Waterfalls and Warplanes
Updated: Mar 7, 2019
BSc (Hons) Optometry, BSc (Hons) Orthoptics,
College of Optometry
With over 80% of incoming sensory information being processed by the visual system, the continuation of good eyesight with increasing longevity is essential for quality life. One of the challenges to maintaining good eyesight is the development of cataract which, for most people, is an age-related event. With modern surgical procedures there is relatively straight forward restorative procedure. However, it has not always been so. Crude knowledge and the putative skills of early cataract pioneers often failed to match their keenness to remedy this defect. Like any new practice, during its evolution there were many casualties of early surgical procedure, intuitive breakthroughs and extensive development which have led to the almost unobtrusive operation used today.
For visual physiologists, the eye can be divided into two components. Firstly, there is the optical system of the cornea, lens and humours which focus light onto the retina. Secondly, there is the sensory component, namely the retina, visual pathway and visual cortex that process that information. It is the former that Simon was concerned with in his presentation.
Optically, the eye requires a dioptric power of +60D to focus images sharply on the retina. Two thirds of this is provided by the cornea and one third by the lens of the eye though this proportion varies in different organisms. The lens possesses the remarkable ability to change shape, altering its base power and permitting the eye to focus at different distances via its connections (zonular fibres) with the circular ciliary muscle. Remarkably for a bodily structure, the lens does not possess a blood supply (to maintain transparency) and tends to be one of the bodily components which ‘fails’ relatively early in the aging process and sooner in certain metabolic conditions (e.g. diabetes) and for those with a genetic predisposition to early lenticular changes.
Anatomically, the lens consists of protein and water suitably contained within a transparent lenticular capsule. The lens continues to grow throughout life thickening and becoming less flexible as age encroaches. Proteins clump, lenticular cells gradually die, causing opaque areas, and these opacities are cataracts. As they coalesce and the cataract grows, the transparency of the lens is compromised and vision dims. The word cataract is derived from Greek (= rushdown) later changed when Latinised (=waterfall or portcullis) hence ‘waterfall’ in the presentation title.
Cataracts may present in different ways, their position within the lens having distinct effects on vision.
The three most common types are (see Fig. 1) are:
Nuclear cataract within the nucleus, or centre of the lens, increase the refractive index of the lens giving a myopic shift;.
Cortical cataract, spokes of cataract extend from the periphery to the centre of the lens and can give doubling effects; &
Subcapsular cataract, often small and positioned on the back surface of the lens. Because it lies at an optically important of the ocular visual system (nodal point), it can be, despite its small size, disproportionally disruptive to vision.
The first cataract pioneers were itinerant practitioners and used a procedure known as couching. Historically, this was first recorded in the ancient worlds of Egypt and India. The Tomb of Ipwy in Egypt (~1,200BC) shows a wall painting (see Fig. 2) of a coucher at work and written reference is made in Sanskrit manuscripts (~800BC). The itinerant nature of their work meant that, with a risky procedure, they were never around to deal with the serious and inevitable complaints which the procedure undoubtedly caused.
Couching (see Fig.3) required a mature cataract with a rigid lens. The coucher penetrated the eye with a small sharper stick at the edge of the cornea and forced the lens down into the vitreous. The optical pathway was opened up and a bright image immediately noticeable. With the dioptric contribution of the lens lost, sight would have been very blurred. The crudeness of the operation risked infection and disruption of the globe, but for many was preferable to no sight at all. The surgical incision was small which minimised infection. Couching continues today in sub-Saharan Africa.
This crude procedure continued for many centuries. Its champion in Europe was ‘Chevalier’ John Taylor (1703-1772), an eye doctor, medical charlatan and self-publicist. He admitted to friends that he had blinded hundreds of individuals with couching. He operated on J.S. Bach and G.F. Handel, both of whom went blind.
Salvation for the cataract suffer came in the mid-18th century with two pioneers. In 1753, London surgeon Samuel Sharp performed the first intracapsular extraction, a technique which used a larger incision to remove the entire lens and capsule. A few years earlier, in France, Jacques Daviel’s (1696-1762) procedure was to open the anterior surface of the lens capsule and extract the cataract (so called ‘extra capsular extraction’). This technique extracted the lens without leaving debris behind which might obscure vision and required a relatively small incision. Extra-capsular extraction remained the procedure of choice until the 1980’s though improvements in hygiene, spectacle lens and contact lens technology certainly made the operation more acceptable.
The Modern Era
The modern era of cataract surgery was led by Moorfields surgeon Harold (later Sir Harold) Ridley (see Fig. 4). His prescient observation in the 1940’s was that Perspex canopies, which protected aircrew, often shattered in action. Perspex fragments which penetrated the globe remained inert within the eye without issues of rejection, in contrast to metallic particles (hence the reference to ‘warplanes’ in the title). Sir Harold’s insight identified the potential of Perspex for making a replacement, Intra-Ocular Lens (IOL’s). The first IOL became available in 1949.
Various styles of IOL were tried. Anterior lenses, fitting in front of the iris were quite chunky and often disrupted and compromised the cornea. Posterior lenses fitted behind the iris were also bulky and increased risks of glaucoma. In this procedure, a sizeable cut was required to remove the cataractous lens and insert a new plastic lens. Suturing closed the cut, but the tensioned stitching induced significant astigmatism (distortion) into the eye.
In a parallel development, Charles Kelman (1930-2004), inspired by ultrasonic dental probes, used phacoemulsification to break up (with ultrasound) the nucleus of the lens and remove the cataract without a need for a large incision. Kai-Yi Zhou’s foldable silicone implant (first used in 1978) allowed for inserting the IOL in a small, foldable state, to open once in place within the lens capsule of the eye.
Current cataract extraction (see Fig, 5) involves a small incision, a phacoemulsification probe then liquifies the cataractous lens and removes it from the anterior chamber, leaving the capsule relatively intact. Through the same small opening, a foldable IOL is inserted and positioned within the lens capsule. The incision does not induce astigmatism and is cut in such a way that when the probe is removed, the shape of the incision self-seals without need for sutures. A relatively simple procedure with high satisfaction ratings!
The goal of achieving a very satisfactory single vision (focussing at one distance) IOL that gives excellent results for the majority of patients has been largely achieved (see Fig.6). But where does the future lie? A challenge has been to produce an IOL which can focus like the natural eye, either by concentric diffraction gratings which provide two different focusing distances (distance and near), or by using an accommodating lens, which shifts focus, like the natural lens, by movement of the ciliary muscle. Other designs have been developed, miniature telescopes, for example, for macular degeneration patients with failing vision.
Waterfalls and warplanes may have seemed disparate entities at the start of the presentation but they were brought together by Simon to give a brilliant exposition of the development of procedures for dealing with that historical medical scourge, the cataract.
UPDATE: Simon also made reference to his involvement in developing the Akamba Health Centre, a worthy and successful project to establish an eye hospital in rural Kenya, where eye care, including basic surgical procedures such as cataract operations, are performed. The project has now begun operations, with trained staff. Donations, including no-longer used glasses, are always welcomed, and the meeting raised £260 in donations, enough for 5-6 cataract operations. For further information, see: http://www.akambaaidfund.org/health/akamba-health-centre