Canine central corneal thickness measurements via Pentacam-HR® , optical coherence tomography (Optovue iVue® ), and high-resolution ultrasound biomicroscopy

Multiple congenital ocular anomalies in three related litters of Jack Russell Terrier puppies

OBJECTIVE

To describe multiple congenital ocular anomalies in three litters of Jack Russell Terrier puppies.

ANIMALS STUDIED

Seven purebred Jack Russell Terrier puppies from three related litters and their four parents.

PROCEDURES

Medical records of the puppies and their parents were evaluated. All dogs underwent a complete ophthalmic examination, followed by bilateral ocular ultrasonography in two of the puppies with complete corneal opacity. One eye from an affected puppy was subjected to histopathology. A complete database of pedigrees was built, and individual inbreeding was evaluated.

RESULTS

The most commonly diagnosed ocular anomalies in the puppies were: various anomalies of the fundus (12/14 eyes); microphthalmia (10/14 eyes); sclerocornea (8/14 eyes); and persistent pupillary membranes (7/14 eyes). Six out of seven puppies had at least two ocular abnormalities, and only one puppy was normal. Four out of seven puppies had sclerocornea, a particular corneal opacity to date described only in Spanish Podenco dogs. No ocular abnormalities were found in the parents examined (4/4). Analysis of the pedigrees showed that all the puppies and two parents were inbred, and the individual values of the inbreeding puppies were greater than 6.25% in two litters.

CONCLUSIONS

Inbreeding with closely related Jack Russell Terriers may result in severe congenital eye abnormalities in puppies.

Corneal thickness and anterior chamber depth of the normal adult horse as measured by ultrasound biomicroscopy

OBJECTIVE

To determine corneal thickness (CT) and axial anterior chamber depth (ACD) using ultrasound biomicroscopy (UBM) in normal adult horses. To compare corneal thickness measurements between UBM and ultrasonic pachymetry.

ANIMALS STUDIED

Sixty eyes of 30 healthy adult horses aged 8-24 years.

PROCEDURES

Ultrasonic pachymetry (velocity of 1640 m/s) was utilized to obtain measurements of the central, superior, temporal, inferior, and nasal cornea. Triplicate images of the same corneal locations were acquired using UBM (50 MHz). Images of the axial anterior chamber were used to measure ACD. Intraocular pressure (IOP) was estimated using rebound tonometry, and axial globe length was measured using ultrasonographic biometry.

RESULTS

CT (mean ± SD µm) measured by UBM was 854 ± 61 (central), 994 ± 58 (superior), 930 ± 57 (temporal), 979 ± 55 (inferior), and 898 ± 48 (nasal). CT measured by UBM was greater than that measured by ultrasonic pachymetry at all locations and was statistically significant at all locations except inferior (p = 0.0006-0.048). No sex nor age effect was detected for CT at any location. The repeatability of ultrasonic pachymetry was superior to that of UBM. Mean ± SD ACD was 5.74 ± 0.41 mm. A weak positive correlation was identified between central CT and IOP and between central CT and axial globe length.

CONCLUSIONS

Normal data for CT and ACD of the adult horse obtained using UBM are provided. CT determined by UBM was greater relative to pachymetry at all corneal locations.

The feasibility of clinical evaluation for anterior uveitis through spectral-domain optical coherence tomography in dogs

OBJECTIVE

To evaluate the clinical application of spectral-domain optical coherence tomography (SD-OCT) for anterior uveitis in dogs.

ANIMALS AND PROCEDURES

Client-owned dogs presenting with anterior uveitis and clinically healthy dogs were enrolled in this study. Included eyes were divided into 5 groups by flare grade and 3 groups by cell grade through slit-lamp biomicroscopy. Each eye was examined using SD-OCT following slit-lamp biomicroscopy. The ratio of aqueous signal intensity to air signal intensity, which is called the aqueous-to-air relative intensity (ARI) index, was used to evaluate the flare grade. Cell number, central corneal thickness (CCT), and the presence of keratic precipitates (KPs) were analyzed on SD-OCT. The OCT parameters, including ARI index, cell number, and CCT, were compared to the slit-lamp clinical flare and cell grade.

RESULTS

Thirty-six eyes with anterior uveitis and 27 healthy eyes were enrolled. The ARI index showed a significant correlation with clinical flare grade (r_s  = 0.811, p < .001). In multiple regression analysis, the ARI index and CCT showed a significant negative correlation (r = -0.258, p = .044). The number of cells on SD-OCT significantly increased with cell grade on slit-lamp biomicroscopy (r_s  = 0.653, p < .001). The clinical flare grade and CCT were significantly correlated in the partial correlation analysis after controlling for age (partial correlation coefficient = 0.471, p = .002). KPs were observed in 61% of the eyes with flare using SD-OCT (22/36 eyes).

CONCLUSIONS

Spectral-domain optical coherence tomography could provide quantitative information, including the ARI index, cell counts, and CCT in dogs. SD-OCT is an auxiliary modality for slit-lamp biomicroscopy when evaluating anterior uveitis in dogs.

The effect of central corneal thickness on intraocular pressure values using various tonometers in the dog

OBJECTIVE

To compare intraocular pressure readings from three different tonometers, the Tono-Pen AVIA® (TP), TonoVet® (TV) and TonoVet Plus® (TV+) and to determine how measurements from each tonometer are affected by central corneal thickness (CCT).

ANIMALS

Ninety dogs.

PROCEDURES

Normal dogs and dogs with ocular disease were selected for study inclusion. Central corneal thickness measurements were gathered with the Pachette 4 ultrasonic pachymeter, and IOP measurements were gathered with the three tonometers in random order. ANOVA or Wilcoxon tests were utilized for overall group comparisons. Linear regression analyses were utilized to determine the association between IOP and CCT.

RESULTS

When comparing tonometers to each other, for all dogs, readings from the TV+were significantly different compared to the TV (p = <.0001) and TP (p = <.0001); however, there was no significant difference between the TV and the TP (p = .999). Linear regression did not find any significant correlation between corneal thickness and IOP readings with any tonometer when looking at normal dogs or when including dogs with ocular abnormalities.

DISCUSSION

This study did not find a significant correlation between an increase in CCT and increase in IOP reading in any tonometer comparison amongst normal and dogs with ocular abnormalities. The TV+produced consistently and significantly higher readings, but measurements did not exceed the expected IOP range in normal dogs. For consistency, the same tonometer should be used when monitoring IOP over time.

Optical coherence tomography of the Tokay gecko (Gekko gecko) eye

OBJECTIVE

To provide images of the anterior and posterior structures of the gecko eye using spectral domain optical coherence tomography (SD-OCT).

ANIMALS AND PROCEDURES

Eight ophthalmologically normal Tokay geckos (Gekko gecko) were used. The nose-cloaca distance and body weight were measured for each gecko. Tomographic images were obtained using SD-OCT without the use of anesthetic or mydriatic agents. The central corneal thickness (CCT), the anterior chamber depth (ACD), and the length of the conus papillaris (CP) were manually measured using OCT images. The thickness of the retinal nerve fiber layer (RNFL) around the CP and the retinal thickness in all four quadrants (superior, nasal, inferior, and temporal areas) were automatically measured using the OCT software program.

RESULTS

The mean values of the nose-cloaca distance and body weight were 13.8 ± 0.9 cm and 41.3 ± 9.0 g, respectively. The mean values of CCT, ACD, and CP length were 177.6 ± 20.9 µm, 1205.0 ± 79.9 µm, and 1546.4 ± 208.8 µm, respectively. The mean value of RNFL thickness was 52.0 ± 8.2 µm, and the superior region was the thickest. The mean value of total retinal thickness was 202.5 ± 9.4 µm, and the temporal region was the thickest.

CONCLUSIONS

Tomographic images of the anterior and posterior segments of the living gecko eye could be obtained using the OCT unit. Multiple retinal layers and anatomical features of the CP were identified.

Baseline retinal OCT measurements in normal female beagles: The effects of eccentricity, meridian, and age on retinal layer thickness

OBJECTIVE

Our aim was to generate baseline optical coherence tomography (OCT) measurements of retinal thickness in female Beagles and to determine how these are affected by meridian, eccentricity, and age.

METHODS

Twenty-three female Beagles, including six puppies (<6 months old), six mature (1.8-8.2 years old), and 11 elderly dogs (>11 years old) were studied. Both retinas of each dog were scanned (in 4 principal meridians) using the Heidelberg Spectralis following ophthalmic examination, refraction, and sedation. In each eye and each meridian, total retinal, outer retinal, and nerve fiber layer (NFL) thickness were measured from the disc rim up to 6 mm peripherally.

RESULTS

The canine retina is thickest dorsally and thinnest ventrally. Total retinal, outer retinal, and NFL thickness decrease progressively and significantly as a function of eccentricity. The greatest eccentricity-dependent thinning occurs dorsally. This thinning is due mostly to NFL tapering, while the eccentricity-dependent change in outer retinal thickness is more moderate, especially in the lateral meridian, possibly due to the presence of the visual streak. The retina is thickest in puppies, but there were no significant differences between mature and elderly dogs.

CONCLUSIONS

Our results provide normative values for total, outer, and inner retinal thickness in female dogs and may facilitate OCT use in the diagnosis of canine glaucoma and inherited retinopathies.

Surgically induced astigmatism in canines following sutured dorsonasal vs dorsotemporal clear corneal incisions

OBJECTIVES

To investigate use of the Pentacam® HR for evaluation of surgically induced corneal astigmatism (SIA) in canines undergoing bilateral phacoemulsification and determine differences between dorsonasal and dorsotemporal clear corneal incisions.

ANIMALS

Client-owned canines undergoing bilateral phacoemulsification.

PROCEDURES

Patients received anterior segment imaging pre-operatively, immediately post-operatively, and 2-4 months post-operatively (follow-up). Total corneal refractive power was used to determine SIA. Surgically induced astigmatism was compared between right and left eyes, representing dorsotemporal and dorsonasal incisions, respectively. Repeated measures analyses were used between time points and paired t test compared SIA between eyes.

RESULTS

Complete imaging series were obtained for seven patients. Follow-up imaging occurred at a median of 112 days (range 60-132 days) post-operatively. For repeated measures analyses, significant differences were found between pre- and immediate post-operative values (P < 0.01), and between immediate post-operative and follow-up values (P < 0.01). There was no significant difference between pre-operative and follow-up values. Surgically induced astigmatism was significantly different between right and left eyes, with values of 2.01 ± 1.24 D and 3.05 ± 1.58 D at 3 mm radius (P < 0.05), and 2.04 ± 1.18 D and 3.06 ± 1.27 D at 4 mm radius (P < 0.05) for dorsotemporal and dorsonasal incisions, respectively.

CONCLUSIONS

Preliminary investigation revealed improvement of corneal SIA 2-4 months post-operatively, but development of significantly more SIA in dorsonasal vs dorsotemporal incisions. This prompts consideration of patient or microscope rotation to create a more dorsotemporal incision when possible.

Anterior segment parameters in normal dogs using the Pentacam® HR Scheimpflug system

OBJECTIVE

To describe and compare normative anterior segment parameters between canine age groups using the Pentacam^® HR Scheimpflug camera (Pentacam).

ANIMALS STUDIED

Thirty-six sedated dogs (60 eyes) of varying ages and breeds were imaged with the Pentacam; only nondiseased anterior segments were included.

PROCEDURES

Dogs were divided into three age groups: Group 1 (1-5 years), Group 2 (6-10 years), and Group 3 (11-15 years). Values assessed included central corneal thickness (CCT), anterior and posterior corneal elevation (ACE/PCE), anterior and posterior corneal curvature metrics, corneal volume (CV), anterior and posterior corneal astigmatism (AA/PA), anterior chamber depth (ACD), anterior chamber volume (ACV), and anterior chamber angle (ACA). Tukey-adjusted pairwise comparisons were performed.

RESULTS

Overall CCT (mean ± SD) was 631.07 ± 59.91 µm. Central corneal thickness was 608.60 ± 48.63 µm for Group 1, 648.57 ± 51.06 µm for Group 2, and 635.37 ± 73.71 µm for Group 3. Anterior corneal elevation (ACE) measured 9.08 ± 0.58 mm, PCE measured 8.04 ± 0.50 mm, and CV was 58.13 ± 5.39 mm³ . Astigmatism values were 1.34 ± 0.94 D for AA and 0.46 ± 0.44 D for PA. Anterior chamber values were 3.76 ± 0.56 mm for ACD, 383.68 ± 66.24 mm³ for ACV, and 23.62 ± 29.33˚ for ACA. Significant differences were found between Groups 1 and 2 for CV (55.08 ± 4.08 mm³ and 60.32 ± 4.19 mm³ , respectively), (P = 0.02).

CONCLUSIONS

Corneal volume significantly increased between Group 1 and Group 2. Central corneal thickness increased from Group 1 to Group 3, but was not significant with the current sample size. There were no other differences between age groups.