Cataract, the opacification of the clear crystalline lens is one of the most commonly dealt with ocular conditions that an optometrist will encounter in practice. For most patients, it is a result of the natural ageing process (although other causes do exist) and with an increasingly elderly population, patients that either require cataract surgery or have undergone it, are growing in number. Statistics from the Royal College of Ophthalmologists show that approximately 330,000 cataract operations are carried out on the NHS each year.
This series will take a look at the morphology of cataract, how it affects vision and discuss the referral pathways for surgery. The second and third part will cover the patient pathway, from preoperative assessment through to surgery and beyond, looking at aspects of treatment and postoperative complications.
Risk factors for acquired cataract
Cataract is a multifactorial disease, with oxidative stress, medication, physical trauma, co-morbidities and increasing age all being factors. Around the fourth and fifth decade of life the lens becomes harder, scatters more light and changes colour, taking on a more yellow and then brown hue (Figure 1).
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This eventually leads to visual disability requiring lens extraction, and replacement with an intraocular lens (IOL) implant to restore vision. Cataract surgery is seen as commonplace in the developed world, with highly predictable outcomes and low complication rates. It may therefore come as a surprise that despite this, it is still the world’s leading cause of blindness (51 per cent)1 due to the lack of access to eye care in developing countries.
The World Health Organization (WHO) report on cataract published in 2001 makes an interesting read.2
‘Over the next 20 years, it is estimated that the world’s population will increase by about one third…..the number of people over 65 years of age will more than double…..will lead to a doubling in the amount of cataract, visual morbidity, and need for cataract surgery. The current 20 million people with severely reduced vision of 3/60 or worse as a result of cataract will have swelled to 40 million by the year 2020.’
Age is the greatest risk factor and unfortunately, it is not preventable. The prevalence of cataract doubles with every decade of life after the age of 40, so that by age 90, everyone is affected.3 However other risk factors often accumulate with age and in some cases, could be modified to try and delay the onset of cataract and thus reduce the need for surgical intervention.
Cataract occurs earlier on in life in developing countries, possibly due to the fact that many are in areas of high incident UV light, with studies showing visually significant cataract occurring up to 14 years earlier in India than in the US.4,5 Studies show that UVB radiation is a risk factor in age-related cataract, as is diabetes, corticosteroid use, smoking and alcohol consumption.6-10 Studies in the UK have also found that genetics play a role in cataract formation. Roughly 50 per cent of nuclear cataract and 66 per cent of cortical cataract have hereditary factors, which also correlates with the findings of population based studies.11-14
Congenital cataract
Cataract can also be congenital and may or may not be associated with birth defects or syndromes. Unilateral congenital cataract tends to be sporadic and associated with abnormal ocular conditions, trauma or maternal infections such as Rubella. Bilateral cataracts are often inherited and associated with other diseases such as hypoglycaemia, trisomy 21 (eg Down’s syndrome), infectious diseases (eg, toxoplasmosis, rubella, cytomegalovirus, herpes simplex) and prematurity.
If a congenital opacity lies on the visual axis, it is considered visually significant as it may lead to visual disability. However if the cataract is small, in the anterior portion of the lens, or in the periphery, no visual loss may be present and surgery may not be indicated until age-related changes start to occur. For example, the patient whose blue dot cataract is shown in Figure 2 did not suffer any visual disability until over 45 years of age. Blue dot cataract is hereditary, autosomal dominant and bilateral. It is very picturesque to look at, with the opacities appearing a bluish colour when viewed with a slit lamp.
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Y sutures
These suture lines (Figure 3) can sometimes be seen in young healthy eyes and are structures that form following the growth of the anterior and posterior lens fibres of the foetal lens and can be recognised from approximately eight weeks gestation. Interestingly, the anterior sutures are in the shape of a Y and the posterior sutures are an inverted Y. These are rarely visually significant.
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Cataract can also be secondary to trauma, ionising radiation and intraocular inflammation and can have an interesting appearance. The cataract shown in Figure 4 was acquired after a squash ball injury.
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Classification of cataract
While cataract is a rather inconvenient condition for the patient to have, when viewed with a slit lamp a cataract can be very interesting to look at. A good photo of a patient’s cataract can speak volumes in terms of explaining the condition and the accompanying symptoms. Patients find photos of their own cataract fascinating and it can be a great way of engaging with your patients on a more personal level. Slit lamp examination through a dilated pupil provides better visualisation of the cataract and enables easier classification.
Cataract is commonly classified according to where the opacification occurs within the lens structure ie morphological classification; cortical, nuclear or subcapsular. If there are opacities present in more than one morphological location it is described as mixed (Figure 1). It can also be classified according to cause; congenital or acquired (age-related, toxic, traumatic, iatrogenic).
Cortical cataract
These are the most common of the age-related cataracts and are also associated with diabetes.15 They begin to form when opaque areas appear in the deep lens cortex. These are filled with small vesicles and contain abnormal amounts of cross-linked proteins, cholesterol and phospholipids. Mechanical ruptures occur between affected and non-affected areas, creating fluid clefts and lamellar separations, giving the cataract its characteristic spoke-like appearance16 (Figure 5).
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Shear stress between the hardening lens nucleus and the lens cortex during accommodation may also be a contributory factor.17 Patients presenting with cortical cataract may complain of glare-related problems and are more likely to have a hypermetropic shift due to the periphery of the lens becoming more thickened, resulting in a more negatively powered crystalline lens.
Nuclear cataract
The fibres on the anterior and posterior lens surface continue to proliferate throughout life, pushing older fibres towards the centre of the lens. This leads to a gradual thickening and yellowing of the lens nucleus (Figure 6), which is often accompanied by a myopic shift in the patient’s refractive error. Patients with this nuclear sclerosis often notice that they no longer need their reading spectacles for close work and may have some have some colour confusion between similar hues (eg navy blue and black).
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The progressive loss of lens transparency leads to a decrease in contrast sensitivity and ultimately visual disability, as patients report needing more light to see and difficulty in performing low contrast visual tasks. It is also well documented that smoking increases the risk of age-related cataracts and in particular, nuclear sclerosis.18 Brunescent cataract (Figure 7) is a type of very mature nuclear cataract that has become much darker as the nucleus has expanded resulting in a much ‘harder’ cataract.
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Posterior subcapsular cataract
Opacities within the lens capsule are called subcapsular cataracts and can be located within the anterior or posterior lens capsule, although the latter are more commonly seen. Posterior subcapsular cataract (Figure 8) is associated with diabetes,15 steroid therapy19 as well as age. As these cataracts frequently lie toward the nodal point behind the lens, a small opacity can have quite a profound effect on visual quality due to significant glare symptoms whilst high contrast acuity may not be affected.
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Anterior opacities are more associated with age and amiodarone therapy,20 but the vision is not usually significantly affected.
Lens vacuoles
Vacuoles are clear, spherical fluid-filled spaces within the lens cortex (Figure 9). There is a positive correlation between the presence of lens vacuoles and the incidence of visually significant cataract requiring cataract surgery within 10 years.21 They tend to occur in isolation and appear to have minimal effect on vision, although they can also be a component of posterior subcapsular cataract.
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Referral for cataract surgery
The treatment for cataract is surgery and IOL implantation, but this does not need to be carried out unless the cataract is significantly affecting vision. Most patients in the UK will have their cataract surgery carried out under the NHS and so at what point should a patient be referred?
Referral for surgery is considered to be appropriate if cataract affects a patient’s ability to carry out daily activities such as reading, driving or looking after someone. There are no national guidelines that state a visual acuity threshold for NHS cataract surgery, although individual NHS Clinical Commissioning Groups (CCGs) have their own criteria outlining when cataract surgery should be offered. Private health insurers do not have visual acuity stipulations either, but a patient does need to be diagnosed with cataract by an ophthalmologist and given an opinion as to whether surgery is warranted.
Referral criteria
The Department of Health commissioned a report in 200022 which led to a dramatic change in the way cataract services were delivered in the UK. Waiting lists dramatically decreased due to more streamlined patient referral pathways and increased patient throughput in NHS units. It steered away from recommending a visual acuity threshold for NHS surgery, but it did lay down the following criteria for referral:
- The cataract, as the main cause, affects the individual’s sight
- The reduction in the patient’s sight has a negative impact on their quality of life
- The patient understands the risks and agrees to have surgery.
However, according the Royal College of Ophthalmologists, a perception exists among some commissioners that cataract surgery is being undertaken too readily on people without significant visual disability, even though little evidence has been presented to support this view. Unfortunately, this has led to some CCGs imposing thresholds for cataract surgery which are based on visual acuity, outside of which they will not fund the procedure.
A wide variation in policies exists, ranging from no restrictions to a refusal to fund surgery until visual acuity has dropped to 6/12 for first-eye surgery or 6/36 for second-eye surgery. Although patients who do not meet the threshold criteria will be considered on a case by case basis, this can be bureaucratic and time-consuming.
Having looked at the restrictive criteria of several CCG areas, the majority appear to have based their criteria around the threshold of a best-corrected visual acuity of 6/12 or worse in the affected eye and stipulate that visual symptoms are impairing the patient’s lifestyle. Examples of this include where reduced vision is:
- Affecting ability to drive
- Substantially affecting ability to work
- Substantially affecting ability to undertake leisure activities such as reading, watching television or recognising faces.
- Significantly increasing the risk of falls.
Some CCGs also provide some exceptions for where the acuity is better than 6/12 in the worse eye such as:
- Cataract is affecting the clinical management of other conditions eg glaucoma, diabetic retinopathy
- Working in an occupation in which good visual acuity is essential eg watchmaker, surgeon
- Significant anisometropia and intolerance to prescribed spectacles after first eye cataract surgery
- Some other significant impact on their quality of life, as a result of visual symptoms which must be documented in the referral.
An example of the latter is if a patient has posterior subcapsular cataract which may only reduce visual acuity slightly, but could cause disability glare in certain conditions that would make it unsafe to drive.
The Gloucestershire Cataract Direct Referral Scheme has a more patient-centred approach and considers visual acuity alongside clinical factors and perceived severity of visual impairment. When a patient’s cataract becomes visually significant, the optometrist uses a Cataract Assessment Questionnaire (CAQ) (Figure 10) to score a patient’s need for referral. The CAQ has three scoring sections, with the visual acuity of both eyes tabulated like a mileage chart. The optometrist reads off the score that correlates with the distance corrected acuity level for each eye. For example, a patient with 6/9 in one eye, and 6/12 in the other would achieve a score of four. Near vision is also allocated a score.
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Clinical considerations such co-morbidities are factored in and a posterior subcapsular cataract on its own would score five points. The final section scores the perceived difficulty of certain tasks (driving, reading etc) due to cataract-induced visual loss. Patients meeting the threshold score of 10 or more may bedirectly referred through a fast-track system. Patients with a lower score can also be referred if the optometrist feels that there is valid reason, and that this is documented on the referral form. While this approach appears to discriminate more reliably between people who need cataract surgery and those who do not, it is yet to be validated and universally adopted.
Referral pathways
Following the Government’s ‘Choose and Book’ initiative in 2005, many direct referral schemes were set up across the country, which improved patient access to cataract surgery. Optometrists were able to directly refer using a C1 form to a cataract surgery provider. The optometrist was then paid an enhanced fee for including the patient’s medical and social considerations for surgery on the referral form, and for their consultation time to go through the ‘Patient Choice’ information with their patients.
From April 1 2014 the responsibility for commissioning of optometry community services passed from NHS England and its Primary Care Trusts to CCGs. Sight tests were not affected as they are commissioned nationally, but community services may only be provided to a patient if the patient’s GP belongs to a CCG which commissions a community service. Each CCG has its own criteria for cataract surgery referral and chooses the method by which referrals must be made. Therefore, different pathways for cataract referral exist across the UK, with some areas being able to directly refer a patient to a hospital of the patient’s choice. Many CCGs have ‘rolled over’ direct referral contracts and will still fund direct referrals from community optometrists whereas in others, direct referral schemes have been decommissioned and all referrals must go through the GP on a GOS18 form.
This can be very confusing if an optometric practice serves a community where its patients’ GPs can belong to one of several CCGs. As confusion can reign, it is not surprising that in some cases, GPs have returned GOS18 forms and requested that the patient be referred directly. Other GPs are dealing with an increased demand for cataract surgery referral and may not consult the patient prior to referring on to a local cataract surgery provider. However, as cataract surgery is elective, the patient does have a right to choose and so the GP must have that discussion about Patient Choice with the patient. Not all patients are aware of this and will simply be referred on for surgery without having any say in where they would like their surgery to be carried out.
Access to cataract surgery
There are significant variations in the rates of cataract surgery between different areas of the country, not all of which can be attributed to known demographic factors. In 2013, the RNIB published a campaign report on cataract surgery entitled ‘Surgery Deferred. Sight Denied’ which highlighted the variance in cataract service provision across England.23 The figures are quite startling with South Reading CCG providing only 267 cataract surgery episodes per 100,000 population in 2012/13 compared to the 1,147 provided by Flyde and Wyre CCG. The report notes that although there is no direct correlation between restrictive referral criteria (in operation by approximately 50 per cent of PCTs/CCGs) and number of cataract surgery episodes, 17 of the 25 CCGs which have had the greatest year on year decline in episodes over a four-year period, have imposed restrictive criteria.
As a managing optometrist, it is crucial to understand that the service provided to a patient is not dependant on the location of the optometric practice, but by the location of the patient’s GP. This may result in some inequality of access to cataract surgery, but unfortunately, this is beyond the optometrist’s control.
Model answers
Correct answer is in bold text
1 Which of the following types of cataract results in maximum visual impact with minimal morphological appearance?
A Nuclear sclerosis
B Cortical
C Anterior subcapsular
D Posterior subcapsular
2 Which of the following is not a modifiable risk factor for cataract formation?
A Age
B smoking
C Ultraviolet radiation
D Infra-red radiation
3 Which of the following infections is not associated with congenital cataract?
A Rubella
B Toxoplasmosis
C Adenovirus
D Herpes simplex
4 Which of the following types of cataract is most likely to cause a hypermetropic shift?
A Cortical
B Nuclear
C Polar
S Posterior subcapsular
5 Which of the following types of cataract is most likely to be related to smoking?
A Cortical
B Nuclear
C Polar
D Posterior subcapsular
6 Which of the following statements about cataract referral is true?
A Referral is appropriate if the reduced vision may represent a danger to the patient or others
B Impact upon ability to contiue in a certain occupation is not relevant
C Glare may have a significant impact on vision and not on high contrast acuity chart measurements
D Different CCGs may have different criteria for treatment
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References
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2 G Brian, H Taylor. Cataract blindness – challenges for the 21st century. Bulletin of the World Health Organization, 2001; 79: 249–256.
3 McCarty CA, Keeffe JE, Taylor HR. The need for cataract surgery: projections based on lens opacity, visual acuity, and personal concern. British Journal of Ophthalmology, 1999; 83: 62–65.
4 Chaterjee A, Milton RC, Thyle S. Cataract prevalence and aetiology in Punjab. British Journal of Ophthalmology, 1982; 66: 35–42.
5 Kahn HA et al. The Framingham eye study: I. American Journal of Epidemiology, 1977; 106: 17–32.
6 Taylor HR et al. Effect of ultraviolet radiation on cataract formation. New England Journal of Medicine, 1988; 319:1429–1433.
7 Klein BEK et al. Cigarette smoking and lens opacities. The Beaver Dam Eye Study. American Journal of Preventive Medicine, 1993, 9: 27–30.
8 Cumming RG, Mitchell P. Alcohol, smoking and cataracts: the Blue Mountains Eye Study. Archives of Ophthalmology, 1997; 115: 1296–1303
9 West SK et al. Sunlight exposure and risk of lens opacities in a population-based study. The Salisbury Eye Evaluation Project. JAMA, 1998; 280: 714–718
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11 Hammond CJ et al. Genes and environment in cortical cataract: the Twin Eye Study. Investigative Ophthalmological and Visual Science, 2000; 41: 2901.
12 Heiba IM. Evidence for a major gene for cortical cataract. Investigative Ophthalmological and Visual Science, 1995; 36: 227–235.
13 Heiba IM. Genetic etiology of nuclear cataract: evidence for major gene. American Journal of Ophthalmology, 1993; 47: 1208–1214.
14 McCartyCA. The epidemiology of cataract in Australia. American Journal of Ophthalmology, 1999; 128: 446–465.
15 Pollreisz A, Schmidt-Erfurth U. Diabetic Cataract—Pathogenesis, Epidemiology and Treatment. J Ophthalmol, 2010; 608751. doi: 10.1155/2010/608751. Epub 2010 Jun 17.
16 Vrensen GF. Early cortical lens opacities: a short overview. Acta Ophthalmol, 2009; Sep; 87(6):602-10. doi: 10.1111/j.1755-3768.2009.01674.
17 Pau H. Cortical and subcapsular cataracts: significance of physical forces. Ophthalmologica, 2006; 220(1):1-5.
18 Ye J1, He J, Wang C, Wu H, Shi X, Zhang H, Xie J, Lee SY. Smoking and risk of age-related cataract: a meta-analysis. Invest Ophthalmol Vis Sci, 2012; Jun 22;53(7):3885-95. doi: 10.1167/iovs.12-9820.
19 Urban RC Jr, Cotlier E. Corticosteroid-induced cataracts. Surv Ophthalmol, 1986; Sep-Oct;31(2):102-10. Review.
20 Flach AJ1, Dolan BJ. Progression of amiodarone induced cataracts. Doc Ophthalmol, 1993; 83(4):323-9.
21 Tan AG, Mitchell P, Rochtchina E, Hong T, Cumming RG, Wang JJ. Lens retrodots and vacuoles and their associations with the prevalence and incidence of age-related cataract. Eye (Lond), 2012; Apr;26(4):568-75. doi: 10.1038/eye.2011.349. Epub 2011 Dec 23.
22 Action on Cataracts. Good Practice Guidance. Department of Health. January 2000.
23 RNIB campaign report. Variation in cataract service provision across England. July 2013.
Michelle Hanratty is senior optometrist at Optegra Birmingham Eye Hospital and an examiner for the College of Optometrists