Clinical pearls in glaucoma.
Optometrists COMMUNICATIONS OCULAR OCULAR EXAMINATION DISEASE Therapeutic opticians KNOWLEDGE OPTIONS Dispensing opticians OCULAR OCULAR EXAMINATION ABNORMALITIES
This article brings together the author's clinical experience in the field of glaucoma along with findings from recent research outcomes. The author provides a range of practical tips to assist practitioners when examining patients with glaucoma.
When Goldmann developed the applanation tonometer he knew that the cornea wasn't infinitely thin so he estimated a typical corneal thickness of 520[micro]m. (1) As patients with normal tension glaucoma (NTG) typically have thinner than average corneas, actual intraocular pressure (IOP) readings should be higher than those indicated by applanation tonometry. (2) A leading glaucoma specialist at Moorfields, Gus Gazzard states: "There is no NTG just primary open angle glaucoma (POAG) with thin corneas." There are no nomograms to convert Goldmann tonometry pressures which take into account corneal thickness that are approved by NICE, as scleral rigidity is also a variable in this equation. (3) Thinner corneas, therefore, may mask cases of glaucoma. Many African-Caribbean/African Americans have thin corneas, which may mean their lamina cribrosa meshwork which supports delicate axons is thinner and flexes more with changes in IOP. (4) African-Caribbean/ African Americans also typically have optic discs which are larger than other racial groups. (5)
Patients with thicker than average corneas frequently record over 21mmHg, particularly with non-contact tonometers, and despite healthy optic nerves and normal visual fields are referred from primary care due to NICE guidelines, which in turn overstretches NHS resources. (6) Fortunately, many areas have local schemes in place to reduce the volume of unnecessary referrals reaching secondary care.
The drainage angle
The crystalline lens is one of the few parts of the body that continues to grow throughout life, which results in narrowing of the drainage angle. For small hyperopic eyes this can lead to acute closed angle glaucoma (CAG) attacks, but in fact 50% of patients have CAG present for years with limited symptoms such as brow pain at twilight. (7) Peripheral iridotomies (PI) can help to avoid closed angle attacks and a common approach is to put two holes in the iris at the 3 and 9 o'clock positions.
Generally, the widest part of the drainage angle is at the bottom and is shallowest at the top due to gravity, so putting the Pi's at the top is less effective. (8) When examining a patient, it is important to align the slit lamp beam horizontally and undertake a Van Herick assessment superiorly and inferiorly.
If patients have loose pigment from the iris, as in the case of pigment dispersion syndrome, it follows the circulation in the anterior chamber; fluid rises when close to the warmer iris and falls lower when near to the colder corneal endothelium. The deposition of pigment on the corneal endothelium follows this pattern resulting in the characteristic Krukenberg spindle. (9)
Clear lens extraction or early cataract surgery can help to remove any possibility of narrow angle glaucoma as modern implant lenses are one third of the thickness of an 80-year-old crystalline lens. (10) The patient can be safely discharged into the community after this surgery. (11)
Selective laser trabeculoplasty (SLT) stimulates macrophages in the drainage angle to phagocytose debris in the angle. The author has seen a response to this treatment within two weeks, but in clinic the response at three months is a key review period to evaluate if IOPs have lowered. (12) The effect seems to be better with high IOPs and appears less effective in cases of NTG. (13) A good response to SLT treatment can reduce the number of different drops that a patient may need to use and the technique is less invasive than previous interventions, namely argon laser trabeculoplasty. (14)
Viewing the anterior chamber angle requires gonioscopy. Inserting a gonioscopy lens is similar to the technique used for inserting a scleral contact lens. Instil a topical anaesthetic, put some gel on the lens, trying not to introduce any bubbles, ask the patient to look up then put in the lens at the bottom, then instruct the patient to look straight ahead and make sure the upper eyelid is over the gonioscopy lens. The top mirror gives the practitioner a view of the bottom angle.
The younger white population who are slightly myopic may present with lens zonules rubbing on the back of the iris causing pigment dispersion syndrome (PDS); (15) this results in iris transillumination, in a ring in the middle of the iris. To see this clinically the practitioner should centre the slit lamp beam in the centre of the pupil and observe the orange reflex through the holes in the iris.
Older female patients can present with moth eaten pupils and transillumination in a ring closer to the pupillary ruff. (16) They will typically have white proteinous deposits in two rings on the front of the crystalline lens--one forms when the pupil is dilated in dim illumination and the other smaller ring results from deposits when the pupil is more constricted in daylight. These rings disappear following cataract surgery and the condition is termed Pseudoexfoliation syndrome, which can result in pseudoexfoliative glaucoma (PXG). With PXG the pigment in the drainage angle is mixed with the white fluffy proteinous material giving the pigment in the angle an appearance of brown sugar when viewed during gonioscopy. (17) In PDS the pigment in the angle is black.
Plateau iris is when the iris has a 's' shape closing the drainage angle as the pupil dilates; this is different to the normal narrow angle and appears as a rolling iris on gonioscopy. These patients may need iridoplasty treatment using an Argon laser instead of the normal Nd:YAG laser. (18)
Iritis can lead to a fall in IOP due to reduced aqueous fluid production although the inflammatory cells produced can block the drainage angle leading to uveitic glaucoma. (19)
If through growth the lens becomes too big for the eye it can result in a condition termed phacomorphic glaucoma. If the crystalline lens leaks due to age or trauma, the contents are inflammatory and can lead to phacolytic glaucoma.
Cataracts can give a false impression of visual field loss although using the pattern deviation data on the output can help to distinguish between focal defects and a diffuse loss in sensitivity. Cataracts can be one of the side effects of having trabeculectomy surgery and the current trend is to extract them later, rather than undertaking both operations together. Trabeculectomy failure is less likely if the surgeon delays cataract surgery by two years. (20)
During cataract surgery, it is possible to simultaneously treat glaucoma with a variety of micro-invasive techniques such as using an iStent (see Figure 14). (21) Previously, surgeons would opt to insert two stents per eye but the cost has become prohibitive and many trusts prefer the use of one only. Research is ongoing to help improve the outcome of stent placement, (22) to try and understand why some cases achieve better results than others. (23) The iStent has just received NICE approval to be used during cataract surgery on patients with glaucoma.
Another micro-invasive approach to glaucoma management is the Xen Gel implant, which is being used in place of trabeculectomies with careful patient selection. (24)
If the patient has retinal surgery then both gas and silicone oil are inflammatory, causing a rise in eye pressure that must be managed for the rest of the patient's life. (25,26)
The optic nerve
NTG is thought to be due to poor perfusion pressure of blood to the optic nerve at night. (27) These patients are usually slender with low blood pressure. The cerebral spinal fluid pressure can rise at night when the patient is supine causing flexure of the optic nerve head lamina cribrosa resulting in damage to the axons. For this reason, it is suggested that NTG patients sleep on a 45-degree wedge to reduce this effect.
Presenting pressures are the measures taken before treatment is initiated. There is some diurnal variation so recording the time of day the IOP is taken is important. (28)
Target pressures may be different for each eye and are set to be achieved to slow down the glaucomatous progression as much as possible. They need to be reviewed if visual field loss is increasing or there is further optic nerve damage. One of the most useful ways to monitor this is to use glaucoma progression analysis on the Humphrey Visual Field Analyser--five visual field assessments are required to evaluate progression. (29)
The Humphrey visual field test is historically based on the original Goldmann points and the central points are not set where early glaucoma can occur. (30) This leaves us in the situation where both the 24-2 test to measure the 24-degree field and the 10-2 test to look at the central visual field are required to determine if there is any central field loss; this is very tiring for patients who often dislike doing visual field assessments. (31)
The author has created the following guide to help patients:
* We are going to measure how big your field of vision is
* Have a good look inside the big dish at all the little holes before we start because we need you to look at the large hole with the amber light straight ahead at the back of the dish, all the time and not look away
* Please don't look at the tiny flashing lights
* You can blink whenever you like
* If you see a light flash somewhere in the bowl, even if it is faint--press the button to tell us that you have seen the light
* If you miss a light flash don't worry, the machine will go back to that spot and show it to you again, and you have four chances to see it
* If you want to stop the machine, hold the button in and it will stop. When you release the button, the machine will start again
* If you press the button quickly the next light will come quickly. If you press the button slowly the next flash takes longer to come. You can drive the machine too fast if you keep pressing the button very quickly so take your time.
A summary of drops, side effects and contraindications is given in Table 1.
With the growth of enhanced services on the increase, optometrists are likely to become more involved in the co-management of patients with suspect or diagnosed glaucoma. The aim of this article has been to present a range of simple clinical tips to assist the practitioner in the management of glaucoma patients.
Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 10 November 2017. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.
CET points will be uploaded to the GOC within 10 working days. You will then need to log into your CET portfolio by clicking on 'MyGOC' on the GOC website (www.optical.org) to confirm your points.
Susan Bowers FCOptom, DipCLP, DipTpAS, DIpTpSP, DipTpIP, FAAO, FBCLA, Higher Cert Glaucoma
About the author
Susan Bowers works in the unstable glaucoma clinic at University Hospitals Coventry and Warwickshire NHS Trust and in the community in Coventry. She has the Certificate in Glaucoma and a Masters in Clinical Optometry from City University, and the Higher Certificate in Glaucoma from Moorfields/UCL. Ms Bowers is past president and fellow of the BCLA, a fellow of the American Academy of Optometry and the College of Optometrists.
Visit www.optometry.co.uk, and click on the 'Related CET article' title to view the article and accompanying 'references' in full.
Course code: C-56802 Deadline: 10 November 2017
* Be able to elicit relevant detail from glaucoma patients during history and symptoms (Group 1.1.1)
* Be able to appropriately assess the anterior segment in patients with glaucoma (Group 3.1.2)
* Understand key risk factors in glaucoma (Group 6.1.8)
* Understand the adverse effects that can arise with glaucoma drugs (Group 1.1.4)
* Be able to assess patients presenting with glaucoma using appropriate techniques (Group 2.1.2)
* Understand the use of a slit lamp for assessment of the anterior segment in patients with glaucoma (Group 3.1.2)
* Understand the management of patients with glaucoma (Group 8.1.3)
Caption: Figure 1 Above--iStent in situ; bottom--relative size of iStent
Table 1 Summary of drugs used to treat glaucoma Drug, strength and Trade name and Side effects and bottle size preservatives contraindications Betaxolol Betaxolol Beta blockers hydrochloride Benzalkonium Transient discomfort 0.5% 5mL chloride (BC), 25%, Disodium edetate tearing 5%, stinging. 0.25% 5mL (DE) conjunctival suspension Betoptic BC, DE and erythema, itching 0.50% 5mL boric acid (BA), BC and DE 0.25% unit dose Preservative free Carteolol Teoptic Photophobia, Hydrochloride BC anisocoria 1.0%, 2.0% 5mL Levobunolol Levobunolol BC, DE Decreased corneal Hydrochloride Sodium sensitivity. 0.5% 5mL metabisulphite (SM) corneal punctate epithelial erosions, 0.5% 5mL, 1.4% Betagan BC, DE, SM insomnia, depression, Polyvinyl alcohol allergic red eye 0.5% unit dose Preservative free, DE 30x0.4mL, 1.4% Polyvinyl alcohol Timolol maleate Timolol Risk of bronchospasm 0.25% 5mL BC (asthmatics and COPD) 0.1% gel 30x0.4g Tiopex bradycardia, 0.25% unit dose Preservative free impotence, reduced 30x0.2mL Timoptol LA gel exercise tolerance 0.25% or 0.5%, Benzododecinium in the elderly 2.5mL bromide Bimatoprost Lumigan Prostaglandins 100([micro]/ml 3mL BC Conjunctival 0.01% Single use hyperaemia, increased 300[micro]g/ml Preservative free eyelash growth, 0.03% 30x0.4mL itching Latanoprost Xalatan 50[micro]g/ml 2.5mL BC Latanoprost 30x0.2mL BC Monopost Preservative free, DE Tafluprost Saflutan Lens changes, 15[micro]g/ml Preservative free, DE dry eyes, transient 30x0.3ml blurring or burning, lid pigmentary deposits, changes in iris colour Travoprost Travatan Blepharitis, corneal 40[micro]g/ml 2.5mL Polyquad PQ-1 punctate epithelial Propylene Glycol erosions, hypertension, headaches, anterior uveitis, upper respiratory tract infections. Can be pro-inflammatory in CMO, reactivate herpes simplex Apraclonidine lopidine Sympathomimetics 0.5% 5mL BC alpha2 Aqonists 1.0% unlicensed for Preservative free Stinging/burning, glaucoma allergy, blurring Brimonidine tartrate Brimonidine Tartrate Conjunctival 0.2% 5mL BC erythema, dry mouth, 0.2% 5mL Alphagan headache, drowsiness, Neuro-protective BC fatigue, dizziness, in NTG gastro intestinal symptoms Acetazolamide Diamox Carbonic anhydrase 250mg tablet inhibitors 500mg powder for Diamox SR Electrolyte injection 250mg Sustained release disturbances. capsule metabolic acidosis, headache, fatigue. blood disorders. rashes Brinzolamide Azopt Bitter metallic 10 mg/mL, 5mL BC, DE taste, burning, dry eyes. Dorzolamide Dorzolamide Conjunctival 2% 5ml BC hyperaemia, (20mg/ml) Trusopt pain, diplopia, 2%, 5mL BC taste disorders, 2% Unit dose Preservative free depression. 60x0.2mL dizziness, shortness of breath, cough, dry mouth, chest pain Pilocarpine Pilocarpine Miosis, burning. 1%, 2%, 4%, 10mL hydrochloride, BC stinging, tearing. Single use minims Pilocarpine Nitrate induced myopia, 2% 20x0.5mL Preservative free ciliary spasm, conjunctival vascular congestion, follicular conjunctivitis, poor low light vision, retinal detachment Combined glaucoma drugs Bimatoprost and Ganfort For side effect see timolol BC separate drugs 300mg/mL and 5mg/mL, 3mL (also triple pack 3x3mL) Unit dose 30x0.4mL Preservative free Latanoprost and Xalacom timolol BC 50[micro]g/ml and Latanoprost and 5mg/mL, 2.5mL Dorzolamide BC Brinzolamide and Simbrinza brimonidine BC 1%, 0.2% 8mL Travoprost and Duotrav timolol 40pg/ml and 5mg/ Polyquad PQ-1, BA mL, 2.5mL (also Propylene glycol triple pack 2.5mLx3) Brimonidine tartrate Combigan and timolol 0.2% BC and 0.5%, 5mL Brinzolamde and Azarga timolol BC, DE 10mg/mL & 5mg/ mL, 5mL Dorzolamide and Dorzolamide and timolol timolol 2% and 0.5%, 5mL BC 5mL Cosopt BC Unit dose 60x0.2mL Preservative free Taptiqom 15pg/mL Tafluprost and and 5mg/mL timolol Unit dose 30x0.3mL Preservative free
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|Title Annotation:||Glaucoma: CET|
|Date:||Oct 1, 2017|
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