Surface and Orbscan II slit-scanning elevation topography in circumscribed posterior keratoconus

Evaluation of Ocular Higher-Order Aberrations in First-Degree Relatives of Patients With Keratoconus

PURPOSE

The aim of this study was to evaluate the corneal higher-order aberrations (HOAs) in first-degree relatives of patients with keratoconus (KCN) and compare with the normal population.

METHODS

In this prospective comparative study, 210 eyes from 105 family members of 28 patients with KCN and 210 normal eyes of 105 controls were enrolled. In each eye, corneal topography, tomography, and aberrometry were performed and compared between the 2 groups.

RESULTS

This study included 61 female (58.1%) and 44 male participants (41.9%) and 105 age-matched and sex-matched controls with normal topographic cornea. In 14 of 105 first-degree relatives (13.33%) of patients with KCN, KCN was diagnosed with a male preponderance (71.5% male, 28.5% female). Tomographic indices and irregularity indices in 3 and 5 mm zone in Orbscan were significantly higher in the relative group. In addition, other irregularity indices of TMS-4 topography including surface regularity index, surface asymmetry index, difference sector index, SDP, and irregular astigmatism index were significantly higher in family members of patients with KCN. The most prevalent topographic pattern in the control group was the symmetric bowtie (57.1%) and in the relative group was the asymmetric bowtie (39.5%). In addition, significantly thinnest corneal pachymetry was detected in the relative group. Root mean square of all HOAs including vertical trefoil, vertical coma, horizontal coma, horizontal trefoil, quadrifoil, and fourth-order spherical aberrations were significantly greater in the relative group than controls.

CONCLUSIONS

Owing to the high prevalence of undiagnosed KCN susceptibility in family members with KCN, keratorefractive surgery should be considered cautiously in these individuals. In addition, comprehensive preoperative examination should be considered to detect subtle topographic and HOAs in these individuals.

Varied Presentations of Posterior Keratoconus: A Clinical Case Series

PURPOSE

To describe the varied presentations of posterior keratoconus.

METHODS

This is a 3-year institute-based retrospective study report from June 2015 to June 2018 that describes 13 eyes of 12 patients with varied presentations of posterior keratoconus, evaluating tomographic changes using Scheimpflug corneal tomography and anterior segment optical coherence tomography. Slit-lamp examination revealed circumscribed nebular corneal opacity with posterior corneal depression.

RESULTS

Eleven patients had unilateral and one had a bilateral presentation. Five patients presented in the first and second decade with a nebular opacity and circumscribed excavation of the posterior cornea. One patient was a 12-year-old girl who presented with systemic manifestations. Seven others were middle-aged adults with superior, central, or peripheral excavation. Two patients had microcornea.

CONCLUSIONS

This is the largest case series on posterior keratoconus, depicting its varied features. Diagnosis of this uncommon condition requires a high index of suspicion, meticulous slit-lamp examination, and systemic evaluation to rule out other associated anomalies. We report a patient of unilateral posterior keratoconus with systemic associations, second such case in the literature.

Posterior keratoconus-clinical aspects and anterior segment optical coherence tomography findings: A case report

PURPOSE:

To describe a case of Posterior Keratoconus (keratoconus posticus); its clinical condition, corneal, refractive response to intracorneal ring implantation (MyoRing), anterior segment optical coherence tomography findings; and micro incisional cataract surgery outcome.

METHODS:

Case report.

RESULTS:

The case was studied with high resolution anterior segment optical coherence tomography (OCT), epithelium OCT, corneal topography, and aberrometry. A MyoRing was implanted and after the development of cataract, microincisional cataract surgery was performed. A large hyperopic shift was observed following the ring implantation. Calculation of the intraocular lens showed poor predictability.

CONCLUSIONS:

Posterior keratoconus is a rare corneal congenital disorder characterized by a posterior corneal elevation. Surprisingly, on the total corneal aberrometry, the coma is within normal levels; in the anterior and posterior corneal aberrometry, all the low order and high order aberrations are outside of normal parameters. The epithelial thickness is normal on the contrary to anterior keratoconus. Micro incisional cataract surgery can be safely performed in these eyes, although a refractive surprise is expected due to errors in the intraocular lens calculation.

Posterior keratoconus

Posterior keratoconus (PKC) is a rare, typically non-inflammatory condition that is characterised by an abnormal posterior corneal curvature, which may be accompanied by overlying stromal opacification. It is usually congenital and can be associated with other ocular and systemic abnormalities. PKC remains a clinical diagnosis, although imaging techniques including ultrasound biomicroscopy and anterior segment optical coherence tomography may be useful tools for confirmation and classification. Genetic studies should be considered, although no specific genetic defects have been identified thus far. As a potential cause of amblyopia, early diagnosis and management are crucial in maximising visual potential. Occasionally, management considerations may also include surgical intervention, such as corneal transplantation. Intraocular lens power calculation at the time of cataract surgery requires special consideration. Here, we review the present literature on PKC and consider future directions in the management of this rare entity.

Measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients

AIM

To evaluate the measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients.

METHODS

A hundred and one eyes of 55 keratoconus patients were enrolled in this study. The mean age was 26.2±8.9 years. The inclusion criteria were keratoconus stage I to III according to the Amsler-Krumeich keratoconus classification. All the measurements were done by the same operator, under the mesopic light condition and repeated with three different optical methods; Visante, Orbscan and Pentacam. The evaluated anterior segment parameters were anterior chamber depth (ACD), central and thinnest corneal thickness (CCT and TCT) and pupil diameter (PD).

RESULTS

THE MEAN CCT MEASURED BY VISANTE, ORBSCAN AND PENTACAM WERE AS FOLLOWS: 462.0±48.1µm, 463.9±60.9µm, 476.5±45.3µm, respectively (P=0.873). The mean ACD values were 3.34±0.33mm, 3.26±0.33mm, 3.49±0.40mm, respectively (P=0.118). The mean PD measurements were 5.11±1.14mm, 4.80±0.85mm, 3.80±1.38mm, respectively (P<0.001). The mean TCT measurements of Visante, Orbscan and Pentacam were 437.9±48.2µm, 447.6±60.6µm and 459.9±44.0µm, respectively (P=0.214). The Visante and Orbscan measured CCT similarly, while Pentacam measured CCT thicker than the other two. The Visante measured TCT thinner than the other two devices. In ACD measurements, Orbscan was the one giving the lowest values. PD was measured differently by the devices.

CONCLUSION

Although TCT, CCT and ACD measurements acquired by Visante, Orbscan and Pentacam in keratoconus patients are similar, PD measurements show large differences among the devices.

Repeatability, reproducibility, and agreement of corneal power measurements obtained with a new corneal topographer

PURPOSE

To study the repeatability and reproducibility of corneal power measurements obtained with a new corneal topographer (Keratograph 4) and assess their agreement with those obtained by a rotating Scheimpflug camera (Pentacam HR) and an automated keratometer (IOLMaster).

SETTING

Eye Hospital, Wenzhou Medical University, Wenzhou, China.

DESIGN

Observational cross-sectional study.

METHODS

One eye of normal subjects was measured 3 times using all devices. Another operator performed an additional 3 consecutive scans using the corneal topographer. One week later, the first operator repeated the corneal power measurements using the corneal topographer. Parameters were flat meridian power, steep meridian power, average power, J0, and J45. The repeatability and reproducibility of measurements were assessed by the within-subject standard deviation (Sw), repeatability (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement between devices was assessed using 95% limits of agreement (LoA).

RESULTS

Intraoperator repeatability and interoperator and intersession reproducibility of all measured parameters showed a CoV of less than 0.3%, a 2.77 Sw of 0.32 diopter or less, and an ICC of more than 0.97. No significant differences in the parameters were noted between the corneal topographer and Scheimpflug camera. Statistically significant differences existed between the parameters analyzed by the corneal topographer and the automated keratometer, except J45. The mean differences between the corneal topographer and the other 2 devices were small, and the 95% LoA were narrow for all measurements.

CONCLUSION

The new corneal topographer had excellent reliability and high agreement with the other 2 devices in corneal power measurements in normal subjects.

FINANCIAL DISCLOSURE

No author has a 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.

Bilateral circumscribed posterior keratoconus: visualization by ultrasound biomicroscopy and slit-scanning topography analysis

This paper documents a rare nonprogressive developmental disorder—bilateral circumscribed posterior keratoconus—in a 60-year-old man referred for a cataract surgery. For the first time ultrasound biomicroscopy was used to visualise the local anterior bulging of the posterior corneal surface with concomitant thinning of the stroma. The amount of localized posterior depression, corneal thickness and the refractive power of both the posterior and anterior corneal curvature were measured using slit-scanning topography analysis (Orbscan).

Determination of corneal volume from anterior topography and topographic pachymetry: application to healthy and keratoconic eyes

PURPOSE

To describe a method to measure corneal volume from topography and pachymetry, and test its clinical use on a sample of healthy human subjects and a case of circumscribed posterior keratoconus.

METHODS

Corneal curvature (PCT 200 corneal topography system; Optopol Technology SA, Zawiercie, Poland) and ultrasonic topographic pachometry on 25 points (Ophthasonic A-Scan/Pachometer III; Teknar Inc., St Louis, MO, USA) were measured on each of 12 young healthy corneas and one cornea suffering from circumscribed posterior keratoconus. Topography and pachymetry data were used to calculate the coordinates for the corresponding points on the posterior surface of the cornea. TableCurve 3D software (Systat Software Inc., Chicago, IL, USA) was used to fit a surface to those points measured. Integration of the surface fitted to the data points, corresponding to the anterior and posterior corneal surfaces, was used to calculate the volume underneath each of them. Subtraction of volumes underneath anterior and posterior surfaces, taking into account an axial offset equal to the central corneal thickness, rendered corneal volume for the central 6 mm of the cornea.

RESULTS

Central corneal thickness ranged from 520 to 630 mum for the healthy corneas. Corneal volumes for this sample analyzed averaged 18.66 +/- 1.15 mm(3) (range 17.25-20.53 mm(3)). For the posterior keratoconic cornea, the affected area was located at about 1.5-2 mm from the corneal center on the 135 degrees hemimeridian of the right eye, observed through topographic pachymetry. Calculated corneal volume for the central 6 mm was 16.072 mm(3), noticeably lower than those found in the sample without pathology, but within the range for corneas presenting with keratoconus.

CONCLUSIONS

Corneal volume is a useful parameter for characterising dystrophic corneas and can aid in the detection of rare anomalies which are hardly detected with corneal topography and/or central corneal thickness evaluation. A potentially useful measure of corneal volume can be calculated from anterior corneal topography and topographic pachymetry data. Values obtained are in good agreement with previous studies using corneal tomography techniques. The methodology has been shown to have potential for retrospective analysis of data, or where no access is available to tomographical techniques.

Topographic evaluation of relatives of patients with keratoconus

PURPOSE

To evaluate topographic corneal changes in relatives of patients with keratoconus (KCN).

METHODS

In a prospective study, 300 eyes of 150 relatives of 45 patients with KCN were evaluated. Complete slit-lamp examination, refraction, and corneal topography were performed for all eyes. The topographic indices for diagnosis of KCN were from Rabinowitz criteria.

RESULTS

The study included 84 (56%) female and 66 (44%) male subjects. Mean age was 32.4 +/- 15 years (range, 16-83 years). KCN was diagnosed in 14% of the subjects and another 7.3% were suspicious for KCN. The overall prevalence of astigmatism was 58%, including 42.1% in the KCN group, 66.7% in the KCN suspect group, and 49.6% in the healthy group. Thirty-one eyes had high regular astigmatism (>1.5 D) including 17 (54.8%) in the KCN group and 14 (45.2%) in the healthy group. Oblique astigmatism was seen in 33 (11%) eyes, including 34.2% in the KCN group, 47.6% in the suspicious KCN group, and 4.6% in the healthy group.

CONCLUSIONS

Relatives of patients with KCN have a high prevalence of undiagnosed KCN. Corneal topography is important for the diagnosis of KCN and KCN suspects in family members of patients with KCN. Therefore, keratorefractive surgery should be considered cautiously in these individuals.