Introduction:
Iris is the colored muscular portion of the eye. It contains a pupil through which light enters the eye. The muscles of the iris determine the amount of light that enters the eye. Defects in the iris cause excessive light in the eye. This problem can be congenital or acquired. Prosthetic iris devices act as artificial iris regulating the amount of light entering the eye. The Iris diaphragms are one of the oldest and most commonly used lenses used in such cases.
What Are Iris-Lens Diaphragm Lens?
These are prosthetic (artificial) iris devices first used by Sundmacher et al. in 1991. Peter Choyce first designed the first device in the 1950s. The first developed lenses were rigid and were blue, green, and brown colors. Modern lenses are made up of poly methyl methacrylate and are black.
These implants are composed of various parts like:
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A diaphragm covers the natural iris. It is made up of flexible and foldable material.
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Flaps to maintain their position inside the eye. These are foot plate-like structures that protrude from the circular periphery.
The diameter of the diaphragm is 11mm to 13 mm, with an opening measuring 3 mm to 4 in diameter. The thickness of the main portion of the diaphragm is 0.15 mm to 0.17 mm. The thickness of the flap ranges from 0.1 to 0.14 millimeters. The surface of the diaphragm is annular, with the main portion having a vault height of about 0.4 to 0.6 millimeters.
What Are the Indications of Diaphragm Lenses?
There are various clinical conditions where an artificial iris diaphragm is used. Such conditions are:
Aniridia:
This is a genetic disorder characterized by complete or partial absence of the iris. It can be a single clinical entity or associated with disorders like Gillespie syndrome (inherited neurological disorder associated with bilateral absence of the iris), WAGR syndrome (inherited disorder with the absence of iris and presence of kidney tumor, and mental retardation). These are associated with different genes like PAX6 and ITPR1.
Coloboma Eye Defect:
This is also an inherited eye defect characterized by the absence of one or multiple eye structures. This occurs due to failed closure of the embryonic fissures (developmental grooves present in the embryo). These defects involve the eyelids, iris, lens, ciliary body (a portion of the eye that help to change the shape of the lens), zonules (fibers that hold the lens), choroid ( a tissue between the sclera and retina), retina, and optic nerve. This is associated with trisomy (presence of extra structure) of 13 or 18 chromosomes or the presence of kabuki syndrome (genetic disorders characterized by the presence of skeletal malformations and growth disorders), Meckel-Gruber syndrome (rare recessive genetic disorder with the presence of multiple cysts in the kidney and other fingers), Rubinstein-Taybi syndrome (genetic disorders with the clinical features of the temporary structure, broad angulated thumbs):
Mydriasis:
Mydriasis is a condition characterized by dilated pupils caused by nerve injury or due to the effect of different drugs like Atropine and Phenylephrine. This may be physiological also.
Iridodialysis:
This is caused by blunt trauma of the eye. This condition occurs when the iris is torn from the ciliary body.
Aphakia:
This condition (aphakia) is associated with the absence of a lens. This condition can be congenital or may be due to the lens removal in cataract surgery or the injury.
What Are the Different Types of Diaphragm Lenses?
Different diaphragm lenses have been developed according to their purpose and usage.
1. Endocapsular Capsular Tension Ring–Based Prosthetic Iris Device:
These are not true diaphragm rings, as the diaphragm used in these cases is segmental. Due to their size and foldability, these lenses are placed using a small coronal incision. When two such implants are placed, a capsular bag is used for implantation to create a peripherally opaque diaphragm. The lenses are brittle and need an intact capsular bag for implantation. There are two types:
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Aniridia Rings: In this type, two of these rings are inserted into the bag to form a closed diaphragm. Examples are morcher type 50C and 50E lenses.
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Partial Aniridia Rings: These rings are useful for managing Colomba eye defects. These are capsular tension rings with a diaphragm. For larger defects, two rings are inserted. Examples are morcher type 96E and 96G lenses.
2. Aniridia Implants: These are true iris-diaphragm lenses that can be used in both aniridia and aphakia cases. Morcher types 67B and 67G belong to this category.
3. Partial Aniridia Implants
These lenses have relatively small aperture sizes, which are useful for defects like iris injury caused by blunt trauma. Morcher type 67 and 67D are examples of the lens used.
4. Foldable Iris Diaphragms
These are foldable lenses made up of elastomers and have spring-like structures.
What Are the Selection Criteria of Diaphragm Lenses?
The type of lens to be used is based on several factors. These are:
1. The Integrity of the Capsule Bag:
The capsular bag provides safety to the lenses. If it is present, an endocapsular tension ring is placed. But in the case of congenital or traumatic aniridia, aphakia is secondary to the previous removal of the congenital cataract, due to which a capsule bag will be absent. In such cases, the iris-lens diaphragm can be used with transscleral suture fixation.
2. Phakic Status:
Phakic lenses are used with high refractive error. In patients suffering from cataracts (cloudy lens), pseudophakic lenses are used and placed in front of the original lens. In aphakic patients who have undergone complete lens removal, iris-diaphragm lenses are used. In pseudophakic conditions, endocapsular capsular tension rings are used.
3. Severity and Extent of the Iris Defect:
The severity and extent of the iris defect determine the nature of the lens to be used. Iris defects can be categorized into three types:
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Iris defect of less than three clock hours.
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Defects range from 3 to 6 clock hours.
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Defects extending more than six clock hours.
For iris defects of less than three hours, partial aniridia rings are used. And defects of more than six houses can be managed using two partial aniridia rings. Patients with an iris defect extending between 3 to 6 hours can be managed by either using a pair of morcher type 50 or morcher type 96.
What Are the Benefits of Diaphragm Lenses?
The benefits of using diaphragm lenses are visual acuity. These lenses reduce photophobia (problem or sensitivity towards light), increase the depth of focus, and reduce spherical and chromatic aberration. As a result, visual acuity improves. Patients with congenital or acquired iris defect often complain of increased glare. Diaphragmatic lenses reduce this problem. Cosmetic correction can also be achieved. A customized iris diaphragm can be useful for cosmetic correction and maintaining the iris color.
Conclusion:
Iris defects can be problematic and can cause serious ocular issues. The use of iris diaphragm lenses can easily resolve these problems. These prosthetic iris devices increase visual comfort and reduce irritations. Modern customized diaphragm lenses also help improve the cosmetic appearance. A proper surgical technique during placement can reduce post-surgical complications like increased intraocular pressure and blood in the space between the lens and eyeball.
