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National Collaborating Centre for Acute Care (UK). Glaucoma: Diagnosis and Management of Chronic Open Angle Glaucoma and Ocular Hypertension. London: National Collaborating Centre for Acute Care (UK); 2009 Apr. (NICE Clinical Guidelines, No. 85.)

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Glaucoma: Diagnosis and Management of Chronic Open Angle Glaucoma and Ocular Hypertension.

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4Diagnosis of patients with ocular hypertension, chronic open angle glaucoma and suspected chronic open angle glaucoma

4.1. Introduction

The correct diagnosis of COAG, OHT and suspected COAG is extremely important for patients since the consequences of both false positive and negative decisions may be severe. Because optic nerve damage from the disease is irreversible, failure to make the diagnosis when the disease is present may be catastrophic and apart from the avoidable suffering endured, the medico-legal consequences are likely to be significant. False positive diagnosis also has serious consequences leading to lifelong inappropriate anxiety, unnecessary exposure to potentially harmful medicines and wastage of resources.

Because COAG is a “primary” diagnosis, it means that it has to be made by the exclusion of other “secondary” causes. It must be differentiated from angle closure disease where there is a mechanical obstruction to the outflow of aqueous humour from the eye and also from all other possible neurological causes of optic nerve damage, including brain tumours, strokes and inflammatory diseases of the eye and brain. Once a patient is given the diagnosis, a lifetime’s sentence of an ever present threat to sight is delivered, since the disease cannot be cured; only controlled.

The definition of COAG includes the concept of a progressive condition and implies that if intervention is not provided, progression will take place. Although the rate of progression is variable it is important that with the diagnosis, an appropriate and as far as possible accurate visual prognosis is given, since this varies widely from a negligible threat to an individual’s sighted lifetime to almost certain and severe loss of sight. Fortunately only a minority of patients with glaucoma will become significantly vision impaired.

In the great majority of cases, a definite diagnosis of COAG should only be made when there is an irrefutable and consistently demonstrable abnormality of visual function in at least one eye. Usually this will be defined by a relative or absolute scotoma in the field of vision demonstrated by standard automated perimetry (SAP). When a person is unable to cooperate with SAP, alternative methods of defining a functional abnormality of the optic nerve should be used. This functional abnormality should be confidently attributed to glaucomatous optic neuropathy to the exclusion of any other cause and corroborated by demonstrable abnormality of the optic nerve in the affected eye(s). On occasions there will be genuine uncertainty, for example not all patients are able to perform visual function tests reliably. Depending on the level and source of uncertainty, other signs of COAG such as ‘obvious’ glaucomatous optic neuropathy may need to be given additional weight in arriving at a considered and accurate diagnosis. A period of observation with repeated clinical measurements may be required to confirm or refute an uncertain diagnosis.

A person may be classified as a COAG suspect when the optic nerve head appearance is suggestive of COAG but the visual fields appear normal, or conversely, where a visual field defect exists yet the optic nerve appears healthy (other causes of visual field defects having been excluded). If the intraocular pressure is raised in the presence of suspicious optic nerve changes the person may be classified as a COAG suspect with ocular hypertension. Where both the visual field and the optic nerve appear normal in the presence of elevated pressure the person is classified as having ‘simple’ ocular hypertension.

In this chapter we examine the accuracy of various diagnostic tests used to assess intraocular pressure, anterior chamber angle, visual field and the optic nerve.

4.2. Intraocular pressure measurement (IOP)

The GDG considered Goldmann applanation tonometry (slit lamp mounted) to be the reference standard in IOP measurement. In order to find out if alternative methods might be equally suitable we searched for evidence comparing non-contact tonometry to Goldmann contact tonometry.

Using Goldmann prisms introduces the potential for cross infection via contaminated prisms. A disposable prism would not have this risk. Consequently, we also compared the accuracy of disposable versus Goldmann prisms to see if disposable prisms are a suitable alternative.

4.2.1. Diagnostic accuracy of non-contact tonometry versus Goldman contact tonometry

See Evidence Table 1, Appendix D and Cost Analysis in Appendix F -1.4

4.2.1.1. Clinical evidence

Table 4-10Non-contact vs. contact tonometry - Clinical study characteristics

OutcomeNumber of studiesDesignLimitationsInconsistencyDirectnessOther considerations
Detection of IOP ≥ 21mmHg53 (a)Diagnostic studySerious limitations (b)Serious inconsistency (c)No serious indirectnessNone
a

One study includes three groups using different machines.

b

States patients were selected randomly but no other details are provided. It is also unclear whether the machines were recalibrated before each use.

c

The results show different sensitivities and specificities for the different groups.

Table 4-11Non-contact vs. contact tonometry - Clinical summary of findings

OutcomeSensitivity %Specificity %NPV %PPV %Prevalence %Likelihood Ratio (+ve)Likelihood Ratio (ve)Quality
Detection of IOP ≥21mmHgRange 40 to 81Range 93 to 95Range 63 to 85Range 71 to 93Range 18 to 31Range 7.54 to 12.47Range 0.16 to 0.63Low

4.2.1.2. Economic evidence

No studies were identified. We conducted a cost analysis on this question. See Appendix F – 1.4 for methods.

Table 4-12Non-contact vs. contact tonometry - Economic study characteristics

StudyLimitationsApplicabilityOther Comments
NCC-AC cost analysis (Appendix F – 1.4)Serious limitations (a)Directly applicable
a

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Table 4-13Non-contact vs. contact tonometry - Economic summary of findings

StudyIncremental costIncremental effectsICERUncertainty
NCC-AC cost analysis (Appendix F – 1.4)Non-contact tonometry costs £0.39 less per patient.Contact tonometry more accurate (a)Not calculatedNot calculated
a

Expert opinion

4.2.1.3. Patient views evidence

No studies were identified.

4.2.1.4. Evidence statements - Non-contact vs. contact tonometry

ClinicalStudies examining sensitivity and specificity of NCT to detect OHT (IOP>21mmHg) demonstrated a wide range of sensitivities with consistently quite high specificity. (LOW QUALITY)
EconomicContact tonometry is more costly than non-contact tonometry when the cost of false positives and false negatives are excluded. The evidence has serious limitations and direct applicability.

4.2.2. Diagnostic accuracy of disposable prisms versus Goldman prisms

4.2.2.1. Clinical evidence

No studies were identified.

4.2.2.2. Economic evidence

No studies were identified.

4.2.2.3. Patient views evidence

No studies were identified.

4.2.2.4. Evidence statements - Disposable versus Goldmann prisms

ClinicalNo studies were identified comparing the diagnostic accuracy of disposable to Goldmann prisms.
EconomicNo studies were identified comparing the costs of disposable to Goldmann prisms.

4.2.3. Recommendations and link to evidence

Recommendations marked by an asterisk (*) are first presented separately due to the difference in supporting evidence. Later these recommendations have been merged into a single recommendation in section 4.7 (Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG) to reflect the importance of considering them together when assessing the presence or absence of OHT or COAG.

Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT intraocular pressure measurement using Goldmann applanation tonometry (slit lamp mounted)
Relative values of different outcomesThe GDG considered Goldmann applanation tonometry to be the reference standard for measurement of IOP. Since important treatment decisions are based on IOP measurements it is imperative to obtain a reliable IOP reading and for the test to have a high sensitivity and specificity. The available evidence suggests that non-contact tonometry could not accurately measure the higher IOP.
Trade off between clinical benefits and harmsAlthough there is no written evidence, the GDG noted that the potential for corneal burn is present if sterilising fluid remains or is allowed to dry on the prism with Goldmann applanation tonometry. Using disposable tonometer prisms could adversely affect the accuracy but would be safer for avoidance of transmission of infectious diseases.
Economic considerationsAlthough contact tonometry is more costly, it also has greater accuracy (expert opinion) than non-contact tonometry and therefore could save costs of inappropriately treating patients for raised IOP. The slit lamp is expensive but it has many other uses including optic nerve stereo biomicroscopy. Using disposable tonometer prisms could increase costs (between £0.70 and £1.40 per patient) but prevent transmission of infective agents.
Quality of evidenceLow quality clinical evidence.
The economic evidence has direct applicability but serious limitations as it is not a full economic evaluation and the summary of effectiveness was based on expert opinion.
Other considerationsHand held methods of tonometry such as Perkins may be useful in a case finding/screening scenario where a person may have difficulty being examined on a slit lamp (for example with curvature of the spine). However there is no evidence to suggest that these methods are equivalent to slit lamp mounted GAT.

4.2.4. Supporting recommendations

RecommendationAdopt professional/Department of Health guidance to reduce the risk of transmitting infective agents via contact tonometry or gonioscopy.
Trade off between clinical benefits and harmsThere is a potential trade off between getting an accurate measurement of intraocular pressure and the risk of infection from contact tonometry.
Economic considerationsNot addressed.
Other considerationsThe GDG decided not to duplicate work carried out by the Department of Health and other professional bodies therefore we refer to any guidance they provide34,97,127,129.

4.3. Central corneal thickness measurement

Central corneal thickness was identified as a risk factor of converting from OHT to POAG (Section 7.4). A variety of options exist for measurement of central corneal thickness. There is no universally accepted reference standard. The GDG did not consider it necessary to investigate in detail comparisons between the various machines available. The GDG decided it was important to consider assessing CCT.

4.3.1.1. Clinical evidence

In Section 7.4 we identify central corneal thickness as a risk factor of converting from OHT to POAG.

4.3.1.2. Economic evidence

In Section 7.3 we define the most cost-effective treatment strategy for patients with OHT. This is based on the risk factors for conversion to POAG, which include central corneal thickness. Its measurement is therefore necessary to select the most appropriate and cost-effective treatment option. See Section 7.3 and Appendix F -1.3 for methods and conclusions.

4.3.1.3. Patient views evidence

No studies were identified.

4.3.1.4. Evidence statements - Central corneal thickness measurement vs. no measurement

ClinicalNo studies were identified which compared the visual outcomes for patients whose clinical management included measurement of CCT compared to those where CCT was not measured.
EconomicThe most cost-effective strategy for treating OHT patients depends on the results of the central corneal thickness measurement. This evidence has minor limitations and direct applicability.

4.3.2. Recommendations and link to evidence

Recommendations marked by an asterisk (*) are first presented separately due to the difference in supporting evidence. Later these recommendations have been merged into a single recommendation in section 4.7 (Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG) to reflect the importance of considering them together when assessing the presence or absence of OHT or COAG.

Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT central corneal thickness measurement
Relative values of different outcomesCentral corneal thickness is significantly associated with POAG development. This was shown by a study that included a multivariate model which adjusted for other known risk factors such as positive family history or West African ethnic origin51. Its measurement is therefore necessary for estimating an ocular hypertensive patient’s risk of developing POAG.
Central corneal thickness can act as a confounder of IOP measurement and is therefore of value in interpreting IOP measurements.
Trade off between clinical benefits and harmsCentral corneal thickness can be measured by contact or non contact methods. Contact methods may be quicker and more accurate but require corneal anaesthesia and are associated with potential corneal injury or transmission of infection.
Economic considerationsThe cost-effectiveness of treatment strategies vary according to the central corneal thickness, therefore this measurement is necessary for prescribing the most cost-effective treatment.
Quality of evidenceNo clinical evidence was found. The economic evidence has minor limitations and direct applicability.
Other considerationsCentral corneal thickness is affected by laser refractive surgery. See NICE IP guidance 164 (www​.nice.org.uk/nicemedia​/pdf/IPG164guidance.pdf)

4.4. Anterior chamber angle measurement

The GDG considered gonioscopy as the reference standard for anterior chamber angle measurement. We searched for data comparing gonioscopy and the following non gonioscopic procedures: iris eclipse or shadow test, Van Herick’s test, slit lamp assessment, Redmond-Smith slit lamp assessment, Scheimpflug anterior segment photography, ultrasound (A-scan), (Ultra)High resolution B-scan, Ultrasound BioMicroscopy (UBM) and anterior segment optical coherence tomography (OCT).

4.4.1. Diagnostic accuracy of non-gonioscopic methods versus gonioscopic methods of measuring anterior chamber angle

See Evidence Table 2, Appendix D and Cost Analysis in Appendix F -1.4

4.4.1.1. Clinical evidence

Table 4-14Van Herick’s test vs. gonioscopic methods - Clinical study characteristics

OutcomeNumber of studiesDesignLimitationsInconsistencyDirectnessOther considerations
Diagnostic accuracy at cut- off ≤ 25% corneal thickness 9,1492Diagnostic studySerious limitations (a)No serious inconsistencySerious indirectness (b)(c)
a

Both studies are in a consecutively selected cohort of patients. In one study9 it is not clear whether Van Herick’s test was performed independently, within a reasonable time frame and in a masked fashion to gonioscopy. Both studies reported full test results for all patients.

b

Both studies are in patients from south-east Asia and the Indian sub-continent where the prevalence of closed-angles tends to be higher.

c

For gonioscopy there are variations between studies in type of gonioscopy lens and grading system used for classification of narrow angles. For Van Herick’s test one study9 uses a modified cut-off grade for of ≤ 25% of corneal thickness as indicative of narrow angles whereas the other study149 uses grade 1 <25% corneal thickness as indicative of narrow angles.

Table 4-15Van Herick’s test vs. gonioscopic methods - Clinical summary of findings

OutcomeSensitivity %Specificity %NPV %PPV %Prevalence %Likelihood Ratio (+ve)Likelihood Ratio (ve)Quality
Diagnostic accuracy at cut-off ≤ 25% corneal thicknessRange: 62 to 85Range: 89 to 90Range: 88 to 89Range: 62 to 87Range: 22 to 44Range: 5.80 to 8.13Range: 0.17 to 0.43Low

Table 4-16Flashlight Test vs. gonioscopic methods - Clinical study characteristics

OutcomeNumber of studiesDesignLimitationsInconsistencyDirectnessOther considerations
Diagnostic accuracy at cut- off of 1/2 shadow 1491Diagnostic studyNo serious limitationsNo serious inconsistencySerious indirectness (a)
Diagnostic accuracy at cut- off of 1/3 shadow 1491Diagnostic studyNo serious limitationsNo serious inconsistencySerious indirectness (a)
a

The study is in patients from the Indian sub-continent where the prevalence of closed-angles tends to be higher.

Table 4-17Flashlight Test vs. gonioscopic methods - Clinical summary of findings

OutcomeSensitivity %Specificity %NPV %PPV %Prevalence %Likelihood Ratio (+ve)Likelihood Ratio (ve)Quality
Diagnostic accuracy at cut-off of 1/2 shadow48838543222.750.63Moderate
Diagnostic accuracy at cut-off of 1/3 shadow86719545222.920.20Moderate

Table 4-18Scanning Peripheral Anterior Chamber Depth analyser (SPAC) vs. gonioscopic methods - Clinical study characteristics

OutcomeNumber of studiesDesignLimitationsInconsistencyDirectnessOther considerations
Diagnostic accuracy at cut- off of suspect angle closure or potential angle closure 91Diagnostic studyNo serious limitationsNo serious inconsistencySerious indirectness (a)
a

The study is in patients from south-east Asia where the prevalence of closed-angles tends to be higher.

Table 4-19Scanning Peripheral Anterior Chamber Depth analyser (SPAC) vs. gonioscopic methods - Clinical summary of findings

OutcomeSensitivity %Specificity %NPV %PPV %Prevalence %Likelihood Ratio (+ve)Likelihood Ratio (ve)Quality
Diagnostic accuracy at cut-off of suspect angle closure or potential angle closure85738671443.160.21Moderate

Table 4-20Non-contact anterior segment optical coherence technology (AS-OCT) vs. gonioscopic methods - Clinical study characteristics

OutcomeNumber of studiesDesignLimitationsInconsistencyDirectnessOther considerations
Diagnostic accuracy at cut- off of ≥ 1 quadrants of the angle closed in either eye1121Diagnostic studyNo serious limitationsNo serious inconsistencySerious indirectness (a)
a

The study is in patients from south-east Asia where the prevalence of closed-angles tends to be higher.

Table 4-21Non-contact anterior segment optical coherence technology (AS-OCT) vs. gonioscopic methods - Clinical summary of findings

OutcomeSensitivity %Specificity %NPV %PPV %Prevalence %Likelihood Ratio (+ve)Likelihood Ratio (ve)Quality
Diagnostic accuracy at cut-off ≥ 1 quadrants of the angle closed in either eye98559768502.200.04Moderate

4.4.1.2. Economic evidence

No studies were identified. We conducted a cost analysis on this question. See Appendix F – 1.4 for methods.

Table 4-22Van Herick’s test vs. gonioscopic methods - Economic study characteristics

StudyLimitationsApplicabilityOther Comments
NCC-AC cost analysis (Appendix F – 1.4)Serious limitations (a)Directly applicable
a

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Table 4-23Van Herick’s test vs. gonioscopic methods - Economic summary of findings

StudyIncremental cost (£)Incremental effectsICERUncertainty
NCC-AC cost analysis (Appendix F – 1.4)Van Herick’s test saves £0.40 per patient.Gonioscopy more accurate (a)Not calculatedNot calculated
a

Expert opinion. See also 4.4.1.1 for clinical evidence.

Table 4-24Non-gonioscopic vs. gonioscopic methods - Economic study characteristics

StudyLimitationsApplicabilityOther Comments
NCC-AC cost analysis (Appendix F – 1.4)Serious limitations (a)Directly applicable
a

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Table 4-25Non-gonioscopic vs. gonioscopic methods - Economic summary of findings

StudyIncremental cost (£)Incremental effectsICERUncertainty
NCC-AC cost analysis (Appendix F – 1.4)A-scan, B-scan and OCT save respectively £0.28, £0.22, and £0.14 per patient.Gonioscopy more accurate (a)Not calculatedNot calculated
a

Expert opinion. See also 4.4.1.1 for clinical evidence

4.4.1.3. Patient views evidence

No studies were identified.

4.4.1.4. Evidence statements - Non-gonioscopic vs. gonioscopic methods

ClinicalVan Herick’s test at a cut-off of ≤ 25% has a reasonable sensitivity and specificity across the two studies for measuring anterior chamber angle. However the evidence is limited because both studies were in Asian/Indian populations with a higher prevalence of narrow angles and one study was of lower methodological quality. (LOW QUALITY)
The flashlight test has a moderate sensitivity and specificity when a third-shadow is used as the cut-off for measuring anterior chamber angle but has a low sensitivity for a cut-off of a half-shadow. However the evidence is limited because both studies were in Asian/Indian populations with a higher prevalence of narrow angles. (MODERATE QUALITY)
Scanning Peripheral Anterior Chamber Depth analyser (SPAC) at a cut-off of suspect angle closure or potential angle closure has a moderate sensitivity and specificity for measuring anterior chamber angle. However the evidence is limited because both studies were in Asian/Indian populations with a higher prevalence of narrow angles. (MODERATE QUALITY)
Non-contact anterior segment optical coherence technology (AS-OCT) at a cut off ≥1 closed quadrant has a high sensitivity but low specificity for measuring anterior chamber angle. However the evidence is limited because both studies were in Asian/Indian populations with a higher prevalence of narrow angles. (MODERATE QUALITY)
EconomicVan Herick’s test, A-scan, B-scan and OCT are less costly than Gonioscopy when the cost of false positives and false negatives are not taken into account. This evidence has serious limitations and direct applicability.

4.4.2. Recommendations and link to evidence

Recommendations marked by an asterisk (*) are first presented separately due to the difference in supporting evidence. Later these recommendations have been merged into a single recommendation in section 4.7 (Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG) to reflect the importance of considering them together when assessing the presence or absence of OHT or COAG.

Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT peripheral anterior chamber configuration and depth assessments using gonioscopy.
Relative values of different outcomesThe GDG considered gonioscopy to be the accepted reference standard assessment for establishing the configuration and condition of the peripheral anterior chamber and drainage angle.
Precise knowledge of the state of the chamber angle is essential to avoid missing angle closure if present.
Trade off between clinical benefits and harmsGonioscopy allows comprehensive visualisation of the interior anterior chamber angle and related structures in a way which is not possible using any of the other tests. However, it is invasive, involves anaesthetic drops and has the potential to damage the surface of the eye if used incorrectly. Other tests are not invasive except high resolution ultrasound. The importance of knowing the angle details outweighs the potential harms and risks. No technique was considered a suitable alternative to gonioscopy in describing the status of the drainage angle. For exclusion of angle closure and accurate diagnosis the reference standard is therefore required.
Economic considerationsEven if gonioscopy costs more than Van Herick’s test, A-scan and B-scan, it has higher precision in detecting angle closure.
Quality of evidenceLow quality clinical evidence in an indirect population.
The economic evidence has direct applicability but serious limitations as it is not a full economic evaluation and the summary of effectiveness was based on expert opinion.
Other considerationsSome patients may not be able to be assessed with gonioscopy. For example, some patients with physical or learning disabilities may be unable to participate in the examination and therefore an alternative test should be offered (see below).
RecommendationUse Van Herick’s peripheral anterior chamber depth assessment test as an alternative to gonioscopy if clinical circumstances rule out gonioscopy (for example, when people with physical or learning disabilities are unable to participate in the examination).
Relative values of different outcomesAs indicated above, the GDG considered precision of the test to be the most important issue. Although Van Herick’s test is not as accurate as gonioscopy, the GDG considered it to be an adequate alternative for use where gonioscopy was not possible.
Trade off between clinical benefits and harmsThe GDG considered it important to get a diagnosis in the interest of providing the correct management plan for all individuals. If the best test is not possible for or desirable to a patient then Van Herick’s test is a suitable alternative.
Economic considerationsOther non-gonioscopic methods are more expensive than Van Herick’s test without adding any useful information.
Quality of evidenceLow quality clinical evidence in an indirect population.
The economic evidence has partial applicability because not direct to a population with physical or learning disabilities. It has serious limitations as it is not a full economic evaluation and the summary of effectiveness was based on expert opinion.
Other considerationsNone

4.4.3. Supporting recommendations

RecommendationAdopt professional /Department of Health guidance to reduce the risk of transmitting infective agents via contact tonometry or gonioscopy.
Trade off between clinical benefits and harmsThere is a potential trade off between getting an accurate assessment of anterior chamber angle and the small risk of infection from gonioscopy.
Economic considerationsNone.
Other considerationsThe GDG decided not to duplicate work carried out by the Department of Health and other professional bodies therefore we refer to any guidance they provide34,97,127,129.

4.5. Visual field measurement

The GDG considered 24-2 SITA Humphrey tests as the reference standard in assessing visual field. We searched for data comparing 24-2 SITA Humphrey tests and the following alternative visual field tests: Henson, Dicon, Octopus, frequency doubling technology (FDT) and Humphrey tests other than 24-2 SITA.

4.5.1. Diagnostic accuracy of Henson, Dicon, Octopus, frequency doubling technology (FDT) or Humphrey tests (other than 24-2 SITA) versus Humphrey tests (24-2 SITA)

No studies were identified.

4.5.1.1. Clinical evidence

No studies were identified.

4.5.1.2. Economic evidence

No studies were identified.

4.5.1.3. Patient views evidence

No studies were identified.

4.5.1.4. Evidence statements - Other perimetry tests vs. Humphrey 24-2 SITA

ClinicalNo studies reported diagnostic accuracy of other perimetry tests compared to Humphrey 24-2 SITA standard.
EconomicNo studies reported cost-effectiveness of other perimetry tests compared to Humphrey 24-2 SITA standard.

4.5.2. Recommendations and link to evidence

Recommendations marked by an asterisk (*) are first presented separately due to the difference in supporting evidence. Later these recommendations have been merged into a single recommendation in section 4.7 (Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG) to reflect the importance of considering them together when assessing the presence or absence of OHT or COAG.

Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT visual field measurement using standard automated perimetry (central thresholding test).
Relative values of different outcomesThe GDG considered accurate identification and quantification of a visual field defect attributable to glaucoma as the most important outcome.
Trade off between clinical benefits and harmsThe GDG considered that without evidence that visual field assessment by another method is at an acceptable level of diagnostic accuracy, the benefit outweighs the potential harm of using another method providing a less certain diagnosis.
Economic considerationsNot addressed.
Quality of evidenceLack of clinical evidence was due to the studies not comparing other perimetric tests against the reference standard Humphrey 24-2 SITA Standard.
Other considerationsImplementation: the GDG recommended testing using a threshold strategy, although this need not be machine specific.
Where Humphrey Field Analyzers are used, the GDG consensus is that 24-2 SITA Standard is preferred.
Where a patient is unable to perform standard automated perimetry reliably, an alternative test of visual field should be considered.
Patient views: patients may find a shorter, easier test from a different machine more comfortable but may prefer the longer Humphrey 24-2 SITA standard test in the knowledge that it is the most accurate.

4.6. Optic nerve assessment

The GDG considered biomicroscopic slit lamp examination by a trained clinician as the reference standard for optic nerve assessment. This is frequently combined with imaging, stereophotography being the imaging standard. We searched for evidence comparing biomicroscopic slit lamp examination with or without stereophotography to Heidelberg retina tomography, optical coherence tomography, scanning laser polarimetry and monoscopic photography.

4.6.1. Diagnostic accuracy of Heidelberg retina tomography, optical coherence tomography, scanning laser polarimetry or monoscopic photography versus bio-microscopic slit lamp examination with or without stereophotography when assessing initial optic nerve damage

See Cost Analysis in Appendix F -1.4

4.6.1.1. Clinical evidence

No studies were identified.

4.6.1.2. Economic evidence

No studies were identified. We undertook our own cost analyses including an analysis to estimate the increase in cost when stereophotography is added to the clinical biomicroscopic slit lamp examination. See Appendix F – 1.4 for methods.

Table 4-26Other optic nerve imaging vs. biomicroscopic slit lamp examination - Economic study characteristics

StudyLimitationsApplicabilityOther Comments
NCC-AC cost analysis (Appendix F – 1.4)Serious limitations (a)Directly applicable
a

Summary of effectiveness was based on expert opinion.

Table 4-27Other optic nerve imaging vs. biomicroscopic slit lamp examination - Economic summary of findings

StudyIncremental costIncremental effectsICERUncertainty
NCC-AC cost analysis (Appendix F – 1.4)Slit lamp examination is cost savingSlit lamp examination is more accurate (a)Slit lamp examination is dominantNot calculated
a

This test is the accepted clinical standard. Other methods (e.g. experts comparing serial stereo disc photographs) are more accurate but impractical for routine use in the NHS. There was no evidence that alternative disc imaging techniques result in better patient outcomes. It was the opinion of the GDG that this is the most accurate method among the practical ones.

Table 4-28Biomicroscopic slit lamp examination with stereophotography vs. Biomicroscopic slit lamp examination - Economic study characteristics

StudyLimitationsApplicabilityOther Comments
NCC-AC cost analysis (Appendix F – 1.4)Serious limitations (a)Partially applicable (b)
a

Not a full economic evaluation.

b

Stereophotography is not commonly available in clinical practice.

Table 4-29Biomicroscopic slit lamp examination with stereophotography vs. Biomicroscopic slit lamp examination - Economic summary of findings

StudyIncremental cost per patient (£)Incremental effectsICERUncertainty
NCC-AC cost analysis (Appendix F – 1.4)0.11Not calculatedNot calculatedNot calculated

4.6.1.3. Patient views evidence

No studies were identified.

4.6.1.4. Evidence statements - Other optic nerve assessment methods vs. stereoscopic slit lamp biomicroscopy

ClinicalNo studies reported diagnostic accuracy of other optic nerve measurement methods compared to slit lamp biomicroscopy with stereophotography.
EconomicStereoscopic slit lamp examination dominates other optic nerve measurement methods. This evidence has serious limitations and direct applicability. Adding stereophotography to slit lamp examination is more costly. This evidence has serious limitations and partial applicability.

4.6.2. Recommendations and link to evidence

Recommendations marked by an asterisk (*) are first presented separately due to the difference in supporting evidence. Later these recommendations have been merged into a single recommendation in section 4.7 (Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG) to reflect the importance of considering them together when assessing the presence or absence of OHT or COAG

Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT optic nerve assessment using stereoscopic slit lamp biomicroscopy.
Relative values of different outcomesThe GDG considered that finding optic disc abnormalities due to glaucoma using visualisation of morphological features of glaucomatous optic disc damage was the most important outcome, and any abnormal disc appearance should be interpreted in the light of other clinical findings.
Trade off between clinical benefits and harmsThe GDG considered that bio-microscopic slit lamp examination is the most important part of the assessment of optic nerve appearance. The GDG also considered that using stereophotography combined with bio-microscopic slit lamp examination is not always practical in the clinical setting. There is no clear evidence that stereophotography or other imaging methodologies provide added value beyond biomicroscopic examination alone. Therefore, biomicroscopic slit lamp examination is recommended. The requirement for an optic disc image is made in a separate recommendation as it is specifically required at baseline and when there is a suggestion of morphological change.
Economic considerationsStereoscopic slit lamp biomicroscopy is less costly and it is the accepted clinical standard. Other methods (e.g. experts comparing serial stereo disc photographs) are more accurate but impractical for routine use in the NHS. There was no evidence that alternative disc imaging techniques result in better patient outcomes. It was the opinion of the GDG that this is the most accurate method among the practical ones. Furthermore the cost of the slit lamp could have been omitted from the economic analysis as this equipment is already adopted for the IOP measurement (see recommendation 4). Adding stereophotography to slit lamp examinations generates more costs with no evidence that provides any added value.
Quality of evidenceThere was a lack of evidence investigating the diagnostic accuracy of other optic disc imaging techniques against the reference standard.
The economic evidence has serious limitations and direct applicability.
Other considerationsPatient views: dilatation for optic disc examination may be required which may affect a patient’s ability to drive afterwards. The requirement for a stereo photograph as well as slit lamp examination may impact on patient time at the clinic.
Alternative tests. Optical coherence tomography requires pupil dilatation. Scanning laser polarimetry and Heidelberg retina tomography usually do not require dilatation though this may be needed for certain patients. There may be a role for these technologies in detection of progressive change through sequential monitoring but evidence is as yet inadequate to support a recommendation in this regard.

4.6.3. Supporting recommendations

RecommendationObtain an optic nerve head image at diagnosis for baseline documentation.
Trade off between clinical benefits and harmsThe GDG decided it is important to have an image of the optic disc from which to determine if there has been a change in its appearance. Without this image as a baseline reference a clinician may not make an accurate assessment of progression of optic nerve damage over time.
Economic considerationsAdding stereophotography to biomicroscopy slit lamp examination increases costs. The economic evidence has serious limitations as it is not a full economic evaluation, and partial applicability as stereophotography is not commonly available in clinical practice.
Other considerationsAlthough stereophotography would be the imaging standard there are other imaging modalities which may also be used, in which case continuity with previous similar images should be available for purposes of comparison.
Recommendation* At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT dilatation of their pupils before undergoing stereoscopic slit lamp biomicroscopy for fundus examination.
Trade off between clinical benefits and harmsAssessment of the optic disc with stereoscopic slit lamp biomicroscopy is most accurately performed when the patient’s pupils are dilated. Without dilatation important ocular co- pathology may be missed. The potential of harm from inducing an acute angle closure attack should not arise because gonioscopy will have been performed prior to dilatation as recommended above. Contraindications to dilatation should be observed and would include possible angle closure and an iris supported lens implant.
Economic considerationsThe cost of dilating drops per patient is about £0.30 per patient which could be offset by the cost of the missed pathology.
Other considerationsPatient views: dilatation for optic disc examination may affect a patient’s ability to drive afterwards due to blurring of vision. The need for an accurate diagnostic assessment however outweighs this inconvenience.
RecommendationEnsure that all of the following are made available at each clinical episode to all healthcare professionals involved in a person’s care:
  • records of all previous tests and images relevant to COAG and OHT assessment
  • records of past medical history which could affect drug choice
  • current systemic and topical medication
  • glaucoma medication record
  • drug allergies and intolerances.
Trade off between clinical benefits and harmsThe GDG considered it important to ensure the continuity of care that all information is available to healthcare professionals when assessing a patient, particularly if the patient was previously seen by a different healthcare professional.
Economic considerationsThere are costs associated with the delivery of care at multiple sites.
Other considerationsNone
RecommendationUse alternative methods of assessment if clinical circumstances rule out the use of standard methods of assessment (for example, when people with physical or learning disabilities are unable to participate in the examination).
Trade off between clinical benefits and harmsThe GDG considered it important to get a diagnosis in the interest of providing the correct management plan for all individuals. If the best test is not possible or desirable for a patient then an alternative method of assessment should be offered, even if it is less accurate.
Economic considerationsNone.
Other considerationsNone.
RecommendationEnsure that all machines and measurement instruments are calibrated regularly according to the manufacturer’s instructions.
Trade off between clinical benefits and harmsMachines need to be regularly calibrated to ensure the correct measurements are being obtained.
Economic considerationsThere are costs associated with the machines calibration but an accurate measurement of clinical parameters could offset these costs.
Other considerationsNone.

4.7. Summary of recommendations on diagnosis of patients with OHT, COAG or suspected COAG

The recommendation marked with an asterisk (*) is the result of the merging of other recommendations in previous sections in this chapter.

  • * At diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT all of the following tests:
    • intraocular pressure measurement using Goldmann applanation tonometry (slit lamp mounted)
    • central corneal thickness (CCT) measurement
    • peripheral anterior chamber configuration and depth assessments using gonioscopy
    • visual field measurement using standard automated perimetry (central thresholding test)
    • optic nerve assessment, with dilatation, using stereoscopic slit lamp biomicroscopy with fundus examination.
  • Adopt professional /Department of Health guidance to reduce the risk of transmitting infective agents via contact tonometry or gonioscopy.34,97,127,129.
  • Use Van Herick’s peripheral anterior chamber depth assessment as an alternative to gonioscopy if clinical circumstances rule out gonioscopy (for example, when people with physical or learning disabilities are unable to participate in the examination).
  • Obtain an optic nerve head image at diagnosis for baseline documentation.
  • Ensure that all of the following are made available at each clinical episode to all healthcare professionals involved in a person’s care:
    • records of all previous tests and images relevant to COAG and OHT assessment
    • records of past medical history which could affect drug choice
    • current systemic and topical medication
    • glaucoma medication record
    • drug allergies and intolerances.
  • Use alternative methods of assessment if clinical circumstances rule out the use of standard methods of assessment (for example, when people with physical or learning disabilities are unable to participate in the examination).
  • Ensure that all machines and measurement instruments are calibrated regularly according to the manufacturer’s instructions.

One study includes three groups using different machines.

States patients were selected randomly but no other details are provided. It is also unclear whether the machines were recalibrated before each use.

The results show different sensitivities and specificities for the different groups.

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Expert opinion

Both studies are in a consecutively selected cohort of patients. In one study9 it is not clear whether Van Herick’s test was performed independently, within a reasonable time frame and in a masked fashion to gonioscopy. Both studies reported full test results for all patients.

Both studies are in patients from south-east Asia and the Indian sub-continent where the prevalence of closed-angles tends to be higher.

For gonioscopy there are variations between studies in type of gonioscopy lens and grading system used for classification of narrow angles. For Van Herick’s test one study9 uses a modified cut-off grade for of ≤ 25% of corneal thickness as indicative of narrow angles whereas the other study149 uses grade 1 <25% corneal thickness as indicative of narrow angles.

The study is in patients from the Indian sub-continent where the prevalence of closed-angles tends to be higher.

The study is in patients from south-east Asia where the prevalence of closed-angles tends to be higher.

The study is in patients from south-east Asia where the prevalence of closed-angles tends to be higher.

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Expert opinion. See also 4.4.1.1 for clinical evidence.

Not a full economic evaluation. Summary of effectiveness was based on expert opinion.

Expert opinion. See also 4.4.1.1 for clinical evidence

Summary of effectiveness was based on expert opinion.

This test is the accepted clinical standard. Other methods (e.g. experts comparing serial stereo disc photographs) are more accurate but impractical for routine use in the NHS. There was no evidence that alternative disc imaging techniques result in better patient outcomes. It was the opinion of the GDG that this is the most accurate method among the practical ones.

Stereophotography is not commonly available in clinical practice.

Copyright © 2009, National Collaborating Centre for Acute Care.

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