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Optometry lectures for all semesters :
Topics -
Ocular anatomy,
Ocular Physiology,
Physical optics,
Geometrical optics,
Visual Optics,
ocular disease,
systemic disease etc
All subjects will be covered on this channel
Just make sure to subscribe and press the bell Icon to never miss a video

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Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>

Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>

Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>

Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>

Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>

Unable to parse item

Invidious encountered an error while trying to parse this item. For more information see below:

Show technical details 
Title: `Missing hash key: "collectionThumbnailViewModel" (KeyError)`
Date: `2026-02-16T08:23:19Z`
Route: `/channel/UC8YVybvY3RBcgQpzQyoBdcA`
Version: `2026.02.07-118d635 @ (HEAD detached at v2.20260207.0)`

<details>
<summary>Backtrace</summary>
<p>
   
```
Missing hash key: "collectionThumbnailViewModel" (KeyError)
  from /usr/share/crystal/src/hash.cr:1198:9 in '??'
  from /usr/share/crystal/src/json/any.cr:149:5 in 'process'
  from src/invidious/yt_backend/extractors.cr:524:17 in 'process'
  from src/invidious/yt_backend/extractors.cr:1035:17 in 'parse_item'
  from src/invidious/yt_backend/extractors.cr:1082:14 in 'extract_items'
  from src/invidious/channels/videos.cr:29:22 in 'get_60_videos:continuation:sort_by'
  from src/invidious/routes/channels.cr:56:36 in 'videos'
  from lib/kemal/src/kemal/route.cr:13:9 in '->'
  from src/invidious/helpers/handlers.cr:31:37 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from lib/kemal/src/kemal/filter_handler.cr:22:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/invidious/helpers/handlers.cr:80:12 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call_next'
  from src/ext/kemal_static_file_handler.cr:127:14 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/handler.cr:30:7 in 'call'
  from /usr/share/crystal/src/http/server/request_processor.cr:51:11 in 'handle_client'
  from /usr/share/crystal/src/fiber.cr:170:11 in 'run'
  from ???
```
</p>
</details>