Chapter 59 - Intraocular surgery Flashcards
1
Q
A
2
Q
What is equine recurrent uveitis (ERU) commonly referred to as?
A
Moon blindness.
3
Q
What percentage of horses with ERU lose vision according to studies?
A
28%.
4
Q
What are the three components of the uveal tract?
A
Iris, ciliary body, and choroid.
5
Q
What does the breakdown of the blood-aqueous barrier cause?
A
Vascular dilation and increased permeability
6
Q
What phenomenon represents the hallmark of uveitis?
A
Aqueous flare, visible as scattered light due to increased protein.
7
Q
What can extensive posterior synechia lead to in ERU cases?
A
Complete blockage of the pupil, resulting in vision loss.
7
Q
What effect do prostaglandins have on intraocular pressure?
A
They cause hypotony (reduced intraocular pressure).
8
Q
Which inflammatory mediators primarily contribute to ERU?
A
Prostaglandins and leukotrienes.
9
Q
A
10
Q
A
11
Q
A
12
Q
A
13
Q
A
14
Q
A
15
Q
A
16
Q
What is iris bombé?
A
Anterior bowing of the iris due to trapped fluid behind it.
17
Q
A
18
Q
A
19
Q
What is a definitive diagnosis of ERU based on?
A
Multiple recurrent episodes of ocular inflammation.
20
Q
What role does Leptospira interrogans play in ERU?
A
It is the most frequently implicated infectious cause.
21
Q
What percentage of vitreous samples from ERU horses tested positive for leptospires in one German study?
A
75%.
22
Q
What ocular condition can mimic uveitis?
A
Corneal ulceration.
23
Q
What is essential before applying topical corticosteroids in uveitis cases?
A
Exclusion of corneal ulceration.
24
What must be evaluated to determine if cataracts have formed due to uveitis?
The lens, ideally after pupillary dilation.
24
What clinical sign may indicate hypotony during an eye examination?
Low intraocular pressure (IOP).
25
What diagnostic procedure can be used to culture pathogens in uveitis?
Aqueous paracentesis.
26
What is a significant risk associated with retrobulbar anesthesia?
Potential trauma to the globe.
27
What is the purpose of using corticosteroids in ERU treatment?
To reduce inflammation and stabilize the blood-aqueous barrier.
28
Which topical corticosteroids achieve therapeutic concentrations in the aqueous humor?
Prednisolone acetate 1% and dexamethasone 0.1%.
29
What is the recommended treatment if a horse tests positive for Leptospira spp. in endemic areas?
Systemic antibiotic therapy.
30
What percentage of normal horses can have elevated serum antibody titers for Leptospira spp.?
19%.
31
What can happen to the lens zonules due to chronic inflammation?
They may be lysed, leading to lens luxation.
32
Why is careful management of general anesthesia critical in ocular surgery?
To prevent further trauma to the globe and reduce postoperative complications.
33
What is the typical postoperative recovery strategy after intraocular surgery?
Smooth recovery from anesthesia.
33
What is the significance of the Tyndall effect in diagnosing uveitis?
It indicates increased protein levels in the aqueous humor.
34
What may be indicated for horses with severe inflammatory responses in the anterior chamber?
Intracameral injection of tissue plasminogen activator.
35
What condition can occur due to secondary glaucoma from ERU?
Increased intraocular pressure leading to vision loss.
36
What must be meticulously preserved if an HA orbital implant is planned?
Conjunctival fornices and extraocular muscles.
37
What should be done if an infected globe ruptures during surgery?
Extensive irrigation of the orbit and broad-spectrum antibiotics.
38
What are the implications of the presence of fibrin in the anterior chamber?
It indicates severe inflammation and can obstruct aqueous humor flow.
39
What might indicate a chronic inflammatory response in the eye?
Cataract formation and retinal scarring.
40
What is the role of mydriatics in ERU management?
To dilate the pupil and alleviate pain.
41
What is a common cause of hyphema in uveitis cases?
Severe intraocular inflammation.
42
What can be used to assist with hemostasis during ocular procedures?
Manual tamponade, hemoclips, or electrocautery.
43
What gauge needle is typically used for intravitreal injections?
A 22- to 23-gauge needle.
44
How far behind the limbus should the needle be inserted for an intravitreal injection?
10 mm.
45
At which position should the needle be inserted during the intravitreal injection?
The 12 o’clock position.
46
How long can ocular levels of triamcinolone persist after injection?
Up to 21 days.
47
What percentage of eyes developed bacterial endophthalmitis in the study on triamcinolone?
33%
48
What is the primary indication for suprachoroidal cyclosporine implantation?
Chronic equine recurrent uveitis (ERU) with frequent recurrences.
49
What size incision is made for the conjunctival approach during CsA implantation?
A 1-cm conjunctival incision.
50
How wide is the scleral flap prepared during CsA implantation?
7 mm.
51
How many horses demonstrated vision retention in the CsA clinical trial?
78% of cases.
52
When is a second CsA implant suggested following the initial surgery?
Approximately 48 months later.
53
What surgical technique is used for vitrectomy in treating ERU?
Pars plana vitrectomy (PPV).
54
What is the most common complication after pars plana vitrectomy?
Cataract formation.
55
What topical medication is administered four times a day before vitrectomy surgery?
NPDex (neomycin, polymyxin B, and dexamethasone).
56
ow long should flunixin meglumine be administered preoperatively?
Beginning 3 days before surgery.
57
How far posterior to the limbus should the first sclerotomy be performed?
10 mm.
58
What is the aspiration vacuum used during vitrectomy?
240 mm Hg.
59
What is the recommended intraocular pressure (IOP) during vitrectomy?
Approximately 40 mm Hg.
60
What type of suture is used to close the sclerotomy after vitrectomy?
4-0 polyglactin 910.
61
What is the function of the custom-made 55-mm oscillating vitrectomy probe?
To remove turbid vitreal material.
62
What percentage of eyes showed no recurrence of uveitis in one study of 38 cases?
87%
63
What complications resulted in vision loss in some horses post-vitrectomy?
Persistent uveitis, glaucoma, mature cataracts, and retinal detachment.
64
What is the result of inserting the vitrectomy probe toward the central vitreous?
Physical removal of inflammatory cells.
65
How is the scleral flap closed after CsA implantation?
With 5-0 to 6-0 absorbable suture material in a simple-interrupted pattern.
66
What indicates the need to interrupt surgery if noted during vitrectomy?
Slight wrinkling of the retina.
67
What is the primary concern during the insertion of the vitrectomy probe?
Avoiding contact with the lens.
68
What suture technique is used to close the conjunctiva after vitrectomy?
Continuous pattern with polyglactin 910.
69
What is the purpose of using a CO2 laser during surgery?
To perform a sclerotomy.
70
What percentage of foals under 30 days had cataracts in one study?
8.6%.
70
describe a pars plana vitertomy
standard two-port PPV is performed with the horse in lateral recumbency under general anesthesia. The eye is prepared for intraocular surgery. After draping, an eyelid speculum is inserted. A lateral canthotomy may improve exposure. With a custom-made globe manipulator (Figure 59-7) or limbal stay suture, the globe is rotated to expose the dorsal bulbar conjunctiva. A limbal-based conjunctival flap is prepared and the sclera exposed medial and lateral to the dorsal rectus muscle. Using a CO2 laser in continuous mode at 50 W, a sclerotomy is performed 10 mm posterior to the limbus. A right-handed surgeon places this first entry to the left of the rectus muscle. The irrigation port is inserted and secured to the sclera with a 4-0 polyglactin 910 suture (Figure 59-8). The irrigation fluid consists of physiologic saline solution with 40 mg of gentamicin added per 500 mL. The fluid bottle is positioned 85 cm higher than the globe to maintain an IOP of 40 mm Hg. The infusion is started at a flow rate of 20 mL/min. A second sclerotomy is performed 10 mm posterior to the limbus and to the right of the rectus muscle (Figure 59-9). The vitrectomy probe is carefully inserted and advanced toward
the central vitreous. A custom-made 55-mm oscillating vitrectomy probe is used at 6.5 Hz with an aspiration vacuum of 240 mm Hg (Figure 59-10). Care is taken to avoid touching the lens (Figure 59-11). The probe is held with the aspiration port facing the surgeon. The port can be visualized through the pupil using an indirect binocular ophthalmoscope (Figure 59-12). With a 20-diopter lens in the left hand and the vitrectomy probe in the right, the vitrectomy is started. The shadow cast on the retina by the probe assists the surgeon in estimating the distance between the probe and the retina. Under continuous irrigation, the vitrectomy probe is removed and the sclerotomy is closed with one or two preplaced simple-interrupted sutures using 4-0 polyglactin 910. Subsequently, the irrigation port is removed. Remaining vitreous usually prevents fluid from escaping through this sclerotomy, which is closed with 4-0 polyglactin 910. The conjunctiva is closed with polyglactin 910 in a continuous pattern. The canthotomy is closed with a figure-of-eight suture using 4-0 nonabsorbable suture material. At the end of surgery, 20 mg of methylprednisolone is injected subconjunctivally into the inferior bulbar conjunctiva.
71
In which horse bloodlines is cataract a dominant trait?
Morgan, Belgian, Quarter Horse, and Thoroughbred.
72
What is the recommended age for cataract surgery in foals?
Before 6 months of age.
73
How is a cataract classified as immature based on lenticular involvement?
15% to 99% involvement.
74
What is the percentage involvement for a cataract to be considered mature?
100%.
75
What is the success rate of vision recovery immediately after cataract surgery according to Brooks et al.?
95%.
75
What technique is used to maintain anterior chamber pressure during phacoemulsification?
Continuous irrigation.
76
What mydriatic solution is used for lens examination, and how long does it take to act?
1% tropicamide, acting within 30 minutes.
77
What is the typical size of the suture used to close the cornea after cataract surgery?
7-0 absorbable suture.
78
What type of lens is often implanted in foals undergoing cataract surgery?
+14D, 21-mm diameter lenses.
79
What type of cataract generally has the best long-term prognosis?
Congenital and traumatic cataracts.
79
What is the typical frequency for administering topical flunixin meglumine post-surgery?
Every 12 hours.
80
What is the preferred neuromuscular blocker for intraocular surgery, and at what dose?
Atracurium besylate at 0.12 to 0.2 mg/kg IV.
81
What should the degree of neuromuscular blockade be monitored with?
A train of four stimulations from a peripheral nerve stimulator.
82
What surgical technique involves a continuous circular capsulorrhexis?
Phacoemulsification.
83
What is used to maintain the anterior chamber during surgery?
2% hyaluronic acid solution.
84
How many applications are recommended when using Nd
laser for cyclophotocoagulation?
55 to 60 applications.
85
What is the normal intraocular pressure (IOP) range in unsedated horses?
17 to 28 mm Hg.
86
What is a reasonable target IOP for glaucoma therapy?
Less than 20 mm Hg.
87
What is the incidence of glaucoma in horses?
0.07%.
87
How much can sedation with xylazine decrease IOP?
23% to 27%.
88
What is a common surgical technique used to reduce IOP in horses?
Transscleral cyclophotocoagulation (TSCP).
89
How far from the limbus should laser applications be placed in Nd
TSCP?
5 to 6 mm.
90
What type of lens is inserted through the corneal incision during cataract surgery?
Intraocular lens (IOL).
91
What should be done immediately following TSCP due to rapid IOP increases?
Aqueous paracentesis.
92
What is the dosage of gentamicin for pharmacologic ablation of the ciliary body?
25 to 40 mg intravenously.
92
What complication can arise from rupturing the lens capsule during ciliary body ablation?
Phacoclastic uveitis.
93
What percentage reduction in IOP can timolol maleate provide after a single dose?
17%.
94
What are gonioimplants used for in equine glaucoma treatment?
Improving aqueous drainage.
95
What is the maximum time for continuous topical anti-inflammatory therapy after surgery?
Several weeks, tapering gradually.
95
How long did one experimental study find gonioimplants reduced IOP?
28 days.
96
What is a significant risk factor for horses undergoing cataract surgery?
Systemic infection.
97
What should be done to minimize inflammation post-cataract surgery?
Administer topical antibiotics and corticosteroids every 4 to 6 hours.
97
What additional procedure is preferred for chronically blind eyes instead of cataract surgery?
Enucleation or evisceration with intrascleral prosthesis.
98
What does the combination of dorzolamide and timolol achieve in glaucoma management?
A 13% decrease in IOP.
99
What are the diameters of IOLs typically available for equine cataract surgery?
21-, 22-, and 24-mm diameters.
100
How long after surgery is the first recheck examination typically performed?
7 to 10 days postoperatively.
101
Pharmacologic Ablation of the Ciliary Body in blind eyes is performed how?
The injection is performed with a 22-gauge needle attached to a 3-mL syringe. The needle enters the globe 7 to 8 mm posterior to the dorsotemporal limbus at a 45-degree angle toward the optic nerve
