Korean Journal of
Veterinary Service

Cataracts have been reported to be associated with various risk factors such as age, environment, genetics, diabetes mellitus, uveitis, trauma and nutritional status, and this eye disease is characterized by the cloudiness or opacity of the eye lens or the capsule bag. Based on the location of opacity, cataracts are generally classified into nuclear cataracts affecting the lens nucleus, cortical cataracts affecting the lens cortex, anterior subcapsular cataracts affecting the front portion of the capsular bag, and posterior subcapsular cataracts affecting the back portion of the capsular bag. In addition, in terms of the degree of opacity, cataract maturity is classified into four stages: incipient, immature, mature, and hypermature (Christine et al, 2011). Cataract surgery has been performed mainly on human eyes, and it has become a commonly used surgical procedure since PHACO was introduced in 1967 (Park et al, 2022). In recent years, the incidence of cataracts in dogs has also been increasing, and these circumstances indicate the need to introduce excellent equipment and perform PHACO in the field of veterinary medicine as in cataract surgery for human patients. A previous study reported that good clinical results were not obtained in 45 out of 290 dogs that underwent cataract surgery, showing a success rate of 84.5% (Harathi et al, 2020). Since cataract surgery is reported to have a high failure rate of 15% or more, it is important to recommend that dog owners should arrange for their dogs to receive cataract treatment or surgery in an early stage of cataracts. Two important factors that determine the success or failure of cataract surgery are preservation of the posterior chamber during the surgical procedure to remove the eye lens and removal of remaining visco-elastic agents and residual lens. To properly address these two factors during cataract surgery using PHACO, excellent surgical equipment and veterinarians’ proficient surgical skills for PHACO are required. Since PHACO requires a small incision in the eyeball, the use of PHACO can decrease damage to the eyeball and reduce the time required for surgery, thereby decreasing the stress of the patient. Also, PHACO makes it possible to maintain the intraocular pressure (IOP) of the anterior chamber below a specific level after surgery, and thus it helps to minimize postoperative sequelae (Cho et al, 2022). After the eye lens is removed by PHACO, implantation of an artificial intraocular lens (IOL) is performed. With respect to the materials of artificial eye lenses, lenses made from polymethyl methacrylate and silicon were mainly used, but hydrophobic acrylic lenses have been increasingly used in recent years (Zheng et al, 2015). Artificial eye lenses were generally spherical in shape, but aspherical lenses have been recently developed. Aspherical artificial eye lenses were designed to reduce positive spherical aberration, and thus they have negative spherical aberration (Montés et al, 2009; Nochez et al, 2010).

For artificial eye lenses for humans, various types are produced according to age and the levels of visual acuity, but artificial eye lenses for dogs currently produced are limited to a small range of types. More specifically, artificial eye lenses for dogs have 4 ring-shaped supports on four sides, and the diameters of artificial eye lenses for dogs are divided into 5 types: 11 mm for very small dogs with a body weight of 2 kg or less, 12 mm for small dogs, 13 mm for medium-sized and large dogs, 14 mm for large dogs, and 15 mm for very large dogs. The level of visual acuity of artificial eye lenses for dogs is almost fixed at +41 diopter (D), and products manufactured by a German company called an-vision^Ⓡ are widely used around the world. In Korea, cataract surgery using PHACO in veterinary hospitals has been recently introduced, and it is limitedly performed only in a small number of veterinary hospitals. While the number of dogs with cataracts has been increasing due to an increase in the number of senior or geriatric dogs and young dogs with genetic defects in breeds such as the Bichon Frisé, veterinary hospitals to treat cataracts in dogs are concentrated in large cities, so it is difficult to provide cataract treatment for dogs. Therefore, this study aimed to analyze and present the entire process of cataract surgery in a dog and the information relevant to ophthalmic practice, such as diagnoses, artificial eye lenses, and surgical equipment required for cataract surgery in dogs in an attempt to confirm the usefulness of the cataract surgery method used by the researcher in the clinical field of veterinary ophthalmology.

Patient animal

12-year-old, neutered male, body weight 5 kg, black poodle visited Hangang Animal Medical Center with a chief complaint of visual impairment. In oculus uterque (OU), the eye lenses became cloudy and white, showing the symptoms of a cataract, and the owner of the dog reported that the cataract symptoms started to appear several months ago for OD and one year ago for OS (Fig. 1). In the electroretinogram (ERG) test (RETIport 3s ERG, Germany), the electrical potential generated by the retina was 0 μV in OD and 51.6 μV in OS, indicating that the total loss of vision occurred in OD while the retina cells of OS exhibited electrophysiological responses. The normal values of ERG are 65 μV or higher, and the measured value of OS was a little below the normal range, but the decision to perform surgery was made at the request of the owner of the patient. The results of the Shirmer tear test (STT; Union, New Jersey) were 18 mm/min for OD and 19 mm/min for OS. Also, when the IOP was measured by tonometry (Icare, Tonovet, Finland), IOP levels were in the normal range with 17 mmHg for OD and 22 mmHg for OS. The patient showed no responses in the menace response test, the dazzle reflex test and the maze test, but exhibited both palpebral reflexes and corneal reflexes. Slit-lamp biomicroscopy (Topcon, Japan), which is a method used to observe and assess the opacity and cataract maturity of eye lenses, showed that the patient had a mature cataract in OD and a hypermature cataract in OS (Table 1).

Table 1 . Evaluation of the eye conditions in the patient dog.

Parameters	OD	OS	Reference range
ERG (mV)	0	51.6	65<
STT (mm)	18	19	15∼20
IOP (mmHg)	17	22	15∼25
Menace response	-	-
Dazzle reflex	-	-
Palpebral reflex	+	+
Corneal reflex	+	+
Maze test	-	-
Slit-lamp	Mature	Hypermature

Figure 1. Turbidity of the lens in the patient dog.

Complete blood count showed that both RBC and WBC levels were in the normal range without any specific symptoms. Meanwhile, biochemical analyses revealed that the BUN level was 32 mg/dL (7∼27 mg/dL), and the serum creatinine level was 2.0 mg/dL (0.8∼1.5 mg/ dL), showing the symptoms of azotemia. However, after relieving the symptoms through perfusion, cataract surgery was performed. Fig. 1 represents the external conditions of the eyeball of each eye of the patient, and it shows the cloudy and white appearance of the eye lenses and vision loss.

Preoperative care for cataract surgery

Regarding the topical treatment of the eyeball, Eyelebo (Levofloxacin 0.5% Hanlim, Pharm. South Korea), Eyemetrone (Fluorometholone 0.1%, Harim, Pharm. South Korea) and Optanac Eye Drops 0.1% (Diclofenac Sodium 1 mg/mL, samil-pharm, Korea) were instilled in the eye TID for 7 days before surgery. In addition, 10 mg/kg of Amocra (Amoxicillin Hydrate & potassium clavulanate 375 mg, KUHNIL Pharm. South Korea) was administered as a systemic treatment BID for 7 days.

To maintain adequate mydriasis during cataract surgery, Mydrin-P (0.5% tropicamide, 0.5% Phenyephrine, Hankugsanten Pharm, South Korea) and Isopto-Atrophine (Atrophin 1% Alcon, Pharm. USA) were instilled three times at 30 minute intervals, starting from 2 hours before surgery. The anesthesia equipment used was Drager Atlan A300 (Germany), and anesthesia was induced by forced circulation for both inhalation and exhalation. As for pretreatment agents for the induction of anesthesia, 0.03 mg/kg of Atropine (Atropine sulfate 0.5 mg/kg, JEIL Pharm. South Korea) was administered SC. In addition, 0.5 mg/kg of Diazepham (Diazepham inj 10 mg/2 mL, SAMJIN Pharm. South Korea), 0.1 mg/kg of Butopanol (Butopanol 1 mg/1 mL, Myeongmum, Pharm. South Korea) and 6 mg/kg of Propofol (Probio 1% Myeong Pharm, South Korea) were administered IV. Also, 0.05 g/kg of Cefalzolin (Cefazolin Inj 1 g, Chong Kun Dang, South Korea) was also administered SC. To maintain anesthesia, isoflurane gas was used as an anesthetic agent, and the ringer lactate solution (Hartnann, Jungweon, PHA. South Korea) was used to maintain adequate perfusion during surgery. To prevent the movement of the pupil during surgery, 0.2 g/kg of Acrium (Atracrium besylate, myeongmum, Pharm. South Korea), a muscle relaxant, was administered IV, and the patient was kept in the supine position.

Cataract surgery

Cataract surgery was performed by using the two-handed PHACO techniques (BAUSCH+LOMB, Stellaris Elite, USA). In terms of the settings of the PHACO machine, in the sculpt mode, the parameters of the PHACO machine were set as follows: the vacuum level of 60 mmHg, the ultrasound power level of 30%, and bottle height of 70 cm. In the segment removal mode, the vacuum level of 210 mmHg, ultrasound power level of 45%, and bottle height of 70 cm were used. In addition, the PHACO machine was set at the pulse mode to facilitate surgery. In the first step of cataract surgery, a 2.8-mm incision was made at the edge of the cornea 2 mm away from the corneal limbus (Fig. 2A, 2B). The incision of the capsular bag was performed by making a round incision with a diameter of 5 mm in the center of the eye lens anterior chamber, and visco-elastic agents (Hyaluronate natrium 15 mg/1 mL, 0.85 mL, Kukje, Pharm. South Korea) were injected into the anterior chamber to maintain the shape of the (capsulorhexis/capsullectomy) chamber and protect the corneal endothelium. Next, the eye lens was separated by performing hydrodissection with a BSS solution (Alcon BSStm, USA), Then, after sculpting was performed using the PHACO handpiece, the divide and conquer technique was used to remove the lens nucleus (Fig. 2C). Thereafter, the lens nucleus and residual lens cortex were removed using the segment removal mode, and the posterior capsule was polished into a clean state (Fig. 2D). Then, considering the eyeball size of the dog, a 12-mm intraocular lens (an-lens, Acrivet 30V-12, D+41.0, USA) was inserted into the capsule bag by using an injector (Fig. 2E, 2F). The corneal incision was closed by using simple sutures with 10-0 Black Nylon (REXLON-black nylon USP10-0, spatula 6 mm 3/8, SMG) (Fig. 2G). In the final step of surgery, when physiological pressure in the anterior chamber was needed, a BSS solution was injected to inflate the anterior chamber (Fig. 2H). At this time, IOP was estimated by digital palpation instead of using a tonometer.

Figure 2. Cataract surgical procedures. (A) Preoperative condition of the OS, (B) Corneal incision, (C) Phacoemulsification, (D) Central opening in the anterior capsule of the lens, (E) Intraocular lens implantation for cataract surgery, (F) Completion of intraocular lens implantation, (G) Corneal suture, (H) Completion of cataract surgery.

Postoperative care for cataract surgery

After surgery, Amocra, an anti-inflammatory agent, was administered BID for 7 days, and eye drops such as Eyelebo 0.5%, Eyemetholone Eye Drops 0.1% (Fluorometholone 1 mg/mL, Genu Pharm, Korea), and Optanac Eye Drops 0.1% were given. To prevent POH after cataract surgery, Cosopt solution (Dorzolamide 2%/timolol 0.5%, Tampere, Finland) was administered from postoperative day 0 for about 3 weeks, and the owner of the dog was instructed to get the dog to wear an Elizabethan collar for 3 weeks.

Cataracts are divided into congenital cataracts and acquired cataracts. Cataracts are the leading cause of blindness, accounting for 47.8% of global blindness, and old age is the single most common risk factor for cataract (Lie et al, 2017). Senile cataracts occur without any physical risk factors. In dogs, cataracts frequently result from the aging process, and the incidence of cataracts in dogs significantly increases after age 8, but young dogs of age 3 or less may develop cataracts in some cases (Kibar et al, 2014). The symptoms of cataracts progress slowly over years. Thus, although the images of objects are blurred and unclear and there is some visual discomfort, patients may frequently not recognize the symptoms. The degree of visual impairment varies depending on the degree of opacity of the eye lens and the location of the lesion, and in case of partial opacity, the images of objects may overlap even in the vision of one eye (Mahbubul et al, 2019). As cataracts progress in dogs, dogs can perceive objects not only in the early stage but also in the middle stage and do not exhibit significant behavioral differences. Thus, it is frequently difficult for dog owners to recognize the symptoms of cataracts in dogs. As a result, only when dogs have underwent a considerable degree of vision loss and the eye lenses have become apparently white, dog owners recognize cataracts in their dogs and take them to a veterinary hospital. At this time, the cataract maturity of the eye lens is likely to have reached the immature stage or a higher stage, and in serious cases, dogs with cataracts are taken to a veterinary hospital when the cataract has progressed to the hypermature stage. In the mature stage, the vision of the affected eye has been almost completely lost, and the patient does not perceive light in some cases. Humans feel uncomfortable in daily activities even in the incipient stage, so 94% or more of cataract patients recover their vision through an early diagnosis and timely treatment or surgery. However, in dogs, cataract diagnoses are made in relatively late stages and thus hardening or liquefaction of the eye lens occurs. As a result, even if cataract surgery is performed using PHACO, the success rate of cataract surgery in dogs is reported to be 85∼90%, showing a lower success rate compared to the recovery rate of human patients (Davidson et al, 1990; Byon et al, 2013).

PHACO is currently used as the standard treatment method for cataracts. Since it requires a smaller incision compared to intracapsular cataract extraction (ICCE) or extracapsular cataract extraction (ECCE), the use of PHACO decreases absolute time required for surgery (Linebarger et al, 1999; You et al, 2020). In addition, this technique allows surgeons to control or maintain IOP at a constant level during surgery. Therefore, even if the rupture of the posterior chamber occurs, it rarely leads to vitreous prolapse, and the risk for complications such as suprachoroidal hemorrhage during or after surgery is lower (Jacobi et al, 2000; Kim and Oh, 2018). PHACO is a surgical method of cataract removal that uses ultrasound energy to break up the cloudy eye lens by making a small corneal incision with a diameter of about 2 mm. When PHACO is performed during catatact surgery, complications may result from damage to corneal endothelium or thermal damage to the surrounding tissues during the operation. In addition, stability of the eyeball anterior chamber needs to be maintained during surgery, and care should be taken to avoid causing damage to the posterior chamber. This study was conducted to present veterinary clinical data on cataract surgery using PHACO in view of the fact that there is a lack of adequate clinical performance and data on cataract surgery in dogs performed in veterinary hospitals in Korea.

The patient was a 12-year-old senior dog. In the ERG test of OD, there were no ERG responses of the optic nerve, indicating the total loss of vision in OD, so a prosthetic eye was inserted to get rid of the cause of sequelae or pain due to IOP elevations that may subsequently occur. OS was diagnosed with a hypermature cataract and showed severe cataract symptoms, but since the IOP level was in the normal range, the decision to perform surgery was made. With respect to the surgical procedure, as shown in Fig. 2, a 2.8 mm corneal incision was made using a corneal incision knife. Then, the eye lens was removed by inserting a PHACO handpiece into the eyeball (Fig. 2C). The IOL is available in a folded state in a small tube, so it was inserted into the eyeball by pushing it like pushing the plunger of a syringe (Fig. 2E). Then, as the final step of surgery, suturing was performed to close the corneal incision (Fig. 2G). While removing the eye lens during surgery, care should be taken in handling the PHACO handpiece to avoid the rupture of the posterior chamber. The tip of the PHACO handpiece aspiration port does not have adhesion resistance, so there is a possibility that when it contacts the posterior chamber, it may tear the posterior chamber. If the rupture of the posterior chamber occurs, it leads to vitreous prolapse into the anterior chamber, resulting in vision loss.

In this study, PHACO time during surgery was 3.13 minutes. If the vacuum level and the ultrasonic power level are set at high levels, PHACO time can be reduced but corneal endothelial damage or the rupture of the posterior chamber may occur. Thus, even though PHACO time is increased, the vacuum level and the ultrasonic power level should be appropriately set to facilitate the surgical process and the management of postoperative complications. To maintain the external shape of the cornea during cataract surgery, intraocular injections of visco-elastic agents are performed. If visco-elastic agents are not used, the intraocular area tends to collapse as soon as a corneal incision is made, making it impossible to perform surgery. These visco-elastic agents must be completely removed after surgery, but some residues of the agents tend to remain in the eyeball. They block the ciliary cleft and obstruct aqueous humor outflow, causing IOP elevations, and the occurrence of POH of 30 mmHg or higher within 72 hours after surgery is reported to be associated with a higher incidence of glaucoma (Biros et al, 2000; Sigle and Nasisse, 2006). Regarding viscoelastics used in the present case of cataract surgery, sodium hyaluronate 15 mg/1 mL manufactured in Korea was administered. Since this product has lower jelly-like properties and a higher moisture content compared to existing viscoelastics, it is easier to remove after surgery. POH due to visco-elastic agents is reported to be the most serious postoperative sequelae occurring after all types of cataract surgery including cataract surgery in humans (Bhutto et al, 2021). Therefore, to prevent POH, Cosopt solution was instilled in the operated eye for 3 weeks after surgery. The postoperative levels of IOP during the first 24 hours after surgery were 19 mmHg, 10 mmHg, and 10 mmHg, respectively, at 2, 3, and 20 hours after surgery. During follow-up, the levels of IOP were 8 mmHg, 7 mmHg, 6 mmHg, and 10 mmHg, respectively, at 1 week, 2 weeks, 3 weeks, and 2 months after surgery. These postoperative changes in the IOP level showed the management of IOP at relatively stable levels without the occurrence of POH.

A lack of proper inflammation management after cataract surgery may result in vision loss due to uveitis caused by bacterial infections, so Amocro, Eyelebo, and Optanac were used to prevent uveitis.

As described above, in this study, the patient recovered the vision of OS through cataract surgery using PHACO and currently performs daily activities without visual discomfort. When performing cataract surgery in dogs, PHACO is a treatment process required for the recovery of the eye. In the future, the introduction of better equipment and technological development based on the accumulated experience of veterinarians are expected to greatly contribute to the recovery of visual function in companion animals as the proportion of senior and geriatric pets is increasing in the population of companion animals.

No potential conflict of interest relevant to this article was reported.