Axial, instantaneous, and refractive formulas in computerized videokeratography of normal corneas

Deep neural network with self-attention based automated determination system for treatment zone and peripheral steepened zone in Orthokeratology for adolescent myopia

PURPOSE

The aim of this study is to develop an automatic model based on deep learning techniques for determining the Treatment Zone (TZ) and Peripheral Steepened Zone (PSZ) following Orthokeratology (OK) treatment.

METHODS

A total of 1346 corneal topography maps were included in the study. A deep neural network based on the Segformer architecture was constructed to automatically detect TZ and PSZ. The model was optimized and trained multiple times, and the areas of TZ, PSZ, and TZ decentration were calculated based on the segmentation results.

RESULTS

The mean Intersection over Union (mIoU) of the overall segmentation results of the model reached over 97% after multiple training with different optimization methods, and the IoU for the TZ and PSZ segmentation tasks were 98.08% and 94.54% in test set, respectively. Moreover, the model demonstrated high consistency with the expert annotation for the TZ segmentation, while a significant difference was found in the PSZ segmentation and expert annotation due to several interference factors.

CONCLUSION

This study presents an efficient and repeatable system for clinical research, based on a deep neural network that accurately determines TZ and PSZ after OK treatment using the Segformer architecture. However, further deployment validation may be necessary.

Comparative postoperative topography pattern recognition analysis using axial vs tangential curvature maps

PURPOSE

To determine prediction accuracy of patient refractive surgery status by novice reviewers based on topography pattern analysis using axial or tangential anterior curvature maps.

SETTING

Four U.S. academic centers.

DESIGN

Prospective case-control study.

METHODS

Image evaluation was performed by novice reviewers (n = 52) at 4 academic institutions. Participants were shown 60 total images from 30 eyes presenting for cataract surgery evaluation with known refractive surgery status, including 12 eyes imaged with Placido-based topography and 18 eyes imaged with Scheimpflug-based tomography. There were 12 eyes with myopic ablations, 12 eyes with hyperopic ablations, and 6 eyes with no previous refractive surgery performed. Each eye was shown in both axial and tangential curvature from either device, reviewed as a single image at a time, and masked to the map type (axial vs tangential).

RESULTS

For the 52 novice reviewers included, accuracy of pattern identification was 82.9% (517 of 624) for tangential vs 55.0% (343 of 624) for axial maps for eyes with myopic ablation (P < .00001), 90.9% (567 of 624) for tangential vs 58.3% (364 of 624) for axial maps for eyes with hyperopic ablation (P < .00001), and 15.4% (48 of 312) for tangential vs 62.8% (196 of 312) for axial maps for eyes with no ablation (P < .00001). There were no significant differences between Placido and Scheimpflug devices and no significant differences across groups based on year of training.

CONCLUSIONS

Tangential curvature maps yielded significantly better pattern recognition accuracy compared with axial maps after myopic and hyperopic corneal refractive surgery ablations for novice reviewers. Using tangential curvature maps, especially for challenging cases, should benefit post-LASIK intraocular lens (IOL) calculator selection and, thereby, improve IOL power calculation accuracy.

Transient changes in refractive error and corneal tomography after 24-h continuous monitoring of intraocular pressure patterns with a contact lens sensor

PURPOSE

To evaluate changes in refractive error and corneal tomographic measurements after 24-h monitoring of intraocular pressure patterns with a contact lens sensor (CLS).

STUDY DESIGN

Prospective, longitudinal, observational study.

PATIENTS AND METHODS

Fourteen eyes of 14 consecutive patients who underwent 24-h CLS monitoring were enrolled. The objective spherical equivalent (SE) refractive error was measured using automated refraction and keratometry. The axial power, instantaneous power, and corneal thickness at the central, paracentral, midperipheral, and peripheral cornea were measured with swept-source anterior-segment optical coherence tomography. Measurements were performed at baseline, immediately after monitoring, and at follow-up visits 2-4 days after monitoring.

RESULTS

The myopic SE increased significantly (P < 0.001) from - 5.1 ± 4.2 to - 6.0 ± 4.0, D after 24-h monitoring with a CLS and returned to the premonitoring level at the second visit (- 5.3 ± 4.4 D, P = 0.315). Decreases in the midperipheral and peripheral axial powers and the paracentral instantaneous power and increases in the central instantaneous power and peripheral corneal thickness occurred after CLS monitoring.

CONCLUSION

Twenty-four-hour monitoring with a CLS resulted in significant increases in the myopic refractive error and corneal central steepening and midperipheral flattening. Although these changes are transient and do not negate the clinical merits of the CLS, clinicians should be aware of these potential adverse events. Three-dimensional evaluation of corneal deformation with anterior segment optical coherence tomography is a powerful tool for assessing and improving the safety, tolerability, and accuracy of CLS devices.

Range of refractive independence and mechanism of action of a corneal shape-changing hydrogel inlay: results and theory

PURPOSE

To demonstrate the independence of visual performance over a range of preoperative refraction and age in presbyopes implanted with a corneal shape-changing inlay (Raindrop Near Vision Inlay).

SETTING

Two multispecialty clinics, Monterrey and Tijuana, Mexico.

DESIGN

Prospective case series.

METHODS

The nondominant eyes of patients were implanted with the hydrogel corneal inlay beneath a femtosecond flap, centered on the pupil. Clinical outcomes included uncorrected near, intermediate, and distance visual acuity (UNVA, UIVA, and UDVA) and patient-assessed task performance in good light and dim light. Statistical analyses assessed the dependencies on preoperative age (45 to 60 years) and preoperative manifest refraction spherical equivalent (MRSE) (-0.5 to +1.5 diopters [D]). Using the inlay effect derived from wavefront measurements, an eye model was created through which letter charts were simulated.

RESULTS

The study evaluated eyes of 188 patients. Postoperative UNVA, UIVA, and task performance at these distances in good light was independent of age and preoperative MRSE (P > .05). Postoperative UDVA was weakly dependent on preoperative MRSE, but distance task performance in good light was not (P > .05). In the treated eye, the mean postoperative UNVA was 20/25, UIVA was 20/25, and UDVA was 20/32. The clinical outcomes are explained by consideration of zones within the pupil generating good near, intermediate, and distance image quality. This was confirmed by visual acuity simulations.

CONCLUSIONS

The continuous center-near power profile induced by the corneal shape-changing inlay provides good visual acuity and performance from distance through near over a 2.0 D range of preoperative refraction and presbyopic age.

FINANCIAL DISCLOSURE

Drs. Steinert, Schwiegerling, Barragán-Garza, and Chayet are consultants to Revision Optics, Inc. Drs. Lang and Holliday and Mr. Roy are employees of Revision Optics, Inc. Drs. Steinert, Schwiegerling, Barragán-Garza, and Chayet have no financial or proprietary interest in any material or method mentioned.

Characterization of corneal structure in keratoconus

The increasing volume of patients interested in refractive surgery and the new treatment options available for keratoconus have generated a higher interest in achieving a better characterization of this pathology. The ophthalmic devices for corneal analysis and diagnosis have experienced a rapid development during the past decade with the implementation of technologies such as the Placido-disk corneal topography and the introduction of others such as scanning-slit topography, Scheimpflug photography, and optical coherence tomography, which are able to accurately describe not only the geometry of the anterior corneal surface but also that of the posterior surface, as well as pachymetry and corneal volume. Specifically, anterior and posterior corneal elevation, corneal power, pachymetry maps, and corneal coma-like aberrometry data provide sufficient information for an accurate characterization of the cornea to avoid misleading diagnoses of patients and provide appropriate counseling of refractive surgery candidates.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Keratoconus: classification scheme based on videokeratography and clinical signs

PURPOSE

To determine in a longitudinal study whether there is correlation between videokeratography and clinical signs of keratoconus that might be useful to practicing clinicians.

SETTING

Cornea-Genetic Eye Institute, Cedars-Sinai Medical Center, Los Angeles, California, USA.

METHODS

Eyes grouped as keratoconus, early keratoconus, keratoconus suspect, or normal based on clinical signs and videokeratography were examined at baseline and followed for 1 to 8 years. Differences in quantitative videokeratography indices and the progression rate were evaluated. The quantitative indices were central keratometry (K), the inferior-superior (I-S) value, and the keratoconus percentage index (KISA). Discriminant analysis was used to estimate the classification rate using the indices.

RESULTS

There were significant differences at baseline between the normal, keratoconus-suspect, and early keratoconus groups in all indices; the respective means were central K: 44.17 D, 45.13 D, and 45.97 D; I-S: 0.57, 1.20, and 4.44; log(KISA): 2.49, 2.94, and 5.71 (all P<.001 after adjusting for covariates). Over a median follow-up of 4.1 years, approximately 28% in the keratoconus-suspect group progressed to early keratoconus or keratoconus and 75% in the early keratoconus group progressed to keratoconus. Using all 3 indices and age, 86.9% in the normal group, 75.3% in the early keratoconus group, and 44.6% in the keratoconus-suspect group could be classified, yielding a total classification rate of 68.9%.

CONCLUSIONS

Cross-sectional and longitudinal data showed significant differences between groups in the 3 indices. Use of this classification scheme might form a basis for detecting subclinical keratoconus.

Intraocular lens power calculation after radial keratotomy: Estimating the refractive corneal power

PURPOSE

To evaluate the most accurate method for corneal power determination in patients with previous radial keratotomy (RK).

SETTING

University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.

METHODS

A retrospective review of data for 16 eyes of 14 patients with a history of RK and subsequent phacoemulsification and posterior chamber intraocular lens (IOL) implantation was performed. Outcome measures included axial length, postoperative topography, type and power of IOL implanted, and postoperative spherical equivalent (SE) refraction at 3 to 6 months. Average central corneal power (ACCP) was defined as the average of the mean powers of the central Placido rings. For each eye, simulated K-readings and different values of ACCP computed corresponding to different central corneal diameters were used in each case, along with the implanted IOL power, to back-calculate the SE refraction (Ref) via the double-K adjusted Holladay 1 IOL formula. The predicted refractive error was hence computed as (Ref - SE), both in algebraic and absolute values.

RESULTS

The ACCP over the central 3.0 mm (ACCP(3mm)) yielded the lowest absolute predicted refractive error (0.25 +/- 0.38 diopters [D]), which was statistically lower than the error for ACCP(1mm) (P<.001) and for the simulated K-value (P = .033). It also resulted in 87.5% of eyes being within +/-0.50 D and 100% within +/-1.00 D of the actual postoperative refraction.

CONCLUSIONS

Corneal refractive power after RK was best described by averaging the topographic data of the central 3.0 mm area. Applying this method, together with a double-K IOL formula, achieved excellent IOL power predictability.

Computerized corneal topography and its importance to wavefront technology

PURPOSE

To review the development and application of corneal topography in refractive surgery.

METHODS

Review of the literature and discussion of recent developments in corneal topography and wavefront technology.

RESULTS

Analysis of corneal topography provides critical information for the preoperative examination of patients before refractive surgery and for the evaluation and treatment of patients with complications after surgery.

CONCLUSIONS

Corneal topography will continue to be a critical diagnostic modality for refractive surgery. Even with the advent of wavefront analysis designed to detect refractive error and aberrations of the eye, it will be necessary to have detailed corneal topographic information to understand the contribution the cornea makes to vision so that custom alteration of that surface can be used to optimize vision. This will be true of the normal eye, but it will be of special importance in eyes with abnormalities that were induced by corneal surgery.

Keratoconus evaluation using the Orbscan Topography System

PURPOSE

To evaluate corneal topography in a series of keratoconus patients using the Orbscan Topography System.

SETTING

Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany.

METHODS

Seventy-one eyes of 38 patients with keratoconus were evaluated. Quantitative topographic parameters were analyzed with special reference to the central point of the cornea, the apex (the point with maximum reading on the anterior elevation best-fit sphere map), and the thinnest point. Evaluation included location, elevation (compared to a best-fit sphere), pachymetry, tangential curvature, and composite curvature. The mirror-image symmetry between the right and left eyes of a patient was also investigated.

RESULTS

Mean patient age was 31.2 years +/- 12.2 (SD). Thirty-three patients (86.8%) had bilateral keratoconus and 5 (13.2%), unilateral keratoconus. Most cones (68/71) were located in the inferior temporal quadrant; 3 were above the horizontal meridian. Mean distance between the apex and the thinnest point was 0.917 +/- 0.729 mm (P < .001). The correlations between apex elevation and apex composite curvature and apex tangential curvature were high (r = 0.94 and r = 0.91, respectively; P < .001). In right and left eyes, there was a correlation between the apex and the thinnest point semi-meridians (r = 0.47 and r = 0.65, respectively; P < .05) but not between the radii of the apex and the thinnest point (r = 0.21 and r = 0.24, respectively).

CONCLUSIONS

The Orbscan system can provide useful and accurate information in defining the morphology of keratoconus and detecting subtle topographic changes present in early keratoconus. It may also improve the results of contact lens fitting and surgical management.

Comparison of changes in manifest refraction and corneal power after photorefractive keratectomy

PURPOSE

To determine which corneal curvature values most closely correlate to change in manifest refraction after excimer laser photorefractive keratectomy.

METHODS

In a prospective study at the Cullen Eye Institute, excimer laser photorefractive keratectomy was performed on 27 eyes of 27 patients (mean age, 38.07+/-6.65 years). Preoperative refractive errors ranged from -2.25 diopters to -8.75 diopters (mean, -5.74+/-2.09 diopters). Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the subjective manifest refraction (corrected for a 12-mm vertex distance) and measured corneal power using standard keratometry (Bausch & Lomb Keratometer; Rochester, New York) and computerized videokeratography (EyeSys Corneal Analysis System; Premier Laser Systems Inc, Houston, Texas). We collected 15 corneal values: standard keratometry and 14 computerized videokeratography values calculated using the axial, instantaneous, and refractive formulas. All calculations were performed with 1.3375 and 1.376 for the refractive index of the cornea. For each of the corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated for this difference the means, SDs, correlations, and regressions.

RESULTS

Mean differences between change in refraction and change in corneal power were lower when for a refractive index of 1.376 than for 1.3375, were lowest for the most central measurement points, and displayed a high SD. A value of 1.408 for the refractive index would be required to optimize the correlation between change in manifest refraction and effective refractive power of the central 3 mm of the cornea.

CONCLUSIONS

For individual patients who have undergone photorefractive keratectomy, changes in corneal values determined by computerized videokeratography or by standard keratometry do not reliably predict change in manifest refraction.