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Glaucoma: Beyond The Cup and Drops

2 CPD in Australia | 1CD in New Zealand | 5 March 2019

By Inez Hsing

Primary open angle glaucoma (POAG) is one of the most recognised forms of glaucoma, however there are numerous presentations of secondary glaucoma, many of which have associations with various other ocular and systemic disease. Given that these patients often require ongoing monitoring, a collaborative, shared care model between optometry and ophthalmology is beneficial in providing the best possible patient care.

LEARNING OBJECTIVES

1.  Identify common risk factors, various presentations and systemic and ocular conditions associated with secondary glaucoma,

2. Know current universal grading systems relating to glaucoma,

3. Be familiar with management of secondary glaucoma including surgical treatment, and

4. Identify factors that can contribute to a successful collaborative care model between optometry and ophthalmology.

Glaucoma is one of the leading causes of visual impairment and blindness in the world.1-4 The term glaucoma describes a heteronymous group of optic neuropathies characterised by structural damage to retinal ganglion cell axons at the level of the optic nerve head.5 The eventual result of this is progressive loss of the visual field unless treatment is initiated. The mainstay treatment for glaucoma remains the lowering of intraocular pressure (IOP).1,3,4,6

The following two case reports offer a brief insight into the current understanding of secondary glaucoma and options for treatment.

Case One

A 72 year old Caucasian male was referred for ophthalmological assessment and management of extensive dot and blot haemorrhages in the left eye.

The patient was asymptomatic, and vision was 6/6 in each eye with a hyperopic correction: R +1.50/-1.25x87, L +1.75/-1.25x80. IOPs were significantly asymmetric and markedly elevated in the left eye: R 18mmHg, L 34mmHg. Pachymetry measurements were within normal range: R 568 microns, L 545 microns.

Clinical examination confirmed a resolving left non-ischaemic retinal vein occlusion (CRVO) with fading intraretinal haemorrhages and early collateral vessels at the disc (Figure 1).

Figure 1. Optos ultra widefield fundus image of the patient’s left eye. Note the resolving intraretinal haemorrhages and the large cup-disc ratio with superotemporal thinning of the neuroretinal rim. Early collateral vessels were also noted to be developing at the optic disc.

 

There was no evidence of secondary cystoid macular oedema (CMO) or neovascularisation of the disc, retina, iris or angle on gonioscopy. Additionally, the anterior chamber angles on gonioscopy were graded as open with low risk of being occludable (Shaffer Grade 3 for 180 degrees, and Shaffer Grade 2 for 180 degrees in each eye). Table 1 and Figure 2 summarise the Shaffer grading system. Historically, this system measured an angle in degrees but a modified form in which a grade is assigned according to the most posterior structure seen is commonly adopted for clinical practicality.7

Table 1. The Shaffer gonioscopy grading system (adapted from Salmon, 20147)

 

Figure 2. The Shaffer gonioscopy grading system in illustrated form (adapted from Salmon, 20147)

 

Fundus examination showed cup-disc ratios of 0.6 in the right eye and 0.65 in the left, with subtle thinning of the superotemporal neuroretinal rim in the left eye. Digital calipers on spectral domain optical coherence tomography (SD-OCT) measured larger than average vertical disc diameters of R 2.08mm, L 2.30mm. Global retinal nerve fibre layer (RNFL) measurements were within normal limits at 119 microns in the right eye and 117 microns in the left, and there was no evidence of sectoral RNFL thinning in either eye (Figure 3).

Figure 3. The patient’s retinal nerve fibre layer (RNFL) measurements taken with HRA+OCT Spectralis (Heidelberg Engineering). Right eye data is displayed on the left, and left eye data on the right. Note the normal global RNFL thicknesses and no sectoral thinning in either eye.

 

24-2 SITA-Standard automated perimetry showed a full field on the right side with strong reliability indices. In the left eye there were scattered superior defects present, however it should be noted that there were 33 per cent false positives present, which may have influenced the field result (Figure 4).

Figure 4. The patient’s visual field test results presented in Humphrey SITA-Standard 24-2 form, originally performed on an Octopus 900 automated perimeter (Haag-Streit). Left eye data is top, and right eye data directly above. Note the higher number of false positives present in the left eye which may have influenced results.

 

Given the CRVO was resolving with no vision threatening sequelae (specifically, no CMO or secondary neovascularisation/neovascular glaucoma), no ocular treatment was indicated for the vein occlusion. There was a known history of treated systemic hypertension which was acknowledged as a risk factor for the CRVO, but no diabetes mellitus. The patient was also asked to undergo a sleep study to investigate the possibility of obstructive sleep apnoea (OSA). Based on the clinical findings and mild field defect in the left eye, the patient was diagnosed with early left side primary open angle glaucoma (POAG). A decision was made to initiate topical hypotensive therapy with a prostaglandin analogue. The patient was commenced on latanoprost 0.005% (Xalatan, Pfizer) every night to both eyes, and an IOP check with the clinical optometrist was scheduled for six weeks later.

At the review appointment, the IOP in the right eye had dropped to 14mmHg in the right eye (22.2 per cent reduction from baseline) and to 29mmHg in the left eye (14.7 per cent reduction from baseline). This was deemed insufficient, particularly for the left eye. After discussion with the treating ophthalmologist, the patient was transitioned to combination therapy in the form of latanoprost 0.005% + timolol 0.5% (Xalacom, Pfizer) every night in both eyes as there were no systemic contraindications to the use of a beta blocker agent (that is, no history of asthma or advanced cardiovascular disease). Additionally, the patient had undergone a sleep study and was found to have mild to moderate OSA (apnoea-hypopnea index (AHI) of 14.7) with mild oxygen desaturation. The recommendation from the respiratory physician was to implement lifestyle changes; specifically weight loss and avoiding a supine position when sleeping. A continuous positive airway pressure (CPAP) trial was recommended if these failed to address OSA symptoms.

A subsequent IOP check with the clinical optometrist six weeks later showed a further reduction of the IOP to R 12mmHg (33.3 per cent reduction from baseline), L 14mmHg (58.8 per cent reduction from baseline). However, the patient expressed intolerance of Xalacom due to ocular irritation and conjunctival hyperaemia. After further discussion with the treating ophthalmologist regarding alternative options, a decision was made to proceed with bilateral selective laser trabeculoplasty (SLT) treatment and Xalacom was subsequently discontinued. The IOPs in each eye remained stable and within target for three months following this. Eight months later, the IOP in the left eye had risen to 26mmHg while the IOP in the right eye remained in the low teens. Given the patient’s previous intolerance of Xalacom, topical hypotensive therapy was re-initiated in the form of preservative-free tafluprost 0.0015% (Saflutan, Mundipharma). The response to treatment was satisfactory and within target range, and the patient reported improved comfort with this preservative-free agent over Xalacom, albeit still with mild irritation on instillation.

At the following six month optometric review, the IOP in the left eye had risen again to 35mmHg. The IOP in the right eye had also become elevated to 20mmHg. Gonioscopy was repeated, which showed progression to primary angle closure (PAC) in the left eye (90 degrees of Shaffer Grade 2, 180 degrees Shaffer Grade 1, and 90 degrees slit angle only), which explained the significant elevation of IOP on this side. On the right side, 90 degrees of Shaffer Grade 3, 90 degrees of Shaffer Grade 2, and 180 degrees of Shaffer Grade 1 were observed (primary angle closure suspect, PACS). Additionally, best corrected vision had deteriorated to R 6/12, L 6/9 with associated bilateral myopic shifts (R -1.50D, L Plano/-0.75x80) due to fairly rapid progression of nuclear sclerotic cataracts. The patient was commenced on pilocarpine 2% to both eyes and bilateral YAG laser peripheral iridotomies were scheduled with the treating ophthalmologist.

YAG laser peripheral iridotomy was performed in a routine fashion. There was also discussion about the role of cataract surgery to both improve vision and to deepen the anterior chamber. A decision was made to proceed with cataract extraction surgery in combination with minimally invasive glaucoma surgery (MIGS) given the history of intolerance to topical medications. Cataract surgery was performed routinely in each eye (left then right) and iStent (Glaukos) trabecular micro-bypass devices were successfully placed into Schlemm’s canal at the time of surgery on each side. Four weeks following surgery, visual acuity had improved to 6/6 on each side. The patient had ceased all topical hypotensive medications two to three weeks prior to this visit, and IOPs had pleasingly remained within target range at 12mmHg in the right eye and 17mmHg in the left.

Discussion

This case highlights multiple ocular and systemic associations with glaucoma, as well as additional treatment options beyond topical medications.

A possible association between glaucoma and obstructive sleep apnoea (OSA) has been well documented in the literature.8-10 OSA is defined as repeated complete or partial obstruction of the upper airways during sleep that results in cessation of breathing and subsequently leads to hypoxia.8,11 The apnoea-hypopnoea index (AHI) measures the combined number of apnoeas (breaks in breathing of longer than 10 seconds) and hypopnoeas (shallow breathing) per sleeping hour and grades the severity of OSA based on this (Table 2).12

Table 2. Grading of OSA severity (adapted from Hensley & Day, 200512)

 

Several papers report a statistically significant higher incidence of OSA in glaucoma patients, and vice versa.8,9,13 Moreover, Yamada and colleagues10 recently found that in a group of 124 glaucoma patients, there was a greater rate of progression of visual field defects (measured by the mean deviation, MD) in those patients with OSA compared to those without OSA. Based on their statistical analysis, they concluded that the presence of OSA could in fact be a significant indicator of visual field defect progression.10

Table 3. The primary angle closure classification system as proposed by the International Society of Geographic and Epidemiologic Ophthalmology (ISGEO) (adapted from Foster et al, 200218)

 

While it is difficult to establish a true cause and effect relationship between OSA and glaucoma, it has been hypothesised that hypoxia and/or increased oxidative stress from OSA results in reduced ocular perfusion pressure (OPP) and is therefore a vascular risk factor for glaucoma.8-10 There has been sufficient evidence in the literature to indicate that all patients with glaucoma or ocular hypertension should be screened for possible OSA symptoms to determine if a formal sleep study is indicated.8-14 Conversely, patients with OSA should be counselled on the importance of undergoing regular eye examinations and being screened for glaucoma.13,14

It is interesting to note that this patient also originally presented with an asymptomatic central retinal vein occlusion (CRVO). Both OSA and elevated intraocular pressure have been found to be closely associated with CRVO.15,16 Additionally, Chen and colleagues17 found an increased risk of conversion to an ischaemic CRVO and development of secondary neovascular glaucoma (NVG) in patients with uncontrolled IOP. This highlights the importance of initiating prompt hypotensive treatment for CRVO patients presenting with elevated IOP, and ensuring they are closely monitored for development of NVG.

Another unique factor in this case was the development of a secondary contributor to the elevated IOP; specifically as the patient developed increasing nuclear sclerotic cataract he also progressed from PACS to PAC in the left eye. The commonly used classification for PAC was proposed by the International Society of Geographic and Epidemiologic Ophthalmology (ISGEO) and published by Foster and colleagues in 2012.18 This system is outlined in Table 3 and distinguishes between patients with glaucomatous optic neuropathy and those who are not yet exhibiting structural/functional glaucomatous changes.

In a similar vein to treatment of POAG, management of PAC includes medical, laser, or surgical treatment options. Given the patient in this case was already on a preservative-free topical hypotensive medication and had a history of intolerance to other glaucoma medications, it was a reasonable decision to pursue non-medical treatments. Because the PAC in the left eye was detected at an optometry visit, 2% pilocarpine was commenced until ophthalmological assessment could be performed. Pilocarpine is a cholinergic agonist which induces contraction of the pupillary sphincter and therefore opens the space between the peripheral iris and trabecular meshwork.2,19

Common non-medical treatments for PAC include prophylactic YAG laser peripheral iridotomy (LPI) and lens extraction (or lensectomy surgery).2,20 The main purpose of a laser iridotomy is to prevent pupil block by equalising the pressure between the anterior and posterior chambers.2 While peripheral iridotomy has a high safety and efficacy profile, a patent PI is unfortunately not fully protective against future development of primary angle closure glaucoma (PACG).2,19 Thus, there has been increasing argument that lens extraction should be considered as an earlier treatment option for PAC given that removal of the crystalline lens and insertion of an intraocular lens (IOL) is associated with the deepening of the anterior chamber depth (ACD) and opening of the anterior chamber angle (ACA).2,4,20

The Effectiveness in Angle-closure Glaucoma of Lens Extraction (EAGLE) study in 2016 was a multi-centre, randomised controlled study of 419 participants that investigated the impact of clear lens extraction in PAC patients versus ‘standard care’ (that is, LPI and/or medical treatment).20 The results were convincingly in favour of surgical intervention – patients who underwent lensectomy surgery had a mean IOP that was 1.18mmHg lower than the laser/medical cohort at three years. This was statistically significant and although clinically this difference appears to be small, there was an additional benefit noted for the lensectomy sub-group where only 21 per cent of subjects required ongoing medical treatment versus 61 per cent in the LPI group. There was also a decreased need for filtration surgery within the lensectomy group, and not unexpectedly, lensectomy had the additional benefit of improving visual acuity. Finally, the EAGLE researchers demonstrated that the cost-effectiveness ratio significantly favoured clear lens extraction over standard care.20

Given the patient in this case had already developed visually significant cataract in combination with PAC in the left eye, a decision was made to proceed with cataract extraction surgery and IOL insertion. The patient also had a documented history of early glaucoma as well as intolerance to topical medications and was therefore an appropriate candidate for combined cataract surgery and minimally invasive glaucoma surgery (MIGS). MIGS has been defined as “surgical procedures with an ab-interno approach, minimal trauma…good safety profile and rapid recovery.”3 It has been primarily indicated for mild to moderate glaucoma.1,3 MIGS devices can be classified based on the mechanism by which they work – trabecular devices like the iStent are placed in Schlemm’s canal to increase trabecular outflow; devices that encourage uveoscleral outflow are known as suprachoroidal devices; and sub-conjunctival devices allow drainage of aqueous into the subconjunctival space.1,3 While a full review of the various MIGS devices is beyond the scope of this article, a meta-analysis of clinical trials investigating the efficacy of various devices found that overall, MIGS has been associated with good reduction of both IOP and number of glaucoma medications.6

The iStent Study Group compared the results of cataract surgery alone (control group) with combined cataract surgery and iStent insertion (study group) in a group of 240 eyes with mild to moderate POAG.5 They investigated the proportion of patients who achieved an IOP of 21mmHg or less without topical hypotensive medications, as well as those who achieved an IOP reduction of greater than 20 per cent. In the study group who underwent combined surgery, 72 per cent of patients achieved an IOP less than 21mmHg with no medications at 12 months, versus 50 per cent in the control group. This benefit was also seen at the 24 month mark (61 per cent of patients in the study group versus 50 per cent in the control group). Additionally, 66 per cent of patients in the study group achieved an IOP reduction of greater than 20 per cent compared to 48 per cent in the control group. There was also a greater mean reduction of the number of topical hypotensive medications within the combined cataract surgery/iStent group of 1.4 medications versus 1.0 in the cataract surgery only group. There was no significant increase in adverse events following combined iStent/cataract surgery compared to cataract surgery alone. Thus, the authors concluded that “implantation of the [iStent] in patients undergoing cataract surgery provided clinically and statistically signi?cant improvements in the management of elevated IOP compared with cataract surgery alone, with a favourable safety pro?le and clinically signi?cant reductions in IOP and medication”.5

The use of MIGS in mixed mechanism glaucoma, where there is both an open angle (trabecular) and closed angle (pre-trabecular) component, similar to that described in this case, has also been investigated. Chansangpetch and colleagues4 assessed and highlighted the need to address both aetiologies. They conducted a retrospective study of 301 eyes divided initially into POAG versus mixed mechanism glaucoma. They further sub-divided each group based on treatment given – cataract surgery alone versus cataract surgery combined with iStent insertion. At the 12 month mark, they again found that combined cataract surgery and iStent insertion in patients with mixed mechanism glaucoma yielded greater success with respect to reducing topical hypotensive medications compared to cataract surgery alone.4

While MIGS has been a welcome addition for glaucoma management, the longevity of the beneficial effect is yet to be fully determined.1,3,4 In this case it was important to emphasise to the patient that he will require ongoing monitoring for possible re-elevation of his intraocular pressures, as well as progression or development of optic disc cupping, RNFL thinning, and visual field defects. There has been significant discussion over the last few years regarding the guidelines and requirements of a shared care, collaborative care plan between ophthalmology and optometry.21,22 Needless to say, prioritisation of patient care remains paramount.

Botha and colleagues23 described implantation of a “stable glaucoma clinic” in a busy ophthalmology clinic in Palmerston North, New Zealand. In this clinic, glaucoma patients were initially assessed by a consulting ophthalmologist and thereafter reviewed by clinical optometrists. Patients who demonstrated glaucomatous progression (as defined by a pre-determined criteria) were referred back to the consulting ophthalmologist. Over a two year period, this model significantly reduced delays in appointment times, which in turn allowed for earlier detection of uncontrolled IOP and disease progression.21 There were also more opportunities to encourage patient adherence to treatment and to provide patient education. They summarised that “an integrated collaborative team approach utilising appropriately credentialed optometrists working within a supportive supervised context provides a safe and effective solution to the chronic ophthalmic disease burden.”21

Similarly, having well established clinical guidelines, accurately identifying patients who are suitable for collaborative care, implementing appropriate timeframes for reviews, and ensuring there are open lines of communication between eye care practitioners involved in a patient’s care, have all been identified as critical factors for successful shared care models.22,23 Referral pathways such as those established by Glaucoma Australia further help to facilitate communication in collaborative care, and also serve as an important tool in optimising patient outcomes.24

Case Two

A 45 year old Vietnamese female was referred by her optometrist for further glaucoma assessment. She had originally presented for new reading glasses and was noted to have enlarged cup to disc ratios and a possible right inferior arcuate scotoma. There was a known family history of glaucoma – the patient reported both her mother and maternal grandmother had been diagnosed with glaucoma in their 50s, and her mother had undergone ‘laser treatment’ for this. The patient herself reported no symptoms and good health, with no reportable history of migraines, systemic hypotension, hypovolaemic injury or Raynaud’s Syndrome.

Visual acuity was 6/6 in each eye with a low hyperopic astigmatic refraction (R plano/-0.75x50, L +0.25/-0.25x115). Intraocular pressures of R 16mmHg, L 17mmHg were measured with iCare tonometry. Pachymetry showed significantly thinner than average central cornea thickness (CCT) of 471 microns in the right eye and 474 microns in the left.

Slit lamp examination showed minimal nuclear sclerosis. Van Herrick’s ratios were noted to be fairly small (approximately 0.2:1 temporally on each side). Gonioscopy showed Shaffer’s Grade 3 inferiorly and Grade 2 for the remaining 270 degrees in both eyes. There was a flat iris configuration noted on each side and this was confirmed on anterior segment optical coherence tomography (AS-OCT) (Figure 5).

Figure 5. A representation of plateau iris configuration (PIC) on anterior segment optical coherence tomography (AS-OCT). Note the shallow anterior chamber depth peripherally as opposed to centrally, and the steep angle of iris insertion (white arrow). Note, due to poor scan quality, the patient’s actual AS-OCT scan was not used – this image has been adapted from Chansangpetch et al, 2018.25

 

Fundus examination showed relatively normal sized optic discs (vertical disc diameters of 1.88mm in the right eye and 1.90mm in the left, as measured with SD-OCT digital calipers) and cup-disc ratios were R 0.6, L 0.7. Global retinal nerve fibre layer (RNFL) thickness was thinned in both eyes (74 microns in the right, and 82 microns in the left). Additionally, there was superotemporal RNFL thinning in each eye (Figure 6). 24-2 SITA-Standard automated perimetry was performed reliably and confirmed a repeatable inferior arcuate scotoma in the right eye (Figure 7).

Figure 6. The patient’s retinal nerve fibre layer (RNFL) measurements taken with HRA+OCT Spectralis (Heidelberg Engineering). Right eye data is displayed on the left, and left eye data on the right. Note the superotemporal RNFL thinning in each eye (right greater than left).

 

Figure 7. The patient’s visual field test results presented in Humphrey SITA-Standard 24-2 form, originally performed on an Octopus 900 automated perimeter (Haag-Streit). Left eye data is top, and right eye data directly above. Note the inferior arcuate scotoma in the right eye corresponding with the previously documented superotemporal retinal nerve fibre layer (RNFL) thinning, as seen in Figure 6.

 

Based on the clinical findings, a diagnosis of bilateral normal tension glaucoma (NTG) and plateau iris configuration (PIC) was made. Given the patient’s young age and strong family history of glaucoma, a decision was made to proceed with bilateral prophylactic YAG LPI treatment. Early topical hypotensive treatment was also initiated with a prostaglandin analogue (Xalatan, Pfizer). In light of the starting IOPs, a target pressure of 11-12mmHg was set for each eye (30 per cent reduction from baseline). Additionally, the patient was referred for magnetic resonance imaging (MRI) of the brain and orbits to exclude the possibility of compressive optic neuropathy or visual pathway lesions. A pressure check was scheduled for six weeks later with the clinical optometrist.

At the six week review, IOPs had dropped satisfactorily to R 10mmHg, L 11mmHg. The patient reported good compliance and tolerance with Xalatan. There were patent peripheral iridotomies on each side, and repeat gonioscopy showed widening of the anterior chamber angle in both eyes (Shaffer grade 3 for 360 degrees on each side). The MRI scan was reported to be normal. The patient was instructed to continue topical therapy and to undergo six monthly glaucoma reviews as part of a collaborative care model between the treating ophthalmologist and clinical optometrist in the practice.

Discussion

Plateau iris configuration (PIC) describes an anterior chamber where the central depth is relatively normal but is shallow peripherally due to a relatively flat iris that angles forward at the root of insertion and/or is positioned anteriorly.26,27 On gonioscopy, it is common to see a steep iris insertion into the angle at the last iris roll.28 After pupil block, PIC is thought to be one of the significant contributors to the development of PAC.29 While PIC describes the status of an angle prior to intervention, the condition ‘plateau iris syndrome’ is reserved for situations where the plateau iris configuration persists despite iridotomy treatment.28

Historically, PIC was thought to have been significantly underdiagnosed due to the subjective and skill-reliant nature of gonioscopy assessment.19,29 In recent times, ultrasound biomicroscopy (UBM) and AS-OCT have also been helpful in the diagnosis of PIC.19,25,26,28,29

Shabana and colleagues29 highlighted key features of PIC on anterior segment OCT imaging. Specifically they found that anterior chamber area and central anterior chamber depth (ACD) were greater in PIC compared to other forms of angle closure like pupil block. Additionally, lens vault (LV), a measure of the distance that the anterior crystalline lens extends beyond an imaginary horizontal between the scleral spurs (Figure 8), was relatively low in PIC, and iris thickness was relatively thick in PIC eyes compared to pupil block patients.

Figure 8. A schematic representation of how lens vault (LV) is determined on AS-OCT. The yellow line represents an imaginary horizontal connecting the scleral spurs.29

 

PIC has been reported to be more prevalent in females, and also tends to occur at a younger age19,30 and with a less significant degree of hyperopia compared to pupil block.28,30 Interestingly, while PACG has long been recognised as being more prevalent in the Asian population,26,29 Li and colleagues found that PIC in fact appeared in both European American and Asian eyes, and in patients both with and without glaucoma.26 They hypothesised that plateau iris may simply be an anatomical variant and not necessarily pathological.26 Additionally, their study found that the prevalence of plateau iris was similar between the European American and Asian cohorts.26 However, the latter group were found to have thicker irides which may account for the higher frequency of presentations of angle closure secondary to plateau iris in the Asian population.26 The finding of thicker peripheral irides in Asian eyes was later also confirmed by Verma and colleagues27 whose Singapore based study was made up primarily of PACG subjects of Chinese ethnicity. Etter and colleagues28 also found, in a small study in 2006, that 50 per cent of patients with PIC had at least one first degree family member with the same condition and they proposed a possible autosomal dominance inheritance pattern with incomplete penetrance. Given the small scale of their study, they proposed further investigations into subsequent generations to explore this idea further.28

Despite PIs, it is important to recognise that angle closure can still occur in patients with PIC, particularly as cataract progresses and/or secondary to mydriasis (either pharmacologically or under dim conditions).19,31 This can occur even years after successful iridotomy treatment.19 As mentioned previously, angle closure in the presence of a patent PI gives rise to the condition plateau iris syndrome.28,30,31 The importance of periodic monitoring with gonioscopy must be emphasised to these patients. Again, there is a potential benefit to collaborative care between optometry and ophthalmology in providing the best possible patient care – namely, ensuring patients maintain compliance with any ongoing topical medications and to promote understanding of their condition.

It is interesting to note that the patient in this case had significantly thinner central corneal thicknesses (CCT) in each eye compared to normal. There is strong evidence in the literature that thin CCT values are an independent risk factor for development of normal tension glaucoma (NTG) – thinner corneas may be a marker for inherent weaknesses in the trabecular meshwork and/or lamina cribosa, hence cupping of the optic discs may begin at a lower IOP in these patients than those with thicker CCTs, which in turn leads to the development of NTG.32,33 This highlights the importance of always checking pachymetry values when measuring IOPs. Additionally, CCT measurements may serve as an indicator for patients who would benefit from closer monitoring or earlier treatment.32

Doyle and colleagues also found that CCT measurements were lower again in NTG patients with other vascular risk factors such as a history of migraine, Raynaud’s Syndrome, hypotension or hypovolaemia, compared to those without these risk factors.33 Although the patient in this case had none of these vascular conditions, it does draw attention to the importance of asking specifically about these conditions during history taking.

Finally, this case also highlights the importance of having a low threshold of suspicion for systemic conditions that could masquerade as NTG. Given the patient’s young age and relatively low IOPs, it was important to exclude the possibility of a space occupying lesion along the optic nerve and visual pathway. Shah, Gordon and Stelzner34 reported a case of a 57 year old gentleman who was originally diagnosed with POAG but demonstrated progressive field loss despite good IOP control. A MRI conducted two years later identified a pituitary adenoma. Their case illustrated that visual field defects from pituitary tumours do not necessarily present with the typical bitemporal hemianopic defect, and delays of as long as 10 years in diagnosing compressive optic neuropathy have been reported.34 Thus, it is important that other potential causes are thoroughly investigated in atypical presentations of NTG and/or apparent progression of visual field defects despite good IOP control.

Conclusion

The two cases described in this article highlight presentations of secondary glaucoma and their association with various ocular and systemic conditions. While there is still no cure for glaucoma, there are many treatment options ranging from medical to surgical. Glaucoma patients require ongoing, periodic reviews to ensure good adherence to recommended treatments and screening for disease progression. When implemented with set guidelines and on appropriate patients, collaborative care models between optometry and ophthalmology can be highly successful in optimising patient care and long term outcomes. 

   

Inez Hsing graduated from Queensland University of Technology in 2008 with First Class Honours and a University Medal. She currently works as a clinical optometrist at the OKKO Eye Specialist Centre in Brisbane, Queensland. Ms Hsing has a particular interest in macular and vitreoretinal disease, and therapeutic management of anterior segment disease and glaucoma. She has served on the Optometry Committee for Glaucoma Australia since 2017.

   

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' A decision was made to proceed with cataract extraction surgery in combination with minimally invasive glaucoma surgery (MIGS) given the history of intolerance to topical medications '