H40.011-023 Open-Angle Glaucoma Suspect, Low Risk

Glaucoma is an optic neuropathy showing distinctive changes in optic nerve morphology without associated pallor. The term “glaucoma” refers to a  group of chronic, progressive optic neuropathies that have in common characteristic morphologic changes at the optic nerve and retinal nerve fiber layer.

The glaucomas are associated with the following clinical features:

• Aqueous outflow restrictions
• Unphysiologic intraocular pressure
• Abnormal ocular perfusion
• Abnormal rate of apoptosis
• Progressive retinal ganglion cell loss
• Characteristic changes in optic nerve anatomy

Conclusion

Glaucoma is a diagnosis of exclusion.  According to the 2015 ICD-10 diagnosis codes, persons are considered open-angle glaucoma suspects based on the number of risk factors they possess.  Low-risk is one or two risk factors.  High-risk is three or more risk factors.  Commonly considered risk factors include:

• Positive family history for glaucoma
• Black or Hispanic race
• Elevated intraocular pressure
• Abnormal optic disc appearance (esp. vertical C/D changes)
• Thin central corneal thickness below 500 microns combined with elevated intraocular pressures

Additional risk factors not included in the ICD-10 listing include the following:

• Low blood pressure
• Sleeping / breathing disorders
• Diabetes
• Angle abnormalities / outflow restrictions
• Prior trauma to globe

For patients diagnosed as glaucoma suspects, there remains some controversy on whether unphysiologic intraocular pressure is the dominant factor involved in developing glaucomatous optic atrophy or if there is a secondary component such as compromised blood flow to the optic nerve head.

Functional Damage to the Visual System

1.  Associated visual field defects

• Reduction in retinal sensitivity
• Constriction of isopters
• Nasal steps
• Paracentral scotomas
• Arcuate scotomas
• Hemifield asymmetry
• Temporal changes in visual field patterns 
• Loss of central acuity

2.  Decreased color vision 

3.  Abnormal visual evoked potential

4.  Abnormal pattern electroretinogram

The main goal in a patient diagnosed as a glaucoma suspect is to accomplish the following:

• Identify patients at high-risk for developing glaucoma
• Establish a baseline of clinical findings for future comparative analysis
• Identify and exclude any oculosystemic conditions associated with open-angle glaucoma
• Consider medical treatment of high-risk patients to prevent or slow down the development of open-angle glaucoma

To obtain the information required to determine a clinical diagnosis of an open angle glaucoma suspect and prescribe a treatment program, the following service components of a medical eye examination should be performed:

•  Patient history
• General medical observation
• Gross visual field
• Pupillary examination
• External ocular examination with biomicroscopy
• Ophthalmoscopy

Patient History

• Patients will usually be asymptomatic in the early stages of glaucoma

Intraocular Pressure

• Measurements above 21 mm Hg
• Asymmetry above 5 mm Hg

Gross Visual Fields

• Normal
• Constrictions

Pupillary Examination

• A relative afferent pupillary defect (RAPD) may be present if one eye is more affected than the other

External Ocular Examination with Biomicroscopy

• Normal

Ophthalmoscopic Examination

• Cup-to-disc ratio > .40/.40
• Cup-to-disc ratio asymmetry > .20/.20
• Vertically elongated cup-to-disc ratios 

Patient is a 64-year-old black female with an optic disc appearance that is suspicious for glaucomatous optic atrophy.

• Cup-to-disc ratio = .75/.70 in the right eye
• Cup-to-disc ratio = .75/.70 in the left eye
• Normal neuroretinal rim
• Normal retinal nerve fiber layer

Retinal Scanning Laser

• Can show attenuation of the retinal nerve fiber layer
• Excavation of the optic disc

Visual Field Examination

Research has shown that over 50% of the nerve fibers in any given retinal nerve fiber layer bundle can be irreversibly damaged before any visual field loss occurs.  Depending upon visual fields to separate those patients with glaucoma from those without the disease would still miss a large number of patients.

For most patients with glaucoma, there appears to be about a five year interval between the loss of enough nerve fibers to create a visual field defect during a visual field examination.  Relying on visual fields alone to diagnose glaucoma could mean delayed treatment for your glaucoma patients and unnecessary loss of visual field in these people.

Visual field defects will depend on the severity of the stage

• No detectable visual field defect
• Mild reduction in retinal sensitivity
• Temporal changes in field patterns

Definite glaucomatous visual field defects

• Arcuate scotomas
• Paracentral scotomas
• Nasal steps

Gonioscopy

Electrodiagnostics

• Visual evoked potential testing evaluates the function of the afferent visual sensory system 
• Electroretinography evaluates the function of the retinal ganglion cells

Serial Tonometry

• Establish diurnal curve

Ultrasound Biomicroscopy (UBM) and/or Anterior Segment Imaging

• Determine iris configuration
• Evaluate anterior chamber anatomy
• Determine the mechanism of primary glaucoma 
• Determine the occludability of the angle

Refraction

• Measurement of visual acuity
• Measurement of visual function

Provocative Tests for Glaucoma

• Risk assessment for angle-closure glaucomas

Open-angle glaucoma suspects are classified based on the number of risk factors present.

• Low risk — One or two risk factors
• High risk — Three or more risk factors

Differential diagnosis will depend on if the damage is observed on the optic nerve or a visual field defect is present. Below is a list of possible differential diagnosis.

Optic Nerve Head

• Congenital and hereditary anomalies of the disc
• Ischemic optic neuropathy
• Compressive lesions of the optic nerve

Visual Field Defect 

• Pituitary tumors
• Ischemic optic neuropathy
• Vascular disease
• Drusen of the optic nerve
• Neurological condition

When initiating treatment, assume that the pre-treatment measurement of intraocular pressure (IOP) is the level that produced damage to the optic nerve.  If the IOP remained at this level, additional damage to the optic nerve would follow.

To treat glaucoma, an IOP level is identified below which further optic nerve damage is unlikely to occur.  This IOP level is the target pressure range and it is selected based on the following:

• Pre-treatment level of IOP
• The rapidity with which the damage to the optic nerve occurred, if that is known
• Patient age
• General health of the patient

Treatment should maintain the IOP at or below the target level.  The status of the optic nerve, visual fields, electrodiagnostics, and the retinal nerve fiber layer are monitored over time for evidence of stability or deterioration.  In the event of further damage, the target pressure range is reset to a lower level.

Pharmacologic Treatment

Select your initial medication based upon target pressure range, medical history, and ocular history.  If the initial medication fails to achieve the target pressure range within one month, discontinue the initial medication and substitute another.

If the second medication fails to achieve the target pressure, begin combination therapy by using two different medications.  If this strategy fails, you could add still a third class of glaucoma medications to the regimen.  With three different eye drops, non-compliance becomes common and laser surgery may be a better treatment option.

Prostaglandins are the most popular class of medications for glaucoma therapy due to their excellent efficacy, safety index and tolerability.  They flatten the diurnal curve significantly and achieve the greatest IOP reduction of any class of topical medication.

Classes of Glaucoma Medications

Prostaglandins

• Lumigan
• Travatan Z
• Zioptan
• Xalatan

Beta-Blockers

• Timolol
• Betagan
• Betimol
• OptiPranolol

Adrenergic Agonists

• Alphagan P 0.1% and 0.15%
• Brimonidine 0.2%
• Propine

Carbonic Anhydrase Inhibitors

• Azopt
• Trusopt

Cholinergic Agonists

• Pilocarpine
• Carbachol
• Echothiophate

Combination Glaucoma Medications

• Cosopt – carbonic anhydrase inhibitor / beta-blocker
• Cosopt PF – carbonic anhydrase inhibitor / beta-blocker
• Combigan – adrenergic agonist / beta-blocker
• Simbrinza – adrenergic agonist / carbonic anhydrase inhibitor

Changing the Treatment due to Side Effects

Prostaglandins

• Red eye
• Eye color change
• Excessive eyelash growth
• Uveitis
• Macular edema

Beta-Blockers

• Bronchospasm
• Pulmonary edema
• Heart failure
• Headache
• Weakness
• Depression
• Lethargy
• Itching
• Stinging
• Blurred vision
• Photophobia
• Loss of libido

Adrenergic Agonist       

• Red eye
• Allergic follicular conjunctivitis
• Dry mouth
• Drowsiness

Carbonic Andydrase Inhibitors   

• Sulfa allergy
• Red eye
• Ocular itching
• Metallic taste
• Paresthesia of fingers or toes
• Headache
• Blood dyscrasias
• Depression
• Loss of libido
• Impotence

Cholinergic Agonists      

• Red eye
• Induced myopia
• Reduced vision in low illumination
• Headaches
• Lens opacities
• Iris cysts
• Increased risk of angle closure
• Increased risk of retinal detachment
• Sweating
• Salivation
• Diarrhea
• Bradycardia
• Dyspnea

Docosanoids

• Eye color change
• Stinging
• Increase in periocular eyelid pigmentation
• Increase in upper eyelid sulcus deepening

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