Glaucoma - Visual Fields

Glaucoma - Visual Fields

• Perspectives on Perimetry

• Visual Field Interpretation

• Foundational guidelines • Catch trials

• Grey scale

• Total and Pattern deviation • Glaucoma hemifield test • Global indices

• Summary

Zeiss-Humphrey Visual Field

Program Strategies of HFA-II

Full Threshold Standard Fastpac SITA- Standard SITA- Fast 30-2 or 24-2 Tests

Standard Automated Perimetry

(white on white)

“Although different structural and functional tests are used to diagnose and monitor glaucoma,

standard automated perimetry (SAP) remains the most widely used methods to assess visual

function loss.”

Swedish Interactive

Thresholding Algorithm (SITA)

SITA Standard: Twice as fast as “full threshold” algorithm

SITA Fast: Twice as fast as “Fastpac”

Requires a powerful computing system (only for HFA-II)

Intuitive and artificial intelligence is the key element

Constant monitoring allows patient to set pace of stimuli

Short Wavelength Automated

Perimetry (SWAP) (SITA-SWAP)

• Theorized to detect functional loss earlier than white on white

• Can be used with an HVF-II units only

• Advise to look for:

• localized color change (from yellow to violet) • an achromatic spot

• If patient has 20/30 or worse NS, use W on W

• If patient is felt to have moderate to advanced glaucoma, use white on white

• SITA-SWAP-much enhanced but clinical value is debated

SITA-SWAP VS SITA-FAST

• “Bengtsson and Heijl, Ophthalmology, July 2006.

• “Surprisingly, there was no significant difference between conventional SAP and the 2 SWAP

programs in diagnostic sensitivity.”

• “SITA-Fast has previously been reported to be able to identify at least as much significant glaucomatous field loss as SITA Standard . . . and to have a

diagnostic sensitivity of more than 90%.”

• “Our results indicate that there may be some

differences in sensitivity between SWAP and SAP, but that those differences are probably smaller than what has been believed previously.”

• SWAP 12 min - - SITA-SWAP 4.1 min - - SITA-Fast 3.5 min.

SAP vs SWAP

• Of 416 patients, 15% were “high risk” for POAG

• Only about half of this 15% converted

• Despite its limitations, SAP has become a standard in

clinical care across the world. SWAP, however, has never gained such widespread acceptance.

• It is possible that SITA SWAP will prove to be useful for

early detection of glaucomatous conversion. To date, there is insufficient evidence for that. We therefore recommend that clinicians use SAP rather than SWAP in their daily

practices to detect early glaucomatous conversion in OHT.

• Although early SWAP visual field defects have been

suggested typically to precede those in SAP in conversion from OHT to POAG, our prospective, longitudinal follow-up study does not support this suggestion. On the contrary, SAP appears to be at least as sensitive to conversion as SWAP in a majority of eyes.

Frequency Doubling Technology

mechanisms in the magnocellular (M-cell)

pathway. These M-cells have large diameter

fibers and comprise only 3% to 5% of all retinal ganglion cells. The damage of these cells in the disease process makes FDT efficient and

effective for the detection of visual field loss.

• Supra-threshold screening in 45 seconds. Full threshold testing in under 4 minutes.

• Tests central 20-30 degrees; patient wears own correction; normal room lighting

Debunking Myths

Once thought rare, optic disc hemorrhages occur in most glaucoma patients.

It has been proposed that IOP fluctuations represent a key risk factor for glaucoma progression, however,

there is no clear evidence to support this concept.

Another myth is that selective perimetric testing (such as SWAP or FTD) can detect VF loss before standard white-on-white perimetry.

Reference: International Glaucoma Review of the World Glaucoma Association, Vol. 10, 2008

Humphrey Matrix

• 2nd generation frequency doubling technology

• Original FDT: tests 17 points with 10 degree targets

• Matrix 24-2 equivalent: tests 55 points with 5 degree targets

• Has 5 threshold tests: N-30, 24-2, 30-2, 10-2, and macular test

• Has small footprint, easy to operate, floppy & CD drives

SITA vs Matrix Study

No significant difference in outcomes

“Each visual field test tended to identify different

subsets of eyes with glaucomatous-appearing optic discs as abnormal.”

Functional changes in glaucoma detection may differ significantly between individuals

Matrix perimetry may not detect more extensive damage as compared to SITA

Perspective On The Grey Scale

Only a general guide to field defects Tested points are six degrees apart The grey scale is an interpolation

Good for educating patients regarding their individual field status

Show patient their grey scale mapping and then one that is normal. This helps the patient

understand their status and need for compliant medical therapy.

Total Deviation (TD)

• The point by point deviation from age-matched normals

• Deviation threshold is +/- 5DB, depending on the points location within the field

• Because of the increased precision of SITA thresholding, deviation threshold is +/- 4 DB

• Displayed in a two-fold format:

• Actual numeric deviation from normal (? value)

• Probability of the response sensitivity being normal (very valuable)

Pattern Deviation (PD)

• A refinement beyond total deviation

• Uses a representative point within the least

diseased portion of the field to establish a new, more sensitive evaluation of the pattern of the field defects

• Working as an “elevator of the entire hill of

vision, it will factor out generalized depression as is commonly seen with cataracts, miotic pupils, and inaccurate trial lenses.

• Also displayed in a two-fold format:

• Actual numeric deviation from normal (? value)

• Probability of the response sensitivity being normal (very valuable)

Glaucoma Hemifield Test

• Assumes that glaucoma does not cause a

generalized global depression of the field of vision

• Takes advantage of the asymmetric field loss patterns generally seen in glaucoma

• Analyzes defects in the superior hemifield and

compares to mirror image locations in the inferior hemifield

• Included in Standard Strategy, SITA, and SITA-Fast, but not in Fastpac

The Global Indices

(MD) Mean deviation

(PSD) Pattern Standard Deviation

- These indices use a number to characterize the visual field.

- Only the probability score beside the raw data

number has any importance. A probability score appears next to the raw data number only if the data deviates significantly from normal.

Mean Deviation (MD)

Simply the weighted average of how much the patient’s overall function deviates from that of age-matched normals.

General barometer of overall field depression (or rarely elevation)

Pattern Standard Deviation (PSD)

Field loss in glaucoma is not diffuse, but rather there are points, or clusters of points, that are irregularly affected

These irregularities are seen as a “pattern” of field loss

PSD is a characterization of localized change in the visual field

When the patterns of field loss are significant, a percent probability is given (P ranges from 10% to 0.5%)

Ultrasummary

• A combined cerebral assessment of:

• Pattern Deviation probability plots as compared to Total Deviation probability plots

• Pattern Standard Deviation probability values

• These probability plots give the greatest VF data guidance to the functional status of the patient’s optic nerves

• Remember: ALWAYS CORRELATE THE

CLINICAL FINDINGS WITH THE VISUAL FIELD STUDIES!

Perspective on Progression

“Because fluctuation in visual sensitivity is a

confounding factor, if a follow-up visual field test discloses progression, it must be repeated at least once – preferably twice – before you conclude that the deterioration is indicative of true progression. Most clinicians know from experience that patients often exhibit apparent visual field progression on a single test, only to have the next test clearly

demonstrate stability relative to the baseline visual fields, and multiple clinical trials have confirmed this.”

Consensus on Visual Fields

“It was generally agreed that the noise level can be very high in VF testing, an a high number of tests is always required to reveal the true trend.”

When in doubt, Repeat the Field!

Glaucoma Progression Analysis

A software program for Humphrey perimeters Statistically analyses all points for progression Can be immensely helpful in detecting VF

progression

Can be done both retrospectively and prospectively A new standard in detecting progression

Optic Nerve Head Image Analyzers

GDX-VCC, OCT, HRT, RTA, etc. Can be helpful in early diagnosis

Limited value in advanced glaucoma Excellent for detection of progression

A COMPONENT of the glaucoma evaluation Not a “litmus test” for glaucoma

Imaging Technology in Glaucoma

“Given the substantial advances in glaucoma imaging, it is important to remind clinicians that current glaucoma diagnosis cannot be solely

instrument-based. Rather the imaging information should be considered as being complementary to other clinical measures.”

International Glaucoma Review of The World Glaucoma Association. Volume 10-3 2008

Nerve Fiber Layer Analyzers

in Perspective

These so-called “objective” nerve fiber layer scanning devices are only relatively objective

compared to highly subjective perimetry. Looking at this next series of GDx scans very nicely

Optic Nerve Imaging

“Given the variability of clinician documentation, imaging may elevate the assessment of the optic nerve by the general clinician, perhaps to the level of a fellowship-trained expert.”

“The clinician who successfully integrates imaging in practice compliments their clinical evaluation

and adjunctive testing.”

Optic Nerve Imaging

“Ongoing advances in imaging as well as

impracticalities associated with obtaining and assessing optic nerve stereo photographs have made imaging increasingly important.”

“These technologies “…should not mislead a

clinician to think that glaucoma diagnoses can be solely machine-based at present. Rather, the

imaging information should be considered as being complementary to other clinical measures.”

RNFL, Neuroretinal Rim, and

Visual Field Progression

• Regarding optic disc photos, “the agreement for assessment of progressive optic disc changes is poor even among glaucoma specialists.”

• RNFL is mostly ganglion cell axons, whereas

neuroretinal rim tissues contain nonneural structures

• Because rate of change within these two tissues may vary with the stage of disease, interpretation of

progression should be evaluated on an individual basis

• “It is plausible that detection of progression with OCT RNFL thickness may not be as effective as

visual field measurement in moderate and advanced glaucoma.” Oph. August 2011

Treatment Goals For POAG

• Establish a target IOP below which optic nerve damage is unlikely to occur

• Maintain an IOP at or below this target level with appropriate therapy

• Monitor VF's and ONH appearance to refine the adequacy of the target IOP

• Optimally balance the benefits of therapy with any side effects

• Educate and engage patients in the management

Diagnosis Does Not

Mandate Treatment

“Although decisions on treatment may not necessarily be made at an early stage, other

appropriate measures, such as close monitoring, may be considered. It was generally agreed that early detection does not automatically imply early treatment and that early detection and early

treatment should be considered separately.”

When to Treat?

• “Patients with normal optic disc and visual field could tolerate an IOP of 30 mmHg for many years without need of treatment.”

• “What it comes down to is . . . treat young patients who are in the high-risk group, and it is worth

watching the elderly in a low-risk group. The

problem remains what to do for those in the middle.”

Ref: A Sommer/Johns Hopkins Univ. Ophthalmology Times. Jan. 2011.

Melton-Thomas: All glaucoma doctors struggle with the decision of whom to treat, and when. Remember: medical care is an art, and equally well-trained doctors commonly differ in clinical decision-making.

Factors Regarding Treatment Initiation

training were associated with physicians being more likely to treat ocular hypertension

• 2 / 58 glaucoma specialists and 4 / 118 ophthalmologists reported treating all patients with an IOP >21 mmHg

Most critical factors: IOP, C/D ratio, and CCT (both groups)

• Rational estimation of “risk of conversion” to OAG is essential for proper clinical decision-making

• Treatment by default or faulty decision-making remains a healthcare crisis in glaucoma patient care management

The Holy Grail in

Glaucoma Management

“At the most basic level we have yet to determine at which stage of disease is the initiation of

treatment superior to natural history.”

Said less eloquently: The ultimate management decision is WHEN to initiate therapy.

Target Range of IOP

• Set target IOP range when initiating therapy

• General guideline: reduce IOP by the % of the

pretreatment baseline IOP. (Example, if the initial IOP is 30 mmHg, try to reduce IOP by 30%,

yielding a target IOP of approximately 20 mmHg.)

• Modify target IOP according to the stage and

severity of the disease ( plus 0-20% for severity, other factors)

• Re-evaluate and adjust over time (years)

• Target IOP ranges

• Low teens (10-13 mmHg) • Mid teens (14-16 mmHg) • High teens (17-19 mmHg)

Expert Perspective on “Target IOP”

“Estimation of target pressure is based on a

patient’s risk factors for progression, the level of IOP that caused damage, the severity of disease, and longevity. There is, of course, no way to

determine in advance which IOP will be safe. There is no evidence that setting a variable target has

clinical value for most patients with chronic glaucoma.”

Target Pressure: Use and Abuse

“Despite recent breakthroughs in our knowledge of risk of progression, we still are making educated

guesses. At all but the highest pressures, not all patients will progress. Some patients may have non-pressure dependent optic neuropathies that are beyond our current understanding and

treatment capabilities. Around half of patients with normal tension glaucoma will not progress even

without treatment.”

Predicting Response to Glaucoma Therapy in

One Eye Based on Response in the Fellow Eye

Conclusions: The change in IOP of one eye due to a medication may be predictive of the subsequent response of the fellow eye to the same medication in glaucoma suspects, but not in patients with

POAG.

Using the fellow eye as a control may confer a more accurate portrayal of the true therapeutic effects of a medicine although further study is needed to support both of these findings.

The Therapeutic Monocular

Trial in Glaucoma

“The most reliable method of assessing drug

effectiveness is by performing a series of pre- and post-treatment IOP measurements, but in practice this has obvious resource implications.”

“The monocular trial provides a significantly more accurate estimate of the therapeutic response

when initiating prostaglandin monotherapy in

untreated eyes. It is particularly helpful in avoiding overestimation of effectiveness and so reducing

the number of patients on inadequate treatment.”

Contrary View on the Monocular Trial

• Spontaneous IOP variation might mask or mimic the true drug effect

• IOP change in one eye may not adequately predict IOP effect in the fellow treated eye

• “There is no useful information about drug

efficacy to be gained by testing only one eye if both need to be treated.”

• And, just for perspective; “Glaucoma is a chronic and slowly progressive disease, and most

patients do not require acute IOP reduction.”

Glaucoma Follow-Up

• Most controlled glaucoma patients are seen

every 3 to 4 months for monitoring of the IOP and ONH status

• Visual Fields and/or a scan are done as

frequently as necessary, and at least once yearly

• A dilated stereoscopic view of the optic nerve should be performed at least yearly, however, a quick look should be done at each visit.

• If control is felt inadequate, more aggressive

follow-up is in order until adequate control of the patient is achieved

Key Excerpts From

Glaucoma Clinical Trials and What They Mean for Our Patients Paul R Lichter, MD, AJO, July 2003

“Extrapolating the results of clinical trials to everyday practice is a challenge not only for the average clinician reading the literature, but also for experts in clinical research.”

“…there is no way for the trial results to indicate whether that treatment will be effective in a particular patient.”

“In contemplating decisions on whether to treat ocular hypertensive patients, we should recognize that letting the patients progress (under careful observation) to frank glaucoma before treating them still will allow for control of the disease in the vast majority of patients. In addition, we know that this control can occur well before there is a threat to interference with activities of daily living.”

“It may be very reasonable to watch for documented progression of mild visual field loss detected at the initial examination before beginning treatment. This way, our patients could avoid the unnecessary burden of nuisance, side effects, and cost associated with a questionable need for treatment. Conversely, if the field loss is moderate or worse to begin with or if the patient had high risk for progression, treatment could be undertaken immediately.”