Effects of cyclophotocoagulation with a neodymium:yttrium-aluminum-garnet laser on corneal sensitivity, intraocular pressure, aqueous tear production, and corneal nerve morphology in eyes of dogs

Retrospective evaluation of surgical outcomes in canine patients with primary and secondary glaucoma following diode endoscopic cyclophotocoagulation

OBJECTIVE

To evaluate the long-term outcome of endoscopic cyclophotocoagulation (ECP) for the treatment of primary and secondary glaucoma in dogs.

ANIMALS STUDIED

Retrospective review of dogs that underwent ECP at two referral centers from 2004 to 2023.

PROCEDURES

Medical records of 389 eyes (301 dogs) following ECP were reviewed. Outcomes evaluated included follow-up time, intraocular pressure (IOP), vision status, additional ECP procedures performed, number of medications, and complications. Patient and surgical variables and their association with IOP control and vision maintenance were evaluated.

RESULTS

Median follow-up time was 18 months. IOP remained controlled in 90% and 95% of patients at 1 and 2 years, respectively, following ECP. IOP was controlled long-term (2 years) in cases with primary (88%) and secondary (99%) glaucoma. Post-operative vision was maintained in 63% and 49% of eyes at approximately 1 and 2 years, respectively. Median time to vision loss was 6.5 months. Repeat ECP was required in 15.4% of eyes at a median of 19 days post-operatively. Eyes that underwent more than one ECP surgery had a significantly longer median time to blindness (13.8 months) than those that underwent a single ECP procedure (3.6 months; p = .0003). The median number of anti-glaucoma medications decreased from three pre-operatively to one at 1- and 2-year post-operatively. Complications included corneal ulceration (28%), blinding hypotony (11%), retinal detachment (11%), and hyphema (10%).

CONCLUSION

Endolaser cyclophotocoagulation is an effective surgery for maintaining long-term IOP control and extending vision in canine patients with glaucoma refractory to medical management.

A review of diagnostic tests for qualitative and quantitative tear film deficiency in dogs

Dry eye disease (DED) is a complex multifactorial condition caused by loss of ocular surface homeostasis from quantitative and/or qualitative tear film deficiency. Schirmer tear test (STT) is often the only diagnostic test used to assess for DED in veterinary practice. STT is invaluable in the diagnosis and monitoring of quantitative tear film deficiency (i.e., keratoconjunctivitis sicca); however, it is not sufficient to optimize therapy and fully recognize other contributing factors for the disturbance in ocular surface homeostasis. The present work reviews diagnostic tests for assessing aqueous tear production in veterinary medicine, as well as the quality of tears, corneal epithelial barrier integrity, and the lacrimal functional unit.

The Clinical Guiding Role of the Distribution of Corneal Nerves in the Selection of Incision for Penetrating Corneal Surgery in Canines

The cornea is one of the regions with the highest density of nerve terminals in the animal body and it bears such functions as nourishing the cornea and maintaining corneal sensation. In veterinary clinical practice, the corneoscleral limbus incision is frequently applied in cataract surgery, peripheral iridectomy, and other procedures for glaucoma. Inevitably, it would cause damage to the nerve roots that enter the cornea from the corneal limbus, thus inducing a series of complications. In this paper, the in vitro cornea (39 corneas from 23 canines, with ages ranging from 8 months old to 3 years old, including 12 male canines and 11 female canines) was divided into 6 zones, and the whole cornea was stained with gold chloride. After staining, corneal nerves formed neural networks at different levels of cornea. There was no significant difference in the number of nerve roots at the corneoscleral limbus between different zones (F = 1.983, p = 0.082), and the nerve roots at the corneoscleral limbus (mean value, 24.43; 95% CI, 23.43-25.42) were evenly distributed. Additionally, there was no significant difference in the number of corneal nerve roots between male and female canines (p = 0.143). There was also no significant difference in the number of corneal nerve roots between adult canines and puppies (p = 0.324). The results of the above analysis will provide a reasonable anatomical basis for selecting the incision location and orientation of penetrating surgery for the canine cornea in veterinary practice.

Outcomes of baervedlt implant surgery in 17 dogs (20 eyes) with primary closed-angle glaucoma (2013-2019)

OBJECTIVE

To report outcomes and follow-up of Baerveldt implant surgery in dogs with primary closed-angle glaucoma (PCAG).

MATERIALS AND METHODS

Record review of client-owned dogs with PCAG that underwent Baerveldt implant surgery during a 6-year period. Postoperative intraocular pressure (IOP), vision and daily number of anti-glaucoma drops at fixed time points (3, 12, and 24 months) were compared with preoperative values; complications were recorded. Success was defined as IOP <20 mm Hg and a positive menace response and navigation/tracking ability.

RESULTS

Twenty eyes (17 dogs) were included. Mean follow-up was 575 days (range 30-1767 days) from implant surgery to last examination. Three months postoperatively 15/20 (75%) eyes had IOP <20 mm Hg and 14/20 (70%) eyes had vision. Twelve months postoperatively 11/17 (65%) eyes had IOP <20 mm Hg and 12/19 (63%) eyes had vision. Twenty-four months postoperatively 8/14 (57%) eyes had IOP <20 mm Hg and 7/15 (47%) eyes had vision. Denominators differ between time points as eyes were included when duration after surgery reached the relevant postoperative time point or failure was documented earlier. Within 3 months postoperatively 16/20 (80%) eyes had ≥1 complication, including transient IOP >20 mm Hg (14/20; 70% eyes), fibrin (12/20; 60% eyes), and hypotony (4/20; 20% eyes). After 3 months, postoperatively 13/16 (81%) eyes had ≥1 complication, including cataracts (13/16; 81% eyes), bleb fibrosis (3/16; 19% eyes), and conjunctival wound breakdown (1/16; 6% eyes). One patient (1 eye) was euthanized for blindness and 5/20 (25%) eyes were enucleated.

CONCLUSIONS

The technique was effective in controlling IOP and maintaining vision in most dogs in this study.

Glaucoma-associated pain results in mechanical sensitivity changes in dogs: A pilot study

PURPOSE

To explore the effects of chronic, uncontrolled glaucoma on pressure sensitivity in dogs before and after enucleation of the painful globe.

METHODS

Client-owned dogs undergoing enucleation for chronic glaucoma with no other sources of pain were enrolled. Normal dogs of similar breeds and skull morphology were enrolled as controls. Craniofacial ratio (CFR) and relative palpebral fissure width (RPFW) were assessed in all patients. Serial mechanical quantitative sensory testing (QST) was performed the day before surgery, and 14, 30, 60, and 120 days after surgery. QST consisted of electronic Von Frey (eVF), and blunt algometry (BA) performed above and below the nonglaucomatous eye, the metacarpus, and metatarsus. Cochet-Bonnet esthesiometry (CB) was also performed on the remaining eye.

RESULTS

Twelve dogs (6 per group) were included. Compared to baseline values, sensitivity tended to decrease over time (increased thresholds) in treatment dogs while it stayed constant or increased slightly in control dogs. The difference in change from baseline sensitivity between control and treatment groups was significant at day 120 using BA at supraorbital (P = .0153), infraorbital (P = .0209), and metacarpal sites (P = .007) and overall (P = .0470). This divergence was also significant using CB (P = .0470) on the opposite cornea. As patient CFR and RPFWV increased, both eVF (P = .005-.023) and BA (P = .004-.041) increased.

CONCLUSIONS

Sensitivity to mechanical stimuli decreased both locally and at remote sites in dogs following enucleation for painful chronic glaucoma. Cranial conformation is associated with differences in sensitivity.

Corneal hypoesthesia, aqueous tear deficiency, and neurotrophic keratopathy following micropulse transscleral cyclophotocoagulation in dogs

OBJECTIVE

To describe ocular surface complications following micropulse transscleral cyclophotocoagulation (MP-TSCPC) in dogs.

ANIMALS STUDIED

Eighteen dogs treated with MP-TSCPC at two institutions for glaucoma management.

PROCEDURES

MP-TSCPC was applied to each eye (avoiding 3 and 9 o'clock positions) with 31.3% duty cycle, 2000-3000 mW energy, and 90-180 seconds duration per hemisphere. Central corneal tactile sensation (CTS) and Schirmer tear test-1 (STT-1) were measured at baseline and ≥2 post-operative visits in each dog.

RESULTS

Corneal sensitivity decreased in 16/18 dogs (89%) by an average of 10%-42% (up to 100% in 4 dogs). CTS decline was rapid (≤1 week) and only fully recovered in 50% of dogs within 8-180 days. Patients' age, glaucoma duration, laser energy, and total energy delivered did not affect CTS at any visit. However, brachycephalic dogs had significantly lower CTS and likelihood to recover full sensation compared with nonbrachycephalic dogs. Aqueous tear deficiency (STT-1 < 15 mm/min) occurred in 8/18 dogs (44%) within 7-270 days, and concurrent signs of keratoconjunctivitis sicca were noted in 2/18 dogs (11%). Neurotrophic corneal ulcers developed in 6/18 dogs (33.3%) and required 16-53 days to heal.

CONCLUSIONS

Corneal hypoesthesia is a common complication of MP-TSCPC in dogs, and can lead to serious adverse effects such as aqueous tear deficiency and neurotrophic corneal ulcers. Brachycephalic dogs represent a population at higher risk. Close monitoring of ocular surface health is recommended for months following MP-TSCPC in dogs.

Corneal sensitivity and aqueous tear production in dogs undergoing evisceration with intraocular prosthesis placement

OBJECTIVE

To determine whether there is an association between evisceration with intraocular prosthesis placement via a dorsal scleral approach and decreased corneal sensitivity or aqueous tear production in dogs.

DESIGN

Prospective study.

PROCEDURE

Twenty-one dogs scheduled to undergo unilateral evisceration with intraocular prosthesis, and with a normal normotensive contralateral eye, based on slit-lamp biomicroscopy, indirect ophthalmoscopy and applanation tonometry, were included in the study. Central corneal sensitivity was measured with a Cochet-Bonnet esthesiometer prior to (week 0) and 2, 7, 14 and 28 weeks following surgery. Other pre- and postoperative data collected were Schirmer's tear test (STT I), Schirmer's tear test with topical anesthesia (STT II), corneal fluorescein retention, and intraocular pressure (IOP; postoperative control eye only). Axial globe length was determined for both eyes. Scleral incision length in the surgery eye was also recorded.

RESULTS

Corneal sensitivity was significantly lower in eyes undergoing evisceration with intraocular prosthesis than in control eyes both preoperatively and postoperatively at all time points. There was no significant difference between preoperative and postoperative corneal sensitivity within the two groups. There was no significant difference in STT I or STT II-values between control eyes and surgery eyes preoperatively. There was a significant difference between preoperative and 2-week postoperative STT I in the surgery eye. There was a significant difference between the preoperative and 28-week postoperative STT II in the surgery eye. The 28-week postoperative STT I-values differed significantly between control and surgery eyes. Corneal sensitivity tended to decrease with increased degree of buphthalmos or with increased scleral incision length, although neither relationship was statistically significant.

CONCLUSIONS

Eyes that have sustained chronically elevated intraocular pressure had decreased axial corneal sensitivity compared to normal eyes, which persisted even after intraocular pressure was reduced. The presence of buphthalmos appeared to be a factor in globes developing decreased corneal sensitivity. Evisceration via a dorsal scleral incision did not result in a significant further reduction in axial corneal sensitivity. A mild reduction in aqueous tear production occurred over time in globes following evisceration with intraocular prosthesis.

Duration of corneal anesthesia following topical administration of 0.5% proparacaine hydrochloride solution in clinically normal cats

OBJECTIVE

To determine duration of corneal anesthesia following topical administration of 0.5% proparacaine hydrochloride solution in domestic shorthair (DSH) cats.

ANIMALS

20 clinically normal DSH cats.

PROCEDURES

Baseline corneal touch threshold (CCT) was established by use of a Cochet-Bonnet aesthesiometer. Treatment consisted of a single 50-microL topical application of an ophthalmic preparation of 0.5% proparacaine solution to a randomly selected eye of each cat. The corneal touch threshold was assessed 1 and 5 minutes after application to the cornea and at 5- minute intervals thereafter for 60 minutes.

RESULTS

Corneal sensitivity, as determined by Cochet-Bonnet aesthesiometry, was significantly reduced from baseline for 25 minutes following topical administration of ophthalmic proparacaine. Maximal anesthetic effect lasted 5 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

As determined by Cochet-Bonnet aesthesiometry, duration of anesthetic effects on the cornea induced by a single topical application of an ophthalmic preparation of 0.5% proparacaine solution in DSH cats is considerably shorter than the reported duration of corneal anesthesia in dogs.

Bilateral cavernous sinus syndrome in dogs: 6 cases (1999-2004)

OBJECTIVE

To determine clinical features, diagnostic imaging abnormalities, underlying disease, disease progression, and outcome in dogs with bilateral cavernous sinus syndrome.

DESIGN

Retrospective study.

ANIMALS

6 dogs.

PROCEDURE

Dogs were included if clinical signs consistent with bilateral cavernous sinus syndrome (i.e., deficits of the third, fourth, and sixth cranial nerves and at least 1 of the first 2 branches of the fifth cranial nerve) were present and a lesion of the cavernous sinus was identified by means of diagnostic imaging or postmortem examination.

RESULTS

5 dogs were evaluated because of problems referable to abnormal ocular motility or pupillomotor dysfunction, and 1 dog was evaluated because of partial motor seizures involving the face and bilateral mydriasis. Four dogs had neurologic signs referable to an extrasinusoidal lesion at the time of initial examination, and the remaining 2 dogs eventually developed extrasinusoidal signs. Besides neuroanatomic location, the only consistent neuroimaging feature was variably intense, heterogeneous enhancement of cavernous sinus lesions. Neoplasia was histologically confirmed as the underlying cause in 5 of the dogs and was suspected in the remaining dog. Median survival time for the 4 dogs that were treated was 199 days (range, 16 to 392 days).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that bilateral cavernous sinus syndrome is rare in dogs but should be suspected in dogs with compatible clinical signs. Affected dogs have a poor prognosis, and dogs with clinical signs of bilateral cavernous sinus syndrome should be systematically evaluated for neoplastic disease.

Combined transscleral diode laser cyclophotocoagulation and Ahmed gonioimplantation in dogs with primary glaucoma: 51 cases (1996-2004)

OBJECTIVE

To evaluate the combined diode laser cycloablation procedure and adjunctive Ahmed gonioimplant use in dogs with primary glaucoma.

DESIGN

Retrospective study.

ANIMALS

48 dogs, 51 eyes with primary glaucoma.

PROCEDURE

Medical records from two large private clinical ophthalmology services were reviewed. Signalment, duration of glaucoma, gonioscopic evaluation, laser power and duration settings, immediate postoperative and final intraocular pressure and visual results, short and long-term visual outcome, and surgical complications were recorded.

RESULTS

The age range of affected dogs was 3.0-14.0 years, with a mean age of 7.5 +/- 2.6 years. Eleven pure breeds were represented, with the most common being the American Cocker Spaniel. The sex distribution was 22 neutered males, 1 intact male, 23 spayed females, and 2 intact female dogs. The right eye was affected in 33 cases, and the left eye in 18 cases. The average total joules, which was administered with the diode laser, was 109.6 +/- 23.6 J. Immediate surgical complications included fibrin formation in the anterior chamber (15), corneal ulcers (4), hyphema (7), and focal retinal detachment (1). Long-term complications included cataract formation (8 total, 2 of which were significant, vision-threatening), elevated intraocular pressure (IOP) (6), unstable gonioimplant (1), and glaucoma recurrence (14). Additional surgeries performed on the eyes over the course of study included: intrascleral prosthesis (4), enucleation (1), resection of fibrotic scar tissue (5), and repeat laser cycloablation (8). The dogs were examined for a mean follow-up time of 17.6 months (range: 2-83 months postoperatively). Twenty-nine cases were followed greater than one year. Vision was maintained in 42/51 eyes (82%) in the immediate short-term of this study. In all cases included in the study, good control of IOP was achieved in 39/51 (76%) of eyes, and IOP was poor or uncontrolled in 12/51 (24%) of eyes. Twenty out of 41 eyes (49%) maintained fair to excellent vision six months after surgery. Twelve months postoperative observations demonstrated that 12/29 (41%) of the eyes were still visual.

CONCLUSIONS

In primary glaucoma, the combined procedure of laser diode cyclophotocoagulation and Ahmed valve implant was associated with return or maintenance of vision in 42/51 eyes (82%) in the immediate short-term of this study, and a long-term IOP control in 39/51 (76%) of the cases, with 12/29 eyes (41%) visual after 12 months.

Duration of effect and effect of multiple doses of topical ophthalmic 0.5% proparacaine hydrochloride in clinically normal dogs

OBJECTIVE

To determine the duration of effect and the effect of multiple doses of topical ophthalmic application of 0.5% proparacaine hydrochloride on corneal sensitivity in clinically normal dogs.

ANIMALS

8 clinically normal dogs.

PROCEDURE

Dogs were randomly allocated to treatment order in a 2 x 2 (period X treatment) crossover study. Treatments consisted of topical application of ophthalmic 0.5% proparacaine (1 drop or 2 drops at a 1-minute interval); treatments were applied to both eyes. A Cochet-Bonnet aesthesiometer was used to determine corneal touch threshold (CTT) before corneal application, 1 and 5 minutes after corneal application, and at 5-minute intervals thereafter for 90 minutes.

RESULTS

The CTT value before treatment differed significantly from CTT values after treatment until 45 minutes after application in the 1-drop group and until 55 minutes after application in the 2-drop group. As determined by use of the Cochet-Bonnet aesthesiometer, a significantly greater anesthetic effect was detected for the 2-drop treatment, compared with the effect for the 1-drop treatment, at 30, 35, 40, 45, 50, and 55 minutes after application. Maximal anesthetic effect lasted for 15 minutes for the 1-drop treatment and 25 minutes for the 2-drop treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Duration of corneal anesthetic effect induced by topical ophthalmic application of 0.5% proparacaine in dogs of this study is considerably longer than that reported elsewhere. Serial application of doses of 0.5% proparacaine increases the duration and magnitude of corneal anesthetic effects.

Corneal nerves: structure, contents and function

This review provides a comprehensive analysis of the structure, neurochemical content, and functions of corneal nerves, with special emphasis on human corneal nerves. A revised interpretation of human corneal nerve architecture is presented based on recent observations obtained by in vivo confocal microscopy (IVCM), immunohistochemistry, and ultrastructural analyses of serial-sectioned human corneas. Current data on the neurotransmitter and neuropeptide contents of corneal nerves are discussed, as are the mechanisms by which corneal neurochemicals and associated neurotrophins modulate corneal physiology, homeostasis and wound healing. The results of recent clinical studies of topically applied neuropeptides and neurotrophins to treat neurotrophic keratitis are reviewed. Recommendations for using IVCM to evaluate corneal nerves in health and disease are presented.