Introduction
In brachycephalic dog breeds, facial retrusion, proximodistal shortening of the snout, and widening of the hard palate has been associated with several genetic loci.1,2,3 Some brachycephalic dog breeds, such as Bulldogs, have been rising in popularity according to the American Kennel Club, and breeders and pet owners worldwide appear to be favoring shorter and smaller brachycephalic features.4 This conformation is also influenced by some breed standards that supported brachycephaly despite many associated health problems.4,5,6,7,8,9,10,11
Common ophthalmic disorders in several brachycephalic breeds include ulcerative and nonulcerative keratitis, keratoconjunctivitis sicca (KCS), prolapse of the nictitans gland, nasal entropion, nasal fold trichiasis, lagophthalmos, and euryblepharon.4,7,9,12,13,14 Among all dogs affected with ocular disorders, brachycephalic breeds appear to be overrepresented in veterinary ophthalmology. This finding is consistent with the literature on ulcerative keratitis that showed brachycephalic breeds, specifically Pugs, Bulldogs, Pekingese, and Shih Tzus, are overrepresented in cases of ulcerative keratitis.15,16 Mazzucchelli et al12 found that prolapsed nictitans glands was diagnosed more commonly in French Bulldogs, English Bulldogs, and Lhasa Apsos. English Bulldogs, Lhasa Apsos, Shih Tzus, and Pugs were all reported to be overrepresented in cases of KCS, compared with the general population.17 This overrepresentation is also apparent in a non–peer-reviewed, 9-year longitudinal white paper by a pet insurance company that reported brachycephalic dogs are 44% more likely to have a submitted claim for conjunctivitis than are nonbrachycephalic breeds.18 In addition, the percentage of claims to the insurance agency because of corneal ulcers and ocular trauma significantly increased (377% and 137%, respectively) during their study period.
These previously noted studies are limited by the absence of confirmation of ophthalmic diagnosis by an ophthalmologist, design of a series of single ocular disease cases within an ophthalmic referral population, socioeconomic bias associated with ensured pets, elementary statistically analysis, or lack of focus on the brachycephalic group. At present, there is a dearth of literature addressing the most common ophthalmic diseases in individual brachycephalic breeds and for an overall population of brachycephalic dogs in an ophthalmology referral population. Therefore, the purpose of the present was to identify the most common ocular disorders and their frequency within 7 brachycephalic dog breeds referred by general practitioners to a tertiary referral center.
Materials and Methods
Animals
Medical records of 7 brachycephalic breeds (Boston Terriers, English Bulldogs, French Bulldogs, Lhasa Apsos, Pekingese, Pugs, and Shih Tzus) presented as an internal or external referral to the ophthalmology service at Cornell University Hospital for Animals from January 2008 to December 2017 were reviewed. Brachycephalic breeds included in the study were subjectively chosen by the research team as having enough dogs to make meaningful comparisons. Dogs included in the present study were required to have medical records with ≥ 1 ophthalmic disorder reported on their ophthalmic examination.
All dogs were examined by, or under the supervision of, a diplomate of the American College of Veterinary Ophthalmology. Slit-lamp biomicroscopy (SL14, SL15, or SL17; Kowa American Corp) and binocular indirect ophthalmoscopy (Omega 2C or Omega 500; Heine USA Ltd) were performed. When indicated, mydriasis was induced to examine the posterior segment of the eye with 1% tropicamide. A Schirmer tear test I (Schering-Plough Corp), fluorescein staining, (Akorn Inc), and intraocular pressure (Tono-Pen; Tono-Pen AVIA; Reichert Technologies; TonoVet; Jorgensen Laboratories Inc) measurements were performed when appropriate.
Medical records review
Data were collected from each dog’s medical record discharge summary, ophthalmic examination form, or both, including patient signalment, diagnosed ophthalmic disorders, affected eyes, and number and dates of visits. Unilateral and bilateral diseases were recorded as well as multiple diagnoses for the same eye.
Statistical analysis
Descriptive statistical analyses regarding breed, sex, age at first examination, anatomic location, diagnosis, and whether diseases were unilateral or bilateral were performed with commercial software (Excel 2018; Microsoft Corp). All data were reported with the number of dogs as the denominator, except for anatomic location where a dog could contribute 1 or both eyes and a single eye could present with ≥ 1 diagnoses, resulting in categorization in > 1 anatomic location.
Univariable analysis between age at first examination and breed was performed with a Welch 1-way ANOVA to account for heteroscedasticity between groups; normality of residuals was confirmed visually. A χ2 test was used to assess potential differences in sex distribution between breeds; all test assumptions were met. Multivariable logistic regression was used to determine breed differences in the odds of developing each of the 5 most common diseases in the study population, with age at first presentation evaluated as a confounding variable and Shih Tzus used as the reference group. Age at first presentation was removed from the model if values were P > 0.10; since breed was the variable of interest, it was retained in all final disease models regardless of statistical significance. The assumption of linear relationships was assessed by examining linearity between the independent variable and log odds of continuous variables remaining in the final models. Data analyses were performed with statistical software (SAS version 9.4; SAS Institute Inc). Values of P ≤ 0.05 were considered significant.
Results
Among the 1,031 dogs that matched the 7 breeds of interest, the inclusion criteria were met by 970 dogs (58 dogs had incomplete medical records, and 3 dogs had normal findings on eye examination). The breed population included the following represented breeds: Shih Tzus (333/970 [34.3%]), Pugs (202/970 [20.8%]), Boston Terriers (161/970 [16.6%]), English Bulldogs (119/970 [12.3%]), Lhasa Apsos (69/970 [7.1%]), Pekingese (48/970 [4.9%]), and French Bulldogs (38/970 [3.9%]). There was a significant (P < 0.001) difference in the distribution of breeds presenting to the ophthalmology service. Shih Tzus were the most common breed and presented at a higher frequency for an ophthalmic examination than all other breeds; French Bulldogs were the least common breed. The study population consisted of 435 (44.8%) females and 535 (55.2%) males (Table 1). There was no significant (P = 0.10) difference in sex distribution between breeds. Males were significantly (P = 0.01) more likely to be sexually intact than females (25% [133/535] vs 18% [79/435], respectively).
Number (%) of dogs characterized by sex distribution and breed for 7 brachycephalic dog breeds in an ophthalmic referral population.
Breed | Dogs | Sexually intact males | Sexually intact females | Castrated males | Spayed females | |
---|---|---|---|---|---|---|
Boston Terrier | 161 (16.6)b,c | 21 (2.2) | 5 (0.5) | 82 (8.4) | 53 (5.5) | |
English Bulldog | 119 (12.3)c | 35 (3.6) | 10 (1.0) | 35 (3.6) | 39 (4.0) | |
French Bulldog | 38 (3.9)e | 12 (1.2) | 5 (0.5) | 9 (0.9) | 12 (1.2) | |
Lhasa Apso | 69 (7.1)d | 4 (0.4) | 5 (0.5) | 30 (3.1) | 30 (3.1) | |
Pekingese | 48 (4.9)d,e | 6 (0.6) | 7 (0.7) | 20 (2.1) | 15 (1.5) | |
Pug | 202 (20.8)b | 27 (2.8) | 23 (2.4) | 88 (9.1) | 64 (6.6) | |
Shih Tzu | 333 (34.3)a | 28 (2.8) | 24 (2.5) | 138 (14.2) | 143 (14.7) | |
Total | 970 (100) | 133 (13.6) | 79 (8.1) | 402 (41.4) | 356 (36.6) |
Different superscript letters represent significant (Bonferroni corrected P < 0.05) differences in breed frequency on the basis of χ2 analysis.
The median age at first examination was 7 years with a range of 23 days to 22 years. Overall, the number of dogs presented for their first examination increased with age. When stratified by breed, Shih Tzus, Boston Terriers, and Lhasa Apsos most strictly followed this trend, whereas Pekingese and Pugs plateaued at 4 to 6 years. English Bulldogs had a unique distribution, with the highest number of these dogs seen at age 1 to 3 years. The number of French Bulldogs presented for their first examination showed little change with age (Figure 1).
Classification of diseases on the basis of anatomic location for all affected eyes demonstrated that 66.3% (1,905/2,873) of all disorders were located in either the cornea (1,014/2,873 [35.3%]) or adnexa (891/2,873 [31%]). The remaining anatomic locations represented 33.7% (968/2,873) of all disorders and were distributed as lens (463/2,873 [16.1%]), retina (141/2,873 [4.9%]), uvea (39/2,873 [1.4%]), vitreous (47/2,873 [1.6%]), orbit (43/2,873 [1.5%]), and other (235/2,873 [8.2%]).
Unilateral disease most commonly affected the orbit (44/44 [100%]), uvea (24/40 [60%]), or a region that did not fit the adopted anatomic criteria (120/236 [50.8%]). Bilateral diseases predominately affected the lens (394/465 [84.7%]) and adnexal structures (738/891 [82.8%]).
In total, there were 140 unique diagnoses, of which 5 conditions affected ≥ 100 dogs and represented 40.4% (1,161/2,873) of all diagnoses in the study. The most prevalent disorders among all breeds were corneal ulcers (373/2,873 [13%]), KCS (294/2,873 [10.2%]), corneal pigmentation (CP; 281/2,873 [9.8%]), immature cataracts (109/2,873 [3.8%]), and uveitis (103/2,873 [3.6%]).
The frequency of all ophthalmic disorders was evaluated for each breed. The 5 most commonly diagnosed ophthalmic disorders, and their frequency of diagnosis, within each breed (Table 2), and the 5 most commonly diagnosed diseases affecting ≥ 100 dogs within the study population were determined (Figure 2). Breed was associated with the odds of developing some of the 5 most commonly diagnosed diseases (Table 3). The odds of a corneal ulcer diagnosis significantly (P = 0.03) differed by breed, with Boston Terriers having greater odds relative to Shih Tzus. The odds of having KCS significantly differed by breed (P < 0.001) as well as by age (P < 0.001), with English Bulldogs and Lhasa Apsos having a greater odds and Boston Terriers having reduced odds relative to Shih Tzus. The odds of KCS increased by 10% for each 1-year increase in age at first examination. The odds of corneal pigmentation (CP) also significantly differed by breed (P < 0.001) and age (P < 0.001), with Pugs and Pekingese having greater odds and English Bulldogs and Boston Terriers having reduced odds relative to Shih Tzus. The odds of CP increased by a factor of 1.1 for each 1-year increase in age at first examination. Immature cataracts differed by breed (P = 0.002) and age (P < 0.001), with Boston Terriers having greater odds, compared with Shih Tzus. The odds of immature cataracts increased by a factor of 1.1 for each 1-year increase in age at first examination. The odds of uveitis did not differ by breed (P = 0.38).
Differences in number (frequency [%]) of the 5 most common ophthalmic disorders within each of the 7 brachycephalic dog breeds in an ophthalmic referral population.
Variable | Shih Tzu | Pug | Boston Terrier | English Bulldog | Lhasa Aspo | Pekingese | French Bulldog | Overall |
---|---|---|---|---|---|---|---|---|
Affected eyes | 1,012 | 558 | 567 | 320 | 201 | 131 | 84 | 2,873 |
Diagnosis | ||||||||
CP | 102 (10.1)b | 128 (22.9)a | — | — | 15 (7.5)b,c | 23 (17.6)a | — | 281 (9.8)b |
DIST | 46 (4.5)c | — | — | 37 (11.6)a | — | — | — | — |
ENTR | — | — | — | 46 (14.4)a | — | — | — | — |
GLAU | 42 (4.2)c | — | 30 (5.3)b | — | — | — | 3 (3.6)b* | — |
IMCAT | — | 23 (4.1)c | 39 (6.9)b | — | 8 (4.0)c† | — | — | 109 (3.8)c |
INCCAT | — | — | 28 (4.9)b | — | — | — | — | — |
KCS | 127 (12.5)a | 51 (9.1)b | — | 36 (11.3)a | 34 (16.9)a | 20 (15.3)a,b | 4 (4.8)b | 294 (10.2)b |
PERF | — | 24 (4.3)c | — | — | — | 7 (5.3)b | — | — |
PNG | — | — | — | 35 (10.9)a | — | — | 4 (4.8)b | — |
PP | — | — | — | — | 14 (7.0)c | — | — | — |
TRICH | — | — | — | — | — | 10 (7.6)a,b | — | — |
ULCER | 112 (11.1)a | 70 (12.5)b | 84 (14.8)a | 43 (13.4)a | 24 (11.9)a,b | 23 (17.6)a | 17 (20.2)a | 373 (13.0)a |
UV | — | — | 34 (6.0)b | — | 8 (4.0)c† | — | 4 (4.8)b | 103 (3.8)c |
P value | < 0.001 | < 0.001 | < 0.001 | 0.67 | < 0.001 | 0.008 | < 0.001 | < 0.001 |
Different superscript letters within a breed (ie, columns) represent significant (Bonferroni corrected P < 0.05) differences in disease frequency on the basis of χ2 analysis.
Indicates conjunctival dermoid, GLAU, keratitis, corneal laceration, and retinal degeneration as the frequency was the same for all these diseases in French Bulldogs.
Both IMCAT and UV are listed for Lhasa Aspo because the frequency was the same for both of these diseases.
— = Not 1 of the 5 most common diagnoses for the breed. CP = Corneal pigmentation. DIST = Distichia. ENTR = Entropion. GLAU = Glaucoma. IMCAT = Immature cataract. INCCAT = Incipient cataract. KCS = Keratoconjunctivitis sicca. PERF = Corneal perforation. PNG = Prolapsed nictitans gland. PP = Pseudophakia. TRICH = Trichiasis. ULCER = Corneal ulcer. UV = Uveitis.
Final logistic regression analysis results for the 5 most commonly diagnosed ophthalmic diseases affecting ≥ 100 dogs within the study population of 7 brachycephalic breeds.
Variable | OR (95% CI) | P value* |
---|---|---|
Corneal ulcer | ||
Boston Terrier | 1.8 (1.2–2.8) | 0.05 |
English Bulldog | 1.2 (0.8–1.9) | 0.53 |
French Bulldog | 1.7 (0.8–3.4) | 0.47 |
Lhasa Apso | 1.0 (0.6–1.8) | 0.25 |
Pekingese | 2.1 (1.1–3.8) | 0.11 |
Pug | 1.1(0.7–1.6) | 0.13 |
Shih Tzu | Reference | — |
Keratoconjunctivitis sicca | ||
Age | 1.1 (1.1–1.2) | < 0.001 |
Boston Terrier | 0.2 (0.1–0.5) | < 0.001 |
English Bulldog | 1.8 (1.1–3.1) | < 0.001 |
French Bulldog | 0.4 (0.1–1.2) | 0.15 |
Lhasa Apso | 1.6 (0.9–2.7) | 0.005 |
Pekingese | 1.0 (0.5–2.0) | 0.45 |
Pug | 0.7 (0.4–1.0) | 0.46 |
Shih Tzu | Reference | — |
Corneal pigmentation | ||
Age | 1.1 (1.1–1.2) | < 0.001 |
Boston Terrier | 0.1 (0.02–0.2) | < 0.001 |
English Bulldog | 0.1 (0.03–0.5) | 0.03 |
French Bulldog | 0.1 (0.02–1.1) | 0.20 |
Lhasa Apso | 0.4 (0.2–0.9) | 0.97 |
Pekingese | 2.0 (1.0–3.9) | < 0.001 |
Pug | 4.2 (2.8–6.3) | < 0.001 |
Shih Tzu | Reference | — |
Immature cataracts | ||
Age | 1.1 (1.1–1.2) | < 0.001 |
Boston Terrier | 2.9 (1.6–5.1) | < 0.001 |
English Bulldog | 0.6 (0.2–2.0) | 0.35 |
French Bulldog | 1.0 (0.2 –4.7) | 0.87 |
Lhasa Apso | 1.0 (0.4– 2.7) | 0.81 |
Pekingese | 0.3 (0.04–2.0) | 0.15 |
Pug | 1.4 (0.7–2.6) | 0.22 |
Shih Tzu | Reference | — |
Uveitis | ||
Breed | — | 0.38 |
Shih Tzus were used as the reference group. The variable age did not meet the inclusion criteria for the final disease models for corneal ulcer or uveitis.
Values of P < 0.05 were considered significant.
— = Not applicable.
Discussion
To our knowledge, this is the largest single-center, retrospective study to catalog ophthalmic diseases in a referral population of 7 common brachycephalic dog breeds. Our study investigated the frequency of ophthalmic diseases in these brachycephalic breeds as a group and between breeds within the ophthalmic referral population.
In the present study, Boston Terriers, Lhasa Apsos, Pekingese, Pugs, and Shih Tzus were commonly seen for the first time at a later stage of their adult life (approx 7 years old), whereas English Bulldogs and French Bulldogs were commonly seen as young adults (approx 2 to 3 years old). A likely explanation for the age of presentation differences is related to the frequency of the most common diseases within each breed. In English Bulldogs, entropion, distichiasis, and prolapse of the nictitans gland all affected > 10% of dogs. In French Bulldogs, prolapse of the nictitans gland and ocular surface dermoids were together responsible for > 8% of all ophthalmic diseases. These common disorders affecting English Bulldogs and French Bulldogs are often diagnosed in a younger population of animals and could help explain the overall differences in age at the time of first examination.12,14,19 The relevance of this finding may be for early referral of dogs of these breeds affected with the conditions. Notably, the number of Shih Tzus seen for a first-time ophthalmic examination increased with age. This was likely related to the fact that this breed is popular within the study’s referral population and is affected with acquired disorders that tend to be chronic and can progress over time.
Ulcerative keratitis was found to be 1 of 5 most common ocular disorders and was overall the most prevalent disease in the brachycephalic breeds included in the present study. When comparing brachycephalic breeds within the study population to each other, all breeds had high odds of developing ulcerative keratitis. The risk for ulcerative keratitis in brachycephalic dogs is likely a result of skull conformation combined with an increased risk for disorders in other ocular and adnexal structures (eg, KCS, distichiasis, and entropion) as well as a decrease in corneal sensitivity.7,9,15,16,20,21,22,23,24,25 The importance of the findings in the present study may indicate that when brachycephalic dogs are referred to ophthalmology specialists, these 7 breeds more frequently receive a diagnosis of ulcerative keratitis, compared with other ophthalmic diseases. This increase in referrals for this condition may reflect the challenges of diagnosing and managing this condition. Often, fluorescein uptake is the only criterion used to diagnose a corneal ulcer; however, with descemetoceles and ulcers with malacia, fluorescein stain uptake may not be present. Additionally, the frequency of corneal ulcers that are referred with a misdiagnosis (eg, ulcers defined by a referring veterinarian as superficial when the ulcer is deep or when dealing with an infection of a nonhealing ulcer in a Boxer) is sometimes subjective but more commonly seen in a referral center. A multicenter study15 performed in 110 primary care facilities found that purebred brachycephalic dogs are 11 times as likely to develop ulcerative keratitis than mixed-breed dogs. Although that study15 compared nonbrachycephalic dog breeds with brachycephalic breeds, there was a relatively small number of cases per each participating veterinary clinic. Since a definitive diagnosis of ulcerative keratitis can be challenging, the frequency of the disorder within the population at risk calculation in that study15 may be limited by the absence of ophthalmic examination performed by a veterinary ophthalmologist. In a study7 performed in a small animal referral hospital, ulcerative keratitis in brachycephalic breeds was 20 times as likely to be present than in nonbrachycephalic dogs. However, nearly half of these cases were not confirmed by a veterinary ophthalmologist.
Corneal pigmentation and KCS were the second most prevalent diseases within the study population of the present study. Keratoconjunctivitis sicca was one of the most commonly diagnosed diseases in all breeds. Despite Boston Terriers having the lowest odds of KCS among all breeds within our study, KCS was close to being part of the 5 most common ocular disorders in this breed. Future multi-referral center studies would help determine whether a high frequency of KCS is still seen in Boston Terriers in referral populations, as the last known study17 reporting on KCS in Boston Terriers was published 30 years earlier.
In our study population, the frequency of CP was highest among Pugs and Pekingese. Although approximately 20% of these dog breeds were affected, data provided by the Orthopedic Foundation for Animal’s Companion Animal Eye Registry (CAER; formally known as Canine Eye Registry Foundation) reported that the frequency of this condition in Pugs has significantly increased from 1999 (27.0%) to 2015 (62.7%).26 In a study27 at the University of Illinois, pigmentary keratitis was diagnosed in 82.4% of all Pugs that visited the ophthalmology service from 2005 to 2010, which is in accordance with the most recent data provided by the CAER.26 As in previous studies,14,28 the present study found CP to be the most prevalent corneal disease diagnosed in Pugs and having the greatest odds for this disease of all the breeds studied. The frequency disparity found between studies evaluating CP may be explained by geographic differences, age of the animals at the time of an ophthalmic examination, differences in study design between studies, or an underreported disease in our medical records. A recent study29 of Pugs in the UK showed medial entropion of the lower eyelid and increasing age of dogs with a pigmentary keratitis diagnosis as possible underlying causes of pigmentary keratitis. Signs of chronic inflammation in Pugs and other brachycephalic breeds with CP have been reported.27,30 On the basis of the high frequency of CP and the dramatic increase of affected Pugs over time, further studies are warranted to investigate this condition because it can substantially impair vision. In the present study, Boston Terriers, English Bulldogs, and French Bulldogs did not have CP included with the most commonly diagnosed ophthalmic diseases. This difference in CP frequency between breeds could be explained by differences in genetic predisposition, conformation, tear film properties, or to the intrinsic characteristics of the cornea.23,27,29,31 However, differences in study design could also explain the disparity.
When comparing the breeds included in our study with data provided by the CAER between 2010 and 2015, French Bulldogs were underrepresented and Shih Tzus were substantially overrepresented.26 The CAER reported26 examinations were most commonly performed for Boston Terriers and had more than twice the number of dogs of the second most commonly seen breed (ie, French Bulldogs) in our study. In contrast, the number of Boston Terriers in our study was less than half of our most prevalent breed (ie, Shih Tzus). These breed proportion differences between our study and the CAER database26 need to be interpreted in light of the reasons for which the animal was presented for an ophthalmic examination. Whereas CAER examinations are usually requested by prospective or active breeders who have subjectively healthy puppies or young dogs within a breeding age, ophthalmic examinations in our study were often performed on dogs referred for treatment of ocular disorders previously identified by referring veterinarians. In addition, many breeders do not have their dogs evaluated with a CAER examination; therefore, the true frequency of ophthalmic disorders reported in purebred dogs is largely unknown.
Similar to Mazzucchelli et al,12 our data set showed that prolapsed nictitans glands occurred with a high frequency in English Bulldogs and French Bulldogs. Although authors of that study12 also reported Lhasa Apsos as commonly having a prolapsed nictitans gland, this diagnosis was not included in the 5 most common ophthalmic disorders for Lhasa Apsos in our study population. In dolichocephalic breeds, the prolapsed nictitans gland condition was suggested to be caused by a complex multigenic mode of inheritance; however, a genetic basis for this disease in brachycephalic breeds remains unknown.32
In our study, there was a high frequency of cataracts in Boston Terriers, Shih Tzus, and Pugs. In contrast, Lhasa Apsos, English Bulldogs, Pekingese, and French Bulldogs had a low frequency of cataracts. Results of previous retrospective studies33,34 show that Shih Tzus and Boston Terriers have an increased frequency of cataracts. Breed predisposition and age are etiologies suggested for cataract formation.34,35 Although our study did not address causes for cataracts, this could be considered in future studies to better characterize this condition in brachycephalic breeds.
As with many retrospective studies, the authors acknowledge several limitations to our study. The results of our study are likely to have a poor validity for the general population of brachycephalic dogs, as our study population was from a referral hospital and not representative of the general brachycephalic population. In addition, brachycephalic breeds that present to a referral hospital are largely influenced by geographic location and socioeconomic background.36 Furthermore, genetic lines within various geographic locations may also affect the frequency of certain ophthalmic diseases. However, the findings of the present study provided valuable data that may increase awareness of commonly referred ophthalmology cases in specific brachycephalic breeds among general practitioners. In addition, understanding that these disorders are commonly referred to an ophthalmology service will also aid in client education. Lastly, although our study was focused on a referral population, the findings can be extrapolated by the general practitioner to help identify and mitigate some commonly seen diseases (eg, CP) by providing an early intervention approach (eg, ophthalmic lubricants or blepharoplasty).
Analysis of English Bulldogs for frequency the 5 most common ophthalmic diseases within the breed and final logistic regression analysis results for uveitis within the study population lack statistically significant findings. This could be the result of a lack of study power, suggesting further studies are warranted. There were inconsistencies in the management of medical records throughout the period in review. For example, a few animals did not have Schirmer tear test I results or intraocular pressures reported in the ophthalmic examination. The authors speculate that this was attributed to ocular surface disorders that precluded performing these diagnostic tests. However, the authors cannot rule out other reasons such as inadvertently neglecting to perform or report these diagnostics or financial limitations by the owner. Additionally, the inconsistent use of mydriatic agents for examination may have resulted in underestimation of lenticular and posterior segment diseases. It is likely that some of the brachycephalic breeds enrolled in our study were not purebred and that the small cohorts among some of the breeds could affect the results when discussing the frequency of certain disorders within a breed. Nevertheless, data presented herein may provide the foundation for further studies directed toward ocular disorders affecting brachycephalic breeds and should be corroborated by other ophthalmic referral centers.
In conclusion, the most prevalent disorders for the brachycephalic breeds in our ophthalmic referral population were corneal ulcers, KCS, CP, immature cataracts, and uveitis. Although all dogs evaluated in the present study share brachycephalic features, the frequency of specific ophthalmic diseases varied between breeds.
Acknowledgments
No third-party funding or support was received in connection with the present study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
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