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Clinical pearls in glaucoma.

In this article, the author shares practical insight and tips on managing patients with glaucoma.
Optometrists            COMMUNICATIONS    OCULAR          OCULAR
                                          EXAMINATION     DISEASE

Therapeutic opticians   KNOWLEDGE         OPTIONS

Dispensing opticians    OCULAR            OCULAR
                        EXAMINATION       ABNORMALITIES


Introduction

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.

The cornea

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 iris

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)

The lens

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.

New horizons

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)

The retina

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.

Intraocular pressures

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)

Visual fields

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.

Glaucoma drops

A summary of drops, side effects and contraindications is given in Table 1.

Conclusion

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.

Exam questions

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.

References

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

Learning objectives

* 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
Author:Bowers, Susan
Publication:Optometry Today
Date:Oct 1, 2017
Words:2706
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