2 The procedure
2.1.1 A cataract is the opacification of the eye's natural lens. It usually develops over a period of time, causing a gradual deterioration in eyesight, and may eventually lead to blindness.
2.1.2 Surgical treatment involves replacing the patient's opacified lens with an artificial lens, which is usually of fixed power (monofocal), requiring the use of reading spectacles for near vision. More recently, intraocular lenses have been developed that allow both distance and reading vision without glasses. These can be either multifocal lenses, which enable both near and distance vision by virtue of the design of the lens itself, or accommodating lenses, which move within the eye in a similar manner to the human lens. Cataract surgery is usually performed under local anaesthesia.
2.2.1 An ultrasound probe is used to break the opacified lens into tiny pieces, which are removed through a small incision in the cornea (phacoemulsification). An accommodating lens rather than a standard intraocular lens is then inserted through the incision. The aim of the procedure is to allow the eye to focus on near as well as distant objects, reducing the need for spectacles.
2.3.1 Only one randomised trial reported that both the patient and the examiner were blind to which lens had been implanted. Two randomised controlled trials reported a statistically significant larger degree of accommodation with accommodating lenses than with monofocal lenses: 1.9 dioptres (D) versus 0 D (p < 0.05), and 1.01 D versus 0.5 D (p = 0.01).
2.3.2 Four randomised controlled trials reported significantly better distance-corrected near visual acuity for eyes with an accommodating lens than for eyes with a standard intraocular lens; follow-up ranged between 6 and 12 months. In one of these studies, the difference was statistically significant at 6 months (J9.3 versus J12.4, p = 0.004) but not at 12 months (J11.5 versus J12.8, p = 0.1), although the 12-month follow-up included only 67% (40/60) of eyes. (Note that a larger J number means less visual acuity.) In another of these studies, 66% of eyes (numbers not reported) with accommodating lenses had distance-corrected near visual acuity of 20/40 or better at 6 months, but this decreased to 49% of eyes at 12 months. The other two studies only reported follow-up to 6 months. No eyes with the standard intraocular lens implant achieved distance-corrected visual acuity of 20/40 or better. For more details, refer to the 'Sources of evidence' section.
2.3.3 Two Specialist Advisers considered this procedure to be a minor variation of an existing procedure. One Specialist Adviser commented that the technology is in the early stages and that more efficacious lenses are likely to be developed in the future. The mechanism of action of accommodating lenses is unclear.
2.4.1 A non-randomised comparative study reported that after 12 months' follow-up, 13% (3/24) of eyes with an accommodating lens required capsulotomy for posterior capsule opacification, compared with 25% (8/32) of eyes with a multifocal lens and 29% (7/24) of eyes with a bifocal lens (p value not reported). Two case series reported capsulotomy for posterior capsule opacification in 14% (37/263) and 18% (12/65) of eyes with an accommodating lens after mean follow-up of 12 and 23 months, respectively.
2.4.2 One randomised controlled trial of 42 eyes reported anterior and posterior capsule opacification in 86% of eyes with an accommodating lens, compared with 25% (5/20) of eyes with a traditional lens (follow-up 12 months; p value not reported). Another randomised controlled trial of 42 eyes reported mild posterior capsule opacification in 21% of eyes with an accommodating lens and 22% of eyes with a monofocal lens after 6 months' follow-up (p value not reported).
2.4.3 A randomised controlled trial reported intraoperative haemorrhage in the anterior chamber in 1 of 40 eyes (3%) with an accommodating lens. A case series reported cystoid macular oedema in 4% (12/324) of eyes with an accommodating lens over a 12-month follow-up period. Persistent cystoid macular oedema was reported in 1% (3/304) of eyes.
2.4.4 A non-randomised controlled trial reported halos in 8% (2/24) and flare, flashes or glare each in 1 of 24 eyes (4%) with an accommodating lens. Higher rates of halos, flare and glare were reported by patients with a multifocal or bifocal lens. For more details, refer to the 'Sources of evidence' section.
2.4.5 The Specialist Advisers listed potential adverse events as including lens decentration, posterior capsule opacification, lens or haptics buckling, development of capsular contraction syndrome and loss of quality of vision.
2.5.1 It was noted that the evidence reviewed on this procedure relates to the treatment of cataract and not to the correction of presbyopia.
2.5.2 It was also noted that accommodating lenses are at a relatively early stage of development and that the technology is evolving rapidly.