Cataract: surgery

Indications for surgery for cataracts

1. Visual improvement is the main objective of surgical cataract treatment, despite the differences in approaches in each individual case. The operation is indicated only with such a degree of cataract development, when the patient's opportunities in daily activities are reduced. If the patient wants to drive a car or continue working, reducing visual functions below the required level necessitates surgical treatment.
2. Medical indications for surgery occur with a damaging effect of cataracts on the condition of the eye, for example in phacolithic or phakomorphic glaucoma. Surgical treatment is also indicated when it is necessary to visualize the eyes in pathological conditions on the fundus (for example, with diabetic retinopathy), which requires observation and treatment using laser-coagulation.
3. Cosmetic indications are more rare. For example, the removal of mature cataracts on the blind eye in order to restore the naturalness of the pupil area.

Preoperative examination

In addition to general medical examination, the patient referred for surgical cataract treatment requires an appropriate lethal ophthalmological examination and special attention.

1. Test of closing-opening of eyes. Heterotrophy can be evidence of amblyopia, in which the prognosis for vision is done with caution. If it improves, diplopia is possible.
2. Pupillary reflex. Since cataract never leads to an afferent pupillary defect, its detection indicates an additional pathology that can affect the outcome of the operation with respect to vision.
3. Attachment of the eye. Dacryocystitis, blepharitis, chronic conjunctivitis, lagophthalmus, ectroion, entropion and neoplasm of the lacrimal gland may predispose to endophthalmitis and require effective treatment before surgery.
4. Cornea. Wide arcus senilis or stromal turbidity may cast doubt on the positive outcome of the operation. "Drop" cornea (cornea guttata) indicates endothelial dysfunction with the possibility of subsequent secondary decompensation after the operation.
5. Front segment. The narrow angle of the anterior chamber complicates the performance of cataract extraction. Pseudoexfoliations indicate a weakness of the zonal apparatus and possible problems during the operation. A poorly widening pupil also complicates the operation, which is the basis for intensive use of myliatrics or planned dilatation of the pupil before capsulorhexis. With a weak reflex from the fundus, it is dangerous to perform capsulorrexis, so it is recommended to stain the capsule, for example, with Trinan blue.
6. The lens. Titan cataracts are important: nuclear cataracts are characterized by density and require more power in phacoemulsification than cortical and subcortical cataracts that require less power.
7. Intraocular pressure. It should be borne in mind any type of glaucoma or ocular hyperthey.
8. Ocular fundus. Pathology of the fundus. For example age-related macular degeneration, can affect the degree of vision recovery.

Biometrics

The extraction of the lens changes the refraction of the eye by 20 dpt. The aphakic eye has hypermetropia of a high degree, so modern cataract surgery involves the implantation of an intraocular lens instead of a surgically removed lens. Biometrics makes it possible to calculate the optical power of the lens to obtain zymmetropia or the desired postoperative refraction. In a simplified version, biometrics takes into account 2 parameters: keratometry - curvature of the anterior surface of the cornea (the steepest and most flat meridians), expressed in diopters or millimeters of the radius of curvature; length of the axis - ultrasound (A-scan) measurement of the anterior-posterior segment of the eye in millimeters.

The SRK formula. This is probably the most commonly used mathematical formula for calculating the optical power of LPO, proposed by Sanders,

P = A-0,9K-2,5L + | (R + 2,5) | -, where

• P is the required optical power of the lens to achieve postoperative emmetropia.
• A - A-constant, which varies from 114 to 119 depending on the IOL.
• L - antero-posterior segment in millimeters.
• K is the mean value of keratometry calculated in diopters.

To optimize the accuracy of preoperative prognosis, a number of other formulas have been developed, including additional parameters, such as the depth of the anterior chamber, as well as the individual characteristics of the surgeon.

Postoperative refraction. Emmetropia is the most ideal postoperative variant of refraction: glasses are required only for fixing a close object (since the IOL is not capable of accommodation). In practice, most surgeons calculate refraction to a low degree of myopia (about 0.25 D) to avoid a possible biometric error. This is due to the fact that for most patients, a weak degree of myopia is more acceptable and even has advantages over postoperative hypermetry, which requires glasses for fixing near and far objects, which is not entirely convenient. When calculating postoperative refraction, it is necessary to take into account the characteristics of the paired eye. If a correction with high refraction is required for it and the operation on it is not indicated, then the postoperative refraction of the other eye should be within 2 dpts in order to avoid binocular mismatch problems.

Anesthesia

For most intraocular operations, local anesthesia does not always have an advantage over the general. The choice is usually influenced by the patient's preferences and the clinical conclusion of the surgical group. Cataract surgery in a day hospital under local anesthesia is less dangerous and is usually preferable for the patient and surgeon, it is economically viable and is the option.

1. Retrobulbaric anesthesia is produced in the muscle funnel behind the eyeball near the ciliary ganglion. This type of anesthesia causes akinesia with a complete or significant restriction of eye movement. A retrobulbar injection requires the appropriate knowledge and experience. Occasionally, it can be accompanied by such serious complications as bleeding into orbit, perforation of the eyeball, intravascular injection, optic nerve damage and brainstem anesthesia. Temporary complications include ptosis and diplopia. When retrobulbar injection often requires a separate anesthesia for paralysis of the circular muscles of the eye.
2. Peribulbar anesthesia is produced through the skin or conjunctiva. Compared with retrobulbar anesthesia, it requires not one injection and a higher dose of anesthetic. The risk of anesthesia of the brain stem decreases, since the needle is shorter, but there is a possibility of hemorrhage and perforation.
3. Parabulbar (subtenon) anesthesia is the placement of a cannula with a blunt end through a hole in the conjunctiva and a tenon capsule 5 mm from the limb into the subtenon space. Anesthetic is introduced beyond the eyeball equator. Despite the good effect and minimal complications, akinesia is not always achieved.
4. Local intra-chamber anesthesia is performed by primary surface anesthesia with drops or gel (proximethacaine 0.5%, ligiocaine 4%) followed by intra-chamber infusion of a diluted anesthetic that does not contain preservatives.

Intraocular lenses

Basic aspects

1. Location. The intraocular lens consists of an optical (central refractive element) and a haptic part that contacts the eye, such as a capsule bag, ciliary fissure or anterior chamber angle, thus ensuring an optimal and stable position (centering) of the optic. Modern cataract surgery with the preservation of the capsular bag allows you to ideally place the intraocular lens inside it. However, complications such as rupture of the posterior capsule may create the need for an alternative location of intraocular lenses. If the intraocular lens is located in the posterior chamber (the haptic part is in the ciliary groove), it is designated as an IK-IOL; if the intraocular lens is located in the anterior chamber (the haptic part is in the corner of the anterior chamber), it is designated as a PC-IOL.
2. Models of intraocular lenses are very many and new ones are being created. Lenses can be rigid or flexible. For the implantation of hard intraocular lenses, the length of the incision is greater than the diameter of the optical part (about 5-6.6 mm). Flexible intraocular lenses can be flexed with tweezers or placed in an injector and implanted through a smaller incision (about 2.5-3 mm). The haptic part is made of polymethyl methacrylate, polypropylene (proline) or polyamide and can be in the form of a loop or plate. In monolithic intraocular lenses, the haptical and optical parts are made of the same materials and do not have joints. In intraocular lenses consisting of three parts, the optical and haptic parts are made of different materials and necessarily connected together. The optical part can have different sizes and shapes. Conventional monofocal, but recently developed multifocal intraocular lenses providing better vision.
3. Rigid intraocular lenses are completely made of PMMA. The composition of PMML depends on the technological process. Intraocular lenses, made by the method of injection of material into molds and turning, consist of high-molecular PMMA, and the method of casting with the help of forms - from low-molecular. Modern rigid intraocular lenses are monolithic, which determines their maximum stability and fixation.
4. Flexible intraocular lenses are made of the following materials:
   • Silicone - haptical in the form of an incomplete loop (consists of 3 parts) or plates (monolithic); cause minimal opacification of the posterior capsule but compared with intraocular lenses made of PMMA;
   • acrylic - consist of 1 or 3 parts, can be hydrophobic (water content <1%) or hydrophilic (water content 18-35%), Some acrylic intraocular lenses do not cause opacification of the posterior capsule;
   • hydrogel - similar to hydrophilic acrylic intraocular lenses, with high content of oxen (38%) and can consist of only 3 parts;
   • Collagen - made of a mixture of collagen and hydrogel, developed recently.

[1], [2], [3], [4], [5]