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Lens disorders: Diagnosis and treatment (Proceedings)
Lens induced uveitis is greatly under-diagnosed and under-treated.
Lens opacities and position will be discussed via lots of photos. Treatment of the associated abnormalities will be discussed. However there are three main points to take home from this discussion:
1. Lens induced uveitis is greatly under-diagnosed and under-treated. We will evaluate what to look for and how to manage it.
2. Even if your clients do not want to pursue lens surgery, an evaluation by an ophthalmologist may save their pet significant problems in the future and them significant cost.
3. Cataract surgery success has continued to improve year by year with newer technologies and is now 80-90% successful. If your clients may want to consider lens surgery, refer them ASAP before complications occur which diminish the percentage of success.
Lens opacities can be classified in many ways such as by size, location, and maturity. Although some classify lens opacities by age, this is typically irrelevant with respect to how they are managed other than young dogs tend to sustain more lens induced uveitis. Congenital development will be discussed so that abnormalities can be recognized and treated appropriately.
A brief description of lens anatomy is important to recognize the origination of new lens fibers as well as the formation of lens suture cataracts. Lens fiber nuclei are positioned at the lens equator at the far periphery behind the base of the iris. If iris dilation is not performed for lens evaluation, newly forming cataracts in this position will be missed. Cataracts in this peripheral location also tend to be rapidly forming and as such provoke a more significant lens induced uveitis. Conversely, as the lens fibers grow and join each other near the mid- lens forming Y sutures, cataracts in this position progress less frequently and in most breeds, may not progress at all. The dog and cat lenses are much larger than humans at 0.5ml and 0.6ml respectively compared to 0.3ml in humans. The lens is predominantly protein. The fibers are arranged in a symmetrical pattern with minimal intracellular structures allowing for maximal light transmission. An extremely thin basement membrane [2-50um] surrounding the lens serves as the lens capsule.
Congenital defects in lens development may lead to abnormally small lenses which fall forward, backwards, or are associated with small globes. These lenses may need to be removed to prevent chronic damage to the cornea and pain from glaucoma but the other intraocular structures need to be evaluated as they may also suffer from maldevelopment. Persistent Pupillary Membrane or PPM may attach strands of the iris to the lens capsule causing focal cataract progression. In rare cases this may be progressive. In some breeds this is considered a reason to not breed and they will fail a CERF, Canine Eye Registry Foundation. In the Besenji, Mastiff, and Corgi the intraocular damage from extensive PPM attachment may be so severe as to blind puppies at birth. Pupil dilation of these pups with 1% Tropicamide at initial examination is important to evaluate the entire lens.
Congenital cataracts are due to many causes such as random abnormalities in development, genetics, toxic or infectious events. Merle Ocular Dysgenesis refers to the significant multiple congenital abnormalities that may occur with breeding merle to merle. The retinal pigment epithelium abnormality leads to retinal dysplasia, detachments, colobomas, iridal dysplasia, glaucoma, and cataracts all to varying degrees. As with many juvenile cataracts these can progress very rapidly with significant associated inflammation. Evaluation of these cases before cataract development is extremely important if owners wish to pursue cataract surgery in that critical evaluation of the retina is important prior to lens opacification. Colobomas, defects in the sclera structure, may warrant a recommendation of preoperative LASER retinopexy. These dogs may also be deaf and preservation of vision is often of great importance to owners.
The Labrador Retriever and Samoyed may suffer from a combination of cataracts and chrondrodysplasia. Their limbs have varying degrees of valgus and varus deformities although the cataracts almost always progress within the first two years of life. These puppies should be monitored over time as glaucoma and retinal detachment may ensue. Young dogs tend to sustain scleral stretching at much lower pressures than adult dogs. If pressures elevate over about 25mmHg, the sclera will stretch and lagophthalmos, inability to close the eyelids, may occur resulting in corneal erosions. Enucleation or intraocular prosthesis should be recommended at this stage. Due to the combination of both recessive and dominant factors of inheritance in these dogs, future breeding of both parents is discouraged.
Feline congenital cataracts, often will not progress. Cats appear to more commonly form central nuclear cataracts, if at all, in utero, and subsequently form normal cortical lens fibers at the periphery. If central vision is significantly impaired or, as in rare cases these cataracts do progress, cats do very well with cataract surgery. They do not tend to form the degree of lens induced uveitis as dogs however it would be recommended that a discussion with owners to watch for signs of uveitis and secondary glaucoma be made. We rarely use topical steroids in cats due to the high risk for recrudescence of feline herpes virus, therefore long term maintenance with these drugs would be discouraged.
Cataract pathology is a bit of a runaway train once the process of progression begins. The lens is predominantly protein and once the protein bonds begin their alteration, normal enzyme balance is altered, anti-oxidant protectors are overwhelmed, and the balance of soluble and insoluble proteins is altered, stopping the process is, at this point, impossible. Anti-oxidant drops claiming to 'cure' cataracts are, therefore, not able to reverse the changes in protein bonds. It's like trying to unboil an egg. Sadly owners have tried using these drops for months on end and when they have discovered that they have spent a lot of money and there has been no benefit, it may well be too late to perform surgery. I have seen many of these cases where lens induced uveitis has not been managed and the retina and/or uvea have been irreparably damaged, and/ or glaucoma irreparably damaged the retina and optic nerve. A few cases where the owners thought it work were actually posterior lens luxations in which the lens ligaments became so inflamed, the lens fell to the back of the eye. When the owner could no longer see the cataract in the pupil, they thought the drug worked. Ironically, the dog was still blind due to glaucomatous or inflammatory damage. Anti-oxidant therapy may have its place in prevention of cataracts as may drugs interfering with the shift in enzyme control in the diabetic lens, however, this remains to be seen.
Management of lens induced uveitis [LIU] is critical to the long term comfort of a pet with cataracts whose owners are not considering cataract surgery. Although surgical success is high at 80-90%, ophthalmologists understand that due to the cost, time commitment, and need for general anesthesia, not all pet owners will pursue cataract surgery. Ideally, at least an examination of a cataract patient to determine the degree of LIU and the need for medication would be warranted. If owners are interested in cataract surgery, referral when cataracts are FIRST seen is critical for high success. Even in diabetics who are not yet well controlled, dogs should be seen in the very early stages of cataract formation. Many veterinarians will refer dogs as soon as they are diagnosed with diabetes as they are well aware of the serious complications that may occur in their patients if inflammation progresses unchecked. Diabetic Miniature Schnauzers in particular may have horrendous inflammation especially if concurrent systemic lipidemia or Cushings Disease complicates their management. I have denied more Miniature Schnauzers cataract surgery due to inflammatory complications than any other breed.
Lens Induced Uveitis [LIU] is managed with a combination of topical and systemic steroidal and nonsteroidal anti-inflammatories, NSAIDs. Clinical signs of LIU may not be dramatic. Owners may not notice a red eye and the most subtle change of lower intraocular pressure may go undiagnosed. Some however, are very cloudy with anterior chamber flare, swelling of the iris, and when severe, keratic precipitates and even hyphema. Basically the presence of a visible cataract should warrant investigation into the high possibility of LIU being present. The goal is to maintain the cataract patient on the least amount of medication that will control the uveal inflammatory response to lens protein leaking out of the abnormally permeable lens capsule. Topical flurbiprofen [Ocufen] or diclofenac [Volteren] are nonsteroidals often prescribed once to four times daily as needed. These will not interfere with systemic diabetic management in the manner of steroidal anti-inflammatories but it should be noted that they are relatively mild. Topical steroidal anti-inflammatories are often necessary in combination with the NSAIDs especially if the LIU is out of control. These drugs do have the potential to cause systemic interference with diabetes management especially in the small dogs. Vexol, rimexolone, is a synthetic steroidal anti-inflammatory which appears to have fewer systemic effects. I will use this on any of my patients who seem sensitive although it has not yet been quantified in the dog. Systemic anti-inflammatory therapy is also needed in some cases that may be severe or those that may have sustained corneal erosions and are not able to receive topical therapy. Of course the best defense is to monitor and manage this inflammation carefully such that these stronger drugs are not needed.
Traumatic Cataracts require much more aggressive anti-inflammatory therapy and for the most part, surgical intervention. Note that if lacerations of the lens capsule are greater than 2- 3mm sufficient lens cortex typically leaks into the anterior chamber to produce severe fibrous inflammation with intractable secondary glaucoma. If a corneal puncture is suspected to have hit the lens capsule, evaluation within hours to days is needed to determine if surgical intervention is necessary. Treatment before referral may involve systemic and topical broad spectrum antibiotics. Ointments should be avoided as they may promote further uveitis by the introduction of oily material. A topical mydriatic is of benefit in that the pupil may require significant time to open if it is inflamed. Systemic steroids may also be of benefit if not contra-indicated in that they may diminish intraocular inflammation while not significantly alter corneal healing.
Juvenile to adult feline cataracts are more commonly secondary to a primary uveitis. These may be unilateral or bilateral. These cases may progress to secondary glaucoma which in the cat typically has minimal clinical signs. This type of cataract may or may not be amenable to surgical correction but prior investigations to the etiology of the uveitis in essential. The majority of these are idiopathic and yet we do see some associated with specific etiologies such as trauma, feline infectious peritonitis, toxoplasmosis, or neoplasia. Lens luxation in the cat is uncommonly primary and most likely observed secondary to chronic inflammation with associated destruction of the zonules. Surgical removal is often successful if subsequent inflammation can be managed.
Lens luxation in the dog is most commonly a breed related zonule breakdown. Terriers, most prominently Jack Russell Terriers, are genetically susceptible to this condition. Sadly these are often diagnosed too late to preserve vision in the first eye affected as glaucoma rapidly occurs. Pet owner education and early ophthalmic examination of the remaining eye may allow for preservation of vision by medical or surgical means. Newer information would indicate that the use of miotics to constrict the pupil restricting a moving lens to the posterior segment, may maintain vision and comfort for prolonged periods of time. Surgical intervention may be required to prevent completely luxated lenses from damaging the cornea, causing glaucoma, retinal detachment or degeneration. Small incision surgery before a lens fully luxates appears to carry a better prognosis than waiting until the lens fully luxates. Anti-glaucoma medication in these cases may be necessary throughout life in order to maintain comfort and/or vision.
Talking to your patients about cataract surgery really requires a team approach. We educate pet owners about the pre and post operative care, the rechecks, the potential complications but the bottom line is that cataract surgery is now highly successful. We see an overall success rate of 90% in the first year. This does decline somewhat over time, however, good communication is the key to happy clients. Good surgery and case selection is the key to happy pets. It is an extremely rewarding surgery to see pets blind at admission to the hospital and visual when they go home hours later. Case selection is much easier with pets that have little or no lens induced uveitis, no goniodysgenesis risk for glaucoma, no abnormal electroretinogram [ERG] tracings, and no risk for anesthesia or post operative stability as with unregulated diabetics. We use small incision surgery just as in people of about 2.7mm. Through this we inject a foldable intraocular lens after removal of the cataract. In contrast to people, dogs and cats always receive sutures due to a less rigid sclera combined with a more active lifestyle in the pet.
Encouraging early referral to an ophthalmologist is important for a multitude of factors:
1. Preventing lens induced uveitis before it starts is important. This will affect overall success rate of cataract surgery the most significantly. Again, even if owners are not opting to pursue surgery, the goal is to keep their pet comfortable. Waiting to refer until cataracts are 'mature' or diabetics are controlled or owners get financing for surgery may place the pet at significantly higher risk for problems associated with acute and/or chronic inflammation.
2. Evaluation of the retina before the cataract opacification prevents direct visualization. Viewing the retina directly allows the greatest accuracy in determining it's normalcy. In some cases, at some ages, the ERG and ultrasound would not be necessary if the retina can be viewed. The cost savings to your client in this situation is significant.
3. Early education and treatment of potential complications can be dramatically altered such as goniodysgenesis now that we have glaucoma shunts and intraocular lasers available. Glaucoma is an aggressive disease in the dog which we talk to all owners about, however, management of those cases with inherited goniodysgenesis prior to surgery may be more assertive.
4. Inflammation and surgery open the blood aqueous barrier to bacterial invasion. Although post operative infectious endophthalmitis is extremely rare, I encourage owners to address other systemic infections such as skin, urinary, or gingiva/teeth prior to surgery.