aphakic eye

Introduction
Cause
Examine
Diagnosis

Introduction

Introduction The aphakia refers to the absence of a lens in the eye, and the absence of a lens in the pupil area is also included in this category, which is called an aphakic state.

Cause

Cause

(1) Causes of the disease

The causes of aphakic eyes include:

1. Congenital lens lack or dislocation.

2. Cataract surgery is the most common cause.

3. Eye trauma.

4. Hereditary eye disease with dislocation of the lens.

(1) Marfan syndrome.

(2) Weill-Marchesani syndrome.

(3) homocycyuria.

(4) Sulfite oxidase deficiency.

5. Hereditary eye disease with subluxation of the lens

(1) Alport syndrome.

(2) craniofacial dysostosis (craniofacial dysostosis).

(3) No iris disease.

(4) Ehlers-Danlos syndrome.

(5) spherical cornea.

(6) Hyperlysinemia.

6. Eye disease that can cause subluxation of the lens

(1) Buphthalmus (buphthalmus).

(2) intraocular tumors.

(3) Cataract during maturity or over-ripening period.

(4) Epidermal exfoliation syndrome.

(two) pathogenesis

1. Optical model eye: A is the model eye of Gullstrand's emmetropia, and the parameters are shown in mm. In terms of refractive power, the cornea is 43.05D, the lens is 19.11D, and the total refractive power of the eye is 58.64D. The aphakic eye can be seen as a height-adjusting eyeball that is unregulated. After removing the lens, the refractive power of the eye is reduced from 58.64D to 43.05D, which is only equivalent to the total refractive power of the cornea. Fig. 1B shows the model eye of the aphakic body. It can be clearly seen as a control. In the aphakic eye, the anterior principal point (H1) and the posterior main point (H2) are almost all on the anterior surface of the cornea, and the first node ( N1) and the second node (N2) are each moved backward from 7.079 mm and 7.333 mm behind the cornea to the vicinity of the cornea 7.754 mm. This fully shows that in the uncorrected aphakic eye, the main point moves forward and the node moves backward. In the process of correcting the aphakic body, the node moves forward. From the control image of the model eye, in the aphakic eye with an axial axis of 23 to 24 mm, the focal point of the parallel rays falls about 31 mm behind the cornea, the front focal length is 23.22 mm, and the front focal length (D1) in the emmetropic eye is 17.048 mm. Therefore, it is necessary to add a highly convex lens that can strongly concentrate the light to compensate for the refractive system of the aphakic body.

2. Symptoms and signs

(1) Vision: In the aphakic eye, the object image is magnified by 33% because the front focal length and the emmetropic eye of the aphakic body are different. In terms of the range of viewing angles, the recorded visual acuity is theoretically better than true visual acuity. The visual acuity is 6/9 in the corrected aphakic eye, which is equivalent to 6/12 in the emmetropic eye.

The anterior focal length D1=17.05mm of the emmetropic eye, the front focal length D1=23.22mm of the aphakic body, the ratio is 23.22÷17.05=1.36, the ratio is from 1 to 1.36, meaning that the object image in the aphakic eye is 1.36 times that in the emmetropic eye. That is to say, an increase of 33%. In the anterior chamber intraocular lens implant, the image is magnified 5%, and in the posterior chamber intraocular lens implant, the image is not magnified.

(2) Adjustment: Because the lens is absent, the adjustment is completely lost, so the near and far vision needs to be corrected with lenses of different diopter.

(3) Corneal astigmatism: When the aphakic eye is obtained by cataract surgery, there is corneal astigmatism, and most of them are retrograde astigmatism. Hennig et al reported that the use of seamless extracapsular cataract extraction, 85.5% of the eyes in the 6 weeks after surgery had an average of 1.41D of retrograde astigmatism, and there was a slight increase in retrograde astigmatism between 6 weeks and 1 year after surgery. The added value is 0.66D. If the cataract surgery is extracapsular enucleation or intracapsular enucleation, corneal astigmatism will be stabilized 45 days after surgery. After phacoemulsification, corneal astigmatism is generally not obvious due to small incision.

(4) Spherical aberration: When a highly convex lens is placed in front of the aphakic lens for correction, only the paraxial light can pass through the main focus, and the refraction of the near-edge of the lens deviates more, and the focal length is shorter than the focal length of the paraxial beam. , thus producing a spherical aberration. When the aphakic body sees the object in front through the highly convex lens sheet, since the distance between the points around the object is different from the optical center of the lens, different angles of the prism image are generated when the object image passes through the lens, when the object image is from the paraxial When the optical axis is moved away from the periphery, the magnification is gradually increased at this time, and the deformation of the object image occurs, which is called pincushion distortion.

As a result, the line becomes a curve through the lens, and the linear world becomes a parabola. When the patient moves the eye, the parabolic surface continues to change their shape. When looking at an object through the periphery of the lens, the object becomes larger, closer, and longer in the direction of the main axis. When the object moves without moving the object, the object appears to move faster.

(5) Chromatic aberration: When the aphakic lens is corrected by wearing a highly convex lens sheet, color light can appear due to the white parallel light passing through the convex lens. The longer the wavelength, the smaller the refractive index, so the focus of the red light after passing through the convex lens Far from the lens, and the focus of the violet light is close to the lens, the peripheral light of the lens has a larger refractive index than the x-axis light (optical center). Therefore, the focus of the colored light generated at the peripheral portion of the lens is different from that of the central portion, that is, when the eyeball sees an object or light through the peripheral portion of the correcting lens, chromatic aberration occurs.

(6) Field of view: The visual field of the aphakic body is reduced, almost half of the emmetropia.

When the aphakic eye is corrected with a highly convex lens, a moving circular dark spot (Fig. 4) appears as a "jack-in-the-box" phenomenon when the patient looks at the object. The so-called annular dark spot means that the central and peripheral visual fields can be seen, and dark spots appear in the range between the center and the periphery of the visual field. This is because the light passing through the center of the lens can be focused on the retina and seen clearly. The light passing through the edge portion of the lens causes poor refraction due to the utility of the prism of the convex lens, and cannot gather on the retina, so that the object cannot be seen. As for the light passing through the lens, no adverse refraction occurs, and the retina can still be reached. The object image is still unclear but still exists, thus forming a ring-shaped dark spot.

When the eyeball is in the home position, when a convex lens correcting lens is placed close to the front of the aphakic lens, a circular dark point of 15o is caused due to the utility of the prism of the lens. When the eyeball turns, the dark spots move in opposite directions. When the eyeball is rotated to the peripheral portion of the lens, the dark spot and the eyeball move in opposite directions, moving toward a more central portion. Thus, when the patient observes an object and turns the eyeball toward the object, the dark spot also moves to block the object. When the eyeball is removed from this object, the dark spot moves again, the object can be seen again, and the object is shaken in or out from the observation point, so it is called the doll box phenomenon.

(7) Binocular vision: In a monocular aphakic eye, it is difficult to obtain binocular monocular function, even in aphakic patients with binocular vision, binocular vision is not always present.

Examine

an examination

Related inspection

Eye function examination eye and sacral area CT examination

The clinical manifestations of aphakic eyes vary depending on the cause, mainly as follows:

1. Wound scar: If the aphakic eye is caused by cataract surgery, especially after extracapsular or intracapsular surgery (ECCE or ICCE), the incision scar can be seen, and the suture can be seen by the suture.

2. The cornea: mostly retrograde astigmatism, especially after ECCE or ICCE.

3. Anterior chamber: Deeper, this is due to the lack of lens and the back movement of the iris.

4. Iris: Due to the lack of support of the lens, it appears as iris tremor, and may also be accompanied by iris defects.

5. Pupil: It appears dark black because the reflected light from the patient's eye cannot reach the observer's eye.

6. Dislocation of the lens: If the lens is dislocated, the dislocated lens can be seen.

7. Residual lens cortex: Partial residual lens cortex was seen mainly after ECCE.

8. Purkinje-Sanson's image: The third and fourth images will not be visible due to the lack of a lens.

9. Ophthalmoscopy: The fundus can be seen at +10D with a direct ophthalmoscope, and the disc is small.

According to the patient's clinical manifestations, combined with optometry and ultrasound examination results can confirm the diagnosis.

Diagnosis

Differential diagnosis

The diagnosis should be differentiated from the following symptoms:

1. Lens shift: Under normal conditions, the lens is suspended by the lens suspensory ligament on the ciliary body, and its center is almost identical to the visual axis. The partial or total loss or disconnection of the lens suspensory ligament due to congenital, traumatic or pathological causes, etc., causes the suspension force imbalance or loss of the lens to cause the lens to leave the normal physiological position called ectopia lentis. The degree of ligament defect or disconnection (partial or complete) lens ectopic is divided into subluxation and liberation/dislocation; according to the cause of lens ectopic, it is divided into congenital, spontaneous and traumatic.

2. Increased lens expansion: In the development of cataract in individual patients, the lens expands due to the absorption of excess water by the lens, which increases the volume of the lens, hinders the smooth flow of water, and causes the internal pressure to rise, and the patient may have severe eye. Pain, accompanied by nausea, vomiting and other symptoms, medically known as secondary glaucoma during the expansion of the lens.

Glaucoma caused by swelling of the lens: glaucoma associated with intumescent cataract refers to glaucoma that occurs during the expansion of senile cataract or opacity after morphological injury in vitro.

3. Lens shrinkage: complicated cataract associated with anterior segment disease, the disease progresses slowly, such as local inflammation can be controlled, turbidity can be stable for a long time without development. As the disease progresses, the degree and extent of turbidity continue to increase and expand, eventually involving the entire lens. During the progression, crystalline substances or calcareous deposits may appear in the lens or in the capsule, and in the advanced stage, the lens may shrink and even calcify.

Concurrent cataract is caused by other diseases of the eye such as uveitis, glaucoma, retinal detachment, retinitis pigmentosa, intraocular tumors and high myopia, which cause crystal turbidity caused by crystal nutrition and metabolism.