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Objectives: To determine the accuracy, precision, and clinical applicability of the ICare® TONOVET Plus (TVP) in cats. Animals and Procedures: IOP readings obtained with the TVP were compared to values obtained concurrently with the original TONOVET (TV01) and Tono‐Pen Vet™ (TP) in 12 normal cats (24 eyes) and 8 glaucomatous LTBP2‐mutant cats (13 eyes) in vivo. Reproducibility of TVP readings was also assessed for three observers in the above cats. The anterior chambers of five different normal cat eyes were cannulated ex vivo. IOP was measured with the TVP, TV01, and TP at manometric IOPs ranging from 5 to 70 mmHg. Data were analyzed by linear regression, ANOVA and Bland–Altman plots. ANOVA was used to assess reproducibility of TVP readings obtained by different observers and an ANCOVA model controlled for variation of individual cats. p <.05 was considered significant. Results: TVP values strongly correlated with TV01 values (y = 1.045x + 1.443, R2 =.9667). The TP significantly underestimated IOP relative to the TVP and TV01, particularly at high IOP. IOP values obtained by 1 observer were significantly higher (~1 mmHg average) compared to the other 2 observers via ANCOVA analysis (p =.0006479 and p =.0203). Relative to manometry, the TVP and TV01 were significantly more accurate (p <.0001) and precise (p <.0070) than the TP in ex vivo eyes. Conclusions: IOP readings obtained with the TVP and TV01 are broadly interchangeable between models and between observers, but subtle differences may be important in a research context. TP readings vastly underestimate high IOP in feline glaucoma. [ABSTRACT FROM AUTHOR]

Purpose: Angle closure glaucoma (PACG) is highly prevalent in dogs and is often refractory to medical therapy. We hypothesized that pathology affecting the post‐trabecular conventional aqueous outflow pathway contributes to persistent intraocular pressure (IOP) elevation in dogs with PACG. The goal of this study was to determine the potential for aqueous angiography (AA) and optical coherence tomography (OCT) to identify abnormalities in post‐trabecular aqueous outflow pathways in canine PACG. Methods: AA and anterior segment OCT (Spectralis HRA + OCT) were performed ex vivo in 19 enucleated canine eyes (10 normal eyes and 9 irreversibly blind eyes from canine patients enucleated for management of refractory PACG). Eyes were cannulated and maintained at physiologic IOP (10–20 mmHg) prior to intracameral infusion of fluorescent tracer. OCT scleral line scans were acquired in regions of high and low perilimbal AA signal. Eyes were then perfusion fixed and cryosections prepared from 10/10 normal and 7/9 PACG eyes and immunolabeled for a vascular endothelial marker. Results: Normal canine eyes showed segmental, circumferential limbal AA signal, whereas PACG eyes showed minimal or no AA signal. AA signal correlated with scleral lumens on OCT in normal dogs, but lumens were generally absent or flattened in PACG eyes. Collapsed vascular profiles were identified in tissue sections from PACG eyes, including those in which no lumens were identified on AA and OCT. Conclusions: In canine eyes with PACG, distal aqueous outflow channels are not identifiable by AA, despite normalization of their IOP, and intra‐scleral vascular profiles are collapsed on OCT and histopathology. [ABSTRACT FROM AUTHOR]

Aim: To examine the use of prophylactic anti‐glaucoma medications in the normotensive fellow eye in dogs with unilateral overt primary glaucoma by veterinary ophthalmology clinicians. Methods: A survey of veterinary ophthalmology clinicians was distributed over two international list serves servicing veterinary ophthalmologists, trainees, and individuals whose practice consisted primarily of ophthalmic patients. The survey was developed following analysis of historical and currently available medical options for control of intraocular pressure and for neuroprotection. Results: Responses from 199 veterinary ophthalmology clinicians were evaluated. While a large variety of topical anti‐hypertensive drugs and protocols were used, the most commonly used medications were aqueous humor production suppressors such as dorzolamide 2.0% ophthalmic solution, timolol 0.5% ophthalmic solution, and a combination product containing both drugs. Latanoprost 0.005% ophthalmic solution was used infrequently for prophylaxis by comparison. The majority of respondents do not use concurrent anti‐inflammatory medications (61.22%), although a sizeable minority used prednisolone acetate, dexamethasone, or ketorolac as prophylactic treatment. Systemically administered ocular anti‐hypertensive agents were rarely used. Only 40% of respondents used neuroprotectant agents; the most commonly prescribed were the calcium channel blocker amlodipine and the nutraceutical Ocu‐Glo™. Recommended intervals between re‐examination by the clinician ranged from one month to one year, with most re‐evaluations occurring every 3 to 6 months. The majority of respondents recommended more frequent assessments of IOP at intervals between once monthly and once every 3 months. Conclusions: Data analysis of medical therapy for the normotensive fellow eye of dogs previously diagnosed with primary glaucoma suggests that there is a great need for well‐designed, prospective, controlled, multi‐center studies to determine which protocols have the greatest efficacy in delaying an overt attack in the previously normotensive eye in dogs with a genetic predisposition to glaucoma. Prospective studies utilizing a carbonic anhydrase inhibitor such as dorzolamide and a prostaglandin analogue such as latanoprost would be reasonable as these two drugs are widely used in the treatment of overt glaucoma and would allow for an exploration of the impact of different mechanisms of action of lowering IOP on the pathophysiology of primary glaucoma. [ABSTRACT FROM AUTHOR]

Objectives: To determine the accuracy and precision of the Icare® TONOVET Plus rebound tonometer and the Tono‐Pen AVIA Vet™ applanation tonometer for intraocular pressure (IOP) measurement in normal ex vivo canine eyes and comparison to earlier models of these tonometers. Animals & procedures: The anterior chambers of six normal dog eyes were cannulated ex vivo. IOP was measured with the TONOVET (TV01), TONOVET Plus, Tono‐Pen Vet™, and Tono‐Pen AVIA Vet™ at manometric IOPs ranging from 5 to 70 mm Hg. Data were analyzed by linear regression, ANOVA and Bland‐Altman plots. A P value ≤.05 was considered significant. Results: Intraocular pressure values obtained using the TONOVET Plus and TV01 were significantly more accurate than with the Tono‐Pen VET and Tono‐Pen AVIA Vet, particularly at higher IOPs (30‐70 mm Hg). Accuracy was not significantly different between any of the devices in the low to normal physiologic IOP range (5‐25 mm Hg). Level of precision was high for all devices, though the TONOVET Plus was more precise than the Tono‐Pen Vet in the 5‐25 mmHg range and the TV01 was more precise than the Tono‐Pen AVIA Vet over the whole IOP range. Conclusions: All devices underestimated IOP, particularly at higher pressures. Rebound tonometers were more accurate over the full range of IOP tested and in the high IOP range; however, there were no significant differences in accuracy among devices in the physiologic IOP range. All tonometers can provide clinically useful IOP readings in dogs, but rebound and applanation tonometers should not be used interchangeably. [ABSTRACT FROM AUTHOR]

Objective: To compare outcomes of surgical intervention and nonsurgical management of canine cataracts. Methods: Records of patients examined for cataracts from January 2007 to February 2018 were divided into two groups: nonsurgical and surgical. The nonsurgical group was further subdivided based on whether the decision not to pursue surgery was elected by owners, or based on ophthalmologist's advice. Inclusion criteria included 6 months of follow‐up. Success in the nonsurgical group was defined as a comfortable eye with no potentially painful complications, and success in the surgical group additionally required vision. Time‐to‐failure (complications) was assessed with Cox proportional hazards models. Results: A total of 72 eyes (41 dogs) were included in the nonsurgical group, and 126 eyes (67 dogs) were surgically treated. There was no difference in gender or age; however, the surgical group had significantly more diabetic eyes (56.3% vs 15.3%; P <.001) and patient eyes with longer follow‐up times (median 37.6 months vs 22.1 months; P <.001) than the nonsurgical group. There was no statistically significant difference in complication rates between the nonsurgical group (15/72 [20.8%]) and the surgical group (23/126 [18.3%]; HR: 2.22 [0.97, 5.0]; P =.060). However, the complication rate in the ophthalmologist‐led nonsurgical group was significantly greater than in the owner‐led nonsurgical group (P =.019) and the surgical group (P =.002). Conclusions: When using relevant outcomes, whether or not a cataractous eye has surgery does not affect long‐term complications; additionally, nonsurgical eyes that are poor surgical candidates have a higher complication rate than eyes deemed suitable for phacoemulsification for which owners elected not to pursue cataract surgery. [ABSTRACT FROM AUTHOR]

The guidelines were developed to assist authors when planning studies and preparing manuscripts for submission to I Veterinary Ophthalmology i and to help ensure that manuscripts published in I Veterinary Ophthalmology i are of the highest ethical standards. I Veterinary Ophthalmolog i y is an international journal with international authors and readership. At the request of readership and supporting membership organizations, the Editorial Board of I Veterinary Ophthalmology i has created, and recently approved, the guidelines for ethical research in veterinary ophthalmology (GERVO). [Extracted from the article]

Objective: To determine the effect of feline congenital glaucoma (FCG) on corneal sensitivity, and relationships between corneal sensitivity, central corneal thickness (CT), and corneal diameter (CD). Animals and Procedures: Corneal sensitivity (estimated by corneal touch threshold [CTT] using Cochet‐Bonnet esthesiometry); CT using ultrasonic pachymetry; intraocular pressure (IOP) using rebound tonometry; and maximal horizontal CD were measured in 16 normal and 14 FCG cats, both males and females, aged 7 months‐3.5 years. All procedures complied with an Institutional Animal Care and Use Committee‐approved protocol. Data were analyzed by linear regression: paired Student's t tests for between‐eye comparisons, and unpaired Student's t tests for comparisons between groups. Relationships between parameters were evaluated by Pearson correlation coefficients and linear mixed effects modeling. For statistical tests, with the exception of values that were Benjamini‐Hochberg adjusted for multiple comparisons, P‐values < 0.05 were considered significant. Results: Mean CTT and CT values were lower in FCG eyes relative to normal eyes, but differences were not statistically significant. Mean CD was significantly larger in FCG eyes relative to normal eyes, and there was a significant negative correlation between CD and CTT in FCG (r = −0.8564, corrected P = 0.005). These associations were confirmed in linear mixed effects models. Conclusions: Eyes with FCG have significantly larger CDs when compared with normal eyes, and larger CDs correlated with decreased corneal sensitivity in this group. Further studies are warranted to explore the effect of buphthalmos and corneal enlargement on corneal sensitivity and innervation in feline subjects with chronic glaucoma. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To determine accuracy and precision of three commonly used tonometers (TonoVet® and TonoLab® (ICare Oy, Finland)—rebound tonometers, and Tono‐Pen VET™ (Reichert, NY)—applanation tonometer) in normal chinchillas, and to establish a normal intraocular pressure (IOP) reference range in this species. Methods: The anterior chambers of three chinchilla eyes were cannulated ex vivo and readings obtained at manometric IOPs from 5 to 80 mmHg, using each of the three tonometers in random order. Data were analyzed by linear regression, ANOVA, and Bland–Altman plots. Tonometry was performed in both eyes of 60 chinchillas (age 8 weeks–16.2 years) using the TonoVet® and relationship between age and IOP analyzed using linear regression. For all statistical tests, P < 0.05 was significant. Results: Intraocular pressure values obtained using the Tono‐Pen VET™ and TonoVet® (in dog calibration mode;‘d’) showed strong linear correlation with manometry within the physiologic and clinically relevant range of IOP (0–50 mmHg). The TonoVet® ‘d’ setting displayed significantly greater precision over the full range of IOP evaluated than the Tono‐Pen VET™, and both TonoVet and Tono‐Pen VET™ were significantly more accurate than the TonoLab® tonometer. Mean ± SD IOP (TonoVet® ‘d’) in chinchillas was 9.7 ± 2.5 mmHg, and the 95% reference interval was 4.7–14.7 mmHg. Conclusions: Both the Tono‐Pen VET™ and TonoVet® provided clinically acceptable estimates of IOP in chinchillas. The TonoVet® provides accurate and precise IOP values, while Tono‐Pen VET™ derived measurements showed greater variability. Values obtained either with the TonoLab® or TonoVet® used in the ‘unspecified’ calibration setting were inaccurate in this species. [ABSTRACT FROM AUTHOR]

Objective To compare rates of retinal detachment ( RD) postphacoemulsification in American Bichon Frises with and without prophylactic retinopexy. Procedures Medical records of 54 Bichon Frises undergoing phacoemulsification with or without prophylactic retinopexy between 2003 and 2013 in one or both eyes were reviewed from five Midwestern university veterinary teaching hospitals. Inclusion criteria were preoperative ERG, at least 6 months of follow-up postphacoemulsification, and the absence of preexisting RD as determined by ophthalmic examination and/or ultrasound. Statistical analyses were performed using chi-squared test, and Wilcoxon rank-sum tests and Wilson confidence intervals with the P-value <0.05 were considered significant. Results Phacoemulsification was performed without retinopexy in 79 eyes (42 dogs, non- PR group) and with prophylactic retinopexy in 23 eyes (12 dogs, PR group). Incidence of diabetes mellitus was 10/42 and 3/12 in the non- PR and the PR groups, respectively ( P = 0.93). Intraocular lens implantation was performed in 40/42 non- PR dogs and 11/12 PR dogs ( P = 0.63, 73/79 vs. 21/23 eyes). At final re-examination, RD occurred in 4/79 eyes without retinopexy, compared to 0/23 RD in the retinopexy group. There was no statistically significant difference in RD rates between the two groups ( P = 0.27). Conclusions These data provide no statistical evidence to support prophylactic retinopexy in Bichon Frises. Due to the low rate of retinal detachment following phacoemulsification without prophylactic retinopexy, the procedure appears to offer limited benefit to offset cost, procedural risk, and risk of extended or repeated anesthesia in Bichon Frises. [ABSTRACT FROM AUTHOR]

Objective To determine the effects of latanoprost on intraocular pressure ( IOP) and pupil diameter ( PD) in cats with inherited primary congenital glaucoma ( PCG) and normal cats. Animals studied and procedures IOP and PD were measured in both eyes ( OU) of 12 adult cats (six normal, six PCG), three times per week for 3 weeks prior to, for 3 weeks during, and for 2 weeks following twice-daily treatment with 0.005% latanoprost to the right eye ( OD) and vehicle to the left (control) eye ( OS). IOP and PD were measured hourly, for 8 h, 1 day prior to, and on the first and last days of treatment. Aqueous humor flow rate ( AHF) was determined at baseline and at the end of the treatment phase in six normal cats. Results Mean IOP was significantly lower in treated vs. control eyes of PCG cats, for up to 8 h following a single latanoprost treatment, and a maximal IOP reduction of 63% occurred in treated eyes at 3 h. Latanoprost acutely lowered IOP in cats with PCG, but this effect appeared to diminish over 3 weeks of treatment. AHF was modestly increased in the treated eyes of normal cats after 3 weeks of latanoprost treatment, although IOP was not significantly affected. Latanoprost caused miosis, with rebound mydriasis at 24 h posttreatment, in the treated eyes of all cats. Conclusions Further research is needed to determine the suitability and efficacy of latanoprost treatment for long-term IOP-lowering in cats with PCG or other forms of glaucoma. [ABSTRACT FROM AUTHOR]

Purpose To describe clinical and pathological features of canine orbital rhabdomyosarcoma ( COR). Methods Retrospective review of patients with COR from the archives of the Comparative Ocular Pathology Laboratory of Wisconsin and the University of Wisconsin Veterinary Medical Teaching Hospital (1983-2014). Results Eighteen cases of COR were identified, all diagnosed in an 8-year period (2006-2014). Affected dogs were typically young (range 1-8; median 2 years), and both sexes were equally represented. Common clinical signs included exophthalmos (16/18) with dorsolateral deviation of the globe (10/18) and elevation of the nictitans (12/18). Ultrasonography, performed in nine cases, revealed an orbital mass with mixed echogenicity and posterior globe indentation. Advanced imaging, performed in nine cases, demonstrated a soft tissue mass with variable contrast enhancement and lysis of the orbital bones (5/9). Histologically, all tumors were subclassified as embryonal rhabdomyosarcoma. All neoplasms demonstrated positive immunohistochemical labeling for desmin, and 14/18 were positive for skeletal muscle actin. Follow-up information was available for 15/18 cases. Older dogs, aged 6-8 years, had no clinical signs of recurrence or metastasis 8-13 months postdiagnosis (4/4). Most younger dogs (9/11), aged 1-4 years, were euthanized within 6 months (median 2.5 months) of diagnosis due to recurrence at the surgical site (5/9) and/or metastasis (5/9). Conclusions Canine orbital rhabdomyosarcoma is a highly malignant neoplasm in juvenile dogs, but may be amenable to surgical resection in older dogs. This duality in biologic behavior may reflect differences in tissue of origin between juvenile onset tumors and adult onset tumors. [ABSTRACT FROM AUTHOR]

Objective To evaluate feasibility and accuracy of intraocular pressure ( IOP) measurement by rebound tonometry in adult red-eared slider turtles and determine the effects of manual and chemical restraint on IOP. Animal studied Seventeen adult red-eared slider turtles. Procedures Intraocular pressure was measured with TonoLab® and TonoVet® tonometers in conscious, unrestrained turtles. To evaluate the effects of manual restraint, turtles were restrained by digital pressure on the rostral head or proximal neck. The effect of two chemical restraint protocols (dexmedetomidine, ketamine, midazolam [ DKM] and dexmedetomidine, ketamine [ DK] subcutaneously) on IOP was evaluated. Triplicate TonoLab® and TonoVet® readings were compared with direct manometry in three ex vivo turtle eyes. Results TonoLab® correlated better with manometry at IOPs < 45 mmHg than TonoVet® (linear regression slopes of 0.89 and 0.30, respectively). Mean (± SD) IOP in unrestrained conscious turtles was significantly lower ( P < 0.01) with TonoLab® (10.02 ± 0.66 mmHg) than with TonoVet® (11.32 ± 1.57 mmHg). Manual neck restraint caused a significant increase in IOP (+6.31 ± 5.59 mmHg), while manual rostral head restraint did not. Both chemical restraint protocols significantly reduced IOP ( DKM: −1.0 ± 0.76 mmHg; DK: −1.79 ± 1.17) compared with measurements in conscious unrestrained turtles. Conclusions Chemical and manual neck restraint affected IOP. Rostral head restraint had no significant effect on IOP and is, therefore, recommended as the appropriate restraint technique in red-eared slider turtles. TonoLab® measurements estimated actual IOP more accurately, within physiologic range, than measurements obtained using the TonoVet®. [ABSTRACT FROM AUTHOR]

Objective To validate intraocular pressure (IOP) readings obtained in cats with the TonoVet® tonometer. Animals studied IOP readings obtained with the TonoVet® were compared to IOP readings determined by manometry and by the Tono-Pen XL™ in 1 normal cat and two glaucomatous cats. TonoVet® and Tono-Pen XL™ readings were also compared in a further six normal and nine glaucomatous cats. Procedures The anterior chambers of both eyes of three anesthetized cats were cannulated and IOP was varied manometrically, first increasing from 5 to 70 mmHg in 5 mmHg increments, then decreasing from 70 to 10 mmHg in 10 mmHg decrements. At each point, two observers obtained three readings each from both eyes, with both the TonoVet® and Tono-Pen XL™. IOP was measured weekly for 8 weeks with both tonometers in six normal and nine glaucomatous unsedated cats. Data were analyzed by linear regression. Comparisons between tonometers and observers were made by paired student t-test. Results The TonoVet® was significantly more accurate than the Tono-Pen XL™ ( P = 0.001), correlating much more strongly with manometric IOP. In the clinical setting, the Tono-Pen XL™ underestimated IOP when compared with the TonoVet®. Conclusions Both the TonoVet® and Tono-Pen XL™ provide reproducible IOP measurements in cats; however, the TonoVet® provides readings much closer to the true IOP than the Tono-Pen XL™. The TonoVet® is superior in accuracy to the Tono-Pen XL™ for the detection of ocular hypertension and/or glaucoma in cats in a clinical setting. [ABSTRACT FROM AUTHOR]

Objectives: To determine accuracy and precision of three commonly used tonometers (TonoVet ® and TonoLab ® (ICare Oy, Finland)-rebound tonometers, and Tono-Pen VET™ (Reichert, NY)-applanation tonometer) in normal chinchillas, and to establish a normal intraocular pressure (IOP) reference range in this species., Methods: The anterior chambers of three chinchilla eyes were cannulated ex vivo and readings obtained at manometric IOPs from 5 to 80 mmHg, using each of the three tonometers in random order. Data were analyzed by linear regression, ANOVA, and Bland-Altman plots. Tonometry was performed in both eyes of 60 chinchillas (age 8 weeks-16.2 years) using the TonoVet ® and relationship between age and IOP analyzed using linear regression. For all statistical tests, P < 0.05 was significant., Results: Intraocular pressure values obtained using the Tono-Pen VET™ and TonoVet ® (in dog calibration mode;'d') showed strong linear correlation with manometry within the physiologic and clinically relevant range of IOP (0-50 mmHg). The TonoVet ® 'd' setting displayed significantly greater precision over the full range of IOP evaluated than the Tono-Pen VET™, and both TonoVet and Tono-Pen VET™ were significantly more accurate than the TonoLab ® tonometer. Mean ± SD IOP (TonoVet ® 'd') in chinchillas was 9.7 ± 2.5 mmHg, and the 95% reference interval was 4.7-14.7 mmHg., Conclusions: Both the Tono-Pen VET™ and TonoVet ® provided clinically acceptable estimates of IOP in chinchillas. The TonoVet ® provides accurate and precise IOP values, while Tono-Pen VET™ derived measurements showed greater variability. Values obtained either with the TonoLab ® or TonoVet ® used in the 'unspecified' calibration setting were inaccurate in this species., (© 2017 American College of Veterinary Ophthalmologists.)

Objective  To validate intraocular pressure (IOP) readings obtained in cats with the TonoVet(®) tonometer. Animals studied  IOP readings obtained with the TonoVet(®) were compared to IOP readings determined by manometry and by the Tono-Pen XL(™) in 1 normal cat and two glaucomatous cats. TonoVet(®) and Tono-Pen XL(™) readings were also compared in a further six normal and nine glaucomatous cats. Procedures  The anterior chambers of both eyes of three anesthetized cats were cannulated and IOP was varied manometrically, first increasing from 5 to 70 mmHg in 5 mmHg increments, then decreasing from 70 to 10 mmHg in 10 mmHg decrements. At each point, two observers obtained three readings each from both eyes, with both the TonoVet(®) and Tono-Pen XL(™) . IOP was measured weekly for 8 weeks with both tonometers in six normal and nine glaucomatous unsedated cats. Data were analyzed by linear regression. Comparisons between tonometers and observers were made by paired student t-test. Results  The TonoVet(®) was significantly more accurate than the Tono-Pen XL(™) (P = 0.001), correlating much more strongly with manometric IOP. In the clinical setting, the Tono-Pen XL(™) underestimated IOP when compared with the TonoVet(®) . Conclusions  Both the TonoVet(®) and Tono-Pen XL(™) provide reproducible IOP measurements in cats; however, the TonoVet(®) provides readings much closer to the true IOP than the Tono-Pen XL(™) . The TonoVet(®) is superior in accuracy to the Tono-Pen XL(™) for the detection of ocular hypertension and/or glaucoma in cats in a clinical setting., (© 2012 American College of Veterinary Ophthalmologists.)

Objective: To determine the effects of topical 0.5% tropicamide on anterior segment morphology (ASM) and intraocular pressure (IOP) in normal and glaucomatous cats. ANIMALS USED: Normal cats and cats with inherited primary congenital glaucoma (PCG)., Procedures: Control IOP curves were performed in untreated normal and PCG cats. In the first experiment, tropicamide was applied OD in eight normal and nine PCG cats. IOP and pupillary diameter (PD) were measured at 0, 30, and 60 min, then hourly until 8 h post-treatment. In a second experiment, six normal and seven PCG cats received tropicamide OD. High-resolution ultrasound images were obtained at 0, 1, 5, and 10 h post-treatment to measure ASM changes. IOP and PD were measured OD at 0, 1, 2, 3, 5, 7, and 9 h., Results: In untreated normal cats IOP OU decreased throughout the day. In PCG cats IOP OU had wide fluctuations over time. In normal cats IOP response varied in the treated eye but did not change significantly in untreated eyes. IOP significantly increased from baseline in both eyes of all treated PCG cats. Increases in IOP were associated with some ASM changes. Cats with PCG had a significantly smaller angle recess areas, diminished ciliary clefts and decreased iris-lens contact. ASM changes were not strongly correlated with IOP in all cats., Conclusions: The ASM of PCG cats is markedly different from normal cats, and clinically significant increases in IOP OU occur in cats with PCG after tropicamide treatment. The mechanism for this increase remains unclear., (© 2011 American College of Veterinary Ophthalmologists.)