Composition and function of crossed cylinder lens (JCC)

Crossed cylinder lens is an optical instrument composed of two cylinder lenses with equal degrees, opposite symbols and vertical axis. A lens handle is attached in the 45 ° direction of the included angle between the positive and negative axes, which is convenient for the inspector to operate. The diopter of the cylinder lens is engraved on the lens handle. The crossed cylinder lens is helpful to determine whether the customer has residual astigmatism, correct the axial position of the cylinder lens and correct the force of the cylinder lens.

Crossed cylinder lens in comprehensive refractometer

Handheld crossed cylinder lens

Preparation

First, the preliminary correction value of astigmatism is obtained by computer optometry or retinoscopy optometry. Secondly, after the subject was relaxed and adjusted by fog optometry, the examination of spherical lens was further determined by red and green optometry (making the minimum dispersion circle on the retina of the subject). Finally, determine the positive and negative axis positions of the crossed cylinderl lens itself, and then measure the axis position of astigmatism first and then the refractive power of astigmatism.

1. Patient Information

Sun Moumou, female, 18 years old. In the third year of high school, she had optometry in March 2015. In January 2019, she had optometry in an optometry center because the original lens was vague. After wearing it for 2 months, she still felt uncomfortable, and she had optometry again in March 2019.

2 Objective Optometry

New lens degrees in January 2019:

R：-10.75DS/-0.50DC × 180 = 0.9 (leading eye)

L：-9.50DS/-2.50DC × 180=0.9

Computer optometry results in March 2019:

R：-12.00DS/-1.00DC × one hundred and seventy

L：-10.50DS/-3.75DC × one hundred and seventy-eight

PD=67mm

Optometry results:

R：-11.50/-1.00 × one hundred and seventy

Add 1.00dc column lens to neutralize the light band

L：-10.00/-2.50 × one hundred and seventy-nine

Add 2.50dc column lens to neutralize the light band

3 Preliminary Diagnosis

In 2015, the old glasses had poor far vision and good near vision, indicating that the degree of the old glasses was low and it was not suitable to continue to wear them. In January 2019, the new glasses: the vision of both left and right eyes could reach 0.9 from far to near, but they still felt uncomfortable. The inspection and analysis are as follows:

Alternate covering: there is a slight exophoric inclination at far and near

Near point NPC: 9cm

Dominant eye: right eye

Test the new glasses:

The focal point optical center of the focimeter is 2mm above the corneal light reflecting point, and there is no vertical difference.

4 Subjective Optometry

a. First check the right eye, put -9.50ds according to the objective optometry combined with the old lens, see 0.3 clear and 0.4 fuzzy; Implanted -1.00dc × 177. The visual acuity was improved but not obvious, so column lens was not added first.

b. The negative spherical lens is added to gradually increase the visual acuity from 0.4 to 0.9, which is difficult to improve; At this time, it is found that -10.75ds, -11.00ds, -11.25ds and -11.75ds have similar visual acuity. Combined with the red and green detection, it is found that the green in the red and green visual mark in the line of 0.7 when looking at -11.25ds, the red and green are equal in the case of -11.50ds, and the red and green visual mark is also similar in the case of -11.75ds. Therefore, take -11.50ds first.

c. On the basis of -11.50ds, put in the astigmatism meter. When looking at the astigmatism meter, there are no symptoms, but the visual acuity is not ideal. Put in the crossed cylinderl lens according to the examination and computer optometry results: when adding -0.50dc, the visual acuity is 0.9-1, when adding -0.75dc, the visual acuity is 1.0-3, and when adding -1.00dc, the visual acuity is 1.0-1. At this time, look at the astigmatism meter and compare it with no cylinderl lens to further determine that the astigmatism is -1.00dc.

d. Use JCC to measure the axial position first. According to the principle of chasing red, the accurate astigmatism axial position is 170 °, and then the astigmatism diopter is accurate. Finally, it is more accurate when astigmatism -1.00dc is determined.

5 Analysis

Using JCC for accurate astigmatism, the premise is that the minimum dispersion circle falls on the retina, that is, the best spherical lens. However, through the red and green analysis -11.75ds, the red and green equal clarity can be achieved. Through the comprehensive analysis, the cylinderl lens is -1.00dc. Taking this as the standard, JCC is used for -11.50ds / - 1.00dc × 170. The coincidence surface of white spots is clear. At this time, the action of column lens is -0.25dc / + 0.50dc × 170, equivalent to -11.75ds / - 0.50dc in front of customers × 170. Compared with the standard value, the difference between the cylinderl lens and the spherical lens is -0.50dc, and the coincidence surface of red dots is clear. At this time, the action of the cylinderl lens is + 0.25dc / - 0.50dc × 170, equivalent to -11.25ds / -1.50dc in front of customers × 170. Compared with the standard value, the difference between the spherical lens and the cylinder lens is -0.20ds and -0.50dc. Therefore, the white point of the two is false "clear".

When white dots coincide

When red dots coincide

6 Red and green test results after the second fog vision (both eyes Plus + 0.75dc)

-11.50DS/-1.00DC × 170 red vision standard definition

-11.75DS/-1.00DC × 170 red and green

-12.00DS/-1.00DC × 170 green standard definition

So -11.75ds / - 1.00dc should be taken × 170

7 Determine the best monocular vision

Let the examinee see the best visual acuity single line visual marker, and measure -11.75ds / -1.00dc with plus or minus 0.25ds × 170, the degree of spherical mirror is determined to be -11.75ds; Measure -11.75ds / -1.00dc with positive and negative 0.25dc × 170, the degree of column mirror is determined to be -1.00dc × 170。

Analysis: long term under correction causes abnormal adjustment and decreased sensitivity, so the spherical mirror measured by objective optometry must have error. To sum up, the error of ametropia correction is the main cause of blur and fatigue.

The visual acuity was not improved significantly and the reaction was slow when the fog was removed for the first time. The second defogging is slightly better, which is generally the recovery phenomenon of abnormal adjustment function. Therefore, during optometry, optometry should be carried out in combination with fog. After optometry, NRA = + 2.00, PRA = -1.75 and adjustment sensitivity should be measured. In this example, the measured values of positive and negative relative adjustment also indicate abnormal adjustment. The low PRA indicates that myopia is completely corrected, and the subject is difficult to adapt, so adjustment function training should be carried out. Then measure the left eye in the same way, and then balance both eyes.

Final optometry results

R：-11.75DS/-1.00DC × 170 = 1.0 (leading eye)

L：-10.25DS/-2.50DC × 179=1.0 

PD=67mm

The visual acuity of both eyes can reach 1.0, and the red and green eyes can see 0.9.

Worth-4-dot detection: at first, we saw 5, and then changed to 4 after using the set

Maddox rod examination: there is 5 ∆ Bi exophoria in the far eye position, 1 ∆ Bu in the left eye and 20 ∆ Bi in the near eye position.

Far Bo: 5 / 9 / 6

Near Bo: ×/ 22/15

This shows that there is visual fatigue in reading, suggesting that the reading distance should not be too close, and attention should be paid to the training of collective function.

8 Final treatment results

R：-11.75DS/-1.00DC × 170 = 1.0 (leading eye)

L：-10.25DS/-2.50DC × 179=1.0 

PD=67mm

The examinee selects the spectacle holder without nose. Considering the distance between the eyes and the reasons for adaptation, the final prescription is:

R：-11.25DS/-1.00DC × 170 =1.0-

L：-9.75DS/-2.50DC × 179 =1.0-

PD：67mm

Necessary tips: pay attention to eye hygiene, carry out collective function training, adjust sensitivity training, and recheck regularly.

9 Return visit after matching

The customer feels comfortable and clear, and the symptoms of visual fatigue disappear, indicating that the error of refractive correction is the key problem in this case, and the abnormal adjustment and collection function is the secondary problem. It can be seen from this case that astigmatism correction is the key and difficult point, and the error of astigmatism correction is one of the main reasons for fatigue and blur.