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Biomedical subjects

S D Klyce

Publications and source records attributed to S D Klyce.

At least 19 recordsLinked to original sources
PubMed1997

Unilateral keratoconus. Incidence and quantitative topographic analysis.

OBJECTIVE: This study was designed to determine the incidence of unilaterality in a population of patients with clinical keratoconus and to compare quantitative descriptors of topography between affected corneas from patients with unilateral keratoconus and corneas of patients with bilateral disease. DESIGN: Retrospective clinical study with new evaluation of some patients. PARTICIPANTS: One hundred sixty-four patients from the University of Texas South-western Medical Center and Wills Eye Hospital who were diagnosed to have moderate-to-advanced keratoconus on the basis of characteristic topographic patterns associated with corneal thinning. INTERVENTION: Corneal topography was evaluated in both eyes of each patient. MAIN OUTCOME MEASURES: Quantitative descriptors of corneal topography were compared between 5 affected corneas of patients with unilateral keratoconus (combined cases from University of Texas Southwestern, LSU Eye Center, and Wills Eye Hospital) and 15 corneas of patients with moderate-to-advanced bilateral keratoconus (1 cornea from each patient). Indices selected for statistical analysis were the Keratoconus Predication Index (KPI), Surface Asymmetry Index (SAI), and Surface Regularity Index (SRI). RESULTS: Three (1.83%) of 164 patients with moderate-to-advanced keratoconus had no topographic evidence of keratoconus in the opposite eye. There were no statistically significant differences in KPI, SRI, or SAI values between the affected corneas of patients with unilateral and bilateral keratoconus. Over a period of 4 years of observation, signs of keratoconus in the previously normal eye developed in a patient with unilateral keratoconus. CONCLUSIONS: The authors found no differences in the quantitative descriptors of corneal topography between corneas with keratoconus from unilateral and bilateral cases. The authors' results suggest that the incidence of "unilateral" keratoconus is very low. Patients initially diagnosed with unilateral keratoconus, if observed for a sufficient period, commonly had signs of keratoconus develop in the opposite eye. The possibility that all cases of unilateral keratoconus may eventually become bilateral cannot be excluded. Therefore, refractive surgical procedures should not be performed on apparently normal corneas when keratoconus is detected in the opposite eye.

Cornea↗
PubMed1997

The annular tinted contact lens syndrome: corneal topographic analysis of ring-shaped irregular astigmatism caused by annular tinted contact lenses.

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.

Adolescent↗
PubMed1997

Disparity between keratometry-style readings and corneal power within the pupil after refractive surgery for myopia.

PURPOSE: Because keratometry readings may no accurately reflect the refractive changes after keratorefractive surgery for myopia, better methods for the assessment of corneal curvature in the postsurgical cornea are needed. METHODS: We developed a procedure to calculate the average central power (ACP) of the cornea within the entrance pupil from videokeratography. Videokeratograph-derived keratometry-style readings (average K; K) and calculated ACPs, as well as the differences between the two values, were compared in four groups: normal corneas (n = 30), corneas with regular astigmatism (n = 30); post-radial keratotomy corneas (RK, n = 85), and post-excimer laser photorefractive keratectomy corneas (PRK, n = 63). Intraocular lens (IOL) powers calculated by using K or ACP in the Sanders-Retzlaff-Kraff formula were compared. RESULTS: In the groups with normal corneas or regular astigmatism, none of the eyes showed a difference between K and ACP > 0.25 D. However, six (7%) of the RK eyes and 16 (25%) of the PRK eyes had differences > 0.55 D; in these eyes, the disparity between IOL powers calculated by using K and IOL powers calculated by using ACP was > 0.5 D. CONCLUSION: These results suggest that basing the calculation of IOL powers on keratometry readings in patients who have undergone RK. PRK, or possibly other refractive procedures may result in a residual refractive error in some eyes. In particular, patients undergoing surgery involving a small optical zone or large attempted correction or both, as well as those with low postoperative keratometry readings, may be at risk for this problem if IOL placement becomes necessary in later years.

Cornea↗
PubMed1996

Prospective study of corneal topographic changes produced by extracapsular cataract surgery.

Cataract surgery is known to induce refractive and corneal astigmatism, but little is known regarding the specific corneal topographic alterations produced by this surgery. We evaluated the corneal topographic effects of extracapsular cataract extraction (ECCE) performed with an 8- to 11-mm posterior limbal incision closed with interrupted sutures and subsequent selective suture removal. Corneal topography was analyzed in 15 eyes with the TMS-1 videokeratoscope preoperatively, before selective suture removal 4-6 weeks after surgery, 2-5 weeks after selective removal of sutures, and at 5 1/2-8 months after surgery. The Surface Regularity Index was significantly increased before suture removal and after suture removal but returned to normal at the final examination. The Irregular Astigmatism Index remained significantly increased at all examinations after surgery. Corneal asymmetry (Surface Asymmetry Index) continued to be significantly increased compared with the preoperative examination after suture removal and at 6 months after surgery. The standard deviation of powers (SDP) was significantly elevated before and immediately after suture removal, but was not significantly different at 6 months. Mean corneal astigmatism remained significantly increased (0.80 +/- 0.11 preoperatively, 1.39 +/- 0.24 at maximum follow-up, p = 0.04). Significant changes in corneal topography occurred in each patient between suture removal and final examinations. A few patients developed against-the-rule astigmatism ranging from 0.6 to 2.2 diopters. ECCE significantly altered corneal tomography compared with the preoperative contour in all patients. In those patients in whom surgically induced nonspherical and noncylindrical distortions occur (radially asymmetrical power distribution, lack of central corneal smoothness), corneal topography may provide information that is useful for management.

Astigmatism↗
PubMed1996

Automated topographic screening for keratoconus in refractive surgery candidates.

PURPOSE: We evaluated an automated corneal topography classification system developed as an adjuvant for screening patients prior to keratorefractive surgery. We screened for patterns suspicious for keratoconus by applying the system to the analysis of a series of patients who presented for evaluation for surgical correction of myopia. METHODS: Both eyes of 53 consecutive patients who were included in a previously reported prospective study were evaluated using the Expert System classification algorithm. This quantitative classification system incorporating eight indices was applied to the videokeratoscopic data from each patient to divide the topographic patterns into keratoconus and non-keratoconus groups. The group assignment of the Expert System classifier was compared with the clinical diagnosis of keratoconus versus non-keratoconus based on the topographic pattern and objective biomicroscopy signs. RESULTS: The Expert System classified eight of the videokeratographs as keratoconus. All five corneas that had clinical evidence of keratoconus were classified as such by the Expert System (sensitivity 100%). The other three corneas that were classified as keratoconus were of patients who wore rigid contact lenses and had pseudo-keratoconus topographic patterns, without other clinical signs of keratoconus. The specificity with which the Expert System detected normal corneas was 97% (98/101). CONCLUSIONS: Evaluation of the videokeratographic data with computerized algorithms designed to detect keratoconus may aid preoperative evaluation and facilitate distinction between keratoconus and some keratoconus-like topographic patterns.

Algorithms↗
PubMed1995

Comparison of methods for detecting keratoconus using videokeratography.

BACKGROUND: The detection of keratoconus patterns on videokeratography is important for screening candidates for refractive surgery and for studying the genetic basis of keratoconus. OBJECTIVE: We compared three quantitative approaches to identifying keratoconus from videokeratographic information to examine the limitations and capabilities of each test and to determine their suitability for use in the clinical setting. METHODS: Videokeratographs typical of clinically diagnosed keratoconus (n = 44) and of various non-keratoconus conditions (n = 132, including normal, with-the-rule astigmatism, contact lens-induced corneal warpage, photorefractive keratectomy, keratoplasty, and pellucid marginal degeneration) were selected. Three methods for detecting keratoconus were used: keratometry (average Simulated Keratometry [SimK] readings > 45.7 diopters [D]); the modified Rabinowitz-McDonnell test (central corneal power > 47.2 D and/or Inferosuperior Asymmetry [I-S] value > 1.4 D); and an expert system classifier (classification based on discriminant analysis and classification tree with eight topographic indexes). Sensitivity and specificity were calculated for each test. RESULTS: Sensitivities were 84% for keratometry, 96% for the modified Rabinowitz-McDonnell test, and 98% for the expert system classifier. Specificities for the three methods were 86%, 85%, and 99%, respectively. In terms of sensitivity, the expert system classifier was significantly better than keratometry (P = .04). In terms of specificity, the expert system classifier was significantly better than either of the other methods (P = .001). CONCLUSIONS: For screening candidates for refractive surgery, where high sensitivity is needed, either the modified Rabinowitz-McDonnell test or the expert system classifier is suitable. For diagnosing keratoconus, where high specificity is more useful, the expert system classifier is more appropriate than the other two methods.

Cornea↗
PubMed1995

Neural network classification of corneal topography. Preliminary demonstration.

PURPOSE: Videokeratography is a powerful tool for the diagnosis of corneal shape abnormalities. However, interpretation of the topographic map is sometimes difficult, especially when pathologies with similar topographic patterns are suspected. The neural networks model, an artificial intelligence approach, was applied for automated pattern interpretation in corneal topography, and its usefulness was assessed. METHODS: One hundred eighty-three topographic maps were selected and classified by human experts into seven categories: normal, with-the-rule astigmatism, keratoconus (mild, moderate, advanced), postphotorefractive keratectomy, and postkeratoplasty. The maps were divided into a training set (108 maps) and a test set (75 maps). For each map, 11 topography-characterizing indices calculated from the data provided by the TMS-1 videokeratoscope, plus the corresponding diagnosis category, were used to train a neural network. RESULTS: The correct classification was achieved by a trained neural network for all 108 maps in the training set. In the test set, the neural network correctly classified 60 of 75 maps (80%). For every category, accuracy and specificity were greater than 90%, whereas sensitivity ranged from 44% to 100%. CONCLUSIONS: With further testing and refinement, the neural networks paradigm for computer-assisted interpretation or objective classification of videokeratography may become a useful tool to aid the clinician in the diagnosis of corneal topographic abnormalities.

Cornea↗
PubMed1994

Screening for corneal topographic abnormalities before refractive surgery.

PURPOSE: The purpose of this prospective study is to evaluate the corneal topography of patients who sought an opinion regarding refractive surgery for the correction of myopia. METHODS: Both eyes of 53 patients were evaluated with a topographic modeling system. Forty-two patients wore contact lenses (84 eyes: 36 rigid contact lenses and 48 soft contact lenses). Ten patients (20 eyes) wore glasses alone and one patient (2 eyes) wore neither glasses nor contact lenses for correction of myopia. RESULTS: Thirty-five (33%) of 106 eyes were found to have abnormal corneal topography. Of the 42 patients (84 eyes) who wore contact lenses, 32 eyes (38%) had irregular astigmatism, loss of radial symmetry, or absence of the normal progressive flattening from the center to the periphery of the cornea, consistent with contact lens-induced corneal warpage. Alterations were more frequent and severe in rigid contact lens wearers. Three patients (5.7%) received a diagnosis of definite keratoconus, a higher incidence than has been reported in the general population. Topographic abnormalities in most, if not all, of the eyes would not have been detected by visual inspection of the photokeratoscopic images alone. CONCLUSIONS: Appropriate preoperative detection and management of corneal topographic abnormalities are essential steps in every refractive surgical procedure. The overall efficacy and safety of procedures such as radial keratotomy and photorefractive keratectomy likely will be improved once the unpredictable variables of contact lens-induced warpage and occult ectatic disease are eliminated by topographic screening before surgery. Patients with keratoconus may be over-represented in the refractive surgery population due to self-selection.

Contact Lenses↗
PubMed1994

Keratoconus and contact lens-induced corneal warpage analysis using the keratomorphic diagram.

PURPOSE: Videokeratography of early keratoconus may be difficult to distinguish from contact lens-induced corneal warpage, even by experienced examiners. Furthermore, topographic irregularity may be judged inconsistently if quantitative standards are not applied. Quantitative measures based on videokeratographic data were developed and evaluated to determine if improved corneal topographic classification can be achieved. METHODS: The Corneal Irregularity Coefficient (CIC) and Corneal Power Coefficient (CPC) were derived from multiple measures of mean corneal power and its variance for 207 videokeratographs of normal, warped, keratoconus, and keratoconus-suspect corneas. CIC was plotted against CPC, creating a distribution of points representing all maps that tended to be grouped according to surface conditions (the Keratomorphic Diagram). Normal, steep, abnormal, and warped zones were defined by CIC and CPC cutoff values chosen to distinguish normal from keratoconus corneas graphically. RESULTS: Seventy of 76 normal corneas were grouped in the normal zone and 6 in the steep zone; 84 of 84 keratoconus corneas were grouped in the abnormal zone; 35 of 35 contact lens-induced warpage cases were grouped in the warped zone; and 10 of 12 keratoconus-suspect corneas were grouped in the warped zone, with 2 in the abnormal zone. Serially plotted data of keratoconus progression and warpage regression demonstrated that the vector displacement of CIC and CPC values may provide a potentially useful means of distinguishing contact lens-induced warpage from keratoconus-suspect corneas. CONCLUSION: The Keratomorphic Diagram aids in classifying and comparing corneal shape by plotting indices along axes with easily recalled scales. The diagram may become a useful tool to assess presurgical corneal surface instability and postoperative progression of corneal shape change due to healing.

Contact Lenses↗
PubMed1994

Alteration of corneal asphericity in rigid gas permeable contact lens induced warpage.

We developed the corneal asphericity index (CAI), which indicates the asphericity of the central cornea using the TMS-1 videokeratoscope, and used the CAI to evaluate both normal corneas and corneas with rigid gas permeable (RGP) lens induced warpage. The CAI (mean +/- standard deviation) for the 22 control corneas was 0.33 +/- 0.26, which indicates that the normal central cornea has a prolate shape. The average CAI for the 24 corneas with RGP lens induced warpage was significantly lower (-0.15 +/- 0.36, P = 0.0001). These data suggest that some corneas have abnormal asphericity in the central cornea when warpage occurs with RGP lenses. CAI is useful for the quantitative assessment of asphericity and topographic abnormalities in the central cornea caused by contact lens induced warpage.

Adult↗
PubMed1994

Automated keratoconus screening with corneal topography analysis.

PURPOSE: Although visual inspection of corneal topography maps by trained experts can be powerful, this method is inherently subjective. Quantitative classification methods that can detect and classify abnormal topographic patterns would be useful. An automated system was developed to differentiate keratoconus patterns from other conditions using computer-assisted videokeratoscopy. METHODS: This system combined a classification tree with a linear discriminant function derived from discriminant analysis of eight indices obtained from TMS-1 videokeratoscope data. One hundred corneas with a variety of diagnoses (keratoconus, normal, keratoplasty, epikeratophakia, excimer laser photorefractive keratectomy, radical keratotomy, contact lens-induced warpage, and others) were used for training, and a validation set of 100 additional corneas was used to evaluate the results. RESULTS: In the training set, all 22 cases of clinically diagnosed keratoconus were detected with three-false-positive cases (sensitivity 100%, specificity 96%, and accuracy 97%). With the validation set, 25 out of 28 keratoconus cases were detected with one false-positive case, which was a transplanted cornea (sensitivity 89%, specificity 99%, and accuracy 96%). CONCLUSIONS: This system can be used as a screening procedure to distinguish clinical keratoconus from other corneal topographies. This quantitative classification method may also aid in refining the clinical interpretation of topographic maps.

Cornea↗
PubMed1993

Standardized color-coded maps for corneal topography.

PURPOSE: Modern videokeratoscopy is useful in assessing corneal shape. The purpose of this study is to compare color-coded topographic maps using standardized scales with 1.0- and 1.5-diopter (D) intervals. The authors assessed the use of the two scales for detecting clinically relevant features of corneal topography such as regular astigmatism, irregular astigmatism, early keratoconus, and contact lens-induced corneal warpage. METHODS: A total of 50 normal corneas, 50 corneas with contact lenses, 50 that had keratoconus (25 early to moderate and 25 advanced), 50 that had penetrating keratoplasty, 20 that had extracapsular cataract surgery, 17 that had excimer laser photorefractive keratectomy for myopia, 10 that had radial keratotomy, 3 that had aphakic epikeratophakia, and 2 that had myopic epikeratophakia were analyzed with a corneal topographic analysis system. Color-coded maps with 1.0-D intervals (Maguire/Waring scale) and 1.5-D intervals (Klyce/Wilson scale) were compared. RESULTS: There were no topographic characteristics that were not appreciated with either scale for corneas with dioptric powers that fell within their ranges. Conversely, for corneas that had powers outside the range of the 1.0-diopter scale, but within the range of the 1.5-diopter scale, the former produced a map in which the flattest or steepest areas were artifactually smoothed. CONCLUSIONS: This study suggests that the Klyce/Wilson scale (constant, 1.5-D intervals) provides the best combination of sensitivity for detection of clinically significant topographic features and the widest range of coverage of powers that are found on a variety of normal, pathologic, and surgically altered corneas. The adoption of the Klyce/Wilson scale by all manufacturers of corneal topographic instruments as a primary standard will facilitate communication and will make the interpretation of corneal topography easier for both the expert and the novice.

Cataract Extraction↗
PubMed1993

Corneal topographic alterations in normal contact lens wearers.

PURPOSE: The purpose of this study is to investigate the corneal topography of visually normal asymptomatic eyes that wore rigid and soft contact lenses compared with visually normal eyes that had never worn contact lenses. METHODS: Thirty-seven normal corneas and 74 corneas in asymptomatic eyes that wore rigid (12 polymethylmethacrylate and 23 gas-permeable) and soft (26 daily-wear and 13 extended-wear) contact lenses for refractive correction underwent slit-lamp examination, keratometry, computer-assisted topographic analysis, refraction, and rigid contact lens over-refraction. RESULTS: Topographic abnormalities tended to be more common and more severe in corneas that wore rigid contact lenses, but significant changes were noted in some eyes that wore daily-wear or extended-wear soft contact lenses. A number of eyes in the rigid polymethylmethacrylate (9 of 12) and rigid gas-permeable (6 of 23) contact lens groups had a correlation between the most frequent resting position of the contact lens and the corneal topography, with relative flattening of the corneal contour beneath a decentered lens. A total of 10 eyes in the rigid contact lens groups had a 1-line decrease in best spectacle-corrected visual acuity attributable to contact lens-induced topographic abnormalities. CONCLUSIONS: Corneal topographic alterations are common in asymptomatic contact lens wearers and are frequently detectable only with computer-assisted topographic analysis. It is important that topographic abnormalities be excluded in contact lens wearing eyes before refractive surgical procedures.

Contact Lenses↗
PubMed1993

Corneal topography of excimer laser photorefractive keratectomy.

The application of the 193 nm excimer laser for keratorefractive surgery promises to deliver a higher degree of precision and predictability than traditional procedures such as radial keratotomy. The development and evaluation of keratorefractive surgery have benefited from the parallel advances made in the field of corneal topography analysis. We used the Computed Anatomy Topography Modeling System (TMS-1) to analyze a Louisiana State University (LSU) Eye Center series of patients who had photorefractive keratectomy for the treatment of myopia with the VISX Twenty/Twenty excimer laser system. The excimer ablations were characterized by a relatively uniform distribution of surface powers within the treated zone. In the few cases that exhibited marked refractive regression, corneal topography analysis showed correlative changes. With topographical analysis, centration of the ablations relative to the center of the pupil could be evaluated. Marked improvement in centration occurred in the patients of LSU Series IIB in which the procedure to locate the point on the cornea directly over the pupil's center during surgery was refined. Corneal topographical analysis provides objective measures of keratorefractive surgical results and is able to measure the precise tissue removal effect of excimer laser ablation without the uncertainties caused by measuring visual acuity alone. Our observations forecast the need for improved aids to center the laser ablations and for the development of a course of treatment to prevent post-ablation stromal remodeling.

Cornea↗