Vision Problems

As light rays pass through one medium to another, such as from air to water, they bend.(1) This is known as refraction. When these rays pass through the eye tissues of the cornea Cornea: The clear, curved surface at the front of the eye through which light enters the eye. Along with the sclera, the cornea provides external protection for the eye. and lens, they are also refracted in a manner that brings them into focus on the retina. When the eye is unable to focus light on the retina, usually because the shape of the eye isn’t quite right, this is called a refractive error. Refractive error: Vision problems caused by an imperfect optical system, most commonly myopia, hyperopia, and astigmatism.


If you’re reading this, chances are you’ve already been dealing with contact lenses or eye glasses to correct your vision. To help you better understand common visual issues, below is a brief overview of the most typical refractive error conditions, as well as eye problems that stem more from aging and the stiffening or clouding of the eye’s lens that can develop in our later years.


Nearsightedness

Also called myopia, Myopia: A refractive error resulting in the inability for the eye to see distant objects. Also referred to as "nearsightedness." Occurs when the eyeball is too long or when the cornea has too much curvature, preventing the light entering the eye from focusing correctly on the retina and resulting in blurry vision at a distance. Eyeglasses, contact lenses, and refractive surgery are treatment options for correcting vision impairment caused by myopia. nearsightedness (blurred distance vision) is the most common refractive error. This happens typically when the eye is too long or the cornea too steep. This extra length causes light from distant objects to focus at a point just short of reaching the retina, which causes the light to disperse and provides the brain with an out-of-focus image.


Farsightedness

The common term for hyperopia, Hyperopia: The medical term for "farsightedness," a refractive error resulting in an inability to see objects at close range. Typically caused by either a cornea with too little curvature or an eyeball that is too short, hyperopia causes light entering the eye to focus improperly on the retina, resulting in blurry close-up vision. Eyeglasses, contact lenses, and refractive surgery are treatment options for correcting vision impairment caused by hyperopia. farsightedness (meaning you can’t see things up close) is caused by an eye that is too short or a cornea that is too flat. The reduced length leaves the cornea and lens Lens: The transparent disc behind the pupil that brings light into focus on the retina. insufficient space to bring together the light rays to a focal point upon the retina, thus focusing the image beyond the retina and, again, sending poor signals to the brain.


Astigmatism

Another term used for poor eye curvature, astigmatism is what happens when the cornea is not round enough but shaped more like a football, which prevents the eye from being able to focus clearly at any distance, near or far.


Presbyopia

This condition typically begins to affect people between the ages of 40 and 50. Presbyopia occurs when the natural lens of the eye ages, thus hardening and losing its flexibility, which typically results in loss of up-close vision and often leads to a need for reading glasses.


Cataracts

Contrary to popular belief, a cataract is not a film that forms over the eye(2) but rather a change in the clarity of the lens inside your eye, allowing less light to pass through. This gradual clouding can make vision less sharp over time. The light that does make it through to the retina is diffused, turning vision blurry.








References1.Oracle ThinkQuest Education Foundation. Light Rays, Refraction. http://library.thinkquest.org/27066/lightrays/nlrefraction.html. Accessed on October 16, 2010.

2.Oregon Academy of Ophthalmology. Public Info: Cataract.

http://www.oregoneyephysicians.org/pages/medinfo-pages/cataract.html. Accessed October 16, 2010.

What are INTACS?

INTACS were approved for the treatment of relatively low degrees of nearsightedness in the 1990's.  INTACs are semi-circular implants that are placed within the stroma of the cornea:  hence they are classified as intracorneal ring segments.  The segments are placed in the mid-periphery of the cornea and improve the uncorrected vision in myopes by flattening the central cornea.  While intracorneal ring segments were effective for low degrees of myopia, laser vision correction was a least as effective as INTACs, and could be performed without incurring the cost of an implant.  The intense competition in the vision correction market prevented INTACS from gaining any significant market share; however, the intracorneal implant has found a niche market by being a popular and effective treatment in the treatment of a corneal condition called keratoconus.

What Happens after Your Cataract Treatment

The postoperative period involves the instillation of drops for a few weeks while the eye heals.  The medications that are applied include Antibiotics and anti-inflammatory agents.  The anti-inflammatory agents (chemically similar to aspirin formulated as a drop.)  Recently, the trend has been to use both types of anti-inflammatory agents, as each type of drug acts through a slightly different pathway.  You will be provided with a medication schedule, and a list of activities to avoid. 

I do ask that patients take a one to two week hiatus from swimming, hot tubs or other activities that could but their eyes in contact with "common" water.  Pools, hot tubs and other forms of common water often serve as breeding grounds for microbes which may infect an incompletely healed surgical wound.  Typically patients resume most of their normal activity level within a few days, as small-incision surgery has largely eliminated the need for an extended convalescence. 

Patients are seen on the day after their procedure, and usually are fully rehabilitated within a month of their treatment.  Congratulations!  It is time to enjoy your new and improved vision!

Am I a Candidate for the Advanced Technology Intraocular Lens?

While most people would select the enhanced optical performance offered by the presbyopic lenses, these implants are not appropriate for all patients. There are a number of conditions and diseases which either decrease or totally neutralize the benefits these lenses can deliver. While many of these limitations are agreed upon by most cataract specialists, there may be room for debate among surgeons, so I will offer you my own guidelines (and preferences) based upon the specific ocular condition. Of course, I have a discussion with each patient who has any of these conditions and is considering optimizing his/her cataract procedure with an advanced technology IOL. Accordingly, these patients realize that their eyes are not 100% typical, and there is the very real possibility that the eyes will not see 20/20 after ANY type of IOL is implanted.

Macular Degeneration

Age-related macular degeneration (ARMD) is the subject of numerous articles, chapters and indeed textbooks. To attempt to describe it in any detail is well beyond the scope of this text. Suffice it to say that macular degeneration is typically an age-related loss of the cells which comprise the retina – the “film” where images are generated in your eye.

While there are a few dissenting opinions at the time this monolog is being printed, most surgeons queried will not recommend the use of multifocal IOLs in patients with moderate to severe macular degeneration. It is typically my custom NOT to implant multifocal presbyopic IOLs in eyes that have macular degeneration. The disease typically is progressive (that is, it gets worse as time passes) so it is questionable if a patient would appreciate any benefit with these lenses. In contrast, I have had success implanting accommodating intraocular lenses (the lenses which flex like our natural lens) in patients with early to moderate macular degeneration. Macular degeneration tends not to affect the performance of the accommodating IOLs – presumably due to their more physiologic mechanism of action.

Severe Dry Eye Syndrome

The cornea is the outer “window” and primary light-bending structure of the eye. The cornea is covered by a thin layer of tears, the precorneal tear film (PCTF). The tear film protects the eye from dust, allergens and infectious agents, as well as serving as an avenue for the immune system. Additionally, a stable, contiguous PCTF is vital for the cornea to fulfill its function as the eye’s primary focusing element.

Dry eye syndrome is the condition when the surface of the eye has a deficient or unstable PCTF. As a result, there are “dry spots” on the surface of the cornea. The dry spots can cause irritation to the extent that the patient experiences excessive tearing – this is caused by the dryness becoming a noxious stimulus which causes a physiologic response similar to the tearing that occurs when there is a piece of sand or dust in the eye. The excessive tear volume actually causes the vision to decrease, in addition to introducing the inconvenience of having tears running down one’s cheek in severe cases.

The patient’s vision may also be affected even when there is not any discomfort or excessive tearing. The dryness may cause an irregularity upon the surface of the cornea which results in light scattering. The process of light scattering introduces a source of inefficiency in the eye’s optical system. A cornea that scatters light is described by ophthalmologists as having aberrations. Aberrations are imperfections which cause light to defocus, resulting in a blurring of images, as light does not pass efficiently to the retina. Highly aberrated corneas prevent ALL IOLs from working optimally, but especially multifocal presbyopic lenses from working effectively. For this reason, I do not recommend placing multifocal intraocular lenses in eyes with severe dry eye.

In contrast, accommodating presbyopic lenses and astigmatism-correcting lenses may be placed in eyes with significant corneal optical aberrations; while the results may not be “perfect” 20/20 vision, the results of cataract surgery in patients with aberrated corneas can be quite gratifying.

Dry eye syndrome is not the only condition which results in cornea-based optical aberrations. Corneal scarring from disease or trauma may introduce optical aberrations. Radial keratotomy was a popular refractive surgery procedure in the 1980s and 90s. The keratotomy incisions induce optical aberrations, and actually induce multifocality of the cornea. Accordingly, most cornea specialists will not place a multifocal IOL in an eye that has had radial keratotomy. Instead, the use of the accommodating presbyopic IOL in “post-RK” eyes has resulted in some excellent outcomes as these patients enjoy the dual benefit of a multifocal cornea combined with an accommodating IOL.

The decision on whether to implant a presbyopic lens (or indeed perform cataract surgery at all!) in a patient with dry eye, or any eye that has corneal disease can be difficult. Among the factors to be considered preoperatively include the degree of dryness, cause of dryness, degree of visual debilitation, visual potential of the eye and patient expectations.

Diabetes Mellitus

The ocular sequelae of diabetes mellitus were among the leading causes of blindness in the United States in the mid to late 1900s. Diabetes affects virtually all of the body’s systems and the eye is no exception. Cornea, lens and retina are all potential targets of this disease. Diabetic retinopathy, like macular degeneration, is a disease which has been well chronicled, and an extensive discussion about diabetic ocular disease is beyond the scope of this text.

The process of diabetic retinopathy is caused by serum glucose compromising the competence of the vascular endothelium. That is, abnormally high levels of blood sugar cause blood vessels to leak into the retina, causing a loss of retinal function – again a process where the “film” of the camera is impaired. I generally do not recommend the multifocal presbyopic intraocular lenses in cases where the patient’s retinal function has been affected (although the accommodating lenses may be considered).

There is one diabetic condition where I typically do NOT recommend either type of presbyopic intraocular lens; the condition is called proliferative diabetic retinopathy. In proliferative retinopathy, the serum glucose has so adversely affected the retinal vasculature that there is a gross lack of oxygen being delivered to the retina. This lack of oxygen, or hypoxia, results in the growth of new abnormal retina vessels which have a tendency to actually bleed inside the eye. Eyes that have this degree of impairment from diabetes do not typically realize a significant benefit from presbyopic IOLs.

Astigmatism-Correcting Intraocular Lenses

The front of the eye serves as a focusing element to bring a sharp image upon the retina.  Creating a sharp retinal image requires that the cornea and lens each create a single focal point.  Generating a single focal point for the cornea requires that the cornea has a round "dome" shape with the same degree of curvature for 360 degrees, therefore no matter what place light enters the cornea, it is bent to the same degree en route to the lens.  Astigmatism, specifically corneal astigmatism, may be described as the condition where the cornea has at least two radii of curvature.  Less technically explained, the outer window of the eye has a more oval or "football" shape.  The two different curvatures of the cornea generate tow different focal points because light rays are bent differently depending upon which part of the cornea they enter; as a result even a perfectly symmetric crystalline lens or standard IOL will not be able to bring the light rays to a single retinal focal point, so the eye does not create a clear image for the patient. 

Before the advent of advanced technology implants removing the cataract involved exclusively removing and replacing the eye's lens and if the eye had significant corneal astigmatism before cataract surgery, the condition would exist after surgery.  The introduction of astigmatism-correcting or toric intraocular lenses finally gave astigmatic patients an answer to correct their vision, no only reversing the effects of the cataract, but actually making their uncorrected vision better than it had been for years - typically decades!  Toric lenses correct vision in a manner that standard single focus lenses cannot - the toric lens, like the astigmatic eye's particular corneal curvature so that the toricity of the IOL neutralizes the patient's corneal astigmatism. 

Correcting or "neutalizing" the corneal astigmatism creates a more precise focal image, thereby reducing or totally eliminating the cornea-induced blur (in ophthalmology speak" this is called "collapsing the Conoid of Sturm" or reducing the distance between the two corneal focal points.

Your Cataract Treatment

Modern cataract surgery is a "day stay" procedure.  Most ambulatory surgicenters (ASCs) and hospitals allow the patient to remain in their clothes and merely wear a gown, cap and shoe covers in the operating room.  Typically, the patients are allowed to have a light breakfast.  On the day of treatment, you will be at the hospital or ASC for about three hours.  The procedure is usually performed under topical anesthesia, which means drops are applied to the eye for comfort, in addition to dilating drops.  The dilating drops increase the size of the pupil so the surgeon has easier access to the cataract.  In addition, an intravenous catheter is placed to facilitate the use of sedation during your procedure. 

You will then be brought into the treatment room where the anesthesiologist and circulating nurse will make sure you are comfortable and well-positioned appropriately the next member of our surgical team, the scrub nurse, will use an antiseptic solution to "prep" your eye.  The scrub nurse will then place a light drape around your eye so that there will be a sterile surgical field.  Alas! We can get to the actual process of removing the cataract and restoring your vision. (see video at http://www.northeastlaser.net/Special-id-85.html)

The surgical microscope will then be positioned about one foot above the operative eye.  The microscope has intense lighting and in combination with the dilation, the brightness can be very impressive.  The light intensity is notable only for a few moments, after which your eye will adapt to the brightness.  The surgeon then places a small eyelid supporting instrument so that you will not have to worry about blinking. 

Utilizing the microscope to magnify your eye, the surgeon creates a small peripheral corneal incision that allows controlled access to the internal structures of the eye.  The surgeon has micro instrument which enable him/her to address the cataract through the pupil.  The next step involves creating a small opening in the cataract capsule.  This opening is about 5 millimeters in diameter, and it is through this opening the surgeon applies ultrasonic energy to gently disassemble the cataract nucleus into tiny fragments.  The cataract fragments are suspended in the balanced saline solution which the surgeon gently rinses from your eye. 

Once the nucleus has been removed, the cortex of the cataract remains.  As the cortex is typically very soft, no energy is needed to disassemble it, and cortical removal is usually performed with a very low power vacuum delivered by an instrument called the irrigation/aspiration hand piece.  Cortical clean-up completes the process of cataract extraction, and the eye is now ready for intraocular lens implantation. 

Today's IOLs are made of very soft, flexible polymers, so they can be folded in order to be placed through the very small corneal incision directly into the capsular bag.  The lens is supported in the capsule by the flexible haptics. 

The surgeon does a final check to make sure the lens is in good position.  The wound is tested to ensure that it is watertight, and the lid supporting speculum is removed.  Immediately following the treatment, the patient is monitored in the post operative holding area and finally discharged. 

AMD and Alzheimer's Disease

A recent literature review examining the common characteristics between Alzheimer's disease and age-related macular degeneration (AMD) indicates that the 2 diseases may share a common pathogenic mechanism and suggests that therapeutic approaches applied to patients with Alzheimer's may offer some benefit to those with AMD.  The review focused on amyloid beta, an amino acid peptide found in both senile plaques of Alzheimer's patients and the drusen of patients with AMD.  Specifically, the review looked at the role the peptide plays as a regulator in the progression from drusen to AMD. 

"Age is a common risk factor for Alzheimer's disease and age related macular degeneration," wrote study author Ohno-Matsui from Tokeyo Medical and Dental University, Japan (Prog Retin Eye Res 2011).  Studies indicate the "long-term course of developing Alzheimer's disease pathology appears quite similar to the long term and progressive development of AMD.  These data support the idea that the retina is a part of the brain, and pathological ageing changes occur in the brain and the retina similarly."

Ohno-Matsui suggested that similar therapies, including anti-amyloid therapies, including anti-amyloid therapies, might be successfully used to treat both groups of patients.  Amyloid beta-targeting drugs originally developed to treat Alzheimer's are expected to be tested in patients with AMD, and pharmaceutical companies are currently developing genetically based and complement-targeted therapies with the goal of reducing complement-related AMD disease processes.  These include therapies targeting C3-convertase, long implicated in the Alzheimer's disease pathogenesis. 

"Although AMD should be considered as a distinct type of 'amyloid disease,' amyloid beta targeting therapies that are being tested in Alzheimer's patients can be applied to AMD," Phno-Matsui said.  "Te reverse should also be considered i.e., therapies tested for AMD should also be tested on Alzheimer's disease patients."