Loay Nawaz Rahman
Imperial College Healthcare NHS Trust, London, United Kingdom
A cataract is a clouding of the lens which can lead to gradual reduction in vision and disturb every day activities such as driving and reading (1). The main symptoms include clouding or blurring of vision, glare, reduced night vision that is noticed when driving, haloes around lights and fading of colours.
There are various risk factors of which increasing age is the most significant one. Others include lifestyle factors such as diabetes, smoking and hypertension, previous ocular trauma or surgery and iatrogenic causes such as use of long-term corticosteroids (which can typically lead to a posterior subcapsular cataract) (2).
Types of cataract
Nuclear cataract
This is a cataract that typically affects the centre of the lens. It may cause near sightedness initially, but with time the lens can become more yellow causing clouding of vision.
Cortical cataract
This is a type of cataract which affects the cortex of the lens. It can present with white opacities at the edge of the lens which gradually extends to the centre.
Posterior subcapsular cataract
In posterior subcapsular cataract, there is opacification in the back of the lens. It can occur by itself or in combination with other types of cataract and commonly affects diabetic patient or those on long-term corticosteroids.
Congenital cataract
Congenital cataract may be present from birth or develop during childhood. It can be associated with conditions such as myotonic dystrophy, galactosemia, neurofibromatosis type 2 and rubella (1).
Cataract surgery
Cataract surgery is the most common surgical procedure in the Western world, where a cloudy lens is replaced by a clear artificial one (3).
Pre-operative considerations
Intraocular pressure (IOP)
Patients who undergo cataract surgery should have a normal pre-operative IOP or controlled glaucoma. If the patient has poorly controlled glaucoma, then a combined cataract-glaucoma surgery can be performed.
Use of alpha-blockers
Patients on an alpha-blocker such as tamsulosin or doxazocin are at risk of developing intraoperative floppy iris syndrome (IFIS) (4). This may limit the dilatation of the pupils using dilator drops and thus mechanical pupillary dilation, where hooks are used to pull the iris apart and widen the pupil, may be indicated.
Cataract Surgery Step-by-Step
Phacoemulsification is the most common method of cataract surgery, where the lens is broken down using ultrasonic energy and an intraocular lens (IOL) is inserted. It is usually performed under local anaesthesia (3).
Pupil dilation
The first step in cataract surgery is pupillary dilatation using dilator drops such as tropicamide. These are applied pre-operatively to allow sufficient time to achieve adequate dilatation.
Local Anaesthesia
Topical anaesthetic eye drops such as tetracaine 0.5% or proparacaine 0.5% are commonly used in cataract surgery. There is also the option to use anaesthetic injections such as a sub-Tenon injection, where anaesthetic agents are injected between the sclera and the Tenon capsule, a thin membrane that envelops the eyeball (5). Anaesthetic injections have the added benefit of allowing for muscle paralysis alongside achieving anaesthesia.
Exposure and corneal incision
The eyeball is exposed using a speculum which pulls the eyelids away. Corneal incisions are then made using a keratome for the insertion of surgical instrumentation. The incisions are performed in a way that allow self-sealing.
Viscoelastic injection
A viscoelastic substance such as sodium hyaluronate is injected into the anterior chamber of the eye to ensure that the intraocular pressure is maintained during surgery (6).
Continuous Curvilinear Capsulorhexis (CCC)
A window into the anterior capsule wall of the lens is created (anterior capsulotomy) in order to allow access to the lens. This involves using a needle or a small pair of forceps to create a circular opening (7).
Hydrodissection & Hydrodelineation
The outer layer (cortex) of the lens is separated from the lens capsule by injecting a fluid wave (hydrodissection). The outer soft epi-nucleus is then separated from the inner harder endo-nucleus through injection of a fluid wave (hydrodelineation). This ensures protection of the lens capsule during lens breakdown (phacoemulsification).
Phacoemulsification
A handpiece using ultrasonic energy is used to breakdown the lens. It is commonly broken down into four pieces, emulsified and aspirated. An irrigation-aspiration probe is then used to aspirate the remaining lens material, by suctioning (aspiration) and injecting saline (irrigation) to prevent the anterior chamber collapsing.
Lens insertion
A foldable plastic lens is injected into the eye through a corneal incision. It is manipulated and held in place via haptics.
Viscoelastic removal
The viscoelastic is removed using the irrigation-aspiration instrument to prevent a significant increase in IOP. This step also aids in the self-sealing of the corneal incisions.
Post-operative Recovery
There is usually a short recovery period after the completion of cataract surgery, and the majority of patients return home on the same day. They are given antibiotic and anti-inflammatory drops post-operatively and advised to avoid heavy lifting or straining for a month.
Complications
Posterior capsular opacification (PCO)
This is when a cloudy opacified layer of scar tissue forms behind the lens implant and causes blurring of vision. It is treated by performing a posterior capsulotomy, where an Nd-YAG laser is used to clear the opacified region, or surgical capsulotomy, which involves manual removal of the lens capsule. The latter is more commonly used for very thick lens opacification(8).
Endophthalmitis
Endophthalmitis is an infection that occurs inside the eye affecting intraocular cavities such as aqueous or vitreous humour. It presents with a hypopyon, which is an exudate rich in white blood cells, and treated with intravitreal antibiotics. During cataract surgery, intracameral antibiotics are administered (an injection into the anterior chamber) to prevent post-operative endophthalmitis (9).
Increased risk of retinal detachment
Retinal detachment occurs when the neurosensory retina, which is the thin later in the posterior segment of the eye involved in photoreception, detaches from the structures below it. Symptoms typically include peripheral vision loss, floaters and flashes of light. Patients who have had cataract surgery are at higher risk of rhegmatogenous retinal detachement (0.5%) when compared with the general population (0.1%) (10).
Macular oedema
Macular oedema is a collection of fluid that occurs in the central part of the retina responsible for central vision (macula) which can cause permanent vision loss. Cataract surgery can irritate the retina causing retinal capillaries to dilate and leak leading to oedema. It is prevented by giving topical anti-inflammatories post-operatively.
Intraocular lens (IOL) dislocation
There is a risk that the artificial lens implant (IOL) can dislocated from the inserted position, causing blurred vision. The patient would require surgical replacement of the lens to treat this.
References
1. Nei.nih.gov. 2021. Cataracts | National Eye Institute. [online] Available at: <https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts> [Accessed 6 December 2021].
2. Mayo Clinic. 2021. Cataracts – Symptoms and causes. [online] Available at: <https://www.mayoclinic.org/diseases-conditions/cataracts/symptoms-causes/syc-20353790> [Accessed 6 December 2021].
3. Hasler, P., 2013. Essential principles of phacoemulsification. New Delhi: Jaypee Brothers Medical Pub.
4. Zaman, F., Bach, C., Junaid, I., Papatsoris, A., Pati, J., Masood, J. and Buchholz, N., 2012. The Floppy Iris Syndrome – What Urologists and Ophthalmologists Need to Know. Current Urology, 6(1), pp.1-7.
5. Calenda E, Olle P, Muraine M, Brasseur G. Peribulbar anesthesia and sub-Tenon injection for vitreoretinal surgery: 300 cases. Acta Ophthalmologica Scandinavica. 2000;78(2):196-199.
6. Higashide. Use of viscoelastic substance in ophthalmic surgery; focus on sodium hyaluronate. Clinical Ophthalmology. 2008;:21.
7. Mohammadpour M, Erfanian R, Karimi N. Capsulorhexis: Pearls and pitfalls. Saudi Journal of Ophthalmology. 2012;26(1):33-40.
8. Karahan, E., Er, D., & Kaynak, S. 2014. An Overview of Nd:YAG Laser Capsulotomy. Medical hypothesis, discovery & innovation ophthalmology journal, 3(2), 45–50.
9. Kessel, L., Flesner, P., Andresen, J., Erngaard, D., Tendal, B. and Hjortdal, J., 2015. Antibiotic prevention of postcataract endophthalmitis: a systematic review and meta‐analysis. Acta Ophthalmologica, 93(4), pp.303-317.
10. Steel D. (2014). Retinal detachment. BMJ clinical evidence, 2014, 0710.