Cataract / Lens Implant Educational Videos

Cataract / Lens Implant Educational Videos

Dr. Chang is considered an authority in the field of "Refractive Intraocular Lenses (IOLs)". To help educate patients about this topic, Dr. Chang wrote the scripts and collaborated with Eyemaginations to develop a series of patient educational videos. Called the “Chang IOL Modules”, these videos are marketed through Eyemaginations and are used by physicians around the Dr. Chang donates his royalties to the humanitarian cataract charities – Project Vision and Himalayan Cataract Project.

Educational Videos

Dr. Chang In the News

Dr. Chang In the News

Within ophthalmology, Dr Chang is widely considered one of the leading cataract surgeons, educators, and clinical investigators in the world. In this capacity, he has often been selected by medical associations to respond to media requests for information.

Dr. Chang In the News

Humanitarian Cataract Surgery

Humanitarian Cataract Surgery

Although curable with surgery, cataracts remain the leading cause of blindness in the world, accounting for more than one half of all blindness. Dr. Chang has used his international prominence to highlight and advance several important cataract efforts. He has traveled to many developing countries to perform and teach cataract surgery to local ophthalmologists.

Humanitarian Cataract Surgery

Flomax & Cataract Surgery

Flomax & Cataract Surgery

The intraoperative floppy iris syndrome was first reported by Drs. David Chang and John Campbell in 2005. This major discovery showed that the most common prostate medications (such as Flomax) cause iris problems during cataract surgery that can lead to many complications if the surgeon does not anticipate them. Dr. Chang has done extensive clinical research and is considered one of the world authorities on how to avoid and manage these problems.

Flomax & Cataract Surgery

Intraocular Lenses for Cataract Surgery

by David F. Chang, MD

To take the place of the clouded human lens, a precisely engineered artificial lens called the intraocular lens, or "IOL", is implanted into the eye at the time of cataract surgery. Unlike a contact lens, it is permanently fixated inside the eye. In this way, it cannot fall out, does not require cleaning, and does not change the appearance of the eye. It produces no sensation, and cannot be felt by the patient.

The IOL is permanent because it is made of a perfectly transparent material that will never cloud. Once in place, it will not move, and unlike an artificial joint or heart valve, there are no moving parts in the lens that could wear out over time. Because it is lightweight and flexible, it will not be affected by physical activities or by rubbing of the eye. Patients can ultimately resume all of their normal activities without any restrictions.

Replacement organs that come from another human body are called transplants. The clear, front part of the eye - the cornea - is the only ocular organ that can be transplanted. Just as we can make perfectly engineered optical lenses for cameras, microscopes, and telescopes, IOL's are man-made. Unlike transplanted organs, there is no shortage of tissue and there is no chance of rejection. The term implant is used because the artificial lens is surgically and permanently placed inside the eye.


Function of the intraocular lens:

Intraocular lenses replace three main functions of the natural human lens. First, like a window, both the cornea and the lens must be perfectly transparent in order for external light and images to be focused onto the retina at the back of the eyeball's interior. Second, the lens acts as a structural partition between the vitreous gel behind it, and the clear fluid-filled chamber in front of it. Finally, it provides necessary focusing power.

The two ocular structures that focus incoming light onto the retina are the cornea and the lens. About two thirds of the total focusing power requirement is provided by the cornea. The lens provides the remaining one third. An eye that has undergone cataract surgery without implantation of an IOL is called aphakic (phakic is the Greek root denoting lens). Without a natural or artificial lens inside, everything is completely defocused, and the eye is functionally blind at all distances. The missing power must be replaced in order to restore useful vision. Besides the intraocular lens, there are two other options that have been used, historically, to accomplish this.

Spectacles: Special glasses, called aphakic spectacles or "cataract glasses", can be used to restore focus after lens removal. Prior to the 1980's, this was the most common way to correct vision after cataract surgery. Prior to the 1970's, it was the only way. This is still the primary method used in some third world countries where artificial lenses and other modern medical technology are not available.

Because so much power must be placed in these glasses, they do not appear or work like conventional eyeglasses. The lenses are extremely thick and heavy, appearing like "coke-bottle" glasses. The exaggerated lens thickness causes the view to be magnified by approximately 25%. Although this is fine for reading, this creates a very distorted and unnatural type of vision during walking. These spectacle lenses compromise depth and peripheral vision, and have optical "blind spots" where images pop in and pop out.

Because of their weight, they are uncomfortable, and the unusual optics makes them extremely difficult to adapt to. Cosmetically, the thickness and power of the lenses magnifies the patient's eyes creating a "bug-eyed" appearance. Finally, such lenses cannot be used for just one eye, because that one eye would see everything magnified by 25% compared to the other eye. This would create a type of double vision that the brain could not fuse together. Aphakic spectacles were therefore not an option when only one eye needed cataract surgery.

Contact lenses: The advantage of contact lenses following cataract removal without an IOL is that they can carry large amounts of optical power without significant magnification (only approximately 5%). The unnatural distortion of aphakic spectacles is avoided. Because the magnification is minimal, this method of correction can be used following cataract surgery in only one eye.

Especially as the eye gets older, it is preferable and safer to remove contact lenses daily. Extended wear contact lenses should not be worn for longer than a week at the most. Contact lenses wear may be more problematic in an older patient for several reasons. With age, the eye surface tends to more dry and prone to discomfort. In addition, the patient must have good eyesight and good manual dexterity to be able to clean, handle, insert, and remove the lens.

The fact that the aphakic eye (no IOL) is functionally blind without the lens makes it more difficult when the contact lens falls out, is lost, or when the patient arises in the middle of the night without it. Unlike a nearsighted patient who can focus on the contact lens when it is held in their hand, an aphakic patient is completely blurred at near. This can make handling the contact lens quite challenging.

In the past, removing a cataract meant that the patient would either have to wear cataract glasses or a contact lens. A patient was therefore trading their preoperative blur, for new problems postoperatively - either the visual distortion of the aphakic spectacles, or the inconvenience of the contact lens. Understanding this, ophthalmologists would often wait until the preoperative disability was so major that even these postoperative compromises would amount to an improvement. This factor, and the previously higher complication rate, meant that many patients were urged to delay cataract surgery in the past. Thus arose the excuse that their cataract wasn't "ripe" yet.

Intraocular lens (IOL): The above discussion reveals why the intraocular lens is one of the most important medical advances in the history of ophthalmology. Because there is no unwanted magnification, the IOL provides the most natural vision of the three alternatives following cataract surgery. It is permanent, requires no care or handling, and comes in a range of powers that can be selected for the individual patient. Nowadays, it is standard for all cataract surgeries.


Anatomy of an intraocular lens:

The central viewing zone is called the optic. This is a clear, round disc measuring 5.5 to 6.5 mm in diameter (about 1/4 inch). The optical power is contained in the optic, and there are generally about 40 powers available for surgeons to choose from. The unit of optical power is called a "diopter".

On opposite sides of the optic are two flexible struts, called haptics. These act like tension loaded springs to automatically center the lens within the eye compartment where they are implanted. Haptics have varying shapes depending on the type of IOL. The most common lens used is the three-piece posterior chamber IOL. It is called a three-piece IOL because the round optic is fused with two plastic haptics that are shaped like curved wires.


Evolution of the intraocular lens:

The pioneer of the intraocular lens was a British ophthalmologist, Sir Harold Ridley. In caring for British aviators with eye injuries during World War II, Dr. Ridley made a critical and interesting observation. He noted that pieces of plastic from shattered airplane canopies that became lodged inside the eyeball were surprisingly well tolerated with little inflammation. He also recognized the tremendous advantages that an artificial lens would provide for cataract patients, and courageously performed the first intraocular lens implant in 1949 in London.

Although the lens, like modern IOLs, was made of PMMA plastic, the prototype design was not ideal and the surgical techniques were limited by today's standards. As a result, the early results were not satisfactory. Although a true visionary, Dr. Ridley's ideas were ridiculed and strongly opposed by the medical establishment and the idea of lens implantation became largely abandoned.

Almost 20 years passed before a pair of Dutch ophthalmologists resurrected the mission of developing an artificial lens. At that time, the entire lens - capsule and all - was removed during cataract surgery. For fixation, these early artificial lenses were either clipped or sewn onto the iris. However, the iris is not rigid, and this created problems with excessive movement of the IOL that intermittently bumped and damaged the cornea.

The next generations of IOLs were designed to rest in front of the iris, and were called anterior chamber IOLs. The junction where the dome-like cornea joins the iris peripherally is called the "angle". For fixation, the two ends of these anterior chamber IOLs were wedged into the angle. Improper sizing and incompatible designs of these initial prototypes again resulted in poor tolerance by the eye or excessive IOL movement that could damage the cornea.

The modern intraocular lens design was the brainchild of an American ophthalmologist, Dr. Steven Shearing. His revolutionary, three piece model was designed to be placed just behind the iris, which is where the natural human lens is located. What was needed was some structure to support the artificial lens, and it took a major advance in cataract surgical technique to provide this.


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David F. Chang, MD is a Summa Cum Laude graduate of Harvard College and earned his M.D. at Harvard Medical School. He completed his ophthalmology residency at the University of California, San Francisco (UCSF) where he is now a clinical professor. Dr. Chang is serving a 5-year term as chairman of the American Academy of Ophthalmology (AAO) Annual Meeting Program Committee, having previously chaired the Cataract Program Sub-committee.

Dr. Chang's CV

Learn about Dr. Chang’s colaboration with Eyemaginations’ development of 3D eye animations


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The material contained on this site is for informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health care provider.
By David F. Chang.