5.88). The topography and best-corrected visual acuity returned to normal within days of discontinuing annular tinted lens use, and the mean SRI decreased to 0.44 (range: 0.21-1.16). Digital imaging of lenses obtained from our patients and of identical control lenses was performed. A masked analysis suggested that the study lenses contain greater amounts of pigment compared to the control lenses., Conclusions: We present ten characteristic signs and symptoms of this condition, which we have named "the annular tinted contact lens syndrome." Corneal topographic analysis is a powerful tool for detecting specific reversible irregularities of the corneal surface associated with the use of annular tinted contact lenses.

Keratometry and corneal topography remain the most important means of evaluating induced corneal changes after surgery and have comparable sensitivities in the paracentral region of the cornea. However, keratometry gives no information about the peripheral cornea or about asymmetry of the cornea. Videokeratography should be performed after cataract surgery in cases in which best-corrected visual acuity is not adequate and there are no other obvious causes for poor vision to determine whether corneal irregularities are present. The recent literature on corneal topographic evaluation of induced astigmatism after cataract surgery suggests that in general, smaller, temporal incisions result in less astigmatism. Preoperatively, corneal topography can be used in the calculation of intraocular lens power as well as incision planning. Postoperatively, it can be used to detect tight sutures, torsion of the wound, internal wound gape, and irregular astigmatism, as well as to guide suture removal. In the future, corneal topography will become increasingly important in the determination of intraocular lens power in difficult cases such as patients undergoing combined cataract extraction and penetrating keratoplasty as well as patients with a history of radial keratotomy or photorefractive surgery.

We conducted a preliminary retrospective study of five eyes that had undergone penetrating keratoplasty (PK) to determine if rigid gas permeable (RGP) contact lenses could be used as splints or molds to improve postoperative corneal topography. RGP lenses were fit 3-6 months (mean: 4.1 months) after PK and 3-4 months (mean: 1.8 months) after removal of the 10-0 nylon suture. Lenses were fit to attain a contact lens resting position centered on the corneal graft. After 4 to 8 months (mean: 6.2 months) of contact lens wear, analysis of corneal topography showed a decrease in simulated keratometry cylinder from 4.7 +/- 0.6 D (mean +/- 1 standard deviation) to 1.8 +/- 0.8 D (P = 0.02) and an improvement in anterior corneal surface regularity (surface regularity index: initial = 1.40 +/- 0.2; final = 1.0 +/- 0.2; P = 0.04). Three eyes were fit with a well-centered RGP lens; two eyes were fit with lenses that rode off-center. Increased irregular astigmatism in the two eyes with decentered contact lenses suggests the importance of centering RGP lenses with respect to corneal grafts. The best corrected spectacle visual acuity either improved or remained unchanged in four of five eyes after contact lens wear. One eye demonstrated a decrease in best corrected spectacle acuity by one Snellen line after 3 months of lens wear. Further clinical studies are needed to determine the potential of postoperative use of RGP lenses to improve corneal surface regularity, to decrease astigmatism, and to optimize visual results.

This article presents a general method of error analysis for reconstruction algorithms employed by corneal topography systems and applies this method to assess the accuracy of the Wang reconstruction algorithms. Using mathematical surface reconstructions, the method detects artifacts introduced in topographic analysis by astigmatism and misalignment. For the Wang algorithms, error introduced by astigmatism was less than 1% of the true value for surfaces with more than 10.00 diopters of astigmatism. A 1-mm translational misalignment of the analyzed surface introduced error of no more than 1.3%. Errors caused by rotational misalignment were less than 3% for misalignments of 5 degrees or less. It is concluded from the error analysis method that the Wang algorithms are sufficiently accurate for use in the analysis of corneal topography. Similar analyses need to be accomplished for the validation of commercially available corneal topography systems.

The authors compared postkeratoplasty astigmatism over a 4-month period after surgery in a randomized, prospective study of two groups of patients (total N = 18) who received two different suture techniques. The test group N = 8) had a single running suture with postoperative suture adjustment; on the basis of computer-assisted topographic analysis, the suture was tightened in the flatter meridian and loosened in the steeper meridian in the first month after surgery. The control group (N = 10) had a standard double running suture procedure with no postoperative adjustment; the single running 10-0 nylon suture was removed 3 months after surgery. Four months after penetrating keratoplasty, mean (+/- standard deviation) astigmatism in the test group was 1.7 +/- 0.7 diopters (D), and all patients had less than 2.6 D of astigmatism. In the control group, mean astigmatism was significantly higher (5.4 +/- 2.4 D; range, 0.7-9.0 D; P less than 0.01). The results suggest that postkeratoplasty astigmatism can be reduced with the single running suture technique accompanied by postoperative suture adjustment.

We placed interrupted 9-0 nylon sutures across the graft-host interface of ten eyes with more than 5 diopters of keratometric cylinder after penetrating keratoplasty in order to steepen the flattest corneal meridian and reduce the amount of corneal cylinder. Placement of compression sutures reduced corneal cylinder by an average of almost 6 diopters one week later. Average corneal cylinder was 5.1 diopters nine to 12 months after surgery. Best-corrected visual acuity with spectacles improved by an average of two Snellen lines (20/60 to 20/40) and uncorrected visual acuity improved by an average of one line (20/300 to 20/200). There were no complications related to placement of the sutures. This procedure provides a rapid and simple method for reducing astigmatism after penetrating keratoplasty.

Our computer-based corneal topography analysis system was used to study the keratoscope photographs (keratograms) from two patients with classic pellucid marginal degeneration and a third patient with no inferior corneal thinning, whose keratoscope mire pattern was suggestive of the condition. All three patients showed marked flattening of the central cornea along a vertical axis and marked steepening of the inferior corneal periphery, which also extended into mid-peripheral inferior oblique corneal meridians. The mid-peripheral cornea gradually decreased in power above the inferior oblique meridians.