blog

diabetes melitus

Wed, 25 May 2011 03:48:30 +0100

Diabetes mellitus (DM) is a major medical problem throughout the world. Diabetes causes an array of long-term systemic complications that have considerable impact on the patient as well as society, as the disease typically affects individuals in their most productive years.^[1]An increasing prevalence of diabetes is occurring throughout the world.^[2]In addition, this increase appears to be greater in developing countries. The etiology of this increase involves changes in diet, with higher fat intake, sedentary lifestyle changes, and decreased physical activity.^{[3, 4]}

Diabetic retinopathy is the leading cause of new blindness in persons aged 25-74 years in the United States. Approximately 700,000 persons in the United States have proliferative diabetic retinopathy, with an annual incidence of 65,000. A recent estimate of the prevalence of diabetic retinopathy in the United States showed a high prevalence of 28.5% among those with diabetes aged 40 years and older.^[5].)

Patients with diabetes often develop ophthalmic complications, such as corneal abnormalities, glaucoma, iris neovascularization, cataracts, and neuropathies. The most common and potentially most blinding of these complications, however, is diabetic retinopathy.^{[6, 7]}

In the initial stages of diabetic retinopathy, patients are generally asymptomatic, but in more advanced stages of the disease patients may experience symptoms that include floaters, distortion, and/or and blurred vision. Microaneurysms are the earliest clinical sign of diabetic retinopathy

Workup for diabetic retinopathy includes fasting glucose and hemoglobin A1c measurements.

Renal disease, as evidenced by proteinuria and elevated BUN/creatinine levels, is an excellent predictor of retinopathy; both conditions are caused by DM-related microangiopathies, and the presence and severity of one reflects that of the other. Aggressive treatment of the nephropathy may slow progression of diabetic retinopathy and neovascular glaucomaAccording to The Diabetes Control and Complications Trial controlling diabetes and maintaining the HbA1c level in the 6-7% range can substantially reduce the progression of diabetic retinopathyOne of the most important aspects in the management of diabetic retinopathy is patient education. Inform patients that they play an integral role in their own eye care.

DR MBA ONYEKWERE

MBBS

diabetes melitus

Wed, 25 May 2011 03:48:30 +0100

Workup for diabetic retinopathy includes fasting glucose and hemoglobin A1c measurements.

DR MBA ONYEKWERE

MBBS

OCULAR EFFECT OF SYSTEMIC DISEASES: THE HYPERTENSIVE AND DIABETIC RETINOPATHIES

Wed, 25 May 2011 03:42:30 +0100

OCULAR EFFECT OF SYSTEMIC DISEASES: THE HYPERTENSIVE AND DIABETIC RETINOPATHIES.

The epidemiological pattern and distribution of Hypertension and diabetes is changing in the developing world, particularly as dietary patterns become more and more westernized. With the attendant increase in the prevalence of these two diseases, ocular involvement becomes more frequently seen in clinical practice. It is important therefore for the optometrist to be able to identify early and advanced ocular signs of these diseases particularly since visual difficulty may be the first presentation.
In this lecture, the epidemiology, pathophysiology, clinical grading of signs and treatment are discussed, and a comparison of fundus changes in the two conditions is also undertaken. The classification of diabetic retinopathy into Non proliferative disease, and clinically significant macular edema is discussed. The grading of hypertension by the Scheie and the Keith-Wegener-Baker system is also described. The potentiation of one condition by the other is highlighted.
Finally, special emphasis is placed on how optometrists can more easily identify these lesions and refer appropriately.

Dr. Femi Babalola

FWCS

latest tools in diagnosis of glaucoma

Wed, 27 Oct 2010 03:38:51 +0100

Glaucoma:The Latest Diagnostic Tools
Today's technologies are faster, more accurate and able to detect glaucoma much earlier.Here's an overview of what's available.
By Mireille P. Hamparian, M.D., Encino, Calif., and Alan L. Robin, M.D., Baltimore, Md.

Recent advances in technology have done a great deal to enhance our ability to detect and treat glaucoma in its earliest stages. And increasing numbers of eyecare professionals are taking advantage of the new technologies.

For example, hundreds of disc imaging systems have been sold during the past decade. More have been sold at the Academy and ASCRS meetings in the past 2 years than in the previous 8 years combined. Not only are the instruments and software better, but reimbursement for related procedures has become much more reasonable.

A major step forward

Previous technologies, which primarily monitored changes in intraocular pressure (IOP), loss of visual function and grossly visible structural changes in the disc, made diagnosing and monitoring glaucoma difficult at best:

The sensitivity and specificity of disc changes and IOP as evidence of glaucoma are less than 50%. (Many patients who present with IOPs greater than 21 mm Hg or large cupping and cup-to-disc asymmetry don't have glaucoma.)
As an indicator of glaucoma, the nerve fiber layer is much more sensitive and specific. However, it's hard to see in vivo, and until recently we've had to rely on qualitative assessments -- sketches and photos of the optic nerve -- to monitor glaucomatous structural damage and progression. In addition, nerve fiber layer photos are difficult to read when the patient is elderly or African-American, and these are the patients most likely to have glaucoma.

In contrast, the new modalities can more reliably measure change in disc size and shape, as well as focal thinning in the nerve fiber layer. This allows us to intervene at an earlier stage of glaucoma progression and monitor those patients who present with elevated IOPs or large cup-to-disc ratios but still have normal perimetry.

Perhaps the most compelling reason to use the new imaging technology is that clinically detectable structural changes in the nerve fiber layer and optic disc can occur years before functional measurements of the optic nerve (such as standard automated perimetry) are able to detect a problem. In fact, a patient may lose half of his optic nerve head axons before perimetric defects become obvious. (Also, visual fields have inter-test variability; you need at least two or three of them to confirm a defect.)

Each of the new technologies has its strong and weak points. For example, some of the new modalities are primarily designed to screen for potential glaucoma, although they can also be used to follow progression of the disease. (Our ability to use these modalities effectively for the latter purpose will increase as we gain more experience with them.)

This article will help you choose which instrument or modality makes the most sense for your practice by reviewing some of the most relevant attributes of the options available.

Perimetry: Frequency Doubling Technology (FDT)

Zeiss Humphrey's FDT is a portable visual field analyzing device that's demonstrated relatively high sensitivity and specificity for detecting visual field loss in eyes with moderately advanced glaucoma. The patient observes a series of alternating light and dark bars, which rapidly switch between black and white. This causes most patients with healthy visual function to perceive twice as many bars as are actually there. (The level of contrast is set so that 99% of normal subjects observe the same effect.)

This frequency-doubling stimulus is presented randomly to a total of 17 different visual field locations within the central visual field.

How it works: We believe the stimulus is detected primarily by a subset of magnocellular retinal ganglion cells that have nonlinear response properties. These magnocellular ganglion cells may be among the first casualties of glaucoma. Hence, inability to experience the doubling phenomena indicates early glaucomatous damage.

Results of an FDT screening are considered abnormal when the following are present:

any defect in the central five locations
two mild or moderate defects in the outer 12 spots
one severe defect in the outer 12 spots.

Results are also considered abnormal if total test time for each eye is greater than 90 seconds.

When any of these criteria are present, the FDT is considered "positive." When you obtain a positive result, you can either quickly repeat the test or perform conventional threshold perimetry.

Advantages of the FDT. These include:

The FDT is very easy for a technician to use; it requires only a few minutes of instruction. The menu is simple, and operation leaves little room for error.
It features a screening mode and a full threshold mode. (The screening algorithm is a quick and accurate tool for glaucoma detection.)
The machine isn't at all intimidating for the patient. It has no perimetric "bowl," so the patient can feel comfortable without claustrophobia.
The FDT tolerates up to 6 diopters of blur, so the technician usually doesn't have to worry about proper spectacle correction.
The test requires no eye drops; it's unaffected by pupil sizes as small as 2 mm.
The test can be performed under normal lighting conditions.
The procedure takes only 45 to 70 seconds per eye to perform.
The FDT has a unique pre-test capability to help you determine which threshold perimetry algorithm (if any) would be best to use.
The instrument is relatively portable. (It weighs about 15 pounds).

Other points to consider. These include:

The test is subjective; it depends on the patient's response.
Because structural loss of retinal nerve fibers may precede functional loss, this technology has limited usefulness for early detection of glaucoma.
Determining which results are normal and which indicate early glaucoma can be difficult.
The FDT may not be useful for long-term follow-up and detection of change.
The FDT printout looks different from the printouts produced by other instruments, which most of us are used to. It requires a little practice to interpret.

Perimetry: The Swedish Interactive Thresholding Algorithm (SITA)

SITA algorithms (used by the Humphrey automated visual field perimeter) have done a lot to revolutionize perimetry. SITA algorithms are designed to perform visual fields similar to those that use the full threshold algorithm, but with one important advantage: SITA algorithms don't depend on the conventional staircase method. For that reason they significantly decrease test times, while still maintaining the integrity of the test results.

How it works: Instead of using the usual staircase methods, which test each area in the visual field once, SITA returns to check a second time -- but only if nearby areas show a suspicious result. (This helps keep the test time short.) As the test proceeds, these functions are updated.

SITA fast. SITA fast differs from SITA standard in the number of crossings, the step size and perhaps most important, the amount of allowable error in the threshold estimate. If a given test result is reliable (based on the patient performance indices the device provides), it can dependably detect scotomas along with their relative depths and help quantify the level of glaucoma damage.

For patients who still can't perform a reliable test with the SITA full threshold because of problems with attention span or rapid fatigue, the SITA fast test can often be quite useful.

Advantages of the SITA algorithm. These include:

Patients and technicians are happier with the shortened test time.
Quicker testing allows you to perform almost 30% more examinations in a given time period. This, in turn, allows you to recoup the cost of the perimeter much more quickly -- and make more efficient use of your technicians' time.
This test has a slightly higher mean sensitivity than tests using earlier algorithms, perhaps because of the shorter testing time and reduced patient fatigue.
Both inter- and intra-test variability of the SITA is comparable to conventional full threshold perimetry. In fact, it displays a little less variability between repeated tests, probably also as a result of reduced fatigue, which allows for earlier and more reliable detection of visual field deterioration.

Other points to consider. These include:

The test is subjective.
It doesn't detect nerve fiber loss at its earliest stage, and therefore doesn't detect glaucoma at its earliest stages.
SITA can't calculate short-term fluctuation or corrected pattern standard deviation.
One of the remarkable things about SITA fast is that it operates most of the time right at threshold. However, this characteristic can limit its utility in a screening situation because its high speed is less tolerant of patient errors than SITA standard.

Note: Some doctors who have worked with this algorithm have concluded that the relative sensitivity of the tests depends on how far the disease has progressed:

SITA standard is much more sensitive than either SITA fast or full threshold in early field loss.
SITA standard and full threshold are comparably sensitive in moderate loss.
In advanced disease, they show minimal difference in sensitivity.

Perimetry: Portability and design advantages

A new perimeter, the Oculus Easyfield, uses familiar technology, but offers practical advantages because of its size and cost. It's the first portable and relatively inexpensive device that can both screen patients for glaucomatous damage and quantify results (making it possible to monitor progression and accurately follow these patients).

Despite its relatively small size and cost, the Oculus Easyfield is a capable glaucoma detection device. Preliminary comparative studies suggest the Easyfield may be more sensitive and specific to moderate and severe glaucoma damage than the FDT test. (Evaluations are currently under way comparing full-threshold perimetry testing by the Easyfield and Humphrey instruments.)

How it works: The technology is similar to conventional computerized static perimetry.

Advantages. These include:

The small size and relatively low cost may increase the cost-efficiency of glaucoma detection.
Unlike most conventional perimeters, the Easyfield
doesn't require the patient to put his head inside a bowl, which some patients find claustrophobic.
If you screen for glaucoma and results are positive, threshold determinations can be made with the same instrument.

Other points to consider. These include:

The Easyfield doesn't provide a large normative database for statistical comparison.
The Easyfield lacks statistical packages for longitudinal follow-up.

The Easyfield and Humphrey FDT are similar in size and price (about $7,000), but the FDT instrument weighs 19 pounds, compared to the Easyfield's 13 pounds.

Scanning laser ophthalmoscopy

The Heidelberg Retina Tomograph II (HRT II) uses confocal scanning laser imaging technology to create a detailed, 3-D topographic map of the optic nerve head. The measurements permit analysis of rim and cup volume, cup shape, and indirect analysis of retinal surface height and other topographic parameters. The HRT II also indirectly calculates the thickness of the nerve fiber layer (NFL). It includes a normative database for comparison, and graphically displays deviation from that database. (It can perform a similar comparison to previous visits by the same patient.)

How it works: The HRT II uses CAT-scan-like technology to record three sequences of cross-sectional images during a 4-second period, and then assembles the resulting data into a 3-D topographic map. First-time measurements are analyzed using regression techniques developed by Moorfields Eye Hospital in London, which evaluate the relationship between neuroretinal rim area and optic disc area.

The instrument also divides the optic nerve and surrounding region into six sectors and evaluates each sector separately. An on-screen color map indicates whether each section falls within normal, borderline or abnormal parameters.

Advantages of scanning laser ophthalmoscopy. These include:

Images may be obtained through undilated pupils and early cataracts.
Low level light is used.
Minimal operator training is required. The HRT II features single-button operation.
The color-coded maps are relatively easy to read and interpret.
The HRT II automatically rejects images that are blurred by poor focus or patient movement. It provides a standard deviation figure for each image that tells you how accurate that measurement was.

(Heidelberg has also recently enhanced the capabilities of the HRT II with an optional macular edema module. This module provides a way to measure macular thickness changes over time using topographic retinal thickness measurements and macular mapping techniques.)

Other points to consider. These include:

Image resolution depends on the optics of the human eye. Cataracts may impede the quality of the image.
Variations in topography can be caused by blood vessels in the cup and fluctuations in IOP, and the optic nerve head.

Scanning laser polarimetry

The GDx and GDx Access nerve fiber analyzers (from Laser Diagnostic Technologies Inc.) measure the retinal nerve fiber layer (RNFL) thickness with a scanning laser polarimeter based on the birefringent properties of the RNFL. Measurements are obtained from a band 1.75 disc diameters concentric to the disc.

How it works: This technology uses a polarized near infrared (780 nm) laser beam to scan across the fundus at the optic nerve head and peripapillary retina. The birefringence causes a change in the state of polarization of the reflected light, known as retardation. The amount of retardation that occurs is linearly related to the thickness of the RNFL.

In vitro measurements in an animal model show excellent correlation between retardation and RNFL thickness, with resolution of measurements at about 13 microns. The GDx displays higher retardation values in the superior and inferior regions of the disc, corresponding to greater RNFL thickness in these areas. The scan also shows reduced retardation over blood vessels, corresponding with the observation that vessels embedded within the RNFL reduce the thickness on top of the vessels.

Advantages of scanning laser polarimetry. These include:

Clinical measurements are highly reproducible.
Readings can be done very quickly.
Operation is straightforward. The technician doesn't need to mark the optic nerve, just center a circle within the optic nerve region.
This technology has a higher sensitivity than the Glaucoma Hemifield test.
Using this technology doesn't require pupil dilation.
Results are independent of the optical resolution of the eye.
This technology is specifically designed to measure the critical retinal nerve fiber layer, where glaucomatous damage can be seen first.
A Both GDx instruments feature an age- and race-related normative database for valuable first visit comparison.

Other points to consider. These include:

Polarizing structures of the eye other than the RNFL may interfere with the retardation values; the cornea (and to a much lesser degree the lens) are also birefringent. (Both instruments include a compensator unit to correct for retardation arising in the lens and cornea.)
Peripapillary atrophy and chorioretinal scars may increase retardation values, although these artifacts are apparent on the image.

Note: Even though retardation values of structures of the eye other than the RNFL can interfere with the accuracy of these measurements, values are constant for any given individual. Consequently, serial scans may be used to follow a patient over time and determine progression of disease.

RNFL thickness values in normal and glaucomatous eyes show considerable overlap because of large variability in the number of axons among normal subjects. Accordingly, the mean retardation values of the GDx vary considerably among normal subjects.

However, retardation ratios of the superior or inferior region compared to the temporal area have good correlation with visual field mean deviation for both normal patients and those with glaucoma. (Sensitivity and specificity can be as high as 96% and 93% respectively.)

The two formats. Differences between the GDx Nerve Fiber Analyzer and the GDx Access include:

The GDx Nerve Fiber Analyzer captures the image with four times more pixels than the GDx Access.
The Access unit is a smaller, more portable unit available for lease only, with a fee-per-exam program. (In contrast, the Nerve Fiber Analyzer must be purchased.) The GDx Access includes software upgrades and services.

The GDx is better suited for a large volume practice with a sizeable glaucoma population. The GDx Access is better suited for a smaller glaucoma population.

Optical coherence tomography

Optical coherence tomography (OCT) is similar to ultrasonography, but it makes its measurements using light instead of sound. For that reason, it has much higher resolution in both axial and lateral dimensions. (The OCT instruments from Zeiss Humphrey have a resolution of 10 microns axially and 20 microns for transverse.)

Because this technology has obvious potential for glaucoma detection, Zeiss Humphrey has recently produced a new version of the instrument -- the OCT2 -- with added features specifically designed to increase the instrument's usefulness in glaucoma detection. The OCT2 lets you monitor three relevant variables: the optic disc, the RNFL, and macular thickness and structure.

How it works: Optical coherence tomography uses low-coherence interferometry to measure the echo time delay of light, which is backscattered from different layers in the retina. (The OCT uses a super luminescent diode with a bandwidth of 30 nm as its light source; the OCT2 uses a broad band of wavelengths.)

The instrument then uses the time delay of the backscattered light to calculate the distance between reflecting surfaces, based on the refractive index of the medium. A constant value of 1.36 is assumed for retinal tissues.

By scanning the beam across the retina, the OCT2 creates a two-dimensional cross-section of the area being scanned. This makes it possible to "see" the structural condition of the internal tissues, including photoreceptors, retinal pigment epithelium and choroid.

The instrument can measure retinal changes directly using nerve fiber analysis or monitor progression using volumetric analysis and checking cup-to-disc ratios. OCT measurements of the RNFL correlate well with the functional status of the eye as measured by automated visual fields.

Coding and Reimbursement

In 1999 the American Medical Association approved procedure code 92135, known as "scanning computerized ophthalmic diagnostic imaging" (previously known as scanning laser glaucoma testing). This code encompasses all of the laser imaging technologies of the optic nerve and nerve fiber layer, including the HRT, GDx and the OCT. The Health Care Finance Administration (HCFA) has approved the code for reimbursement for Medicare patients.

Some other useful facts about reimbursement:

The national average Medicare reimbursement allowable for these procedures is $59.68 per eye.
These tests can only be billed once a year for patients diagnosed as glaucoma suspects. For all other glaucoma diagnoses, the code can be billed twice a year.
Fundus photography can't be billed the same day if code 92135 is used. However, your office can bill visual fields on the same day.
The code for an FDT screening is 92080. (In Baltimore, Md., it's reimbursed at $60.43 for two eyes.)
The SITA visual field test is coded as 92083. (It reimburses at $65.95 for two eyes in Baltimore, Md.)
Coding for perimetry and fundus photography is per patient, but coding for computerized imaging is per eye.

-- Mireille P. Hamparian, M.D., and Alan L. Robin, M.D.

Advantages of OCT technology. These include:

Unlike ultrasonography instruments, OCT instruments are noncontact.
The OCT2 includes a limited age-related normative database.
The OCT 2 can compare current scans to previous scans of the same patient.
The OCT2 can scan in a straight line, or in a circle (which is particularly useful for scanning the optic disc). In addition, it can scan a series of concentric circles and create a donut-shaped retinal nerve fiber layer thickness map, or make a series of straight-line scans through a single point and use the information to analyze disc structure.
In most cases, the performance of the OCT isn't affected by the refractive state of the eye, minimal nuclear sclerosis or media opacities.
In addition to optic nerve measurements for detection of glaucoma, the OCT can be used for diagnosing diseases of the retina, as well as the anterior segment and cornea.

Other points to consider. These include:

It requires pupil dilation.
Posterior subcapsular and cortical cataracts can significantly impair the quality of measurements.
The normative database is still small.
Although the depth values of the scan are independent of the optical dimensions of the eye, the length of a scan across the fundus does depend on the optical dimensions of the individual eye.
The assumption of a constant value for magnification results in a small error in standard deviation.
Although significant differences in RNFL thickness between groups of normal and glaucomatous subjects have been demonstrated, considerable overlap of individual measurements between the groups exists because of variability of RNFL thickness in normal subjects (as discussed earlier).

Everybody wins

This new generation of technology makes it possible to do a much better job of catching glaucoma early and monitoring its progression. In addition to quantifying various aspects of optic nerve topography and retinal nerve fiber structure that were previously very difficult to assess, the technologies offer our practices a host of benefits:

The simpler, more user-friendly nature of the new technologies means that a less-trained technician (requiring less salary) can operate them. This also allows for better utilization of manpower.
The need for less training means less trauma when a technician leaves your practice. (In contrast, performing fundus photography requires great skill, so replacing a good technician can be a real problem.)
We can evaluate our patients more profitably because tests take less time.

Future advances in technology and design will no doubt offer even greater benefits for patients and practices alike. But in the meantime, today's options have plenty to offer, and both your practice and your patients stand to benefit. If you've been considering purchasing some new instrumentation to help bring your practice into the 21st century, there's no time like the present.

Characteristics that Count

For these new technologies to have value in today's clinical practice, certain requirements should be met:

The technology must be able to detect glaucoma earlier and be more sensitive for assessing disease progression than previous technology.
The new technology should provide immediate validation of the quality of its results.
Research must demonstrate the clinical relevance of the measurement data. For example, can the data be used for categorizing individual patients? Can it differentiate between early glaucoma and late glaucoma? Can it distinguish patients with ocular hypertension and other risk factors from primary open-angle glaucoma (POAG) patients?
Costs associated with the use of the new modality -- including the cost of the machine itself and the cost of necessary associated equipment and manpower -- must be justifiable. Does using the instrument result in cost savings for the practice? Or, if there is increased cost, can this be justified by benefits such as reduced numbers of patients under review, less frequent or time-consuming visits, and/or improved data from which treatment decisions can be made?
The time required to acquire and analyze data must be reasonable.
The new technology should be easy to integrate into existing clinic structures.
The technology must be patient-friendly.
The patient should be able to perceive a benefit from using it.
The instrument should be easy for a technician to use and maintain so that minimal additional training is required.
Results should not require extra processing (i.e. film processing).
Resulting data should be easy for a clinician to understand so that he can instantly put the results into clinical practice.
Testing time must be short enough to prevent patient fatigue from becoming a confounding factor.

-- Mireille P. Hamparian, M.D., and Alan L. Robin, M.D.

Dr. Robin is a world-recognized leader in the diagnosis, medical management and surgical treatment of glaucoma. He's clinical professor of ophthalmology at the University of Maryland, an associate professor at the Wilmer Institute of the Johns Hopkins School of Medicine and adjunct clinical professor for the Department of Veteran Affairs in the Maryland healthcare system. He has published and lectured extensively, and is a member of the editorial board of Graefe's Archives of Ophthalmology.
Dr. Hamparian is a glaucoma specialist in Enrico, Calif.

WHATS GLAUCOMA

Fri, 23 Jul 2010 07:04:15 +0100

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Glaucoma

Eye Diseases and Conditions Slideshow

Pink Eye Slideshow

Medical Author: Lawrence J. Schwartz, MD
Previous Medical Editor: Leslie J. Schoenfield, MD, PhD
Medical Revising Author: Camille Hylton, MD
Medical Revising Editor: William C. Shiel Jr., MD, FACP, FACR

What is glaucoma?
How common is glaucoma?
What causes glaucoma?
What are the risk factors for glaucoma?
What are the different types of glaucoma?

Open-angle glaucoma
Closed-angle glaucoma
Patient Discussions: Glaucoma - Effective Treatments
Find a local Eye Doctor in your town

How is glaucoma diagnosed?
How often should someone be checked (screened) for glaucoma?
How is glaucoma treated?

What is in the future for glaucoma?
Glaucoma At Glance
Related WebMD video on glaucoma treatment
Glaucoma treatment using laser surgery

Save Your Sight - Glaucoma Screening

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Barbara K. Hecht, PhD

Glaucoma is the term applied to a group of eye diseases that gradually result in loss of vision by permanently damaging the optic nerve, the nerve that transmits visual images to the brain. The leading cause of irreversible blindness, glaucoma often produces no symptoms until it is too late and vision loss has begun.

An elevation in the pressure within the eye (the intraocular pressure, or IOP) is generally, but not always, associated with the development of glaucoma, although additional factors are also likely to play a role in its development. The optic nerve fibers inside the eye are damaged, resulting in vision loss that begins in the peripheral fields of vision. Glaucoma usually affects both eyes, but one eye may be more severely affected than the other.

Get more information about the types of glaucoma »

TOP SEARCHED GLAUCOMA TERMS:

symptoms, treatment, causes, medications,signs, research, prevention, surgery

What is glaucoma?

Glaucoma is a disease of the major nerve of vision, called the optic nerve. The optic nerve receives light from the retina and transmits impulses to the brain that we perceive as vision. Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.

Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.

How common is glaucoma?

Worldwide, glaucoma is the leading cause of irreversible blindness. In fact, as many as 6 million individuals are blind in both eyes from this disease. In the United States alone, according to one estimate, over 3 million people have glaucoma. As many as half of the individuals with glaucoma, however, may not know that they have the disease. The reason they are unaware is that glaucoma initially causes no symptoms, and the loss of vision on the side (periphery) is hardly noticeable.

What causes glaucoma?

Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. Glaucoma with normal intraocular pressure is discussed below in the section on the different types of glaucoma. The optic nerve, which is located in back of the eye, is the main seeing nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 and 22 mm (millimeters) of mercury. When the pressure is too low, the eye becomes softer, while a too high pressure causes the eye to become harder. It turns out that the optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.

The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is produced constantly by the ciliary body, which surrounds the lens of the eye. The aqueous humor then flows through the pupil and leaves the eye through tiny channels called the trabecular meshwork. These channels are located at what is called the filtering, or drainage angle of the eye. This angle is where the clear cornea, which covers the front of the eye, attaches to the base (root or periphery) of the iris, which is the colored part of the eye. The cornea covers the iris and the pupil, which are in front of the lens. The pupil is the small, round, black-appearing opening in the center of the iris. Light passes through the pupil, on through the lens, and to the retina at the back of the eye. Please see the figure, which is a diagram that shows the filtering angle of the eye.

Legend for figure: This diagram of the front part of the eye is in cross section to show the filtering, or drainage angle. This angle is between the cornea and the iris, which join each other right where the drainage channels (trabecular meshwork) are located. The arrow shows the flow of the aqueous fluid from the ciliary body, through the pupil, and into the drainage channels. This figure is recreated from Understanding and Treating Glaucoma, a human anatomy board book by Tim Peters and Company Inc., Gladston

Glaucoma patients struggle with applying eyedrops

Fri, 23 Jul 2010 06:54:19 +0100

(Reuters Health) - People in most need of sight-preserving eyedrops may be the least successful in landing the therapy in their eyes, suggests a new study.

Buildup of internal eye pressure is one of the main causes of the vision damage associated with glaucoma, a potentially blinding disease that affects more than 4 million Americans, according to the Glaucoma Research Foundation. Standard treatment relies on self-administering pressure-lowering eyedrops.

But based on observations of a large number of people with glaucoma, researchers found that more than half struggled to apply these eyedrops properly -- including many patients who thought their technique was perfect.

"Getting eyedrops into the eye is not the same as asking a patient to swallow a pill, or use a skin cream," lead researcher Dr. Amy Hennessy of The Johns Hopkins Bloomberg School of Public Health, in Baltimore, told Reuters Health in an email. "It's easier said than done."

After noticing that many of their glaucoma patients were doing a "miserable job" of putting drops in their eyes, frequently launching them onto cheeks and eyelids, Hennessy and her colleagues decided to videotape about 200 glaucoma patients with impaired vision as they gave themselves eyedrops the way they would at home.

Most patients had been using eyedrops for at least 6 months, but when the researchers watched the videos, more than a quarter were unable to get a drop into their eye, they report in the journal Ophthalmology.

And of those that could, only about 40 percent managed to administer just one drop -- the prescribed amount -- onto the eye without touching the bottle to its surface. The average number of drops instilled was almost one and a half.

The study was partly funded by Alcon, an eyedrop manufacturer. One of the authors is an Alcon employee, and another has consulted for the company.

Applying either too few or too many drops could lead to insufficient treatment and faster progression of glaucoma, explained Hennessy. For example, patients could run out of the medicine before insurance allows them to refill their monthly prescription.

"What was more surprising was that patients also had a poor perception of their abilities to administer drops," she added. A quarter of the patients who denied ever touching the bottle to the surface of their eye were observed doing just that, putting them at risk of infection.

A few of the video recordings did pleasantly surprise the team, and provided hope that the challenge was not insurmountable. "Some patients who could no longer see the eye chart had developed a system of localizing the drop over their eye," said Hennessy, "and got it in correctly -- every time!"

The researchers also looked to see what kind of factors, including sex and years with glaucoma, might influence successful application of the eyedrops. In the end, only age appeared important: Patients at least 70 years old were 60 percent less likely to apply the drops successfully compared to younger patients.

Hennessy suggests that these findings highlight the need for eye care providers to teach patients the best way to administer the drops, which is usually with a mirror, tilting the head back and placing the drop in the eye while holding down the lower eyelid. Family members and certain devices may also be of help.

"Glaucoma patients are not the only ones using drops -- other areas of eye care also rely on drops," she said. "So this is not a small problem, especially with our aging population."

SOURCE: link.reuters.com/rum98m Ophthalmology, online June 25, 2010.

eye safety

Thu, 22 Jul 2010 00:01:45 +0100

A Guide to Sunglasses

Glaucoma can make eyes highly sensitive to light and glare, with some glaucoma medications exacerbating the problem even further. Sunglasses are an easy solution that makes life more comfortable when outdoors, while also providing critical protection from the sun’s damaging ultraviolet (UV) rays.

Long-term exposure to UV rays can damage the eye’s surface as well as its internal structures, sometimes contributing to cataracts (clouding of the lens) and macular degeneration (breakdown of the macula). Ophthalmologists and optometrists now recommend wearing sunglasses and a brimmed hat whenever you’re in the sun long enough to get a suntan or a sunburn, especially if you live at a high elevation or near the equator.

The good news is that sunglasses don’t have to be expensive to protect your eyes and they can often be found at the local drugstore. Unfortunately, a high price is not always a guarantee of high quality and protection. Part of the difficulty is that standards and labeling regarding UV protection are voluntary, not mandatory—and can be confusing.

Here are some things to keep in mind when shopping for sunglasses:

Look for UV protection

Don’t be deceived by color or cost. The ability to block UV light is not dependent on the darkness of the lens or the price tag. While both plastic and glass lenses absorb some UV light, UV absorption is improved by adding certain chemicals to the lens material during manufacturing or by applying special lens coatings. Always choose sunglasses that are labeled as blocking 99-100% of UV rays. Some manufacturers’ labels say “UV absorption up to 400nm.” This is the same thing as 100% UV absorption.

Fitovers

Fitovers are sunglasses that can be worn over your regular prescription glasses and they often provide the wraparound feature.

Wraparounds

Wraparounds offer added protection. Sunglasses that wrap around the temples prevent the sun’s rays from entering from the sides. Some studies have shown that enough UV rays enter around standard sunglass frames to reduce the protective benefits of the lenses.

Ensure they block enough light

Sunglasses should screen out 75-90% of visible light. To determine if a pair is dark enough, try the glasses on in front of a mirror. If you can see your eyes easily through the lenses, they probably are too light.

Check lenses for quality

Look for a uniform tint, not darker in one area than in another. To check for imperfections in the lenses, hold the glasses at arm’s length and then look through them at a straight line in the distance, such as the edge of door. Slowly move the lens across the line. If the straight edge distorts, sways, curves or moves, the lens is flawed.

Special features

Determine which special features you need or want. Like cars, sunglasses often have a variety of “extras” from which to choose:

Polarized.

Mirror coatings.

Gradient.

Photochromic.

Impact resistant.

FDA

Eye safety

Remember, even the best sunglasses cannot protect your eyes from certain intense light sources. Arc welding, tanning lights, snowfields or gazing directly at the sun (even during a solar eclipse) all require special protection to prevent damage.

reviewed June 26, 2008

This article appeared in the July 2009 issue of Gleams.Subscribe