Iris cysts are hollow cavities in the eye filled with secretion. They come in various sizes, numbers, shapes, pigments and can be free-floating, attached to the pupillary margin or within the

posterior chamber The posterior chamber is a narrow space behind the peripheral part of the iris, and in front of the suspensory ligament of the lens and the ciliary processes. The posterior chamber consists of small space directly posterior to the iris but anterio ...

. Most frequently iris cysts don't cause any issues, but they can cause problems like: " fly biting" behavior, corneal endothelial pigment, lens capsular pigmentation, altered iris movement, decreased aqueous outflow with subsequent

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...

or block the vision when grown too big. They can be acquired or innate. Possible causes are inflammation, drug-induced, uveitis, a trauma, tumor-induced, parasitic or implantation. Most frequently iris cysts are benign and need no treatment. Sometimes iris cysts are causing problems and need to be deflated. Iris cysts can be treated with trans corneal diode laser treatment, fine-needle aspiration or surgical excision. For the treatment of iris cysts is a conservative approach favored.

Introduction

Mackenzie diagnosed the first iris cyst in 1830, which was a posttraumatic iris cyst in the anterior chamber. Because of the wide variety of iris cysts, a categorization was needed. This categorization was proposed by Shields in 1981 and was based on 2 main groups: primary and secondary cyst. Primary cysts origin is neuroepithelial, and rarely causes any issue. Primary cysts can be subcategorized based on their location in the eye. However, secondary cysts can cause problems like decreased vision, secondary glaucoma, uveitis or corneal

edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...

and origin from implantation,

metastasis Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...

, miotics or parasites. Secondary cysts are further categorized based on their origin.

Brief overview of the anatomy of the iris

The iris is a thin circular structure in the eye which consists of two layers, on top is the stroma and underneath the pigmented epithelial cells. It separates the eye in the anterior and posterior chamber, is responsible for the eye's color, and its function is to regulate the size of the pupil. By controlling the size of the pupil it regulates the amount of light reaching the retina. Depending on the amount of light, the iris opens with high intensity light and closes with low intensity light. The iris is able to control the size of the pupil due to radial and circular muscles which attach to the stroma. The circular muscle, sphincter muscle, contracts in a circular motion, making the pupil smaller, but by contracting the radial muscles, dilator muscles, the pupil enlarges.

Primary cyst

The classification of primary cysts is according to the categorization of Shields. The origin of primary cysts is neuroepithelial. Primary cysts are rarely causing any problems, fluid-filled and have smooth surfaces. They are subcategorized according to their location in the eye. Pupillary cysts, also central cysts, are located from the pupillary margin to the iris root, midzonal cysts are located from the iris root to the

ciliary body The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The aqueous humor is produced in the non-pigmented portion of the ciliar ...

, and peripheral cysts are located at the iridociliary sulcus. Free-floating cysts can occur in the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

vitreous chamber The vitreous chamber is the space in the eye occupied by vitreous humor. Structure Within the vertebrate eye, there are considered to be three chambers: anterior, posterior, and vitreous. It is important to note that the eye can also be classifie ...

and are usually dislodged epithelium cysts. Cysts of the iris stroma are anteriorly located and as they develop, they usually cause deformation of the iris and need treatment. Especially the

congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...

secondary cysts require often treatment. They are usually unilateral and solitary. Acquired secondary cysts, on the other hand, require very rarely treatment and often occur at a later age.

Secondary cyst

Secondary cysts are usually unilateral and solitary and have a smooth surface. Secondary cysts may obstruct the eye's vision, cause intraocular pressure or iris displacement. The categorization of secondary cysts is categorized according Shields categorization. Secondary cysts are classified into 6 subcategories. *Implantation cysts are the most common secondary cysts. They can originate from a surgical trauma or a penetrating wound. An invasion of

conjunctiva The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithelium ...

l or corneal epithelial cells creates the cyst. *Drug-induced cysts are related with the use of miotics or

latanoprost Latanoprost, sold under the brand name Xalatan among others, is a medication used to treat increased pressure inside the eye. This includes ocular hypertension and open angle glaucoma. It is applied as eye drops to the eyes. Onset of effects i ...

but can get smaller after stopping inducing the drug. *Uveitic cysts can arise when the eye is or has been

inflamed Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecu ...

. *Tumor-induced secondary cysts are caused by a tumor. *The rarest iris cyst is the parasitic cyst, which can develop with the presence of a parasite. *At last secondary cysts can be caused by a systematic disorder like:

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

Menkes syndrome Menkes disease (MNK), also known as Menkes syndrome, is an X-linked recessive disorder caused by mutations in genes coding for the copper-transport protein ATP7A, leading to copper deficiency. Characteristic findings include kinky hair, growth ...

malignancies Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...

Diagnosis

Iris cyst must be differentiated from other kinds of possible "bodies" in the eye. After the body has been established as an iris cyst, it must be categorized as primary or secondary. It is necessary to differentiate secondary cysts even further.

Clinical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions about the patient ...

can achieve this differentiation with the use of multimodal imaging techniques like UBM, ultrasound B-scan (USB), anterior segment optical coherence tomography (as-OCT) and

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

Clinical presentation

Primary cysts come in various sizes and number but are usually fluid-filled, with regular borders and a smooth surface. The iris could be slightly displaced anteriorly because of a primary cyst, but normally no problems occur with primary cysts. Secondary cysts cause most of the times problems, and thus also need treatment. Secondary cysts usually have a rough surface, irregular borders, solitary and unilateral. Possible problems could be displacement of the iris, iritis and raised intraocular pressure. A clinician should also be able to tell the difference between a cyst and a tumor. The main differences are that cysts usually cause displacement or the iris whereas a tumor arises and grows into the iris stroma. In the presence of an intrinsic or sentinel vessel than you probably have to deal with a tumor. The last main difference can be shown with

transillumination Transillumination is the technique of sample illumination by transmission of light through the sample. Transillumination is used in a variety of methods of imaging. Microscopy In microscopy transillumination refers to the illumination of a sample ...

, since transillumination always creates a shadow with a tumor but almost never with a cyst.

Ultrasound B-scan (USB)

Ultrasound B-scan (USB) uses wavelengths of 10-20 MHz to form an image of the eye. USB can be used to identify the extension of the iris cyst in either the anterior or posterior chamber. It can also be used to identify midzonal cysts behind the iris and to determine whether there is

involvement. The preferred method to determine ciliary body involvement, however, is not USB but ultrasound biomicroscopy.

Ultrasound biomicroscopy (UBM)

Ultrasound biomicroscopy, (UBM) has a higher resolution than USB and it also uses soundwaves with a higher frequency from 50 to 100 MHz. UBM is used for the identification of thin ultrastructure's and for internal echogenicity of cysts. Due to the high resolution small cysts can easily be distinguished, multilocated cysts are easy to find and it is easier to determine whether the cyst is bilateral. The only disadvantage of UBM is its limited penetration. Despite this disadvantage, UBM is still the golden standard for the diagnosis of iris cysts.

Anterior segment optical coherence tomography (AS-OCT)

AS-OCT has the highest resolution of all diagnosis methods but it has a major disadvantage. AS-OCT creates a heavy shadowing caused by the iris pigment epithelium regarding iris lesions. AS-OCT is used to show the anterior border of an iris lesion. The internal structure of the cyst and what is behind the cyst, however, is not that clear due to heavy shadowing. That is why UBM is preferred over AS-OCT, the borders will be less visible but with UBM the whole structure of the cyst and the surrounding tissues is shown.

Fine-needle aspiration (FNA)

Fine-needle aspiration, FNA, is only used if every other method has failed to establish what kind of cyst it is and if it is presumably a solid tumor. FNA is used as a last diagnosis method because it is the most invasive method since the eye has to be penetrated with a needle. FNA has been very successful with differentiating tumors with cystic spaces, like

melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye ( ...

adenoma An adenoma is a benign tumor of epithelial tissue with glandular origin, glandular characteristics, or both. Adenomas can grow from many glandular organs, including the adrenal glands, pituitary gland, thyroid, prostate, and others. Some adenom ...

s or metastatic tumors. FNA can also be used as a treatment.

Other ancillary procedures

MRI is not used as a diagnosis method by itself. It is more used as a method to gain some extra information about the cyst. Magnetic resonance imaging can establish very well whether the cyst is in contact or attached to the sclera or whether the cyst is a primary tumor.

Treatment options

Observation

The preferred treatment option is observation, since most iris cysts do not hurt or cause any pressure. A

veterinarian A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, vet ...

however prefers to check the cyst from time to time to make sure that the cyst does not grow and does not cause any problems or pain. If the cyst is growing, causing pain or some issues over time, then the cyst will need another treatment.

Fine-needle aspiration

Fine-needle aspiration (FNA) is, as discussed earlier, also a diagnosis method but can also be used as a treatment. With FNA a very fine needle is inserted in the eye in the cyst. The purpose of the needle is to penetrate the membrane of the cyst, so that the cyst will deflate. This method has proven to be successful but there is a possibility that the cyst will not disappear fully but only shrink. If the cyst has shrunk enough that it is not causing any pain or trouble anymore, then a second treatment might not be necessary. But if the cyst is still causing an issue after the treatment, the treatment must be repeated, or another method has to be used.

Intracystic injection of absolute alcohol

Intracystic injection of absolute alcohol has proven to be a very effective method. The alcohol gets injected in the cyst through a needle which is penetrating the eye from outside into the cyst. The injection of the alcohol regresses the cyst or will at least stabilize it. It can take a few weeks before the cyst has disappeared fully. A common side effect of this method is an

inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

in the anterior chamber, but this can easily be treated with

topical steroid Topical steroids are the topical forms of corticosteroids. Topical steroids are the most commonly prescribed topical medications for the treatment of rash, eczema, and dermatitis. Topical steroids have anti-inflammatory properties and are classifie ...

s (cream or gel with anti-inflammatory properties).

Antimitotic agents

Antimitotic agents Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...

are used mainly when a cyst is resistant to all other treatments apart from surgery, since surgery is the last resort. Antimitotic agents are injected into the cyst and left inside for 5 minutes; after 5 minutes the agents are rinsed out.

have the side effect of creating a small

which can easily be treated with

s. Antimitotic agents stop the mitose of the cells of the cyst by interfering with a particular phase of the cell cycle, which stops the cyst from growing and will eventually kill the cells and thus the cyst.

Laser therapy

Laser therapy is a treatment which has to be repeated several times. The treatment gets repeated every week until the cyst is gone. Despite not having the highest success rate it is nowadays the most preferred treatment against iris cyst because it is the least invasive method since the eye doesn't need to be punctured or cut. Two kinds of laser beams can be used for laser therapy: thermal (

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

or argon laser) and Nd:YAG laser. Sometimes both methods are combined for a better result since thermal laser can harden the cyst and stop the intracystic fluid production and Nd:YAG can perforate the cyst membrane and drain the cyst.

Surgical

Surgery is considered to be the last resort because surgery has the highest chance at complications. The surgical approach depends on where the cyst is located, how big the cyst is and the number of cysts.

The stepwise minimally invasive strategy

There are many options when treating an iris cyst. Mentioned above are the most used treatments but in the past there have been other methods but they haven't been successful enough to be still used today. A clinician has to consider a lot of things when choosing a treatment. The golden rule when treating iris cysts however is to choose the least invasive method. That means that cysts which are not causing any problems will not be treated but observed. The least invasive treatment is laser therapy and is, therefore, also the preferred method to treat an iris cyst. Depending on the kind of cyst, the clinician will choose either antimitotic agents or AS-OCT, if laser has failed or if laser is not possible. It is unlike that FNA will be used due to its low potential for removing the cyst. Surgery is the most invasive method and the one with the highest chance of complications. That is why surgery is the last resort.

References

{{Reflist Dog diseases Disorders of iris and ciliary body