A comparison of central corneal thickness measured using noncontact methods and ultrasonic pachymetry

Aim

The aim of this study is to compare central corneal thickness (CCT) measurements in healthy eyes using ultrasonic pachymetry (UP) with values obtained using anterior segment spectral domain optical coherence tomography (SD-OCT), the Scheimpflug camera system, and noncontact specular microscopy.

Material and Methods

One hundred and twenty-five eyes of 117 healthy individuals (56 women, 61 men) were included. All patients underwent consecutive CCT measurement with UP, the Scheimpflug camera, anterior segment SD-OCT, and specular microscopy. The four devices could be read. Measurements from the four devices were classified in pairs and compared using the paired t-test. Relations between the devices were analyzed using the Pearson test. An alpha error level of P < 0.05 was regarded as statistically significant.

Results

The mean age of the healthy individuals included in the study was 34.75 ± 14.55 years (20-76). Mean CCT values were 541.21 ± 29.24 μm with UP, 539.26 ± 29.27 μm with the Scheimpflug camera system, 532.21 ± 29.53 μm with SD-OCT, and 534.45 ± 29.20 μm with specular microscopy. The differences in measurements at the paired t-test were statistically significant (P < 0.001 for all). However, measurements using the four devices exhibited significant mutual correlation (P < 0.001 for all).

Conclusions

CCT can be measured using different devices. Noncontact methods have now begun replacing UP, regarded as the gold standard. Although CCT values obtained from different devices were correlated, the difference between these measurements was statistically significant. Therefore, the same device should be used for measurement in the diagnosis and follow-up of diseases such as corneal ectasia and glaucoma where corneal thickness is important.

The crested caracara (Caracara plancus) eye: Morphologic observations and results of selected diagnostic tests

PURPOSE

To provide a descriptive investigation about relevant features of the crested caracara's eye (Caracara plancus) and bony orbit, as well as provide data for ophthalmic tests.

METHODS

Morphological observations and the following diagnostic tests were performed: Schirmer tear test (STT), conjunctival flora evaluation, corneal touch threshold (CTT), intraocular pressure (IOP), central corneal thickness (CCT), B-mode ocular biometry, palpebral fissure length (PFL), and corneal diameter (CD) in 19 healthy birds, plus two macerated skulls. Not all birds were used for each test.

RESULTS

STT: 7.84 ± 3.05 mm/min; CTT: 2.46 ± 1.10 cm; IOP: 19.18 ± 3.07 mmHg; CCT: 0.31 ± 0.02 mm; PFL: 13.32 ± 1.06 mm; CD: 10.26 ± 2.43 mm; Axial globe length: 1.89 ± 0.06 cm; Anterior chamber depth: 0.27 ± 0.06 cm; Lens axial length: 4.55 ± 0.06 cm; Vitreous chamber depth: 1.2 ± 0.07 cm. The most frequent conjunctival bacterial isolates were Corynebacterium sp. (10/23.8%), Staphylococcus sp. (9/21.42%), Streptococcus sp. (7/16.6%), and E. coli (7/16.66%). The large lateral part of the palatine bone likely plays a role in the ventral protection of the globe against the impact of prey. Observed results are generally reflective of increased body mass compared to other Falconiformes, with values approaching those of similar sized Accipitriformes.

CONCLUSIONS

These data may help veterinarians recognize peculiar morphologic features and perform a more accurate diagnosis of eye diseases of this avian species.

Comparison of central corneal thickness measurements with standard ultrasonic pachymetry and optical devices

BACKGROUND

To compare the repeatability and agreements of central corneal thickness measurements of healthy individuals obtained by Scheimpflug-Placido topographer (Sirius), anterior segment spectral domain optical coherence tomography (Spectralis) (AS-OCT), optical biometry (AL-Scan) and ultrasonic pachymetry.

METHODS

Sixty-four eyes of 32 subjects with no ocular or systemic diseases were included in this study. Central corneal thickness measurements performed with Sirius, AS-OCT, optical biometry AL-Scan and ultrasonic pachymetry were compared. Bland-Altman analysis was used to demonstrate agreement between methods. Intra-examiner repeatability was assessed by using intraclass correlation co-efficients (ICCs).

RESULTS

Sixty-four eyes of 32 patients were enrolled (25 male and seven female). The mean age was 23.8 years (range 21-28 years). The mean central corneal thickness was 560.8 ± 37.2 μm, 528.8 ± 32.0 μm, 546.4 ± 33.8 μm, 543.4 ± 35.8 μm for the ultrasonic pachymetry, optical biometry AL-Scan, Sirius and AS-OCT values, respectively. The thickest mean central corneal thickness (560.8 ± 37.2 μm) was obtained from ultrasonic pachymetry. The thinnest mean central corneal thickness (528.8 ± 32.0 μm) was obtained from optical biometry AL-Scan. All four modalities of central corneal thickness measurements correlated closely with each other. Intra-examiner repeatability was excellent for all devices with ICCs > 0.90.

CONCLUSIONS

In conclusion, although measurements obtained by various methods correlate well, the measurements are not directly interchangeable. Between ultrasonic pachymetry and the three optical instruments tested, significant diferences can be seen. Therefore, the same imaging method should be used in corneal thickness follow-ups.

Effects of 5% sodium chloride ophthalmic ointment on thickness and morphology of the normal canine cornea

OBJECTIVE

To determine the effect of 5% sodium chloride ophthalmic ointment (5% NaCl) on thickness and morphology of the normal canine cornea using ultrasonic pachymetry (USP), in vivo confocal microscopy (IVCM), and Fourier-domain optical coherence tomography (FD-OCT).

METHODS

Five healthy laboratory Beagles received ophthalmic examinations including USP, IVCM, and FD-OCT prior to and at fixed intervals following treatment. The right and left eyes were treated with 5% NaCl and artificial tears ophthalmic ointment (AT), respectively, every 2 hours for 4 treatments/d (days 2-9), and then hourly for 7 treatments/d (day 10). Treatment groups were statistically compared using mixed-effects linear regression.

RESULTS

Treatment with 5% NaCl resulted in a 12 μm decrease in corneal thickness from baseline (P < .001), while there was no significant difference in corneal thickness between values obtained at baseline and following treatment with AT (P = .82). Epithelial cell density significantly increased from baseline (530 ± 52 cells/mm² ) to 577 ± 43 and 567 ± 15 cells/mm² with 5% NaCl and AT, respectively (P = .003 and .005, respectively). However, keratocyte cell density in the anterior and posterior stroma and endothelial cell density did not significantly differ following treatment with 5% NaCl or AT ointment (P > .05).

CONCLUSIONS

Short-term topical treatment with 5% NaCl decreased corneal thickness in normal dogs with no observable changes in corneal morphology or signs of ocular toxicity.

Corneal Thickness in Highlanders

Patyal, Sagarika, Amit Arora, Arun Yadav, and Vijay K. Sharma. Corneal thickness in highlanders. High Alt Med Biol. 18:56-60, 2017.

BACKGROUND

Corneal thickness is an important parameter with diagnostic and therapeutic implications. Various studies have highlighted increase in corneal thickness in lowlanders on ascending to high altitude. However, there are no studies in the published literature pertaining to corneal thickness of the highlanders who are inhabitants of such altitudes. Hence, study was carried out with objective to determine the corneal thickness of highlanders living at heights of more than 11,000 feet and compare it with corneal thickness of lowlanders.

MATERIALS AND METHODS

The highlander participants of the study consisted of inhabitants of Ladakh region of India at an altitude of 11,000 feet or more and lowlander participants consisted of inhabitants at an altitude of 1500 feet. A total of 254 highlanders and 212 lowlanders participated. A mean of 25 measurements of central corneal thickness (CCT) of every participant was obtained for each eye using ultrasonic pachymeter.

RESULTS

The mean age of the participants was 41.8 (15.9) and 47.7 (17.7) years among lowlanders and highlanders, respectively. The highlanders had 11.95 μm lower mean CCT reading compared to lowlanders after adjusting for age and sex (p value <0.001). There was no statistically significant difference in mean CCT readings of right eye and left eye in either lowlanders or highlanders. Age also had a significant effect after adjustment for location and gender (p = 0.001). CCT decreased by 0.31 μm with every year increase in the age. Gender had no statistically significant effect.

CONCLUSION

This study found statistically significant difference in CCT measurements between highlanders and lowlanders. The thinner corneas of highlanders may have a bearing on diagnosis and treatment of glaucoma, refractive surgery, contact lens fitting implantation of Intacs, and astigmatic keratectomy done on such patients. The study also opens the scope of further research in the area.

Central corneal thickness measurements in normal dogs: a comparison between ultrasound pachymetry and optical coherence tomography

OBJECTIVE

To compare central corneal thickness (CCT) measurements obtained from normal canines using a spectral-domain optical coherence tomography device (SD-OCT) and an ultrasonic pachymeter.

ANIMALS

Fifteen clinically normal dogs.

PROCEDURES

Dogs were briefly anesthetized with propofol. Central corneal thickness measurements were obtained from both eyes of each animal four times by one operator using a SD-OCT system. The CCT was automatically calculated using the pachymetry software generated from eight radial scans, 6 mm in length. Ultrasonic pachymetry was then performed in both eyes of each animal by one operator five times in succession. The CCT was recorded for each modality and compared statistically for agreement and bias.

RESULTS

Fifteen dogs (seven castrated male, eight spayed female) with a mean age of 2.3 ± 1.3 years were examined. The mean CCT for all eyes examined via SD-OCT and ultrasonic pachymetry (velocity set at 1636 m/s) was 587.72 ± 32.44 μm and 598.54 ± 32.28 μm, respectively. Ultrasonic pachymetry consistently overestimated CCT as compared to OCT by a mean value of 10.82 μm (P < 0.0001). No significant difference in CCT was found based on the age or sex of the animal. There was no significant difference in CCT measurements between replicates performed by the same operator for each modality. The coefficient of variation within and between imaging modalities was low (range 0.63-2.5%). The intraclass correlation coefficient comparing methods was 0.92.

CONCLUSIONS

Correlation between modalities was excellent; however, ultrasonic pachymetry set at a standard velocity of 1636 m/s overestimates CCT as compared to OCT.

Reliability of RTVue, Visante, and slit-lamp adapted ultrasonic pachymetry for central corneal thickness measurement

PURPOSE

To evaluate reliability of Fourier-domain optical coherence tomography (OCT) (RTVue), time-domain OCT (Visante), and slit-lamp adapted ultrasonic pachymetry (SL-US) in the measurement of central corneal thickness (CCT).

MATERIALS AND METHODS

Thirty healthy volunteers visited our clinic 3 times and fifty eyes were measured by one physician. RTVue and Visante were randomly performed, and then SL-US, in which the ultrasound probe was inserted into the Goldmann tonometry mount, was done. During the second visit, each measurement was repeated 3 times. Measurements on the second visit were averaged, and agreement among the instruments was investigated with Bland-Altman plots.

RESULTS

RTVue showed smaller repeatability coefficient than Visante and SL-US (4.7, 8.3, and 7.7 μm, respectively). Intersession reproducibility of RTVue and Visante was worse than their repeatability. CCT of RTVue was estimated to be maximally different by 11.8 μm from CCT of Visante and 8.8 μm from CCT of SL-US. The repeatability coefficient of SL-US was 7.7 μm and its reproducibility was similar to the repeatability.

CONCLUSION

CCT measured by RTVue showed good reliability and generally agreed with Visante and SL-US. SL-US was as reliable as triple touching conventional US even with a single touch on the cornea.