Managing cataracts in diabetic patients
The literal meanings of cataract and diabetes are themselves interesting and amusing – ‘Cataract’ means ‘waterfalls’; diabetes means ‘excessive water falls’ (excessive urination). Diabetes has implications in cataract management and vice versa. In this article, we discuss in brief these implications without much jargon.
The eye is always compared to a camera (though it should be the other way round). Just as the lens in a camera focuses on objects, the crystalline lens in our eyes focuses for various distances.
Now, let us take a closer look at the structure of the lens. We can compare the structure of a lens to that of a mango. The outer covering (skin) is called ‘capsule’. The front part of the capsule is ‘anterior capsule’ and the back part ‘posterior capsule’. The central (seed) portion is the ‘nucleus’ and the surrounding portion (pulp) is called as ‘cortex’. The nucleus thickens with age. It is very soft in younger people and as the person becomes older, it correspondingly becomes harder.
Any opacity or cloudiness in this crystalline lens is called ‘cataract’. Depending on the location of cataract, it is classified into various types. The most common types of cataract are ‘Nuclear sclerotic cataract’ in which the nucleus hardens and ‘Posterior capsular cataract’ in which the posterior capsule is opaque.
Cataract may occur because of age (senile cataract), injury (traumatic cataract), by birth (congenital cataract), due to diseases like diabetes (diabetic cataract) or various other reasons.
The symptoms of cataract depend on the amount of cataract and the position of cataract. Early cataracts don’t cause any visual problems.
Nuclear sclerotic cataracts may cause changes in the glass power, usually a myopic shift, i.e. the patient’s power becomes more minus. This is beneficial to some patients since their near vision becomes clear even without glasses. This is called ‘second sight’. But this is only temporary because the distant vision will become worse with more hardening.
Posterior capsular cataracts cause visual symptoms even in early stages, since they occur in the centre of the lens. They cause intolerable glare, especially during night driving. (Imagine driving at night wearing a glass, which has scratch marks right in the centre). Posterior capsular cataracts are more common in diabetics, even in younger individuals.
As the cataract progresses the visual symptoms become worse. The clarity of vision becomes worse.
When the cataract matures, the patient will hardly be able to see his/her own fingers.
The treatment of cataract is essentially surgical. There is no proven medical treatment for cataract. We, as Indians, should be proud of the fact that cataract surgery was invented by ancient Indians. The cataract is removed surgically and is replaced with an artificial intraocular lens.
The cataract surgery was done manually earlier, which was replaced by a procedure called as ‘Phacoemulsification’. In phacoemulsification, the eye is entered through a small, self-sealing incision (2-3mm) in the cornea (black part of eye); a small opening (around 5mm) is made in the anterior capsule of the lens (remember the front portion of the mango skin!); the hard nucleus is broken into pieces using a ultrasound probe; the broken nuclear pieces and then the remaining cortex is aspirated through the same probe. Into the remaining bag, an artificial intraocular lens (5-6mm in size) is inserted. Since this lens is foldable, it is able to enter through the smaller incision.
Though very simple to explain, a lot of expertise and technical finesse is required to perform this procedure.
Nowadays, phacoemulsification is performed under topical anaesthesia itself (only anaesthetic drops are applied to numb the eyes; no injections are given).
Cataract surgery is one of the most commonly performed procedures (in the whole body) and also one with the most successful outcome. Intraocular lens is the most commonly implanted artificial implant in the body. Hence one need not have any unnecessary fears regarding cataract surgery.
Then the subsequent question rises, when to plan for the cataract surgery? The timing of surgery is purely subjective, i.e. it depends on the visual needs of the patient and thus varies from patient to patient.
The general consensus is to choose the option of surgery when you find that your day to day activities are affected by cataract.
The other indication for cataract surgery, especially in a diabetic, is when visualisation of the retina is precluded by the presence of cataract.
Let us take a look at the implications of diabetes on cataract and vice versa.
1. Diabetic patients have an earlier incidence of cataract than the general population. Studies indicate that in patients with Type-I DM, there are structural changes in the crystalline lens. Hence these patients are more prone to develop cataract in younger age itself.
2. As we have seen earlier, posterior sub capsular cataract is more common in diabetic patients; it is sometimes referred to as ‘Diabetic cataract’. Since this type of cataract is central in position, it causes glare and early visual difficulties and may need early surgical intervention.
3. In patients with dense cataracts, visualization of the retina (the sensitive back part of the eye, equivalent to the film in a camera) becomes difficult.
Diabetic retinopathy can lead to irreversible loss of vision. Hence, in patients with higher risk of diabetic retinopathy, early surgery might be necessary, even if the patient doesn’t have significant visual difficulties.
4. During cataract surgery, the patient’s glycemic control should be in normal range. Patients with kidney disease, heart disease or foot infection should be assessed well before taking them up for surgery.
Rapid preoperative glycemic control is not desirable.
Though nowadays cataract surgery has become a day care procedure, it is preferable to admit a diabetic patient for at least a day to monitor the glycemic control.
5. Cataract surgery can worsen the progression of diabetic retinopathy, especially diabetic macular oedema (swelling of the centre point of the retina).
Hence detailed evaluation of the retina and treatment, if necessary, should be done before cataract surgery.
6. The intraocular lens to be implanted has to be chosen properly, since some types of lenses may interfere with treatment of diabetic retinopathy later.
7. After the surgery, patients have a general tendency to relax. Glycemic control during postoperative period is very essential for good healing and prevention of infection. So monitoring glucose levels during this period is equally important.
Cataract surgery in a diabetic patient is not the responsibility of the ophthalmologist alone. It should be a team work involving the ophthalmologist, diabetologist, nephrologists and even the podiatrist.
Everyone in this world has a ‘right to sight’, let not diabetes deprive one of this right. Have a clear view about diabetic eye diseases and in turn, have a clear view of the world.
Source: Dr. John Benno D.O., Consultant Opthalmologist. M.V.Hospital for Diabetes & Prof. M.Viswanathan Diabetes Research Centre
Image: Getty Images